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A central theme for conservation is understanding how animals differentially use, and are affected by change in, the landscapes they inhabit. However, it has been challenging to develop conservation schemes for habitat‐specific behaviors.Here we use behavioral change point analysis to identify behavioral states of golden eagles (Aquila chrysaetos) in the Sonoran and Mojave Deserts of the southwestern United States, and we identify, for each behavioral state, conservation‐relevant habitat associations.We modeled behavior using 186,859 GPS points from 48 eagles and identified 2,851 distinct segments comprising four behavioral states. Altitude above ground level (AGL) best differentiated behavioral states, with two clusters of short‐distance movement behaviors characterized by low AGL (state 1 AGL = 14 m (median); state 2 AGL = 11 m) and two associated with longer‐distance movement behaviors and characterized by higher AGL (state 3 AGL = 108 m; state 4 AGL = 450 m).Behaviors such as perching and low‐altitude hunting were associated with short‐distance movements in updraft‐poor environments, at higher elevations, and over steeper and more north‐facing terrain. In contrast, medium‐distance movements such as hunting and transiting were over gentle and south‐facing slopes. Long‐distance transiting occurred over the desert habitats that generate the best updraft.This information can guide management of this species, and our approach provides a template for behavior‐specific habitat associations for other species of management concern., Despite the importance of linking habitat use to specific behaviors, this is almost never done, in part because of the many challenges in understanding where and when individual behaviors occur. Here, we use long‐term, short‐interval, and highly precise GPS data as input to recently developed models to interpret animal behavior from telemetry data to identify where and when behavioral states occur. Subsequently, we link these behavioral states to habitat, as a mechanism to identify the environmental correlates of each behavior, and to infer potential threats to these animals based on those behavior‐specific habitat associations.

Anticoagulant rodenticides (ARs) are commonly used to control rodent pests. However, worldwide, their use is associated with secondary and tertiary poisoning of nontarget species, especially predatory and scavenging birds. No medical device can rapidly test for AR exposure of avian wildlife. Prothrombin time (PT) is a useful biomarker for AR exposure, and multiple commercially available point-of-care (POC) devices measure PT of humans, and domestic and companion mammals. We evaluated the potential of one commercially available POC device, the Coag-Sense® PT/INR Monitoring System, to rapidly detect AR exposure of living birds of prey. The Coag-Sense device delivered repeatable PT measurements on avian blood samples collected from four species of raptors trapped during migration (Intraclass Correlation Coefficient > 0.9; overall intra-sample variation CV: 5.7%). However, PT measurements reported by the Coag-Sense system from 81 ferruginous hawk (Buteo regalis) nestlings were not correlated to those measured by a one-stage laboratory avian PT assay (r = − 0.017, p = 0.88). Although precise, the lack of agreement in PT estimates from the Coag-Sense device and the laboratory assay indicates that this device is not suitable for detecting potential AR exposure of birds of prey. The lack of suitability may be related to the use of a mammalian reagent in the clotting reaction, suggesting that the device may perform better in testing mammalian wildlife

Most raptor populations are declining and nearly a fifth are threatened with extinction; thus there is a need to increase collaboration to ensure efficient and effective research, management, and conservation. Here, we introduce the Global Raptor Impact Network (GRIN; www.globalraptors.org), a tool to enhance collaboration and conservation impact of the raptor research community. We provide an overview of the history and current state of GRIN, including plans for expansion. Predecessors to GRIN include The African Raptor DataBank, which was launched in 2012 to ascertain the conservation status of raptors across Africa; and the Global Raptor Information Network, which was launched in the late 1990s as a website to provide information regarding diurnal raptors and facilitate communication among researchers. GRIN expands the data collection and storage capabilities of the African Raptor DataBank to a global scale via mobile application. We have implemented data-sharing rules to ensure the safety of sensitive species, and users of the GRIN mobile app can designate their records as confidential. GRIN staff and partners are developing analyses of species' population trends and geographic distributions to aid in conservation assessments. GRIN is also developing systematic reviews, detailed bibliographies, and online accounts that will summarize the state of knowledge for each raptor species. We hope that GRIN will benefit the entire raptor research community and aid in the collaboration necessary to help raptor populations thrive in the Anthropocene.

During the course of a plague epizootic, decimation of rodent host populations may result in the transfer of fleas to alternate or phoretic hosts, including to sympatric raptors that prey on rodents. We studied flea abundance and flea species assemblages on burrowing owls (Athene cunicularia hypugaea) in southwestern Idaho before (2012 – 2014), during (2015 – 2016), and after (2017) an epizootic of plague in Piute ground squirrels (Urocitellis mollis). We examined (1) if a larger proportion of burrowing owl nests contained fleas, (2) the likelihood that owls within a high flea abundance class increased, and (3) if owls harbored ground squirrel fleas during the epizootic. Using a flea abundance index assigned to 1,184 owls from 236 nests, the proportion of nests and the likelihood that owls had high flea abundance decreased rather than increased during epizootic years. Moreover, of 3,538 collected fleas from owls at 143 nests, no fleas were species that Piute ground squirrels typically harbor. Instead, Pulex irritans was the predominant flea collected in all study years (> 99%). Thus, although raptors may play a role in plague, there was no evidence that the die-off of ground squirrels resulted in higher flea intensity in burrowing owls or that they served as frequent accidental or phoretic hosts for ground squirrel fleas that could potentially be infectious with Yersinia pestis.

Illegal killing of nongame wildlife is a global yet poorly documented problem. The prevalence and ecological consequences of illegal killing are often underestimated or completely unknown. We review the practice of legal recreational shooting and present data gathered from telemetry, surveys, and observations on its association with illegal killing of wildlife (birds and snakes) within conservation areas in Idaho, USA. In total, 33% of telemetered long‐billed curlews (Numenius americanus) and 59% of other bird carcasses found with known cause of death (or 32% of total) were illegally shot. Analysis of spatial distributions of illegal and legal shooting is consistent with birds being shot illegally in the course of otherwise legal recreational shooting, but snakes being intentionally sought out and targeted elsewhere, in locations where they congregate. Preliminary public surveys indicate that most recreational shooters find abhorrent the practice of illegal killing of wildlife. Viewed through this lens, our data may imply only a small fraction of recreational shooters is responsible for this activity. This study highlights a poorly known conservation problem that could have broad implications for some species and populations of wildlife.

Breeding dispersal, the movement between successive breeding sites, is important to many aspects of life history and population dynamics but poorly understood for many raptor populations. We used longitudinal data collected from Burrowing Owls (Athene cunicularia) nesting in southwestern Idaho from 1994–2007 to examine characteristics of breeding dispersal behavior. First, we measured frequency and distance of breeding dispersal and compared those to published results from other owl populations. The dispersal frequency (78%, n = 86) was greater than previously reported for any Burrowing Owl population and for most owl species. The mean distance dispersed (835 ± 98 m [SE]) was slightly greater than reported distances for most other Burrowing Owl populations. Second, we examined factors associated with two decisions owls faced between breeding seasons: whether to move to a new nest site (dispersal likelihood), and how far to move if dispersing to a new site (dispersal distance). We assessed the pot...

Western Burrowing Owls (Athene cunicularia hypugaea) frequently nest near agricultural lands. In southwestern Idaho, greater population density in agricultural landscapes appears to be driven in part by reliable and abundant prey populations. However, these potential benefits may be offset if agricultural land use increases pesticide exposure, especially during the sensitive reproduction period. Thus, we investigated the extent to which Burrowing Owls nesting near croplands within the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA), Idaho, were exposed to organophosphate (OP), carbamate (CB), and/or organochlorine (OC) pesticides. We examined plasma cholinesterase activity, OP and CB residues in foot-wash samples, and OCs in soils and whole egg contents collected from owls and their nests along a distance gradient from agricultural fields. We further measured eggshell thickness to assess potential for thinning from OC exposure. There was no inhibition of cholinesterase activities in adult or nestling owls near agriculture, and foot-wash samples from adults tested negative for OP and CB pesticides. The OC p,p′-DDE, a metabolite of DDT, occurred in eggs at 27 of 58 nests, but there was some evidence that concentrations increased with increasing distance from agriculture. Concentrations of p,p′-DDE in eggs were relatively low compared to harmful levels in other avian species, were not correlated with eggshell thickness, and did not appear to reduce nesting success. Neither DDT, its metabolites, nor any other OCs were detected in soil samples from local owl breeding areas. These results indicate that p,p′-DDE, organophosphate, and carbamate exposure were not causing toxicity or reproductive impairment of Burrowing Owls in the NCA during our study years.

Highway programmes typically focus on reducing vehicle collisions with large mammals because of economic or safety reasons, while overlooking the millions of birds that die annually from traffic. We studied wildlife–vehicle collisions along an interstate highway in southern Idaho, USA, with among the highest reported rates of American Barn Owl Tyto furcata road mortality. Carcass data from systematic and ad hoc surveys conducted in 2004–2006 and 2013–2015 were used to explore the extent to which spatial, road geometric and biotic factors explained Barn Owl–vehicle collisions. Barn Owls outnumbered all other identified vertebrate species of roadkill and represented > 25% of individuals and 73.6% of road‐killed birds. At a 1‐km highway segment scale, the number of dead Barn Owls decreased with increasing numbers of human structures, cumulative length of secondary roads near the highway and width of the highway median. The number of dead Barn Owls increased with higher commercial average annual daily traffic (CAADT), small mammal abundance index and grass rather than shrubs in the roadside verge. The small mammal abundance index was also greater in roadsides with grass vs. mixed shrubs, suggesting that Barn Owls may be attracted to grassy portions of the highway with more abundant small mammals for hunting prey. When assessed at a 3‐km highway segment scale, the number of dead Barn Owls again increased, with higher CAADT as well as with greater numbers of dairy farms. At a 5‐km scale, the number of dead Barn Owls increased with a greater percentage of cropland near the highway. Although human conversion of the environment from natural shrub‐steppe to irrigated agriculture in this region of Idaho has probably enhanced habitat for Barns Owls, it simultaneously has increased risk for owl–vehicle collisions where an interstate highway traverses the altered landscape. We review some approaches for highway mitigation and suggest that reducing wildlife–vehicle collisions involving Barn Owls may contribute to the persistence of this species.

Wind energy development is rapidly expanding in North America, often accompanied by requirements to survey potential facility locations for existing wildlife. Within the USA, golden eagles (Aquila chrysaetos) are among the most high-profile species of birds that are at risk from wind turbines. To minimize golden eagle fatalities in areas proposed for wind development, modified point count surveys are usually conducted to estimate use by these birds. However, it is not always clear what drives variation in the relationship between on-site point count data and actual use by eagles of a wind energy project footprint. We used existing GPS-GSM telemetry data, collected at 15 min intervals from 13 golden eagles in 2012 and 2013, to explore the relationship between point count data and eagle use of an entire project footprint. To do this, we overlaid the telemetry data on hypothetical project footprints and simulated a variety of point count sampling strategies for those footprints. We compared the time an eagle was found in the sample plots with the time it was found in the project footprint using a metric we called “error due to sampling”. Error due to sampling for individual eagles appeared to be influenced by interactions between the size of the project footprint (20, 40, 90 or 180 km2) and the sampling type (random, systematic or stratified) and was greatest on 90 km2 plots. However, use of random sampling resulted in lowest error due to sampling within intermediate sized plots. In addition sampling intensity and sampling frequency both influenced the effectiveness of point count sampling. Although our work focuses on individual eagles (not the eagle populations typically surveyed in the field), our analysis shows both the utility of simulations to identify specific influences on error and also potential improvements to sampling that consider the context-specific manner that point counts are laid out on the landscape.

Owing to habitat loss, changes in farming practices, urbanization, and high mortality through vehicle collisions, barn owls Tyto alba are a species of conservation concern in portions of their range. This species can be secretive and difficult to survey, particularly away from breeding sites, so factors related to barn owl occurrence often remain unknown. We conducted nighttime broadcast surveys for barn owls during the early- and post-breeding seasons and used an occupancy modeling framework to understand how factors related to landcover, landscape features, and human development related to occupancy in southern Idaho, USA. We also assessed the effectiveness of using broadcasts of conspecific vocalizations to improve owl detection. Barn owls were detected during 52 of 666 point counts and at 37 of 222 locations in the early-breeding season and 50 of 198 point counts and 31 of 66 locations in the post-breeding season. The probability of detecting barn owls was 0.32 ± 0.06 (SE) and 0.45 ± 0.07 (SE) during the early- and post-breeding seasons, respectively. Based on analysis within 1-km buffers surrounding point-count locations, occupancy in the early-breeding season increased with percentage of crop coverage and presence of trees and decreased with background noise. Post-breeding season occupancy increased with stream length and decreased with area of development and distance from the Snake River, a major geologic feature that likely provided roost sites in its canyon walls and riparian woodlands and a dispersal corridor for juveniles. Broadcast of barn owl vocalizations increased detection probability as much as nine times. Thus, incorporating call broadcast into future barn owl surveys should help investigators reduce false conclusions of absence. Ultimately, understanding factors influencing occupancy of barn owls will facilitate effective conservation, especially in light of population pressures related to factors such as roadway mortality and loss of nesting sites with increased urbanization.

Migration allows animals to live in resource-rich but seasonally variable environments. Because of the costs of migration, there is selective pressure to capitalize on variation in weather to optimize migratory performance. To test the degree to which migratory performance (defined as speed of migration) of Golden Eagles (Aquila chrysaetos) was determined by age- and season-specific responses to variation in weather, we analyzed 1,863 daily tracks (n = 83 migrant eagles) and 8,047 hourly tracks (n = 83) based on 15 min GPS telemetry data from Golden Eagles and 277 hourly tracks based on 30 s data (n = 37). Spring migrant eagles traveled 139.75 ± 82.19 km day−1 (mean ± SE; n = 57) and 25.59 ± 11.75 km hr−1 (n = 55). Autumn migrant eagles traveled 99.14 ± 59.98 km day−1 (n = 26) and 22.18 ± 9.18 km hr−1 (n = 28). Weather during migration varied by season and by age class. During spring, best-supported daily and hourly models of 15 min data suggested that migratory performance was influenced most st...

Bird species, including raptors, can often be categorized into two groups depending upon their response to alterations in clutch size while laying. For some, clutch size is predetermined prior to the start of laying (i.e., determinate species). In contrast, the clutch size of indeterminate layers can be influenced by external factors present at the time of laying. Using field experiments, our objective was to examine the egg-laying responses of female Western Burrowing Owls (Athene cunicularia hypugaea) to manipulations of clutch size. To assess whether Burrowing Owls are determinate or indeterminate egg-layers, we altered female clutch size by removing or adding one egg during the laying period. At the time of egg removal or addition, the resident female had 1–5 of her own eggs present in her clutch. We compared the size of completed clutches of both removal and addition nests to the size of completed clutches at control nests. Mean clutch size at removal nests (x = 8.3 eggs, SE = 0.44, n = 9) ...

Few studies have examined the patterns of co-occurrence between diurnal birds such as woodpeckers and nocturnal birds such as owls, which they may facilitate. Flammulated Owls (Psiloscops flammeolus) and Northern Saw-whet Owls (Aegolius acadicus) are nocturnal, secondary cavity-nesting birds that inhabit forests. For nesting and roosting, both species require natural cavities or, more commonly, those that woodpeckers create. Using day and nighttime broadcast surveys (n = 150 locations) in the Rocky Mountain biogeographic region of Idaho, USA, we surveyed for owls and woodpeckers to assess patterns of co-occurrence and evaluated the hypothesis that forest owls and woodpeckers co-occurred more frequently than expected by chance because of the facilitative nature of their biological interaction. We also examined co-occurrence patterns between owl species to understand their possible competitive interactions. Finally, to assess whether co-occurrence patterns arose because of species interactions or selection of similar habitat types, we used canonical correspondence analysis (CCA) to examine habitat associations within this cavity-nesting bird community. We found that Flammulated Owls co-occurred more with Hairy Woodpeckers (Picoides villosus), Northern Saw-whet Owls co-occurred with Northern Flickers (Colaptes auratus) and Red-naped Sapsuckers (Sphyrapicus nuchalis) and, when primary excavators were considered as a group, each species of owl was positively associated with the presence of woodpeckers. The owl species were distributed independently of one another suggesting a lack of competitive interactions. The CCA had relatively low explanatory power but suggested that habitat associations alone did not explain the patterns of positive co-occurrence we observed: Flammulated Owls and Hairy Woodpeckers associated with different habitats and Northern Saw-whet Owls, Northern Flickers, and Red-naped Sapsuckers appeared as habitat generalists. We interpret these patterns of co-occurrence and habitat use as evidence that woodpeckers facilitate presence of these species of owl and suggest management for forest owls could also include focus on the diurnal species with which they appear to associate.

Spatially explicit models depicting species occupancy offer a useful conservation tool for land managers. Using occurrence data collected in 2009 and 2010 from the Boise National Forest, Idaho, we developed distribution models for Flammulated Owls (Psiloscops flammeolus) and Northern Saw-whet Owls (Aegolius acadicus) to explore associations between habitat factors and owl occupancy. We then spatially applied these models in a Geographic Information System. We considered land cover and topographic variables at three spatial scales: 0.4-km, 1-km, or 3-km-radius plots centered on point-count locations (n = 150) with resolution of land covers at 30 m. Flammulated Owls occupied 27 (18%) point-count locations and occurred in areas with a higher proportion of Douglas-fir (Pseudotsuga menziesii) at the 0.4-km scale, less diverse land cover composition at the 1-km scale, and in south-facing aspects at the 3-km scale. Northern Saw-whet Owls occupied 45 (30%) point-count locations and were associated with...

We examined the temporal, spatial, and demographic factors that influenced roadway mortality of barn owls (Tyto alba) along a 248-km stretch of Interstate 84 in southern Idaho using systematic road surveys. Counts of dead animals from surveys can be underestimated because of sampling biases; therefore, we also conducted experiments to assess the effects of search and removal bias on the estimates of roadway mortality of owls. We conducted surveys every 2 weeks over a 2-year period and detected 812 dead barn owls (unadjusted mortality rate of 1.64 owls/km/yr). After adjusting this estimate for search and removal bias, we documented mortality rates of up to 5.99 owls/km/year. Owl mortality was not random in relation to sex, age class, or location along the highway. Females and juveniles, which represent individuals more likely to disperse long distances, were killed more frequently than males and adults. During the nonbreeding season, owls were killed more often near agricultural lands than in shrub-steppe, but this pattern was not apparent during the breeding season. Owls were also killed more often on portions of the roadway closer to the Snake River canyon, perhaps because of the availability of nest and roost sites. Mortality rates differed markedly between the 2 years of study, which could have been related to variability in weather and its subsequent effect on owl productivity. Our data suggest that barn owls in this region may not persist under this level of mortality without significant immigration or management. Thus, roadway management to reduce or prevent owl use of roadways, reduce rodent populations near major roads, alert motorists to the presence of owls, or otherwise reduce the chances that vehicles and owls collide would improve barn owl survival and population persistence. © 2012 The Wildlife Society.

Increases in yolk androgens within and among avian clutches have been correlated with decreased incubation time, increased aggression within a nest, increased begging behaviour, decreased immune response, and decreased life span. Although the mechanisms that lead to variability in yolk androgens within and between clutches are not completely known, yolk androgens can be a function of both social and environmental conditions. We were interested in if and how nesting density, laying date, and laying order influenced yolk androgens in Western Burrowing Owls ( Athene cunicularia hypugaea (Bonaparte, 1825)) in which nest density varies considerably. In 2006 and 2007, we used radioimmunoassay to quantify the concentrations of testosterone, 5α-dihydrotestosterone, and androstenedione in the egg yolks from one early and one late-laid egg in 47 nests of Burrowing Owls located in the Morley Nelson Snake River Birds of Prey National Conservation Area in southern Idaho. Nesting density had no detectable effect on yolk androgens. Yolk androgens varied temporally and peaked in the middle of the laying season while being low before and after this time period. Within nests, late-laid eggs had higher testosterone and dihydrotestosterone than early-laid eggs; adrostendione exhibited a similar pattern in one but not both years of our study. It is possible that the seasonal pattern in yolk androgens that we observed is related to aspects of mate quality for females or declining chances of fledging success for later nesting females, whereas rises in egg androgens between early and late eggs within clutches could reflect a mechanism to assist nestlings from late-laid eggs that hatch one to several days after their siblings to better compete for resources within the nest or promote survival in the presence of larger siblings.

Western burrowing owls (Athene cunicularia hypugaea) are ground-dwelling owls distributed through- out western North America. Because of population declines, this species is considered endangered in Canada, and burrowing owls are listed as a species of conservation concern in states of the western USA. Korfanta et al. (2002) previously presented primers for seven microsatel- lite loci in burrowing owls. Parentage and relatedness studies require a larger number of markers for accuracy and precision. Here, we developed and characterized 18 addi- tional microsatellite DNA loci, and we tested these loci in 23 individuals. The number of alleles per locus ranged from 2 to 11; two loci deviated from Hardy-Weinberg equilibrium following Bonferroni correction; we did not detect linkage disequilibrium following Bonferroni cor- rection; and the probability of exclusion for parent pairs using all loci was (0.9999. We envision these loci will facilitate detailed analyses of the genetic mating system of burrowing owls, which is poorly understood.

Broadcasts of conspecific vocalizations are used to increase detection rates on surveys of secretive bird species, yet the assessment of detectability necessary to fully interpret such survey data is frequently lacking. We used radiotelemetry to evaluate the probability of detection of 17 radio-tagged male Flammulated Owls (Otus flammeolus) using conspecific broadcast surveys in Idaho during 2005 and 2006. Probability of detection among the 11 paired, five unpaired, and one unknown pairing status owls was 100% during the pair-bonding and incubation periods of the breeding season, after which it declined to less than 15% during the postfledging period. Paired males showed a different pattern than unpaired males. Following hatching of eggs, detectability of paired males declined gradually over a 6-week period, whereas detectability of unpaired males dropped sharply for a 4-week period before increasing during the postfledging period. We suggest that surveys for Flammulated Owls be conducted during the pair-bonding and incubation periods when high detectability permits stronger inference concerning the presence or absence of owls based on broadcast survey detections.

Western Burrowing Owls (Athene cunicularia hypugaea) are small, ground-dwelling owls of western North America that frequent prairie dog (Cynomys spp.) towns and other grasslands. Because they rely on rodent prey and occupy burrows once or concurrently inhabited by fossorial mammals, the owls often harbor fleas. We examined the potential role of fleas found on burrowing owls in plague dynamics by evaluating prevalence of Yersinia pestis in fleas collected from burrowing owls and in owl blood. During 2012-2013, fleas and blood were collected from burrowing owls in portions of five states with endemic plague-Idaho, Oregon, Washington, Colorado, and South Dakota. Fleas were enumerated, taxonomically identified, pooled by nest, and assayed for Y. pestis using culturing and molecular (PCR) approaches. Owl blood underwent serological analysis for plague antibodies and nested PCR for detection of Y. pestis. Of more than 4750 fleas collected from owls, Pulex irritans, a known plague vector in portions of its range, comprised more than 99.4%. However, diagnostic tests for Y. pestis of flea pools (culturing and PCR) and owl blood (PCR and serology) were negative. Thus, even though fleas were prevalent on burrowing owls and the potential for a relationship with burrowing owls as a phoretic host of infected fleas exists, we found no evidence of Y. pestis in sampled fleas or in owls that harbored them. We suggest that studies similar to those reported here during plague epizootics will be especially useful for confirming these results.

Pulex irritans L. is a cosmopolitan flea species that infests a wide variety of hosts. In North America it generally parasitizes large wild mammals, but in the Pacific Northwest an association has emerged between P. irritans and the western burrowing owl ( Athene cunicularia hypugaea ). While investigators have recognized this association for decades, it has not been clear if P. irritans feeds on burrowing owls, or if the owls serve exclusively as phoretic hosts. Here we describe using a real-time assay that was originally developed to identify bloodmeals in Ugandan cat fleas ( Ctenocephalides felis Bouche) to detect burrowing owl DNA in P. irritans collected from burrowing owls in southern Idaho. Of 50 fleas tested, 12 had no detectable vertebrate bloodmeal. The remaining 38 (76%) contained burrowing owl DNA. The assay did not detect vertebrate DNA in unfed fleas exposed to owl or mouse pelts and is therefore unlikely to detect DNA in fleas from vertebrates that have served exclusively as phoretic hosts. We conclude that P. irritans feeds on burrowing owls. We discuss the potential implications of this finding for burrowing owl conservation and enzootic plague dynamics.

IDENTIFICACION DEL SEXO EN CUATRO ESPECIES DE LECHUZAS DE IDAHO: ADN Y MORFOMETRIA Para determinar el sexo de individuos de algunas especies dimorficas de rapaces en el campo se emplean cuadros morfometricos. Sin embargo, usualmente existe un rango en el que las medidas de los dos sexos se sobrelapan, por lo que es imposible determinar el sexo de algunas aves. Ademas, algunas especies son monomorficas, por lo que el sexo de los individuos no puede determinarse con base en su morfologia externa. Las tecnicas basadas en ADN que se enfocan en los genes conservados CHD para determinar el sexo, han sido empleadas en rapaces. Utilizamos dos de estas tecnicas para determinar el sexo de 365 individuos de la especie Athene cunicularia, 78 de Otus flammeolus, 249 de Aegolius acadicus y nueve de Megascops kennicottii. Para A. acadicus comparamos los resultados derivados de los cuadros morfometricos con los obtenidos mediante tecnicas basadas en ADN. El cuadro morfometrico presento una exactitud del 96%, suponiendo q...

Western burrowing owls (Athene cunicularia hypugaea) are endangered in Canada and several western U.S. states. Population declines have been linked with control measures aimed at burrowing mammals and loss of nesting habitat. The owls frequently associate with irrigated agriculture throughout portions of their western U.S. range. To determine potential factors driving the association of burrowing owls with agriculture, we examined availability of suitable nest burrows (burrow availability hypothesis), abundance of potential prey (prey availability hypothesis), and predation of nest burrows (predation hypothesis) for owls nesting in the Snake River Birds of Prey National Conservation Area in southwestern Idaho during 2001–2002. Nest burrow availability did not differ between agricultural and nonagricultural habitats, and occupancy rates of owls in artificial burrows were greater near agriculture. More rodent prey species were live-trapped in agricultural habitat compared with nonagricultural habit...

To investigate the potential expression of territorial behavior of Burrowing Owls (Athene cunicularia) in southwestern Idaho, we used a playback protocol to determine if Burrowing Owls actively defended their nesting site from conspecifics, and if so, to determine the extent of their territorial boundaries. Eighty-eight percent of male Burrowing Owls responded to the broadcast of conspecific primary calls. All responsive males uttered primary calls, and many owls approached the broadcast speaker, exhibited white-and-tall stances, and bobbed. Females responded less frequently than males, but one female whose mate was presumably dead exhibited an intense response to the playback trial. There were no differences in number of primary calls uttered, number of white-and-tall stances performed, or number of bobs of focal males among three broadcast distances: (0 m, 50 m, and 100 m) from the active nest burrows. However, focal owls approached the broadcast speaker more closely at broadcast distances of 0...

We investigated whether wing morphology differed between the sedentary House Finches (Carpodacus mexicanus) of western North America and the introduced population of eastern North America, as the latter has developed migratory behavior since its inception. Wing morphology differed between eastern and western House Finches. Eastern House Finches had shorter proximal primaries and a longer outer primary, perhaps reflecting a thinner and more pointed wing, although no disparity in wing length was detected. Since we interpret these differences in wing shape as modifications for flight capability, we believe that initial evidence for morphological divergence relative to migratory habit between eastern and western House Finches has been established here. Confirmatory studies to determine if wing morphology varies according to the gradient in expression of migratory behavior throughout the range of eastern House Finches are now warranted. La Forma Alar en Carpodacus mexicanus Difiere en Relación a los Hábitos Migratorios entre el Este y Oeste de Norte América Resumen. Investigamos si la morfología del ala difería entre individuos sedentarios de Carpodacus mexicanus del oeste de Norte América y la población introducida en el este de Norte América, la cual ha desarrollado un comportamiento migratorio desde su inserción. La morfología del ala difirió entre las poblaciones de C. mexicanus del este y del oeste. Los individuos del este tuvieron primarias proximales más cortas y primarias externas más largas, lo que quizás refleja un ala más fina y más puntiaguda, aunque no se detectó una diferencia en el largo del ala. Ya que interpretamos estas diferencias en la forma del ala como modificaciones para la capacidad del vuelo, creemos que se ha establecido una evidencia inicial de divergencia morfológica en relación con el hábito migratorio entre las poblaciones de C. mexicanus del este y del oeste de Norte América. Actualmente, son necesarios estudios que confirmen y determinen si la morfología del ala varía de acuerdo al gradiente de expresión del comportamiento migratorio a través del rango de distribución de la población de C. mexicanus del este.

Eggs (n = 367) collected from wild Peregrine Falcon (Falco peregrinus anatum) nests between 1976 and 1990 in Colorado and New Mexico were artificially incubated and hatched. We retrospectively examined these data for variation in egg length, breadth, and initial mass of hatchlings to resolve questions about relationships among egg size, chick size, and sex; and egg size related to first and second clutches and years. Egg length and breadth were significantly related to chick mass at hatching. Neither egg size nor hatchling mass were related to sex. Egg breadth slightly increased and then decreased over the years eggs were collected, which possibly reflects a re-established and then aging wild falcon population or other environmental variation. We also evaluated clutch sex ratios relative to theory based on sexual size dimorphism and local resource competition. Sex ratios did not significantly differ from 1:1 within first or second clutches separately or when combined. Thus, Peregrine Falcons in this population apparently did not skew clutch sex ratios in accordance with local resource competition or Fisherian theory.Huevos de Halcones Peregrinos: Tamaño, Sexo de los Pichones y Proporción de Sexos en la NidadaResumen. Huevos (n = 367) colectados de nidos silvestres de halcones peregrinos (Falco peregrinus anatum) entre 1976 y 1990 en Colorado y New Mexico fueron incubados artificialmente hasta eclosionar. Examinamos esos datos retrospectivamente en cuanto a la variación en la longitud y ancho del huevo y el peso inicial de los pichones para contestar preguntas sobre las relaciones entre tamaño del huevo, tamaño del pichón y sexo, y entre el tamaño del huevo con relación a primeras y segundas nidadas y años. La longitud y el ancho del huevo estuvieron significativamente relacionados con la masa del pichón al eclosionar. El tamaño del huevo y el peso del pichón no estuvieron relacionados con el sexo. El ancho de los huevos aumentó ligeramente y luego disminuyó a través de los años en que los huevos se colectaron, lo que posiblemente refleja una población silvestre de halcones re-establecida y posteriormente senescente, u otro tipo de variación ambiental. También evaluamos la proporción de sexos en las nidadas con relación a la teoría basada en el dimorfismo sexual de tamaño y la competencia local por recursos. Las proporciones de sexos no difirieron significativamente de 1:1 entre primeras o segundas nidadas separadamente o de forma combinada. Por tanto, los halcones peregrinos en esta población aparentemente no sesgaron la proporción de sexos en sus nidadas de acuerdo a la competencia local por recursos o a la teoría Fisheriana.

Both sexes of adult Western Screech-Owls (Otus kennicottii) sing in response to playback of conspecific song within their territories. Two primary songs are the bounce and double trill. Using sonographic analysis of tape-recorded vocalizations, our study quantified characteristics of bounce and double trill songs uttered by individuals within a population of Western Screech-Owls inhabiting riparian woodlands in southwestern Idaho. We asked if songs of males and females differed and, if so, how accurately could songs be classified by sex. On average, male bounce songs were ∼30% lower in frequency than bounce songs of females, but song duration, note duration, number of notes per bout, and internote duration did not differ. Similarly, double trill songs of males were significantly lower in frequency than those of females, and double trill songs uttered by females had significantly greater internote distances in the leading portion. A discriminant model based on frequency at maximum amplitude of bounce songs correctly classified all males and females in our sample. Presence of sex-specific patterns of vocalizations in that species would allow owls to assess the sex of potential intruders and respond appropriately. Moreover, sonographic analysis of Western Screech-Owl songs provides a means for noninvasive classification of sex.

Using radiotelemetry, we monitored dispersing juvenile Western Burrowing Owls (Athene cunicularia hypugaea) within a migratory population in southwestern Idaho during 1994 and 1995. Owls remained within natal areas for an average (± SE) of 58 ± 3.4 days post-hatching before moving permanently beyond 300 m, which was our operational cutoff for dispersal from the natal area. On average, owls dispersed on 27 July (range: 15 July to 22 August), which was approximately 4 weeks after fledging. After initiating dispersal, juveniles continued moving farther away from their natal burrows and, by 61–65 days post-hatching, they had moved 0.6 ± 0.2 km. Each juvenile used 5.1 ± 1.2 satellite burrows, and individual satellite burrows were used for up to 14 days. The average date on which we last sighted radio-tagged juveniles was 13 August, and all but one juvenile departed the study area by early September. Our study illustrates the importance of satellite burrows to dispersing Burrowing Owls.

Variation in timing and distance of dispersal movements of juvenile birds may result from differences in competitive ability. Dispersal by low-ranking juveniles may be initiated before dominants if the latter force subordinate siblings from natal areas. Conversely, when vacant territories are limited and are acquired on a first-come first-served basis, selection could operate on young to disperse as early as possible. In this case, dominant individuals with priority of access to resources in the natal area will mature more quickly and are expected to disperse first. If costs of dispersal increase with dispersal distance, dominant juveniles are expected to disperse shorter distances. Alternately, if there are advantages to long-distance dispersal, then dominants, which are in better condition, should disperse further than subordinates. We examined effects of social rank on the timing and distance (to wintering area) of dispersal movements by juvenile western screech-owls, Otus kennicottii, in southwestern Idaho. Based on observations of aggressive interactions made using video cameras attached to nestboxes, we assigned dominance ranks to nestlings within nine broods. We radiotracked young throughout the postfledging period to determine order of dispersal, and we located them after leaving their natal areas to determine distances to apparent overwintering areas. In six of seven broods, for which dispersal information could be recorded, the most dominant juvenile dispersed first. Moreover, in five of seven broods, the least dominant individual was the last individual to disperse, and the order of dispersal matched the dominance hierarchy in four of seven broods. In contrast, social status did not affect postfledging dispersal distance. We conclude that social dominance relationships influenced the timing of dispersal in juvenile western screech-owls but not distance travelled to overwinter sites. Copyright 1999 The Association for the Study of Animal Behaviour.

Preening is the principle behavioral defense used by birds to combat ectoparasites. Most birds have a small overhang at the tip of their bills that is used to shear through the tough cuticle of ectoparasitic arthropods, making preening much more efficient. Birds may also scratch with their feet to defend against ectoparasites. This is particularly important for removing ectoparasites on the head, which birds cannot preen. Scratching may be enhanced by the comb-like serrations that are found on the claws of birds in many avian families. We examined the prevalence and intensity of ectoparasites of barn owls (Tyto alba pratincola) in southern Idaho in relation to bill hook length and morphological characteristics of the pectinate claw. The barn owls in our study were infested with 3 species of lice (Phthiraptera: Ischnocera): Colpocephalum turbinatum , Kurodaia subpachygaster, and Strigiphilus aitkeni . Bill hook length was associated with the prevalence of these lice. Owls with longer hooks were more likely to be infested with lice. Conventional wisdom suggests that the bill morphology of raptors has been shaped by selection for efficient foraging; our data suggest that hook morphology may also play a role in ectoparasite defense. The number of teeth on the pectinate claw was also associated with the prevalence of lice. Owls that had claws with more teeth were less likely to be infested with lice, which suggests that larger pectinate claws may offer relatively more protection against ectoparasitic lice. Experiments that manipulate the bill hook and pectinate claw are needed to confirm whether these host characters are involved in ectoparasite defense. Finally, we recovered mammalian ectoparasites from 4 barn owls. We recovered species of mammalian lice (Phthiraptera:Anoplura) and fleas (Siphonaptera) that are commonly found on microtine rodents. The owls probably acquired these parasites from recently eaten prey. This represents 1 of the few documented cases of parasites "straggling" from prey to predator.

We performed a series of population and pedigree analyses to examine the viability of a small Red-cockaded Woodpecker (Picoides borealis) population located at the Savannah River Site, in Barnwell and Aiken counties of South Carolina. The population’s existence and future survival are precarious. As few as four individuals, including just one breeding pair, comprised this population in 1985. Now, primarily because of experimental transformation of birds from other areas, the population has increased to 25. As of 1990, genealogy pedigree analysis showed that the respective contribution of 14 founders to the extant population has not been equal. Founder gender equivalents are low (5.4) but could reach 9.2 if poorly-represented founders were to produce offspring. The fraction of founder gene diversity retained in the current population is 0.91. Successful recovery strategies would ensure 95% probability of population survival while maintaining 90% heterozygosity for 200 years. Viability analyses indicated that, depending on relative effects of inbreeding depression and stochastic environmental events, the Savannah River Site population has a 68–100% chance of extinction during this period. Annual translocation into the population of at least three females and two males for a 10-year period will achieve a 96% probability of survival for 200 years. Even with translocation of numerous males and females per year (up to 50 of each), the 90% heterozygosity goal may not be achieved. We discuss recommendations for choosing individuals for translocation logistical constraints on achieving recovery objectives, and limitations of our modeling approach. Realizamos una serie de analisis de poblacion y anallisis genealogicos para examinar la viabilidad de una pequena poblacion del pajaro carpintero cabeza roja (Picoides borealis) localizada en Savannah River Site, en los condados de Barnwell y Aiken de Carolina del Sur. La existencia de la poblacion y su futura superviviencia son precarias. En 1985, esta poblacion consistia solo de cuatro individuos, incluyendo una pareja de adultos. En la actualidad, y debido principalmente al traslado experimental de aves de otras areas, la poblacion a aumentado a 25. En 1990, un analisis “gene drop pedigree” demostro que la contribucion respectiva de los 14 individuos fundadores a la poblacion existente no ha sido equitativa. Los equivalentes de los genomas fundadores son bajos (5.4) pero podrian llegara a 9.2 si los fundadores pobremente representados produjesen descendencia La fraccion de la diversidad genetica de los individuos fundadores mantenida en la poblacion actual es de 0.91. Estrategias exitosas de recuperacion podrian asegurar una probabilidad de supervivencia poblacional del 95%, manteniendo al mismo tiempo un 90% de la heterocigosidad, por 200 anos. Los analisis de viabilidad indicaron que, dependiendo de los efectos relativos de la endocria y eventos ambientales estocasticos, la poblacion de Savannah River Site tiene, durante este periodo, una probabilidad de extincion del 68–100%, aproximadamente. El traslado anual de por lo menos tres hembras y dos machos por un periodo de 10 anos permitiria alcanzar una probabilidad de supervivencia de un 96% durante 200 anos. Aun con el traslado de numerosos machos y hembras por ano (hasta 50 de cada uno), no se podria llegar a alcanzar la meta de 90% de heterocigosidad. Discutimos recomendaciones para la eleccion de los individuos a ser trasladados, limitaciones logisticas para alcanzar los objetivos y limitaciones de nuestro metodo de modelado.

Proximate factors responsible for the initiation of natal dispersal are poorly understood. Parental aggression, one possible factor, does not appear to initiate natal dispersal in young eastern screech-owls, Otus asio. Instead, intrinsic or innate factors may influence dispersal, resulting in increased activity near the time of dispersal. To examine the role of endogenous factors, screech-owl nestlings (approximately 15 days of age) were isolated and their activity levels monitored with digital pedometers for 20 weeks. Activity levels of captive owls (N=5) typically increased prior to the time they would have dispersed if not taken into captivity, then decreased following this time. Similarly, activity levels of free-living, radio-tagged juveniles (N=3) increased until shortly after dispersal, then decreased during the postdispersal period. Captive owls gained mass for several weeks following their estimated fledging date, and then, despite ad libitum feeding, either sustained or lost mass around the time when dispersal normally occurs in free-living birds. Captive owls again gained mass during the post-dispersal period. Reduced mass near the time of dispersal may be adaptive in that lighter birds may be more competent in flight and, therefore, more capable of dispersing. The effects of extrinsic factors other than parental aggression are currently unknown, but these results suggest that natal dispersal in eastern screech-owls is influenced by intrinsic factors and appear to support a ‘dispersal restlessness’ model for the initiation of natal dispersal.

Three hypotheses that attempt to explain latitudinal sex ratio variation on wintering grounds are: 1) the behavioral dominance hypothesis, 2) the arrival time/sexual selection hypothesis, and 3) the body size/physiological hypothesis. Testing these hypotheses is difficult because many predictions are not mutually exclusive. By examining migratory behavior and winter distributions of House Finches (Carpodacus mexicanus), a species in which females dominate males despite their smaller size, we controlled for confounding effects of body size on behavioral dominance. We examined U.S. Fish and Wildlife Service records of House Finches banded throughout the eastern United States following their introduction in 1940. These data suggest the evolution of partial migration among the introduced population of finches, with a trend in recent years (1975-1989) for females to migrate farther than males. The proportion of males on wintering grounds varied significantly and consistently with latitude in the East. Sex ratios north of 380N latitude were malebiased, while those south of this were female-biased. Similar patterns were not apparent among western House Finches during winter or in the eastern population during the breeding season. Of the three hypotheses, only the body size hypothesis correctly predicts the pattern observed among wintering finches. Therefore, different energetic constraints facing male and female House Finches, perhaps related to body size, may be influencing migratory behavior and winter distributions.

Habitat destruction and global climate change are two major threats to the persistence of ecosystems. The probability that a species survives such changes depends on its ability to track environmental shifts, either by moving between patches of habitat or by rapidly adapting to local conditions. This explains why the evolution of dispersal has become an integrative topic of paramount importance in evolutionary and behavioral ecology, as demonstrated by a recent conference*. A wide panel of researchers, who highlighted the recent major advances and the most promising lines of future research, were present at this meeting.

A model that explains natal dispersal in resident screech-owls is presented and examined. The model is based on interactions among hormonal changes, body condition and social stimuli. It predicts that corticosterone, an adrenal glucocorticoid known to stimulate locomotor and foraging activity, increases in blood plasma prior to dispersal through a combination of endogenous and exogenous events. This mediates the locomotor activity that underlies dispersal behaviour. Juveniles in good body condition (i.e. those with sufficient fat reserves) will disperse when corticosterone increases. Birds in poor body condition will not, but they will increase their foraging activity under the influence of corticosterone. Dispersal of siblings will reduce aggression and/or competition for food, enabling the remaining juveniles to improve their body condition and disperse. Initial studies on screech-owls, Otus asio and O. kennicottii, have produced results that are generally consistent with the model. For example, captive juvenile screech-owls showed increased locomotor activity in the weeks leading up to the time when free-living juveniles are dispersing, and activity levels declined thereafter. Peaks in corticosterone corresponded with periods of high locomotor activity (i.e. at the time of dispersal) in captive owls. Finally, field studies indicate that dominant juveniles, which are presumably in better physical condition, initiated dispersal before their more subordinate siblings. Copyright 1998 The Association for the Study of Animal Behaviour.

We used a standard handling protocol to examine the stress response of captive young western screech-owls during their active (nighttime) and inactive (daytime) periods and to compare the stress responses of captive and free-living owls. Circulating corticosterone levels were significantly higher during the inactive period than in the active period in this nocturnal species. This suggests that the daily pattern of corticosterone secretion is reversed in nocturnal birds and is correlated with activity period rather than with the light/dark cycle. Young (ca. 4-5 mo old) screech-owls of both sexes showed increases in plasma corticosterone up to 30 min after capture, followed by significant decreases at 60 min. This pattern is similar to those of other species of birds examined previously, except that decreases in corticosterone at 60 min rarely have been observed. Such decreases may be the result of physiological differences between adult and young birds, habituation to handling in captive birds, or the effects of body condition. Corticosterone levels and the response to capture and handling were comparable in captive and free-living owls, which suggests that the captive owls were not subjected to chronically high levels of stress.

Human consumers of wildlife killed with lead ammunition may be exposed to health risks associated with lead ingestion. This hypothesis is based on published studies showing elevated blood lead concentrations in subsistence hunter populations, retention of ammunition residues in the tissues of hunter-killed animals, and systemic, cognitive, and behavioral disorders associated with human lead body burdens once considered safe. Our objective was to determine the incidence and bioavailability of lead bullet fragments in hunter-killed venison, a widely-eaten food among hunters and their families. We radiographed 30 eviscerated carcasses of White-tailed Deer (Odocoileus virginianus) shot by hunters with standard lead-core, copper-jacketed bullets under normal hunting conditions. All carcasses showed metal fragments (geometric mean = 136 fragments, range = 15-409) and widespread fragment dispersion. We took each carcass to a separate meat processor and fluoroscopically scanned the resulting meat packages; fluoroscopy revealed metal fragments in the ground meat packages of 24 (80%) of the 30 deer; 32% of 234 ground meat packages contained at least one fragment. Fragments were identified as lead by ICP in 93% of 27 samples. Isotope ratios of lead in meat matched the ratios of bullets, and differed from background lead in bone. We fed fragment-containing venison to four pigs to test bioavailability; four controls received venison without fragments from the same deer. Mean blood lead concentrations in pigs peaked at 2.29 microg/dL (maximum 3.8 microg/dL) 2 days following ingestion of fragment-containing venison, significantly higher than the 0.63 microg/dL averaged by controls. We conclude that people risk exposure to bioavailable lead from bullet fragments when they eat venison from deer killed with standard lead-based rifle bullets and processed under normal procedures. At risk in the U.S. are some ten million hunters, their families, and low-income beneficiaries of venison donations.

Although wildlife managers and researchers frequently use a variety of artificial burrow systems (ABS) to attract or supplement habitat for western burrowing owls (Athene cunicularia hypugaea), no previous studies have examined effects of ABS configuration on owl use. We examined choice of ABS configurations by nesting western burrowing owls in southwestern Idaho during 1997-98. To assess potential selection for chamber size, we placed clusters of 3 ABS around natural nest sites used 1995-97. Each cluster contained 3 burrows, each with a standard tunnel diameter but 3 different chamber sizes (707 cm 2 [small], 900 cm 2 [medium], and 1,750 cm 2 [large] of floor space). To assess potential choice for tunnel diameter, we placed clusters of 2 ABS in suitable burrowing owl habitat. These clusters offered 2 tunnel diameters (10 and 15 cm), each with a small chamber. Annual and combined distribution of use indicated that burrowing owls used ABS with large nest chambers and 10-cm-diameter tunnels. We detected no differences in clutch size or number of fledglings among chamber sizes, between tunnel diameters, or between cluster types (i.e., 2 or 3 ABS), although differences in number of fledglings between years exist ed for both types of clusters. Burrowing owls may use ABS with Iarge chambers and small tunnel diameters to reduce negative effects of overcrowding, to gain the most favorable microclimate for developing juveniles, or to help deter larger ground-dwelling predators. Our results indicate that researchers and resource managers interested in managing burrowing owl habitat should consider ABS composed of (1) chambers with >900 cm 2 of floor space, and (2) 10-cm-diameter tunnels.

The degree to which DNA similarity is related to kinship and population structure in natural populations was investigated for a small population of cooperatively-breeding Red-cockaded Woodpeckers (Picoides borealis) in the western Piedmont region of South Carolina. An independent pedigree was established from records of color-banded individuals. Results of DNA profiles were then examined relative to this pedigree. DNA similarity among unrelated woodpeckers averaged 0.55 ± 0.01 (SE). The mean number of DNA bands scored and similarity did not significantly differ between founders and the current population. Examination of parentage in 10 families indicated that multiple paternity did not occur when band by band comparisons or similarity values were compared among parents, helpers, and offspring. Thus, Red-cockaded Woodpeckers were monogamous in this population. DNA similarity among all individuals ranged from 0.32-0.78. Distribution of these similarity values by kinship resulted in some overlap with other kin values. Therefore, specific similarity values could not be assigned a kinship value without knowledge of the pedigree. However, least-squares linear regression indicated that similarity was significantly related to kinship (P < 0.05). These results indicate that use of DNA profiles may be important in quantifying population structure, however, they must be used in conjunction with a known pedigree before any assessment of kinship among individuals is made. Band by band comparisons remain a viable technique for examination of parentage when all putative parents have been sampled.