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According to theory, habitat selection by organisms should reflect underlying habitat-specific fitness consequences and, in birds, reproductive success has a strong impact on population growth in many species. Understanding processes affecting habitat selection also is critically important for guiding conservation initiatives. Northern pintails (Anas acuta) are migratory, temperate-nesting birds that breed in greatest concentrations in the prairies of North America and their population remains below conservation goals. Habitat loss and changing land use practices may have decoupled formerly reliable fitness cues with respect to nest habitat choices. We used data from 62 waterfowl nesting study sites across prairie Canada (1997-2009) to examine nest survival, a primary fitness metric, at multiple scales, in combination with estimates of habitat selection (i.e., nests versus random points), to test for evidence of adaptive habitat choices. We used the same habitat covariates in both analyses. Pintail nest survival varied with nest initiation date, nest habitat, pintail breeding pair density, landscape composition and annual moisture. Selection of nesting habitat reflected patterns in nest survival in some cases, indicating adaptive selection, but strength of habitat selection varied seasonally and depended on population density and landscape composition. Adaptive selection was most evident late in the breeding season, at low breeding densities and in cropland-dominated landscapes. Strikingly, at high breeding density, habitat choice appears to become maladaptive relative to nest predation. At larger spatial scales, the relative availability of habitats with low versus high nest survival, and changing land use practices, may limit the reproductive potential of pintails.

Wild bees may benefit from the restoration of natural areas in agricultural regions. The abundance and diversity of wild bee species responds to the amount of nesting and foraging habitat, but it is less clear how the distribution of these resources (e.g., the landscape complexity) may affect bees. We implemented a pseudo-experiment to disentangle the effects of three components of landscape complexity for wild bees in a Canadian Prairie cropland region. We used an algorithm to identify 146 sites that minimized correlations in indices of patch richness (i.e., the diversity in land cover types) and contagion (i.e., their degree of interspersion), and that collectively captured a cross-section of landscape contexts that differed in the relative proportion of cropland to other non-crop land covers. We trapped bees at these locations repeatedly over time (1119 unique collection events; equivalent to 10,471 trap-days over two consecutive years), identifying 22,493 bees of 213 taxa, in order to model trends for bees at different times of the season. We found that increasing patch richness may support a greater number of bee taxa, but individual bee taxa varied considerably in their response to components of landscape complexity. The effect on the total abundance of wild bees was temporally-variable, with the amount of cropland positively associated with abundance earlier in the season when mass-flowering crops are in bloom, and negatively later in the season when semi-natural areas are likely to provide the most forage. The response of bee abundance to contagion also varied temporally, and demonstrated a “humped” effect later in the growing season, suggesting there is an optimum in the complementary resources provided by adjacent habitat types. Our study shows that increasing the amount or diversity of non-crop land covers in this region is not likely to have a consistent effect for the majority of species across the season. We argue that modifying croplands to support wild bees is likely to be a complex task, requiring study of the functional responses to landscape of bee species present in the region, and their interactions with the phenological variability in resources.

Creation of grassland communities is a popular approach to conserve grassland-nesting waterfowl and songbirds. Much uncertainty remains regarding the most appropriate seed mixtures and the type and frequency of management. We conducted line-transect songbird surveys in grasslands converted from cropland to native and tame grass-forb mixtures and managed by burning (native only) or haying (native and tame) in Saskatchewan and Manitoba, Canada. Fields were 1–9 years post-management (YPM). Our objective was to improve our understanding of the effects of management regime (native hayed, native burned and tame hayed fields) and frequency (YPM) on passerine density and occurrence in planted grassland. We found limited support for an effect of management regime on passerine density and occurrence in both provinces. Vesper sparrow (Pooecetes gramineus) occurrence in Saskatchewan was greatest in tame hayed fields, and clay-colored sparrow (Spizella pallida) density in Manitoba was greater in tame hayed fields than in native burned fields up to 5 YPM. Years post-management most strongly influenced the occurrence of vesper sparrows in Saskatchewan and sedge wrens (Cistothorus platensis); common yellowthroats (Geothlypis trichas); clay-colored, Savannah (Passerculus sandwichensis), Le Conte's (Ammodramus leconteii), and Nelson's (A. nelsoni) sparrows; and bobolinks (Dolichonyx oryzivorus) in Manitoba. Five of the 8 species influenced by YPM exhibited a year-dependent non-linear response such that they reached their greatest density 4–5 YPM. Our results indicate that the type of stand (native or tame) or management (burning or haying) matters little to the grassland songbird community occupying planted cover fields and that the frequency of management will likely depend upon local environmental conditions in a given region or year. Some form of management of planted grasslands, however, should occur every 4–6 years to maintain habitat for a number of generalist grassland species. © 2017 The Wildlife Society.

Timing of breeding varies among waterfowl species and individuals, with strong effects on reproductive success, and may be related to habitat quality. Here, we analyse the start, span, and end of the nesting season for nine upland-nesting duck species at 166 Canadian Prairie–Parkland sites over 34 years to better characterize nesting patterns and test whether and how species respond to May pond abundances. Nesting metrics were compared between single-site versus multiple-site studies over 7 years to evaluate the effects of spatial scale and methodology. Strong, consistent differences in start of nesting were found among duck species, being earliest for Northern Pintail (Anas acuta L., 1758) and Mallard (Anas platyrhynchos L., 1758), followed by Northern Shoveler (Anas clypeata L., 1758), American Green-winged Teal (Anas crecca carolinensis Gmelin, 1789 = Anas carolinensis Gmelin, 1789), Blue-winged Teal (Anas discors L., 1766), American Wigeon (Anas americana Gmelin, 1789), Gadwall (Anas strepera L., 1758), and lastly by Lesser Scaup (Aythya affinis (Eyton, 1838)) and White-winged Scoter (Melanitta fusca deglandi (Bonaparte, 1850)). Span and end of nesting were related to May pond abundances, but the strength of these relationships varied among species, presumably reflecting the flexible (re-)nesting potential of individuals of some species in response to wetland-habitat quality.

Agricultural intensification is a widespread driver of global pollinator decline that subsequently threatens the associated provisioning of ecosystem services. In North America's Prairie Pothole Region, wetlands surrounded by grassland were once abundant on the landscape, but now generally exist within a matrix of agriculture. We assessed whether restoration of these grassland-wetland complexes from cropland could be used as a potential tool for mitigating wild bee decline, using a 25-year restoration chronosequence. We also monitored the development of bee nesting and food resources to better establish the mechanisms that drive return to a restored habitat. Our objective was to assess whether restoration of grassland-wetland complexes can return bee communities to a reference state (i.e. remnant native grassland-wetland habitats), and to ascertain the timeline over which these changes occur. We found bee diversity increased following restoration and approximated reference sites after 1–4 years, while the diversity of non-Bombus species analyzed separately resembled reference sites after around 5–10 years. Floral diversity also increased following restoration from cropland but remained slightly lower than reference sites through time. Changes to bee species composition were driven more by floral species composition than time since restoration. Our results suggest that restored grassland-wetland complexes are able to provide food and nesting resources to bees within agriculturally dominated landscapes, and that restoration can recover wild bee communities to a reference state. On a broader scale, they underscore the utility of retaining patches of non-cropped and restored land within agroecosystems as a pathway for mitigating pollinator decline.

Understanding factors that influence the demography of grassland species in agricultural landscapes is essential given the amount of land under agricultural production. Winter wheat is promoted by avian conservation organizations in North America because it provides cover early in the breeding season without much disturbance to nesting waterfowl. We conducted point-count surveys in fields of winter wheat, spring wheat, summerfallow, planted grassland and native grassland to determine: 1) the relative benefits of winter wheat to songbirds, 2) the extent to which cropland suitability changes over the breeding season, and 3) the extent to which the surrounding landscape influences songbird abundance. Horned lark (Eremophila alpestris), Savannah sparrow (Passerculus sandwichensis) and vesper sparrow (Pooecetes gramineus) were most commonly recorded in wheat and summerfallow fields, and their abundance varied over the breeding season and with the amount of native grassland in the surrounding landscape. Horned lark was more abundant in winter wheat early in the breeding season and its abundance increased with the amount of native grassland in the surrounding landscape. Savannah sparrow abundance increased in all field-types over the breeding season and decreased in cropland fields as the amount of native grassland in the surrounding landscape increased. Programs that encourage or incentivize winter wheat seeding in grassland-dominated landscapes will yield the greatest benefits for horned lark whereas Savannah sparrows would derive the greatest benefit in cropland-dominated landscapes. However, such programs must target cultivated fields to ensure that grassland obligate species are not compromised.

Climate change is altering global temperature and precipitation regimes, and the ability of species to respond to these changes could have serious implications for population dynamics. Flexible species may adjust breeding dates in response to advances in spring phenology. Furthermore, in migratory bird species, conditions experienced during the non-breeding season may have cross-seasonal effects during the subsequent breeding season. We evaluated species-specific responses to antecedent non-breeding (winter) and current breeding (spring) conditions. We used a data set composed of 21,230 duck nests from 164 sites in the Canadian Prairie Pothole Region, 1993–2011, to determine how environmental conditions influenced timing of nesting and subsequent nest survival in eight duck species representing varying life-histories. We tested how species responded in timing of nesting and nest survival, respectively, to El Nino Southern Oscillation (ENSO) conditions experienced during the preceding non-breeding season (winter; Dec–Feb), and spring (Mar–Jun) temperature and moisture conditions on the breeding grounds. Ducks tended to nest earlier in warmer springs; however, in El Nino winters, with warmer spring temperatures, nesting tended to be later. We did not find evidence for direct effects of environmental variables on nest survival; however, evidence of indirect effects of winter conditions on nest survival for some species via strong direct effects on timing of nesting provides new insights into mechanisms for cross-seasonal effects on reproductive success.

The Prairie Habitat Joint Venture (PHJV) delivers conservation programs for the Canadian portion of the Prairie Pothole Region under the North American Waterfowl Management Plan. The PHJV Assessment was designed to evaluate biological assumptions and effectiveness of PHJV conservation activities. Our objectives were to 1) test whether waterfowl reproductive success increased in response to the full suite of PHJV habitat treatments, and 2) quantify the relationships between mallard (Anas platyrhynchos) vital rates and landscape variables. We focused on examining the association of mallard vital rates with covariates measured at the study-area scale. We collected information on vital rates from 3,214 radio-marked female mallards at 27 study areas mainly throughout the Aspen Parkland ecoregion of Manitoba, Saskatchewan, and Alberta in 1993–2000. We used a modeling framework and information-theoretic techniques to test hypotheses about putative effects of environmental covariates on adult female and duckling survival, nesting effort, and nest survival. Additionally, we constructed a stage-based matrix projection model of mallard population growth (λ) to estimate the sensitivities of population growth rates to variation in vital rates. Nest survival was positively related to the amount of herbaceous vegetation on study areas and total precipitation for the 12 months prior to nesting. Nesting effort was positively related to wetland inundation in July. Duckling survival was positively related to the proportion of seasonal wetlands holding water in July and negatively related to the number of days in June and July when the minimum air temperature dropped below 10° C. Adult female survival rate was positively related to both the proportions of grassland and wetland habitats measured at the study-area scale (65 km2), though these factors interacted such that the positive relationship with proportion of wetlands was strongest on study sites with high proportions of grassland. The stage-based projection model constructed using mean vital rates indicated that populations were declining (mean λ = 0.95, median λ = 0.98, 5th percentile = 0.68, 95th percentile = 1.38). Variance-stabilized sensitivities indicated that population growth was most responsive to variation in vital rates for after-second-year birds and that nest survival was the single vital rate to which populations were most sensitive. A prospective simulation revealed that, as expected, sensitivity to nest survival is likely to decrease at higher levels of nest survival. Despite evidence that nest survival was higher in PHJV habitat treatments than surrounding habitats, our a priori PHJV treatment index was unrelated to mallard vital rates estimated at the 65-km2 scale. Although mallard populations were affected by several weather variables and land uses, efforts to increase populations should focus on improving nest survival rates, which currently are below approximately 30%. © 2014 The Wildlife Society.

Radiotelemetry is frequently used to measure habitat use, movements, and survival in birds; presumably, outfitting adult females with radiotransmitters does not influence juvenile survival, but this critical assumption is rarely tested. We evaluated whether the timing or type of transmitter deployed on adult female mallards (Anas platyrhynchos) reduced duckling survival estimates in the Canadian Prairie Pothole Region, 1993–1995. The best-approximating model suggests that, compared with 2 other trap–transmitter combinations, ducklings raised by mallard females trapped prior to nest initiation and outfitted with anchor–suture transmitters had poor survival. The 30-day survival rate of ducklings raised by female mallards equipped with anchor–suture transmitters prior to nest initiation was lower than survival of ducklings attended by females equipped prior to nest initiation with abdominally implanted transmitters or females marked during late incubation with anchor–suture transmitters. Studies of reproductive success deploying anchor–suture transmitters on female waterfowl trapped prior to nest initiation may have biased results because of possible negative consequences to offspring survival. © 2012 The Wildlife Society.

Periodic treatment of established stands of dense nesting cover (DNC) is a recommended practice to maintain cover quality, but little information exists on the magnitude and duration of treatment effects on nesting waterfowl. During 1998–2001, we examined the effect of management treatments on vegetative characteristics and waterfowl nest success and density in fields of DNC seeded to introduced and native grass and forb mixes in the parklands of Saskatchewan and Manitoba. We measured vegetation height—density and litter depth within fields and located and monitored 1,927 duck nests within 33–42 fields/yr ranging in size from 6 ha to 62 ha. We considered a series of models examining the influence of grass type and management treatment (GTMT) and years post-management (YPM) on vegetative characteristics, nest success, and nest density while including covariates potentially affecting these response variables. Visual obstruction and litter depth were lowest in native-burned fields and greatest in in...

Renesting is an important strategy for coping with nest loss in many species of birds. We investigated renesting behavior of radiomarked Mallards (Anas platyrhynchos) breeding in the Canadian Prairie Parklands and found that females were persistent renesters, replacing >57% of 4,112 destroyed nests. Renesting propensity was most affected by nest initiation date, with ∼90% of unsuccessful females renesting if destroyed clutches had been initiated in April but

Waterfowl nesting in annual croplands has remained a little-known aspect of waterfowl nesting ecology because of the inability of many studies to systematically search this habitat through the nesting season. Where searches have been conducted, they are generally restricted to the period prior to seeding, and many nests found are destroyed by the seeding operation. Consequently, fall-seeded crops have been promoted as an alternative cropping practice that could increase nest survival of waterfowl nesting in croplands. During 1996–1999, we conducted 3–4 complete nest searches on 4,274 ha of cropland, including spring-seeded wheat and barley, winter wheat, and fall rye in southern Saskatchewan, Canada. Using suites of predictive models, we tested hypotheses regarding relative nest abundance and nest survival among crop types and tested the influence of several landscape-scale covariates on these metrics. Apparent nest densities were higher in fall-seeded crops (winter wheat: 0.39 nests/ha, fall rye...

We explored predictive models relating body condition and age to nesting propensity, timing of nest initiation, clutch size of first nests, aggregated nest survival, hatching success, and timing of hatch in Mallards (Anas platyrhynchos). Nesting propensity had a positive linear relationship with body condition, and second-year (SY) females had a lower probability of nesting than after-second-year (ASY) females (84% and 94%, respectively, at average body condition). Females in better body condition initiated nesting ∼15 days earlier than those in poor condition, and SY females nested ∼4 days later than ASY females at average body condition. Clutch size of first nests exhibited a curvilinear decline with body condition, such that large clutches were characteristic of females in the best condition that nested early. Nest survival and hatching probability were unaffected by body condition. Younger females had somewhat lower nest survival (11%) than older females (14%), which, in combination with rene...

Social indices were developed to assess breeding productivity of waterfowl based on weekly roadside surveys of social groupings (i.e., pairs, lone M, flocked M). We calculated social indices for mallard (Anas platyrhynchos) populations breeding on 16 study sites in the Canadian parklands from 1993 to 1998 using 7 previously developed indices. We also calculated duckling:pair ratios from our roadside counts, and we obtained independent measures of nesting effort, nesting success, female success, and fledging rate for these same 16 sites from a concurrent telemetry study. Social indices were correlated (r2 = 0.28–0.67) with telemetry-based measures of breeding productivity in 5 of 7 cases, with the strongest relationships deriving from indices that emphasized renesting effort. The 2 ineffective social indices (r2 ≤ 0.13) both measured early onset of nesting activity. Duckling:pair ratios could be calculated more easily from the same survey data and also were correlated (r2 = 0.26–0.48) with measure...

An animal's reproduction and survival depend critically on the choices it makes when selecting a habitat for breeding. Therefore, we expect animals to select breeding habitats that confer fitness benefits. For mallards (Anas platyrhynchos), previous research has shown that populations are most sensitive to variation in nest survival rates; thus, we expect strong selection for safe nest sites. We used patterns of nesting success to predict nest distributions. We compared distributions of nests from radio-marked mallard females (n = 1,710) to random locations using logistic regression and modeled how nest-site locations were related to a number of landscape metrics measured at several spatial scales. Consistent with predictions derived from patterns of nesting success, mallard nest sites were best modeled using habitat attributes measured at the scale of the vegetation patch containing the nest, though ultimately habitat features measured at multiple scales improved predictions. Similarly, for most habitat ...

Dense nesting cover (DNC) has been a conspicuous component of habitat management for upland-nesting ducks for >30 years, but its benefits for nesting ducks have been contentious. During 1994–1999 we monitored 3,058 dabbling duck (Anas spp.) nests in 84 DNC fields located throughout the Canadian Parklands to examine sources of among-field variation in nest density and nesting success. Nest density averaged 1.51 (SE = 0.15) nests/ha and overall nesting success was 20.4%, but there was pronounced annual variation in both estimates. Nesting success increased with increasing field size (range = 6–111 ha), but nest density remained constant. Nest density increased with percent wetland habitat within DNC fields and declined with percent perennial cover in the surrounding 2.4 × 2.4-km landscape, but these variables were not important for predicting nesting success. Nest abundance and nesting success roughly doubled in fields seeded with alfalfa (Medicago sativa) or sweet clovers (Melilotus spp.), but the...

Despite greater harvest rates of males, mallard (Anas platyrhynchos) populations exhibit male-biased sex ratios, presumably because females experience greater mortality during breeding seasons than do males. Nest success and adult female survival during the breeding season greatly impact mallard population growth; however, no study has evaluated breeding-season survival of males and females simultaneously using radiotelemetry. We captured, radiomarked, and monitored 90 male and 272 female mallards during 2 breeding seasons in the Prairie-Parkland region of Canada (Manitoba 1998, Saskatchewan 1999). Model-averaged estimates of female breeding season (i.e., 15 Apr–14 Jul) survival probabilities were 0.84 (SE = 0.031) in 1998 and 0.71 (SE = 0.040) in 1999. Estimated survival probabilities of paired males were 0.99 (SE = 0.016) in 1998 and 0.98 (SE = 0.025) in 1999; survival estimates for unpaired males were 0.92 (SE = 0.052) in 1998 and 0.85 (SE = 0.083) in 1999. Female mortality was greatest during...

Early hatched waterfowl are more likely to enter the breeding population. Managers' primary tool to increase nesting success in the Prairie Pothole Region (PPR) of North America is managing upland vegetation for duck nesting cover. To determine whether managed covertypes affect early-season nesting success, we modeled seasonal variation in nesting success using >17,000 duck nests found in managed and unmanaged covertypes in prairie Canada from 1993 to 2000. Nesting success was higher in most managed covertypes than in unmanaged covertypes early in the nesting season. Planted cover appeared to be the best managed covertype for increasing early-season nesting success as it had high early-season nesting success, and was selected by nesting ducks in greater proportion than its availability; however, nesting success in planted cover declined later in the nesting season while nesting success in most unmanaged covertypes increased. Nevertheless, even with reduced nesting success late in the season, planted cover was more productive than surrounding unmanaged covertypes. Future waterfowl management efforts should focus on providing safe nesting cover early in the nesting season.

To determine the benefits to grassland birds of converting cropland to hayland in southern Saskatchewan, Canada, we quantified the relative nest abundance and success of grassland nesting birds in haylands and the influence landscape variables have on these parameters. We found nests of 26 species of grassland nesting birds, primarily waterfowl and vesper sparrow (Pooecetes gramineus). With the exception of the northern pintail (Anas acuta), few nesting attempts were recorded for species of high priority in the Prairie Pothole Bird Conservation Region. Mayfield nest success for all waterfowl (20 and 13% in 1999 and 2000, respectively) was high relative to previously reported nest success estimates in other habitat types—especially spring-seeded cropland—and was near levels thought to be required to sustain populations (15–20%). Vesper sparrow nest success (39 and 33% in 1999 and 2000, respectively) also was high relative to that reported in other studies. Haying destroyed few nests as wet weather...

In accordance with the differential allocation hypothesis, females are expected to increase their reproductive investment when mated to high-quality males. In waterfowl, reproductive, investment increased when captive female mallards (Anas platyrhynchos) were mated to more attractive males, but information for wild ducks is lacking. Studies of waterfowl mating systems have focused primarily on the importance of plumage coloration of males and female mate choice, whereas investigations of reproductive ecology examine female attributes and virtually ignore the role of males in investment decisions. Here, we used unique data for 253 pairs of wild mallards to test whether females mated to high-quality males would increase reproductive effort and reproduce more successfully. We derived measurements of female and male body size and condition, and indices of male plumage quality, and related these traits to patterns of reproductive effort and performance of females. Consistent with predictions, yearling females nested earlier and had higher nest survival when mated to males with better plumage scores. Furthermore, when paired with larger bodied males, yearling females renested more often, and nest and brood survival increased among older females. Although the strength of male effects varied with breeding stage and female age or experience, this is one of a few studies to demonstrate an additive effect of male quality on investment and success of females, in free-ranging birds.

The effort expended on reproduction may entail future costs, such as reduced survival or fecundity, and these costs can have an important influence on life-history optimization. For birds with precocial offspring, hypothesized costs of reproduction have typically emphasized nutritional and energetic investments in egg formation and incubation. We measured seasonal survival of 3856 radio-marked female Mallards (Anas platyrhynchos) from arrival on the breeding grounds through brood-rearing or cessation of breeding. There was a 2.5-fold direct increase in mortality risk associated with incubating nests in terrestrial habitats, whereas during brood-rearing when breeding females occupy aquatic habitats, mortality risk reached seasonal lows. Mortality risk also varied with calendar date and was highest during periods when large numbers of Mallards were nesting, suggesting that prey-switching behaviors by common predators may exacerbate risks to adults in all breeding stages. Although prior investments in egg laying and incubation affected mortality risk, most relationships were not consistent with the cost of reproduction hypothesis; birds with extensive prior investments in egg production or incubation typically survived better, suggesting that variation in individual quality drove both relationships. We conclude that for breeding female Mallards, the primary cost of reproduction is a fixed cost associated with placing oneself at risk to predators while incubating nests in terrestrial habitats. RESUME. L’effort investi a la reproduction peut avoir une incidence sur les couts futurs – comme un faible taux de survie ou de fertilite – et ces couts peuvent grandement influencer l’optimisation du cycle biologique. Chez les oiseaux dont les jeunes sont nidifuges, les couts hypothetiques de la reproduction sont surtout lies aux efforts nutritionnel et energetique investis dans la formation des œufs et a l’incubation. Dans le cadre de cette etude, nous avons mesure le taux de survie saisonnier de 3 856 Canards colverts (Anas platyrhynchos) femelles munies d’un emetteur radio, de leur arrivee sur les aires de nidification jusqu’a ce que l’elevage des jeunes soit complete ou jusqu’a l’echec de la nidification. Le taux de mortalite etait de 2,5 fois plus eleve chez les femelles qui couvaient leurs œufs en milieu terrestre, tandis qu’il a etait a son plus bas niveau saisonnier au moment de l’elevage des jeunes en milieu aquatique. Le taux de mortalite a aussi varie en fonction de la date : il etait a son maximum au moment ou de nombreux Canards colverts nichaient, ce qui laisse croire que le changement de proies dans la diete des predateurs communs pourrait exacerber le risque de mortalite chez les femelles a toutes les etapes de la nidification. Meme si les efforts investis dans la ponte et l’incubation ont eu un effet sur le taux de mortalite, la plupart des relations n’etaient pas conformes aux predictions de l’hypothese des couts de la reproduction; les femelles qui ont grandement investi dans la production d’œufs ou l’incubation ont eu un meilleur taux de survie, ce qui donne a penser que la variabilite de la qualite individuelle etait responsable des deux relations. Nous concluons que, chez les femelles nicheuses de Canard colvert, le cout principal de la reproduction est un cout fixe associe au risque de predation lie a l’incubation d’œufs en milieu terrestre.

We studied the food habits of canvasbacks (Aythya valisineria) at Catahoula Lake (inland) and the Mississippi River Delta (coastal), Louisiana, from November 1987 to February 1988. Plant foods comprised >97 aggregate percent dry mass of the canvasback diet. The proportion of plant material eaten did not vary with sex, age, or month, or differ between study sites or nocturnal and diurnal collections. Tubers of chufa flatsedge (Cyperus esculentus) and common arrowhead (Sagittaria latifolia) made up 94% of the canvasback diet at Catahoula Lake. Common and grassy arrowhead (Sagittaria graminea) tubers and American bulrush (Scirpus americanus) rhizomes and seeds formed 94% of the canvasback diet at the Mississippi River Delta. Consumption of specific food taxa did not vary with sex, age, or month at either study site. Canvasbacks at the Mississippi River Delta preferred seeds of American bulrush over all other foods, but American bulrush rhizomes were underrepresented in the diet. Densities of subterranean plant foods at Catahoula Lake and the Mississippi River Delta are apparently higher than at other major canvasback concentration areas and enable canvasbacks wintering in Louisiana to improve their physical condition before spring migration.

We used publically available data on duck breeding distribution and recently compiled geospatial data on upland habitat and environmental conditions to develop a spatially explicit model of breeding duck populations across the entire Prairie Pothole Region (PPR). Our spatial population models were able to identify key areas for duck conservation across the PPR and predict between 62.1 – 79.1% (68.4% avg.) of the variation in duck counts by year from 2002 – 2010. The median difference in observed vs. predicted duck counts at a transect segment level was 4.6 ducks. Our models are the first seamless spatially explicit models of waterfowl abundance across the entire PPR and represent an initial step toward joint conservation planning between Prairie Pothole and Prairie Habitat Joint Ventures. Our work demonstrates that when spatial and temporal variation for highly mobile birds is incorporated into conservation planning it will likely increase the habitat area required to support defined population goals. A major goal of the current North American Waterfowl Management Plan and subsequent action plan is the linking of harvest and habitat management. We contend incorporation of spatial aspects will increase the likelihood of coherent joint harvest and habitat management decisions. Our results show at a minimum, it is possible to produce spatially explicit waterfowl abundance models that when summed across survey strata will produce similar strata level population estimates as the design-based Waterfowl Breeding Pair and Habitat Survey (r2 = 0.977). This is important because these design-based population estimates are currently used to set duck harvest regulations and to set duck population and habitat goals for the North American Waterfowl Management Plan. We hope this effort generates discussion on the important linkages between spatial and temporal variation in population size, and distribution relative to habitat quantity and quality when linking habitat and population goals across this important region.

We examined the effects of investigator activity on hatching rates of radio-marked wild female Mallards (Anas platyrhynchos), and evaluated the efficacy of radio-telemetry to minimize nest disturbance, characterize vegetation at nest sites, and mark nests for later relocation. Differences in hatching rates between birds that were flushed once (experimental) and those never flushed (control) approached significance (P = 0.086). However, hatching rates did not differ (P = 0.588) between the two groups when nests where investigator activity caused abandonment (30% of experimental nests) were removed from analysis. If the nest remained active, flushing the bird and visiting the nest once did not appear to increase the likelihood of the nest being depredated. We were able to locate 92% of radio-telemetry marked nests (control) after the female was no longer tending the nest. Radio-telemetry provides a technique to collect relatively unbiased nesting data for Mallards without disturbing the female.

As part of the Prairie Habitat Joint Venture (PHJV) Habitat Assessment Project, we radiomarked and tracked daily 2,249 female mallard ducks (Anas platyrhynchos) in the Prairie Pothole Region (PPR) of Canada. We conducted our study at 19 different 54- to 78-km 2 sites for 1 year per site from 1993 to 1998. We estimated female survival probability during the 90-day period following arrival on the breeding area and employed information-theoretic approaches to select among competing models that described factors affecting survival probability. We investigated the relationship between female survival and 3 periods of the nesting season, female age (yearling vs. older), upland habitat treatments, longitude, and habitat variables. Our model estimates of female survival probability ranged between 0.62 (SE = 0.028) and 0.84 (SE = 0.018) and averaged 0.76 (SE = 0.004) for the 90-day period. The best approximating model indicated that female survival was (1) lowest when most females were nesting, and (2) depended on longitude and percent wetland habitat such that survival was lowest at western sites with low wetland densities. Management efforts to reduce wetland loss, especially in western regions of the Canadian PPR, may positively influence female survival. Upland habitat restorations designed to improve nest survival may not have a concurrent impact on female survival unless a significant portion of the nesting population is affected.

Relationships between vital rates and population growth rate (λ) are critical to understanding and managing population dynamics. Considerable study of the midcontinent mallard (Anas platyrhynchos) population has been directed to understanding how vital rates respond to environmental fluctuations and management, but inference to the relative importance of specific vital rates to λ remains weak. We used analytic and simulation-based sensitivity analyses of a stage-based matrix model of female midcontinent mallards to compare the relative importance of vital rates to λ. For each vital rate, we estimated mean values and process variation (biological variation across space and time) for females breeding on sites of approximately 70 km 2 in the Prairie Pothole Region (PPR) of the United States (Montana, North Dakota, South Dakota, Minnesota) and Canada (Saskatchewan, Manitoba, Alberta). We conducted perturbation analyses (i.e., analytic sensitivities and elasticities) to predict the relative influence of changes in vital rates on λ. We conducted variance decomposition analyses to assess the proportion of spatial and temporal variation in λ explained by process variation in each vital rate. At mean values of vital rates, analytic sensitivity of λ was highest to nest success and survival of adult females during the breeding season and non-breeding season; hence, equal absolute changes in these vital rates would be predicted to result in the largest Δλ, relative to other vital rates. Variation in sensitivities and elasticities across process variation in vital rates was primarily explained by variation in nest success and survival of ducklings. Process variation in breeding parameters was driving variation in λ: vital rates explaining the most variation were nest success (43%), survival of adult females during the breeding season (19%), and survival of ducklings (14%). Survival of adult females outside the breeding season accounted for only 9% of variation in λ. Our analyses suggested that predation processes on the breeding grounds were the primary proximate factors limiting population growth.

We assessed nutritional constraints on clutch size in Mallards (Anas platyrhynchos) by observing incidence and consequences of continuous laying—the sequential production of eggs in two or more nest bowls. Continuous laying behavior was detected in 278 of 3,064 radiotracked Mallards (9.1%). Continuous laying females produced an average of 12.12 total eggs (SD = 2.70, range 5–18, n = 69), versus 8.90 eggs for normal nesting females (SD = 1.67, range 4–14, n = 587). On average, continuous laying females were 25 g heavier than noncontinuous laying females, and body mass was positively correlated with egg production among continuous laying females. Nest success was not affected by continuous laying, but continuous laying females that abandoned their nests were more likely to be young or to have laid a greater number of eggs. A large component of the breeding Mallard population can lay more eggs than they typically do, and there appear to be minimal consequences of that behavior. These observations appear inconsistent with the egg-formation hypothesis.

Radiotelemetry is an important tool in many studies of waterfowl ecology and management, but some studies have indicated that harnessed-radiopackages affected the behavior and survival of marked birds. Transmitters attached mid-dorsally with sutures, glue, and a subcutaneous, stainless steel anchor-shaped wire (hereafter anchored backpacks) may eliminate such problems. Therefore, we compared various measures of reproduction and survival rates of wild mallards (Anas platyrhynchos) radiomarked with abdominal implants and anchored backpacks at 5 study sites located in the aspen-parkland biome of the Prairie Pothole Region of Canada. We also compared our tracking ability between abdominal implants and anchored backpacks and determined retention time of anchored backpacks. Females with anchored backpacks devoted significantly fewer days to egg laying and incubation and initiated fewer nests than did females with implants. At one site, females with backpacks had significantly lower survival rates than females with implants. At 3 of the remaining 4 sites, females with anchored backpacks had lower survival rates than females with implants, but these results were not significant. We detected no difference in our tracking ability between anchored backpacks and abdominal implants (63 of 136 [46%] with anchored backpacks, and 140 of 319 [43%] with implants were monitored successfully from the time they were trapped to 30 June at each site). Two anchored backpacks were known to have fallen off and 11 were suspected to have fallen off, out of 198 backpacks (average retention time for anchored backpacks was 43 ± 5.8 days for those that lost their transmitter). Our results suggest that anchored backpacks may have negatively affected reproduction and survival rates of wild mallards.

Although radio transmitters have been used extensively in waterfowl research for 20 years, effects of these devices on wild breeding mallards (Anas platyrhynchos) are largely unknown. Therefore, we compared various measures of nesting effort for mallards radiomarked with harnessed backpacks, sutured backpacks, and abdominal implants. The proportion of females that nested varied (P < 0.05) by transmitter type: 5 of 9, 16 of 16, and 5 of 5 females nested with harnessed backpacks, implants, and sutured backpacks, respectively. Females with harnessed backpacks initiated fewer (P < 0.0001) nests than birds with other transmitter types and devoted fewer (P = 0.007) days to egg laying and incubation than birds with implants. Our results suggest that studies using harnessed backpacks may underestimate nesting effort, hen success, and recruitment