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Seabirds are known to associate with marine mammals to facilitate prey capture. These occur when mammals either force prey near the surface or provide small scraps of larger prey victims. Gray whales (Eschrichtius robustus (Lilljeborg, 1861)) have been observed to provide invertebrate prey to a variety of seabird species; however, there are no published reports of Marbled Murrelets (Brachyramphus marmoratus (Gmelin, 1789)) feeding in association with gray whales. We observed Marbled Murrelets foraging within several metres of gray whales off Vancouver Island, British Columbia, feeding on epibenthic zooplankton in 2006 and 2008. Join-count statistics identified significant clustering (p = 0.1) of 258 Marbled Murrelets within 300 m of 39 feeding gray whales in June of 2006, and no association between 3 gray whales and 34 Marbled Murrelets in June and July of 2008, marking a foraging association conditional on the abundance of both gray whales and their prey, but potentially significant to Marbled Murrelet survival and fecundity.

Conserving genetic variation is critical for maintaining the evolutionary potential and viability of a species. Genetic studies seeking to delineate conservation units, however, typically focus on characterizing neutral genetic variation and may not identify populations harboring local adaptations. Here, variation at two major histocompatibility complex (MHC) class II B genes was characterized in four populations of marbled murrelets Brachyramphus marmoratus, a threatened species in which little neutral genetic population structure has been detected. High diversity, as well as evidence of balancing selection, was detected in exon 2 of these genes. Genetic population structure based on MHC markers was uncorrelated to genetic structure estimated with neutral markers, suggesting that selection played a more important role in shaping population structure at these markers than genetic drift. A high proportion of alleles and inferred peptides were unique to a single population, with the Aleutian Islands and southeast Alaska having the highest richness of both. Murrelets sampled in Oregon had low MHC exon 2 allele and inferred peptide richness, and were significantly differentiated from individuals sampled in the Aleutian Islands based on the frequency of exon 2 alleles. In addition, murrelets sampled in Oregon were differentiated from murrelets in both the Aleutian Islands and southeast Alaska based on inferred peptide frequencies, suggesting that the Oregon population could be prioritized for conservation measures. More broadly, combining information from neutral and adaptive genetic markers can improve the delineation of conservation units in threatened species.

Little is known about space use by Common Ravens (Corvus corax) in coastal old-growth redwood (Sequoia sempervirens) forests in northern California despite their identification as nest predators of federally threatened Marbled Murrelets (Brachyramphus marmoratus). We used radio-telemetry to examine home range sizes and space use of breeding Common Ravens in Redwood National and State Parks (RNSP), California, in 2009 (N = 3) and 2010 (N = 8). Mean home range size was 182.5 ha and no home ranges were >2 km from roads or human-use areas. Ravens exhibited high site fidelity between years, and we found little overlap in the home ranges of adjacent ravens. Areas where ranges did overlap were centered on anthropogenic food sources near territory boundaries. Areas most frequently used by ravens were near roads, old-growth edge, bare ground, and in mixed hardwood and prairie habitats; areas near human-use areas and in old-growth habitat were used less by ravens. Mean perch height of ravens (52 m, N = 38) in redwood trees was similar to the mean height of Marbled Murrelet nests in RNSP (48 m). In RNSP, Marbled Murrelet nests that have been located were in old-growth forest within 2 km of roads. The attraction to anthropogenic resources with frequent use of roads and old-growth edges and their tendency to perch high in the canopy may increase the likelihood of ravens locating and predating nests of murrelets in RNSP. RESUMEN Uso del espacio por Corvus corax en habitat de anidacion de Brachyramphus marmoratus en el norte de California Poco se conoce sobre el uso del espacio por Corvus corax en los bosques maduros costeros de Sequoia sempervirens en el norte de California a pesar de que han sido identificados como depredadores de nidos del federalmente amenazado Brachyramphus marmoratus. Usamos radio telemetria para examinar el tamano de los rangos de hogar y el uso del espacio de C. corax en reproduccion en Redwood Parque Nacional y Estatal (RPNS), California, en el 2009 (N = 3) y 2010 (N = 8). El promedio del tamano del rango de hogar fue de 182.5 ha y ningun rango de hogar fue >2 km desde las carreteras o areas usadas por humanos. C. corax mostro una alta fidelidad a lugares entre anos y encontramos poca superposicion en los rangos de hogar de C. corax adyacentes. Areas en donde los rangos se traslaparon se concentraron en fuentes de alimento antropogenico cercanas a los limites del territorio. Las areas usadas con mayor frecuencia por C. corax estuvieron cerca de las carreteras, bordes de los bosques maduros, suelo expuesto y en la mezcla de habitat de pradera y bosque; areas cerca de areas usadas por humanos y habitat de bosque maduro fueron usadas poco por C. corax. La altura promedio de las perchas de C. corax (52 m, N = 38) en arboles de S. sempervirens fueron similares a la altura promedio de los nidos de B. marmoratus en RPNS (48 m). En RPNS, los nidos de B. marmoratus que se han localizado en bosque maduro dentro de un rango de 2 km desde la carretera. La atraccion a recursos antropogenicos con frecuentes usos de carreteras y bordes de bosques maduros, y la tendencia a percharse alto en le dosel puede incrementar la probabilidad de que C. corax localice y deprede nidos de B. marmoratus en RPNS.

Managers of marine protected areas (MPAs) must often seek ways to allow for visitation while minimizing impacts to the resources they are intended to protect. Using shipboard observers, we quantified the “zone of disturbance” for Kittlitz’s and marbled murrelets (Brachyramphus brevirostris and B. marmoratus) exposed to large cruise ships traveling through Glacier Bay National Park, one of the largest MPAs in North America. In the upper reaches of Glacier Bay, where Kittlitz’s murrelets predominated, binary logistic regression models predicted that 61% of all murrelets within 850 m perpendicular distance of a cruise ship were disturbed (defined as flushing or diving), whereas in the lower reaches, where marbled murrelets predominated, this percentage increased to 72%. Using survival analysis, murrelets in both reaches were found to react at greater distances when ships approached indirectly, presumably because of the ship’s larger profile, suggesting murrelets responded to visual rather than audio cues. No management-relevant covariates (e.g., ship velocity, route distance from shore) were found to be important predictors of disturbance, as distance from ship to murrelet accounted for > 90% of the explained variation in murrelet response. Utilizing previously published murrelet density estimates from Glacier Bay, and applying an average empirical disturbance probability (68%) out to 850 m from a cruise ship’s typical route, we estimated that a minimum of 9.8–19.6% of all murrelets in Glacier Bay are disturbed per ship entry. Whether these disturbance levels are inconsistent with Park management objectives, which include conserving wildlife as well as providing opportunities for visitation, depends in large part on whether disturbance events caused by cruise ships have impacts on murrelet fitness, which remains uncertain.

Spatial patterns of marine predator communities are influenced to varying degrees by prey distribution and environmental gradients. We examined physical and biological attributes of an estuarine fjord with strong glacier influence to determine the factors that most influence the structure of predator and prey communities. Our results suggest that some species, such as walleye pollock (Theragra chalcogramma), black-legged kittiwake (Rissa tridactyla), and glaucous-winged gull (Larus glaucescens), were widely distributed across environmental gradients, indicating less specialization, whereas species such as capelin (Mallotus villosus), harbor seal (Phoca vitulina), and Kittlitz's murrelet (Brachyramphus brevirostris) appeared to have more specialized habitat requirements related to glacial influence. We found that upper trophic level communities were well correlated with their mid trophic level prey community, but strong physical gradients in photic depth, temperature, and nutrients played an important role in community structure as well. Mid-trophic level forage fish communities were correlated with the physical gradients more closely than upper trophic levels were, and they showed strong affinity to tidewater glaciers. Silica was closely correlated with the distribution of fish communities, the mechanisms of which deserve further study.

We document here a decline of nearly 30% in the Marbled Murrelet (Brachyramphus marmoratus) population of Washington, Oregon, and northern California between 2000 and 2010. The Northwest Forest Plan is an ecosystem-management plan for federal forest lands in the Pacific Northwest of the United States that incorporates monitoring to determine if species' conservation objectives are met. To evaluate the plan's effectiveness in conserving populations of the murrelet, a species associated with older, late-successional forests, we estimated the murrelet's density in near-shore marine waters of Washington, Oregon, and northern California south to San Francisco Bay. We sampled annually, using line transects and distance estimation. We divided the study area of about 8800 km2 into five geographic subareas corresponding to existing murrelet-conservation zones. Annual population estimates for the plan ranged from an estimated 23 700 (95% CI: 18 300 to 29 000) birds in 2002 to a low of 16 700 (95% CI: 13 1...

Although seabirds search large areas for food, their distributions often correlate with physical characteristics of the marine environment that can serve to aggregate prey. Kittlitz's murrelets Brachyramphus brevirostris are found almost exclusively in Alaskan waters, where they are closely associated with glacial fjords, suggesting that the distribution of this bird might be tightly linked to specific physical habitat characteristics of the fjords. We investigated relation- ships among locations used by Kittlitz's murrelets, water column characteristics, and landscape features in Harriman Fjord and Heather Bay, Prince William Sound, Alaska, USA. In Harriman Fjord, Kittlitz's murrelets were observed in shallow water near upwelling areas, indicated by a cold-water wedge near the surface (~10 m depth) in temperature-depth profiles. In Heather Bay, Kittlitz's murrelets used locations closer to the glacial moraine than the average available habitat. The temperature-depth profiles at these locations showed a cold, fresh surface layer (near surface to 5 m depth); however, the temperature-depth profile variable was statistically insignificant, likely because of small sample size. Although the best temperature-depth profile variables were dramatically different between the 2 fjords, both of these glacially influenced water column char- acteristics may serve to concentrate prey at an optimal depth, allowing Kittlitz's murrelets to focus their effort at predictable foraging locations. Given the widespread wasting of glaciers throughout their range, Kittlitz's murrelets may face increased pressure as changes in water column dynamics within glacial fjords affect the distribution and concentration of preferred prey.

Although nest prospecting, natal philopatry, and nest-site fidelity have been observed in many alcids, few data demonstrate these behaviors in Marbled Murrelets (Brachyramphus marmoratus). Prior to the 2003 breeding season, we installed a permanent video camera adjacent to a Marbled Murrelet nest site that had been used in 2001 and 2002. Video recordings in 2003 detected the simultaneous presence of 3 murrelets in alternate plumage on the nest branch, once during the incubation period, and once during the chick period. We did not observe aggression, suggesting familiarity between the extra-pair birds and site holders, and possibly avoidance of detection by predators. Without banded individuals we hypothesize extra-pair visitations at an active nest reflect nest-site prospecting, natal philopatry, or nest-site fidelity.

Industrial timber harvesting typically creates forest edges with altered microclimate regimes, causing reduced growth and survival of some canopy epiphytes. This process has implications for the marbled murrelet (Brachyramphus marmoratus), a threatened seabird that nests on moss platforms in old-growth forests of the coastal Pacific Northwest in North America. We investigated microclimate and epiphyte availability in old-growth forests of southwestern British Columbia, Canada. We contrasted mean and maximum temperature, mean humidity, mean vapor pressure deficit (VPD) and mean epiphyte cover and platform tree density between forest edge and interior plots at hard edges (recent clearcuts), soft edges (regenerating forest) and natural edges (rivers and avalanche chutes). Differences measured in VPD and epiphyte availability varied due to edge proximity and edge-type. Hard edges had fewer trees with suitable marbled murrelet nest platforms relative to adjacent interiors, and hard-edged patches had t...

Identifying factors that influence growth throughout development is important for understanding the consequences of variation in resource quality on recruitment. Marbled Murrelets ( Brachyramphus marmoratus (J.F. Gmelin, 1789)) are threatened seabirds that are extremely cryptic in their nesting behaviour, which makes it challenging to understand how juveniles allocate resources during development. From a single capture at sea, we analyzed stable carbon isotopes in feathers and blood of juvenile murrelets to infer diet composition during both the pre- and the post-fledging periods. Consistent with the challenges juveniles face during their first year of life, we found that wing and bill growth were prioritized in the nest, whereas development of energy stores was delayed until after nest departure. We also found that diet quality after nest departure influenced bill size and body condition, two body components that continue to grow after independence. Our results provide evidence that murrelets strategically allocate resources according to their stage of development and that the availability of high-quality prey is likely to be important to juvenile development. These results identify a potential mechanism through which feeding conditions may influence reproduction of murrelets and demonstrate the utility of stable isotopes to examine the influence of diet quality on growth over multiple stages of development.

Little is known about seabird distributions at night. Densities of Marbled Murrelets (Brachyramphus marmoratus, hereafter “murrelets”) and potential prey were determined along fixed-width transects in spring and summer of 2007 and 2008, and compared during night and day in two regions of Port Snettisham, near Juneau, Southeast Alaska. Murrelets moved from a shallower, more sheltered inner region, used during the day for foraging and staging for inland flights (2007 night densities = 15 ± 13 murrelets·km-2; 2007 day densities = 172 ± 67 murrelets·km-2), to a deeper, more exposed outer region, further from shore, during dark hours (2007 night densities = 113 ± 61 murrelets·km-2; 2007 day densities = 41 ± 23 murrelets·km-2). Prey school density and relative prey density were significantly higher at night in the inner region compared with the outer region (2.2 times higher prey school density and 3.8 times higher relative prey density), suggesting that murrelets were not redistributing themselves to...

The expansion of human activities into rural areas and natural landscapes has resulted in widespread increases in the abundance of synanthropic species that threaten rarer native species. Quantitative assessments of how much impacts need to be reduced to reach acceptable levels of risk to the affected species are rarely conducted prior to the implementation of control measures, and it is perhaps not surprising that many efforts have not yielded the desired outcome. Here, we used matrix-based population viability analysis models to show that reducing predation by rapidly growing corvid populations on marbled murrelet (Brachyramphus marmoratus) nests likely constitutes an effective means for recovering a declining murrelet population in central California. For example, a modest 40% reduction in predation reduced extinction risk dramatically from 95.8% to 4.6% over 100 years and a 60% reduction resulted in a stable population (k = 1) when the proportion of breeders, renesting rates, and corvid predation rates were assumed to be 0.77, 0.13, and 0.69, respectively. However, nest predation would only need to be reduced by 40% to produce a stable population if corvid management was coupled with a modest increase in after-hatch-year survival from 0.896 to 0.910. Corvid control resulted in greater gains in murrelet population size when the maximum number of breeders was allowed to increase over the projection period, as might be expected if the amount of old-growth nesting habitat increased over time, but extinction risk was insensitive to the presence of a carrying capacity. Approximately half of known murrelet nests in central California are within 1 km of heavily used campgrounds in a single state park, indicating that significant gains in viability could be achieved by targeting efforts in small areas providing corvid food subsidies. Risk assessments such as ours can provide quantitative prioritization rationale for efforts intended to mitigate the impacts of synanthropic species on threatened species.

Distance sampling along a line transect is used commonly for monitoring changes of birds' abundance at sea. A critical yet rarely tested assumption of line-transect-sampling theory is that all birds along the transect line (i.e., directly in front of the boat) are detected or that probability of detecting a bird on the line can be estimated. As part of a long-term research and monitoring program for the Kittlitz's Murrelet (Brachyramphus brevirostris), we tested the assumption of complete detection of murrelets on the water along a transect line directly in front of a moving boat. Following standard survey procedures, we approached groups of murrelets (n = 57) at sea and recorded their distance, response (diving or flying), and duration of response. Flying murrelets (n = 27) were easily detected, but diving birds (n = 30) were more difficult to detect because of the duration of their dive. The probability that a bird dove and remained underwater long enough to avoid detection was low because bir...

Nest platforms (mossy pads, limbs, and deformities >15 cm in diameter) are key requirements in the forest nesting habitat of the threatened Marbled Murrelet ( Brachyramphus marmoratus (J.F. Gmelin, 1789)). Little is known about factors that affect the availability of platforms or the growth of canopy epiphytes that provide platforms. We examined variables affecting these parameters in coastal trees in British Columbia using data from 29 763 trees at 1412 sites in 170 watersheds. Tree diameter (diameter at breast height (DBH)) was the most important predictor of platform availability in the pooled data and within each of six regions. In most regions, platforms become available at DBH > 60 cm, but on East Vancouver Island, DBH needs to be >96 cm and possibly on the Central Coast >82 cm. Other regional predictors of platforms included tree height, tree species, and to a lesser extent elevation, slope, and latitude. Most (72%) trees providing platforms had epiphytes (mainly moss) covering one third or more of branch surfaces and 81% had intermediate or thick epiphyte mats. Mistletoe deformities provided

The marbled murrelet (Brachyramphus marmoratus) is an endangered seabird that nests in coastal forests from Alaska to California. The value of these forests for human use, coupled with the difficulty of determining whether a forest stand is occupied by nesting marbled murrelets, poses a dilemma for land managers. Should they implement a costly survey to gather information on whether a potential nest site is occupied, or should they allow human use, effectively assuming the site is unoccupied? This article demonstrates the application of the partially observable Markov decision process (POMDP) as a framework for addressing this question. The analysis yields a policy in which the optimal action is a function of the decision-maker’s subjective probability that a potential nest site is occupied by marbled murrelets. By incorporating stochastic state dynamics and the choice of whether to invest in learning, the POMDP provides a formal representation of adaptive management when active learning is possible.

In northern British Columbia, nests of the Marbled Murrelet (Brachyramphus marmoratus) were first reported in burrows at Marble Island (1901), Cox Island (1920), and Banks Island or Porcher Island (1921), but none were subsequently accepted, and the 1901 and 1920 nests were considered to be Ancient Murrelet (Synthliboramphus antiquus) nests. We collated and reconsidered available information on these 3 nests (including obscure literature, recently uncovered correspondence, and museum records) to re-evaluate their authenticity and clarify past literature, concluding that the 1920 nest should be considered the first possible but unverified nest of the Marbled Murrelet, whereas 1901 and 1921 nests were more convincingly dismissed as belonging to Ancient Murrelet and probably Rhinoceros Auklet (Cerorhinca monocerata), respectively. The 1901 nest also represented the first documented breeding of the Ancient Murrelet in British Columbia, actually at the Limestone Islands.

Marbled Murrelets (Brachyramphus marmoratus) nest predominantly in the canopies of large old-growth conifers, and are listed as Threatened in Canada and 3 US states mainly as a consequence of reductions in this habitat due to logging. We assessed the re-use of nest sites (nest trees) by murrelets in British Columbia using 3 types of data: 1) evidence o fr eturn of adults to the same nest site; 2) evidence of multiple nests within the same tree; and 3) re-checking known nest trees in subsequent seasons for evidence of re-use. All 3 methods showed evidenc eo f re-use of nest trees in different years, but there were marked regional differences in the degree of re-use. Re-use of nest trees was most frequent in regions with extensive loss of nesting habitat due to logging (Southern Mainland Coast and East Vancouver Island), and rare in a less disturbed region (West Vancouver Island). Overall, 26 of 143 (18%) nest trees climbed showed evidence of multiple nesting in separate seasons. Management of nesting habitat should incorporate these results by providing greater protection of habitat in regions where habitat is sparse, and by minimizing predation risk where murrelets more frequently re-use nest sites. Since re-use of nest sites is infrequent, managers should aim to provide murrelets with multiple choices for nest sites, such as maintaining large tracts of old- growth forest with many large trees containing potential nest platforms.

Genetic assignment methods provide an appealing approach for characterizing dispersal patterns on ecological time scales, but require sufficient genetic differentiation to accurately identify migrants and a large enough sample size of migrants to, for example, compare dispersal between sexes or age classes. We demonstrate that assignment methods can be rigorously used to characterize dispersal patterns in a marbled murrelet (Brachyramphus marmoratus) population from central California that numbers approximately 600 individuals and is only moderately differentiated (F(ST)similar to 0.03) from larger populations to the north. We used coalescent simulations to select a significance level that resulted in a low and approximately equal expected number of type I and II errors and then used this significance level to identify a population of origin for 589 individuals genotyped at 13 microsatellite loci. The proportion of migrants in central California was greatest during winter when 83% of individuals were classified as migrants compared to lower proportions during the breeding (6%) and post-breeding (8%) seasons. Dispersal was also biased toward young and female individuals, as is typical in birds. Migrants were rarely members of parent-offspring pairs, suggesting that they contributed few young to the central California population. A greater number of migrants than expected under equilibrium conditions, a lack of individuals with mixed ancestry, and a small number of potential source populations (two), likely allowed us to use assignment methods to rigorously characterize dispersal patterns for a population that was larger and less differentiated than typically thought required for the identification of migrants.

Successful conservation of threatened species is often hindered by a lack of long-term data required to identify the vital rates contributing to population decline and the extrinsic factors influencing those rates. Museum collections can provide a valuable resource for reconstructing the historic demography and diet of otherwise elusive species. Here, we used age ratios (the relative number of hatch-year to after-hatch-year individuals) to examine the hypothesis that population declines in a threatened seabird, the marbled murrelet Brachyramphus marmoratus, are due to declines in reproductive success over the past 150 yr. We also used stable-nitrogen isotopes to exam- ine the hypothesis that variation in reproductive success over this period is related to the quality of food received by young in the nest. Age ratios from at-sea surveys conducted from 1994 to 2001 were significantly lower than museum collection age ratios for the period 1860 to 1950. Stable-nitrogen isotope values indicated that the trophic feeding level of marbled murrelet nestlings declined signif- icantly (-2.6‰) from 1854 to 2008. Our results suggest that the reproductive success of marbeled murrelets breeding in the Salish Sea has declined over the past 150 yr and that declines in nestling diet quality may be partly responsible. Overall, our results support the idea that managers should consider the quality of both nesting and marine foraging habitat as they attempt to improve repro- ductive success and population growth rate in this threatened species.

The Kittlitz's Murrelet (Brachyramphus brevirostris) is a poorly-known species of alcid and a seabird of conservation concern. Nesting murrelets were discovered at Agattu Island in the western Aleutian Islands, and a field study provided new information on nest site selection, chick growth rates and reproductive success. Twelve ground nests were located in upland habitats (441 masl) at inland areas of Agattu (2.3 km from shore). All nests contained one egg or chick. Murrelets tended to nest in association with a ground cover of orange crustose lichens, bare ground, small rocks and graminoids. Estimates of growth rates for the body mass of nestling Kittlitz's Murrelets were lower (KL < 0.10) than published estimates for other small-bodied alcids with semiprecocial young (KL = 0.14 to 0.23). Murrelet young departed from nests after 30 days of growth at 47% of adult mass but at 80% of adult wing length. Optimal wing-loading may ensure successful dispersal flights from terrestrial nest sites to ocea...

The effects of forest fragmentation on bird populations have been studied primarily as static phenomena. Yet when forests are allowed to regenerate, local edge contrast and landscape matrix composition change with time, and we would expect fragmentation effects to change accordingly. Describing this process is critical for the conservation of avian species sensitive to forest fragmentation, including the Marbled Murrelet (Brachyramphus marmoratus), a seabird threatened by ongoing harvest of old-growth forest nesting habitat. We experimentally assessed potential murrelet nest predation probability in four regions of southwestern British Columbia, Canada. We compared the fates of 448 simulated murrelet nests at paired edge and interior treatments, at sites with "hard" edges (recent clearcuts), "soft" edges (regenerating forest), and natural edges (i.e., riparian areas). Motion-sensitive digital nest cameras enabled us to focus on known predators of real nests, and patterns of nest fates did not differ between real and simulated nests. Using information-theoretic model selection (AIC) with the combined data set (116 sites), we assessed effects at patch (approximately 13 ha), landscape (approximately 1700 ha), and regional (approximately 96000 ha) scales. Nest disturbance probability at hard edges was 2.5 times that of interior sites, but soft edges had less than half the disturbance probability of interiors. There was no edge effect at natural edges. At the landscape scale, overall avian disturbance risk declined by as much as 50% with increasing amounts of regenerating forest in the surrounding matrix. These results indicate that initially negative fragmentation effects decrease as forests regenerate, at both patch and landscape scales. There was no evidence that these patterns differed between regions. Predator surveys suggested that Steller's Jays drive patterns of nest predation risk at the regional scale. Assuming that corvids are the most important predators, larger reserves of habitat will lessen negative hard-edge effects. Smaller reserves should be embedded in a protective matrix of regenerating forest to reduce predation risk at both patch and landscape scales. Our results suggest that dynamic fragmentation effects are generalizable across widespread regions and can be broadly applied to both murrelet management and the conservation of old-growth forest-breeding birds in general.

Seabirds maintain plasticity in their foraging behavior to cope with energy demands and foraging constraints that vary over the reproductive cycle, but behavioral studies comparing breeding and nonbreeding individuals are rare. here we characterize how Marbled Murrelets (Brachyramphus marmoratus) adjust their foraging effort in response to changes in reproductive demands in an upwelling system in central California. we radio-marked 32 murrelets of known reproductive status (9 breeders, 12 potential breeders, and 11 nonbreeders) and estimated both foraging ranges and diving rates during the breeding season. Murrelets spent more time diving during upwelling than oceanographic relaxation, increased their foraging ranges as the duration of relaxation grew longer, and reduced their foraging ranges after transitions to upwelling. When not incubating, mur relets moved in a circadian pat ter n, spending nighttime hours resting near flyways used to reach nesting habitat and foraging during the daytime an...

Vessel-based transects have been a mainstay of seabird research for decades, yet there has been surprisingly little effort to evaluate the detectability of seabirds within strip transects. Dis- tance sampling methods offer an opportunity to quantify detectability and assess the proportions of birds on the water that may be missed during strip transects. Three summers of line-transect surveys were analyzed using the program Distance to model detection functions of 6 seabird taxa (marbled murrelet Brachyramphus marmoratus, rhinoceros auklet Cerorhinca monocerata, common murre Uria aalge, pigeon guillemot Cepphus columba, pelagic cormorant Phalacrocorax pelagicus, gulls Larus spp.). We tested the effects of covariates (year, observers, sea state, and cluster size) on detec- tion function estimation. Year and observer were the most important covariates for some but not all species. For a 300 m wide transect (150 m on either side), 20 to 80% of birds were detected, depend- ing on species, year, and observer. Detectability was highest for cormorants (60 to 90%) and fairly similar among other species (typically 40 to 60%). Sea state had a significant effect on encounter rate for murrelets suggesting that g(0), detection probability near the transect line, may be

This article discusses the role of international law in environmental governance in the Arctic. It does so from the perspective of bird conservation. Challenges in the latter field are introduced, including the impact of climate change on Arctic bird habitats and the incidental mortality of seabirds in Arctic fisheries. The ability of the current international legal framework in the Arctic to meet these challenges is scrutinised, and future scenarios for its enhancement are explored, including the conclusion of (a) new legally binding agreement(s). Five species receive particular attention as part of this exercise: gyrfalcon (Falco rusticolus), ivory gull (Pagophila eburnea), spoon-billed sandpiper (Eurynorhynchus pygmeus), Kittlitz’s murrelet (Brachyramphus brevirostris) and Brünnich’s guillemot (Uria lomvia). Special attention is also devoted to the issue of seabird bycatch.

Flexibility in activity time budgets allows animals to cope with heterogeneous and changing environments. Many marine predators, such as seabirds, exhibit flexibility in their foraging behaviour to buffer reproductive success against periods of low prey availability. Over 3 years, 2004 to 2006, we studied the foraging behaviour of a threatened seabird, the marbled murrelet Brachyramphus marmoratus in southwestern Vancouver Island, British Columbia, Canada. An information-theoretic approach was used to compare among factors (temporal, spatial, environ- mental, and competitors) that may influence diving activity. We also quantified local prey availability by hydroacoustic surveys and regional oceanographic conditions (chlorophyll a concentrations and upwelling indices) to investigate relationships between diving activity, food supply and environ- mental conditions. Prey indices varied spatially, seasonally, and annually, showing reduced prey availability during incubation and chick-rearing of 2005. Upwelling indices and chlorophyll a concentrations, as an index of primary productivity, were delayed in 2005. Year and breeding phase had the greatest impact on diving activity, with additional variation among sites. Murrelets increased diving activity in years and seasons with scarce prey and poor oceanographic conditions (incubation and chick-rearing 2005) and decreased diving activity at sites with high prey availability. There was a linear relationship between diving activity and food availability, suggesting no clear thresholds in response to decreases in prey. Despite their flexible activity budgets, increased foraging effort by murrelets in 2005 was inadequate to ensure average levels of reproductive success. Thus, flexible for- aging behaviour by murrelets may be ineffective to buffer reproductive success when environmental conditions are extremely poor.

The marbled murrelet (Brachyramphus marmoratus) is a small Pacific seabird with a breeding range that extends from the Aleutian Islands to central California. Throughout most of its breeding range, it uses mature and old-growth coniferous forests as nesting habitat. Although most murrelets seem to nest within 60 km of the coast, occupied nesting habitat has been identified as far as 84 km from the ocean in Washington state. Due to the extensive inland distances within which birds are known to breed, the area requiring surveys to identify breeding sites can be enormous. Therefore, the standard 2-year survey protocol can be expensive and time-consuming for forest management agencies and companies to administer. We developed a logistic regression model to determine whether a suite of forest structural characteristics could be used to reliably predict occupancy of a forest patch by marbled murrelets. We tested the performance of the final model using cross-validation procedures and a sample of indepe...

We examined the marine distribution and behavior of newly fledged juvenile (hatching year; HY) and adult (after hatching year; AHY) Marbled Murrelets (Brachyramphus marmoratus) off southwest Vancouver Island, British Columbia, to test whether assumptions associated with estimating productivity are met in this area. Productivity estimates for murrelets use HY:AHY ratios from marine surveys, which assume limited emigration and that juvenile and adult birds are similarly distributed. We examined observations from June–August, 1994–2005. Behavioral data were collected from land-based surveys via instantaneous scan sampling. Locations of murrelets at sea were mapped from cliff-top vantage points using a theodolite; Geographic Information Systems (GIS) was then used to compare the distances from shore of juveniles and adults. Data from boat surveys were analyzed using GIS kernel density analysis to compare adult and juvenile murrelet distributions at sea. At fine scales (1–100 m), juveniles were associ...

Summer breeding populations of Kittlitz's Murrelets (Brachyramphus brevirostris) have declined by 80–90% in southeastern Alaska during the past 25 years. Boating activities overlap considerably in space and time with Kittlitz's Murrelets in Glacier Bay, and disturbance could affect individuals by causing them to fly away from preferred foraging sites, thereby disrupting foraging bouts or resting periods. We observed the effects of vessel activity on Kittlitz's Murrelets at sea for each of three response variables (density, group size, and behaviors) in Glacier Bay. Response variables were characterized at three time-scales of inference: immediate (instantaneous response to vessel passage), short-term (response that persisted 30 min after vessel passage), and daily (response on days with different vessel traffic rates). Group size was not affected by vessel activity. By contrast, near-shore densities were suppressed temporarily by vessel passage but recovered within the day. Density effects did no...

Kittlitz's Murrelet (Brachyramphus brevirostris) is a rare seabird whose populations are concentrated in glaciated areas of Alaska. Declines in some parts of its range have led to increased concern over population viability. The remote and cryptic nesting habits of Kittlitz's Murrelets, in contrast to colonial seabirds, preclude monitoring their populations at nest sites and necessitate use of at-sea surveys to count birds. We compared surveys for seabirds in Glacier Bay, Alaska, during 1991, 1999, and 2000, to identify trends in the local Kittlitz's Murrelet population. The surveys conducted in 1999–2000 covered much of the same habitat as those conducted in 1991 but differed in aspects of survey design (i.e., start and stop points, navigation methods, and amount of offshore sampling). We developed a technique using a geographic information system to extract and recompile data from the 1999–2000 surveys that allowed spatially “matched” comparisons with the 1991 survey transects. This comparison ...

Niche overlap and resource partitioning have seldom been investigated in the marine habitats of seabirds but are obvious determinants of community and population status. We investigated interspecific differences in densities and spatial aggregations of seabirds during summer (June–August) off southwest Vancouver Island, British Columbia. Two 300-m-wide parallel transects were sampled along 66.6 km of shoreline in 1993–1996, centered 200 m and 600 m from shore. Analysis focused on the threatened Marbled Murrelet (Brachyramphus marmoratus) and three other fish-eating alcids. Densities of Marbled Murrelets were among the highest reported at sea in the species' range; they were concentrated close to shore (>75% within 0.6 km and virtually all within 2.0 km of shore), usually in water

Breeding seabirds have been well studied but seabird ecology during the nonbreeding season is poorly understood because many species disperse far from breeding colonies to molt at sea. We characterized the timing of prebasic molt and postbreeding dispersal, described postbreeding dispersal movements, and estimated changes in body mass during molt for Marbled Murrelets (Brachyramphus marmoratus; Alcidae) in central California, 1999–2004. According to mark–recapture and at-sea surveys, 248–315 of 496–637 individuals (43–50%) used Ano Nuevo Bay, located immediately adjacent to nesting areas, for their prebasic molt in August–October. Long-distance dispersal (≥ 100 km) from Ano Nuevo Bay by radiomarked Marbled Murrelets was low during breeding (9–13%, n = 46), but was greater for individuals radiomarked at the end of the breeding season (69–90%, n = 20). The mean dispersal dates were 18 May and 21 October for the breeding and postbreeding samples, respectively, and postbreeding dispersal occurred an ...

The Kittlitz's Murrelet (Brachyramphus brevirostris) is a rare, non-colonial seabird often associated with tidewater glaciers and a recent candidate for listing under the Endangered Species Act. We estimated abundance of Kittlitz's Murrelets across space and time from at-sea surveys along the coast of Alaska (USA) and then used these data to develop spatial models to describe abundance patterns and identify environmental factors affecting abundance. Over a five-week period in the summer of 2005, we recorded 794 Kittlitz's Murrelets, 16 Marbled Murrelets (B. marmoratus), and 70 unidentified murrelets. The overall population estimate (N, mean +/- SE) during the peak period (3-9 July) was 1317 +/- 294 birds, decreasing to 68 +/- 37 by the last survey period (31 July-6 August). Density of Kittlitz's Murrelets was highest in pelagic waters of Taan Fjord (18.6 +/- 7.8 birds/km2, mean +/- SE) during 10-16 July. Spatial models identified consistent "hotspots" of Kittlitz's Murrelets, including several small areas where high densities of murrelets were found throughout the survey period. Of the explanatory variables that we evaluated, tidal current strength influenced murrelet abundance most consistently, with higher abundance associated with strong tidal currents. Simulations based on the empirically derived estimates of variation demonstrated that spatial variation strongly influenced power to detect trend, although power changed little across the threefold difference in the coefficient of variation on detection probability. We include recommendations for monitoring Kittlitz's Murrelets (or other marine species) when there is a high degree of uncertainty about factors affecting abundance, especially spatial variability.

ABSTR AC T Habitat fragmentation can cause population declines greater than those expected from habitat loss alone. This can result from detrimental ‘‘edge effects’’, which occur when predation rates are higher at habitat edges relative to interiors. The marbled murrelet (Brachyramphus marmoratus) is a threatened seabird which nests in old-growth forests, a habitat that is being fragmented by ongoing harvest. There is little consensus on the magnitude of edge effects on marbled murrelets, or how they might vary by edge-type. We compared the fates of experimental murrelet nests at paired edge and interior locations at 52 sites in two regions of south-western British Columbia, Canada. Sites were chosen at ‘‘hard’’ edges (recent clearcuts), ‘‘soft’’ edges (regenerating forest), and natural edges (i.e., riparian areas). We used nest cameras to distinguish disturbances caused by known predators of real nests. Accounting for landscape-scale fragmentation, disturbances by avian predators were significantly more frequent at hard edges relative to interiors, but less frequent at soft edges. There were no edge effects at natural-edged sites. These results imply that detrimental edge effects adjacent to recent clearcuts may decline with time due to successional processes. Survey data suggest that this pattern was caused by Steller’s jays (Cyanocitta stelleri), who were observed more often at hard edges than soft edges in one region. Where corvids are important predators, we recommend that managers maintain reserves that lessen the amount of hard edge per patch area. Harvest adjacent to reserves should proceed in stages

Burger and Page (this volume) evaluated our models of habitat preferences and breeding success of a threatened seabird, the marbled murrelet (Brachyramphus marmoratus), based on the largest available set of confirmed nest-sites found in coastal old-growth forest of the Pacific North-West. We believe our study documented novel and unexpected patterns of landscape-level distribution of marbled murrelets in both heavily logged and relatively intact old-growth landscapes and provided insights into how these patterns influence their reproduction, and, eventually, management. Considering the importance of the issue and to ensure appropriate and responsible use of the information we welcome discussion, detailed scrutiny and evaluation of our original results. Burger and Page claim to have identified flaws with model interpretation, data quality, statistical approaches, presentation and interpretation of our results that would invalidate our conclusions. We respond that most of their critique is irrelevant and/or misdirected with respect to our study and the interpretation of GIS data models, and that valid aspects of their claims do not critically affect our conclusions.

Zharikov et al. (2006: Landscape Ecology 21:107–120) modeled the nest-site habitat use of marbled murrelets (Brachyramphus marmoratus) in Desolation Sound (DS) and Clayoquot Sound (CS), British Columbia. They compared known nest sites, located with radio-telemetry, with randomly-located points within the same areas. Their conclusions suggest that murrelets tended to nest in disproportionately smaller fragments within the more disturbed DS landscape; streams, steeper slopes, and lower elevations were selected in both landscapes; murrelets nested closer to recent clearcuts than would be expected in the DS landscape; and survivorship of nestlings was greater in areas with recent clearcuts and was positively correlated with recent habitat fragmentation. These conclusions are contrary to current management guidelines in British Columbia, and therefore require close scrutiny. Our detailed examination reveals flaws in their use of data, application of modeling, and most seriously, interpretation of the results. Problems include: conceptual errors in the interpretation of models; inappropriate spatial resolution; confusing use and interpretation of fragmentation and patch size data; overemphasis of statistically significant but biologically trivial results; and ignoring some contradictory studies. We conclude that it would be risky to apply the results from Zharikov et al. in the selection of murrelet nesting habitat for management purposes in British Columbia. Our review identifies issues that may arise in other ecological modeling studies and stresses the need for biological realism in addition to statistical rigour.

Unlike other alcids, Marbled Murrelets (Brachyramphus marmoratus) typically nest solitarily on large platforms in the upper canopy of old-growth coniferous trees. Although Marbled Murrelets exhibit characteristics that minimize the risk of predation, habitat fragmentation has likely increased the risk of nest predation by corvids. Using a video camera at a nest in northern California, we observed nest fates for 4 yr (2002–2005). These recordings revealed two cases of egg predation by a Steller's Jay (Cyanocitta stelleri) and a Common Raven (Corvus corax), respectively. In both instances, the egg was carried from the nest site, leaving no evidence that nesting had occurred. Our observations revealed (1) the need to be conservative in estimates of nesting attempts and nesting success of Marbled Murrelets based only on the presence or absence of eggshell fragments or feces, (2) that not all predation attempts were successful, and (3) that murrelets may be more susceptible to predation early in the incubation period when adults may be less attentive to eggs and, after hatching, when young are less than 14 d old. We encourage efforts to minimize anthropogenic activities that may increase local corvid densities or disturb murrelets during the early incubation period. SINOPSIS Contrario a otros alcidos, la uria (Brachyramphus marmoratus), anida comunmente, de forma solitaria en grandes plataformas en el docel de bosques maduros de coniferos. Aunque estas aves exhiben caracteristicas que minimizan el riesgo de depredacion, la fragmentacion de habitat ha incrementado el mismo, particularmente por parte de corvidos. Utilizando una camara de video en un nido en el norte de California,observamos el fracaso de nidos por cuatro anos (2002–2005). Las grabaciones revelaron dos casos de depredacion de huevos por parte de Cyanocitta stelleri y Corvus corax, respectivamente. En ambos casos, los huevos fueron cargados, y no se dejo evidencia de depredacion. Nuestras observaciones revelan: (1) la necesidad de ser conservador cuando hace estimados de intentos de anidamiento y exito de anidamiento de urias basado en la presencia o ausencia de fragmentos de cascarones o heces fecales, (2) que no todos los intentos de depredacion fueron exitosos, y (3) que el ave estudiada pudiera ser mas suceptibles a la depredacion temprano en el periodo de incubacion, cuando los adultos pudieran darle menor atencion a los huevos, y luego del eclosionamiento, cuando los pichones tienen menos de 14 dias. Fomentamos los esfuerzos para minimizar actividades antropogenicas que puedan incrementar las densidades locales de corvidos o el disturbio de urias durante las etapas tempranas de incubacion.

1. For the overwhelming majority of species, we lack long-term information on the dynamics of populations. As a consequence, we face considerable uncertainty about how to discriminate among competing hypotheses of population decline and design conservation plans. 2. The marbled murrelet Brachyramphus marmoratus is a small seabird that nests in coastal old-growth forest but feeds year-round in near-shore waters of the north-eastern Pacific. Although a decline in nesting habitat is the primary reason why marbled murrelets are listed as threatened in Canada, nest predation and food availability may also influence population abundance. To examine the hypothesis that murrelet populations are influenced by variation in diet quality, we analysed stable-carbon and -nitrogen isotopes in feathers of museum specimens collected in the Georgia Basin, British Columbia. 3. Between 1889 and 1996, we found a decline in stable isotopic signatures that was approximately equal to a 62% drop in trophic feeding level. We also found that the estimated proportion of fish in murrelet diet was related closely to murrelet abundance over the past 40 years, as estimated from volunteer surveys. Using these isotopic data, we modelled population size as a function of variation in reproductive rate due to changes in diet quality and found that our model matched closely the 40-year field estimates. We then applied our 107-year isotopic record to the model to back-cast estimates of population growth rate to 1889. 4. Our results suggest that, up to the 1950s, murrelet populations in the Georgia Basin were capable of growing and were probably limited by factors other than diet quality. After this period, however, our results imply that murrelets were often, but not solely, limited by diet quality. 5. Synthesis and applications. Protecting nesting habitat may not be sufficient to rebuild populations of this highly secretive and threatened seabird and recovery might also require the restoration of marine habitat quality, as well as a better understanding of how ocean climate affects prey abundance and reproductive rate. Combined with contemporary demographic data, stable isotope analysis of historic samples provides a unique opportunity to reconstruct population histories for species where we lack long-term information.

1. The marbled murrelet Brachyramphus marmoratus is a threatened Alcid nesting in old-growth coastal forests from central California to Alaska. Logging has greatly reduced the amount and altered the pattern of the species' nesting habitat. Landscape fragmentation effects on the breeding ecology of the species are poorly understood because of the inaccessibility of nest sites. 2. Using radio-telemetry, 157 marbled murrelet nests were located in two old-growth areas in British Columbia, Canada, with different logging histories. Probable breeding success was estimated from nest attendance patterns by radio-tagged parents. Information-theoretic and hypothesis-testing methods were used to model breeding distribution (used vs. random unknown sites) and success (successful vs. failed nests) within c. 50-km radius extents at a scale of 2·3-km radius landscapes. Intersite transferability of distribution models was tested. 3. Breeding distribution was positively related with old-growth patch proximity, edge density (natural and artificial) and contrast, proportion of landscape under old-growth or core habitat, and interspersion of old-growth patches; it was negatively related with coastal zone proximity and mean old-growth patch size. Breeding success was negatively affected by the edge contrast, coast proximity and proportion of young forest, probably reflecting the distribution of nest predators. 4. All distribution models discriminated well between used and random landscapes within the training area. Intersite model transferability was good for 50% of the models. The models less predictive of the training site (area under the curve 0·676-0·738) were more transferable, probably because at the training site, which had considerably less old-growth nesting habitat (18% of extent) than the testing site (55%), breeding distribution was driven by a different subset of predictors. 5. Synthesis and applications. Geographic information system (GIS) data were helpful in discriminating between landscapes known to be used by nesting marbled murrelets and those with unknown breeding status. Previous indirect inferences about landscape-level effects on breeding distribution in the birds were shown to correspond with their true nesting distribution. Our results suggest that habitat fragmentation per se need not have a negative effect on the birds beyond that as a result of habitat loss, unless associated with an increased abundance of predators. Our results fine-tune the existing habitat conservation guidelines by suggesting that protection of old-growth forest adjacent to clearcuts is important. We provide a means for desktop classification of marbled murrelet landscapes. We advise the application of several different models, depending on the amount of remaining old-growth forest, to evaluate the consistency of predictions.

We investigated relationships between oceanographic processes, prey availability, diet and the reproductive success of the marbled murrelet Brachyramphus marmoratus (Alcidae), a feder- ally threatened seabird. We predicted that cooler ocean conditions (which increase primary produc- tivity in this eastern boundary upwelling system) should result in heightened prey availability and hence higher reproductive success for the murrelet. We also expected that murrelet diets should reflect those potential prey species that are most abundant during any given season or year. Oceano- graphic conditions were considered at 2 spatial scales: synoptic (Northern Oscillation Index, NOI; Pacific Decadal Oscillation Index, PDO; the North Pacific Index, NPI), and local (upwelling index, UI; sea surface temperature, SST; strength of the spring turnover). To infer seasonal and annual variation in murrelet diets in central California, we used stable isotope analyses of δ 15 N and δ 13 C in murrelet feathers and prey tissues during the pre- and postbreeding seasons of 1998 to 2002. Isotopic signa- tures of 10 species of potential prey clustered into 3 distinct groups (low, mid and high trophic level seabird prey). During 1999 to 2001, when more krill (low trophic level prey) were available, murrelet δ 15 N and trophic level were lower prior to breeding than after breeding, whereas pre- and postbreed- ing diets were similar during 1998 and 2002 when fewer krill were available. δ 13 C was always lower in prebreeding than postbreeding diets, which tracked availability of 13 C enriched juvenile rockfish and market squid. Diet did not differ by sex for either isotope. Murrelet productivity (juvenile:adult ratios) was positively correlated with both rockfish and krill abundance. PDO, NOI, UI, spring turnover strength and NPI indices were unrelated to murrelet productivity and to prey abundances. Murrelet productivity was also positively related to the proportion of mid trophic level prey in postbreeding diets, and thus negatively related to the proportion of low and high trophic level prey consumed. Fur- thermore, productivity was markedly higher following the apparent 1998 to 1999 PDO regime shift to cooler conditions. These data suggest that cooler local temperatures support increased availability of krill and juvenile rockfish to murrelets, and that this improves murrelet reproductive success.

The Marbled Murrelet (Brachyramphus marmoratus Gmelin) is a small threatened seabird of the Pacific coast of North America. Through simulation modelling we varied the long-term minimum amounts and quality (nesting density) of old-forest nesting habitat to examine effects on murrelet population viability, our measure of population resilience. Applying diffusion approximations we estimated population longevity and persistence probability under uncertainties of at-sea demography and onshore edge effects affecting nesting success, time scale, spatial scale, and subpopulation structure. We cast our analysis in a Bayesian belief and decision network framework. We also applied the framework to spatially explicit land-use and murrelet inventory data for the northern mainland region of the British Columbia coast. We found a diminishing expected value of persistence probability (EVP), for a single independent population, below a nesting capacity of ≈5000 nesting pairs (≈15 000 birds), accelerating below 2000 pairs. A strategy of multiple semi-independent subpopulations provided a higher joint EVP across a wide range of total nesting capacity. There was little improvement in EVP, for any number of subpopulations, above 10 000 – 12 000 pairs (≈36 000 birds, 45%–60% of coastwide population estimate in 2001). Depending on estimates of nesting density, 12 000 pairs would require between 0.6 and 1.2 million ha of potential old-forest nesting habitat.

AbstractThe Marbled Murrelet (Brachyramphusmarmoratus) is a highprofile, federally threatened seabird, but noreliable estimates of population trends at inlandbreeding areas exist for this species. We conductedland-based radar studies of Marbled Murrelets at3–7 sites on the Olympic Peninsula,Washington, in 1996–2002 and 2004 to estimatepopulation changes and to examine relationshipsbetween our counts and oceanographic conditions,murrelet productivity, and regional at-sea countsof murrelets. Morning radar counts of murreletsvaried significantly among and within sites but didnot decline from 1996–2004, suggesting thatthe inland breeding population of murrelets isstable in this area. A retrospective power analysisindicated that we had a 25% and 56%chance of detecting 2% and 4% annualdeclines, respectively. Thus, if relatively smallannual declines did occur during our study period,there is a high probability that they would havegone undetected, even though they could add up to abiologically important decline over time. It isunlikely that murrelets on the Olympic Peninsuladeclined by ≥6% annually, however,because retrospective analyses indicated that powerto detect such declines was >88%. Therewas no significant relationship between radarcounts and at-sea counts or productivity ofmurrelets in the nearby San Juan Islands during thestudy period. We also did not detect a relationshipbetween radar counts and mean sea-surfacetemperatures or the Northern Oscillation Index,suggesting that variation in oceanographicconditions (e.g., the strong 1998 ElNiño event) was not associated withvariation in morning radar counts of MarbledMurrelets. A prospective power analysis indicatedthat small (2%–4%)annual declines could be detected with reasonablyhigh power (≥80%) with thecurrent radar sampling design by extending thestudy to 11–15 years.

The marbled murrelet (Brachyramphus marmoratus) is a threatened seabird that nests in old-growth forests in the Pacific Northwest. Despite concern for this species, little has been published on murrelet nesting habitat in the coast redwood (Sequoia sempervirens) region. Here we present the first comprehensive study of marbled murrelet nesting characteristics in redwood forests based on confirmed nest sites. In this study, we 1) described habitat characteristics at 17 murrelet nest sites in the Santa Cruz Mountains, California, USA, located using radiotelemetry and visual searches, and 2) compared nest sites with random sites located in nearby stands and centered on trees ≥120 cm diameter at breast height (dbh [potential nest trees or PNTs]). All 17 nests were located in stands of old-growth redwood forest and the mean dbh of nest trees was 210 cm (SD = 91 cm). Eighty-two percent of nests (90% of telemetry-found nests) were in unharvested stands and 18%, all on private property, had been lightly h...

Spatial environmental gradients can greatly affect the distribution of organisms, but studies investigating how the spatial arrangement of samples along these gradients influences power of monitoring programs to detect trends are lacking. Spatial gradients in environmental processes may remain relatively constant, or change over different time intervals and spatial dimensions. We investigated the influence of transect layout and replication on the power to detect population declines in the Marbled Murrelet (Brachyramphus marmoratus), a threatened seabird found in a highly dynamic nearshore environment. In Marbled Murrelet populations in our study area, no a priori gradient along the shoreline was apparent, whereas a predictable decline in abundance offshore occurred. We characterized the spatial and temporal variation in the offshore gradient by: (1) fitting flexible curves to historical abundance data from 13 site–year combinations in California and Oregon and (2) applying clustering routines to the fitted offshore probability distributions to reveal three distribution patterns that varied among sites and annually within sites. Power of sampling schemes was derived by a simulation where nine transect designs of equal effort detected population declines over 10 years within an 80 km × 2.5 km sampling unit either with or without stratification, based on data-generating distributions that were an approximation to the observed data. Our simulations suggested several designs had high power to detect trends at an annual decline rate of 2, 4, and 6%, produced relatively unbiased population estimates and slopes of the trend, and were logistically feasible: (1) stratified and unstratified zigzags and (2) ten 8 km transects placed at random distances parallel to shore in two strata. For murrelets, layouts that adequately sample along-shore and offshore in both high-density and low-density areas were most robust to heterogeneity and shifting environmental gradients in both along-shore and offshore dimensions. Our approach shows how pilot survey data and an understanding of spatial gradients or heterogeneity can help design a powerful sampling layout.

The Marbled Murrelet (Brachyramphus marmoratus) was listed as threatened in 1992, primarily because of loss of its old-forest nesting habitat. Monitoring conducted over the first 10 years following implementation of the Northwest Forest Plan shows at-sea murrelet populations appear to be stationary, but recruitment is very low and demographic models project a 4-6% annual rate of decline. Monitoring of nesting habitat indicated there were about 1.6 million ha of higher-suitability nesting habitat on all lands at the start of the plan, about half of which occurred on federal lands. Most (88%) of higher-suitability habitat on federal lands was protected within reserves. Over the past 10 years, losses of habitat due primarily to fire have totaled about 2% on federal lands. Losses have been much greater (12%) on nonfederal lands, due primarily to timber harvest. Habitat is expected to accrue within reserves as younger forest matures and attains sufficient diameter to support nesting sites. At-sea estimates of population size are strongly and positively correlated with amounts of adjacent nesting habitat at a broad scale, supporting the idea that amounts of nesting habitat are a primary driver in wide-scale murrelet population distribution. Conditions at sea, however such as temperature regimes, prey availability, and pollutants, continue to affect murrelet populations. The system of large reserves seems to have achieved the short-term objective of conserving much of the remaining nesting habitat on federal lands. These reserves are also likely to contribute to the long-term objective of creating large, contiguous blocks of nesting habitat. The plan has a primary role in conserving and restoring nesting habitat on federal land but will succeed in this role only if land allocations calling for such protection are in place for many decades.

Coastal marine ecosystems worldwide have undergone such profound transformations from over-fishing that trophic interactions observed today might be artifacts of these changes. We determined whether the trophic level of an endangered seabird, the Marbled Murrelet (Brachyramphus marmoratus), has declined over the past 100 years after the collapse of Pacific sardine (Sardinops sadax) fisheries in the late 1940s and the recent declines of similar fisheries in central California. We compared stable-isotope signatures of delta15N and delta13C in feathers of museum specimens collected before fisheries decline with values in murrelet feathers collected recently. Values of delta15N in prebreeding diets declined significantly, 1.4 per thousand or 38% of a trophic level, over the past century during cool ocean conditions and by 0.5 per thousand during warm conditions, whereas postbreeding values of delta15N were nearly constant. The delta13C values in prebreeding diets declined by 0.8 per thousand, suggesting an increased importance of krill in modern compared with historic prebreeding diets, but postbreeding diets did not change. Stable-isotope mixing models indicated that the proportion of energetically superior high-trophic-level prey declined strongly whereas energetically poor low-trophic-level and midtrophic-level prey increased in the prebreeding diet in cool years when murrelet reproduction was likely to be high. Decreased prey resources have caused murrelets to fish further down on the food web, appear partly responsible for poor murrelet reproduction, and may have contributed to its listing under the U.S. Endangered Species Act.

Radar and audiovisual surveys are important tools for identifying nesting habitat and developing inland conservation strategies for the marbled murrelet (Brachyramphus marmoratus), a threatened seabird that nests in old-growth forests in the Pacific Northwest, USA. Theoretically, counts from these 2 approaches (radar and audiovisual surveys) in different habitats depend on both habitat-specific densities and detection probabilities, which could result in spurious or mask differences among habitats if murrelets are more detectable in certain habitat types. Therefore, we used simultaneous audiovisual and radar surveys to estimate detection probabilities and quantify the relationship between detection probabilities and habitat in coastal redwood forests of northern California, USA. Radar and audiovisual counts were highly correlated (r = 0.65) based on 156 simultaneous surveys, but audiovisual surveys detected only 20.2% (2.6 SE) of murrelets detected by radar, whereas radar detected 75.6% (6.3 SE) of murrelets detected by audiovisual surveys. Murrelets tended to be easier to detect with both audiovisual and radar surveys when there were relatively large areas (>35 ha) of unharvested, old-growth forest at the survey site, probably because birds tended to fly slower and circled more over old growth. Detection probabilities were strongly affected by a variety of other factors including weather, time relative to sunrise, observer, and murrelet behavior. Murrelet counts were positively but weakly correlated to the area of unharvested old growth at the survey site for audiovisual and radar surveys, but this relationship disappeared when we corrected for the effect of habitat on detection probabilities. Our results indicate that raw counts should not be used as indices of nesting densities in different habitats and underscore the need to model heterogeneity in detection probabilities among habitats using available sampling designs and statistical methods. Nevertheless, we recommend using radar instead of audiovisual surveys for counting murrelets in forested areas because detection probabilities were much higher for radar than audiovisual surveys, radar is less likely to detect the same group of murrelets multiple times, and radar surveys can be conducted in poor viewing and hearing conditions.

Weused pilot data collected in 2001–2004 to compare the power of radar and audiovisual survey approaches to detect trends in breeding population size and differences in trends between populations of marbled murrelets (Brachyramphus marmoratus) in northwestern California. Radar counts of murrelets were almost triple in inland Reserves than in Conservation Areas, and audiovisual counts were 7 times greater. Variation in counts was statistically significant among survey sites but not among years. Although annual variation in radar counts was not statistically significant (P = 0.13), mean radar counts more than tripled from 2001 to 2002, a difference that we considered to be biologically significant, and the radar counts reflected a large increase in the proportion of breeders between these 2 years as determined by radiotelemetry in another study (Acord et al. 2004). Audiovisual counts were much more variable than radar counts overall (CV = 1.10 versus 0.41) and within survey sites (CV = 0.94 versus ...

The distribution of marine birds relative to water clarity was examined in the nearshore waters of Monterey Bay, California. I conducted nine at-sea surveys in 1999 and 2000 and simultaneously recorded water clarity and the density of five taxa of marine birds. Among plunge-divers, Forster's Terns (Sterna forsten) occurred more frequently than expected over turbid water ( 5 m Secchi depth). Turbidity in Monterey Bay may be caused by suspended organic matter, including phytoplankton, during summer and fall. Forster's Tern may prefer such areas because small fish are likely to occur near this potential food source. Brandt's Cormorants probably rely on vision to catch fish near the bottom and turbid water may reduce available light and limit visual acuity. The distribution of Brown Pelicans (Pelecanus occidentalis), Western/Clark's Grebes (Aechmophorus occidentalis!clarki?), and Marbled Murrelets (Brachyramphus marmoratus) did not appear to be influenced by turbidity levels, indicating that some seabirds use marine habitats with a wide range of water clarities.

We developed 31 novel, polymorphic microsatellite loci in the marbled murrelet (Brachyramphus marmoratus), a critically endangered seabird. Variability was tested on 15 individuals from the Santa Cruz, California population, with each locus characterized by two to 12 alleles. Observed levels of heterozygosity ranged from 0.13 to 0.93. These loci provide a valuable means of assessing the population structure and demographic parameters of this species, which may be critical to its conservation across a fragmented habitat.

We estimated annual local survival rates for after-hatch-year (≥1-yr old) marbled murrelets (Brachyramphus marmoratus) in central California using Cormack-Jolly-Seber mark–recapture models and radiotelemetry, and we modeled the effect of oceanographic conditions, sex, and radiotagging. We captured 331 after-hatch-year murrelets from 1997 to 2003, of which 117 were radiotagged. Recapture rates were best modeled using a term that reflected differences in capture effort among sampling occasions (peffort) and ranged from 0.068 to 0.166. The most highly ranked model (ΦPDO+radio, peffort) indicated that survival rates were positively related to the strength of the Pacific Decadal Oscillation (PDO) and were negatively affected by radiotransmitters in the year following tagging. Mortality was relatively low in warm-water years, perhaps because murrelets flew inland to breed less frequently and were less exposed to avian predators. Two competing models indicated that survival in the year following tagging...