Nest Initiation Date Research Articles

Wood duck nest survival and duckling recruitment is minimally affected by interspecific brood parasitism from hooded mergansers and black-bellied whistling-ducks.

In the southeastern United States, wood ducks (Aix sponsa) have historically experienced interspecific brood parasitism (IBP) primarily from hooded mergansers (Lophodytes cucullatus), but the recent northward expansion of black-bellied whistling-ducks (Dendrocygna autumnalis) has added a new complexity to these interactions. We monitored nest boxes in Louisiana to evaluate the influence IBP had on wood duck daily nest survival rate (after, DSR) and duckling recruitment. We monitored 1,295 wood duck nests from 2020-2023 and found 112 (8.7%) were parasitized by hooded mergansers and 148 (11.5%) by whistling-ducks. Parasitic egg-laying by hooded mergansers lowered wood duck DSR, while DSR for nests parasitized by whistling-ducks was comparable to clutches containing only wood duck eggs. We considered the wood duck capture histories of 2,465 marked female ducklings and 540 banded adult females to estimate a duckling recruitment probability for the entire study period. We recaptured 50 ducklings as adults; 6 (12.0%) hatched from clutches parasitized by hooded mergansers, 1 (2.0%) from a clutch parasitized by a whistling-duck, and 43 (86.0%) from clutches containing only wood duck eggs. The duckling recruitment probability was 0.039 (95% credible interval = 0.028, 0.051). Nest initiation date had a negative effect on recruitment, wherein most recruits hatched from nests initiated earlier in the season. Given only ~9% of wood duck nests contained hooded merganser eggs, we conclude IBP writ large had no detrimental effect on DSR at a population level. The lower DSR of clutches parasitized by hooded mergansers is potentially linked to a high abundance of early-season parasites that produce "dump nests" and these clutches are often abandoned without being incubated. Despite ongoing parasitism by hooded mergansers and the range expansion of whistling-ducks, wood duck productivity in Louisiana appears to be minimally affected by interspecific brood parasitism.

Why do avian responses to change in Arctic green-up vary?

Global climate change has altered the timing of seasonal events (i.e., phenology) for a diverse range of biota. Within and among species, however, the degree to which alterations in phenology match climate variability differ substantially. To better understand factors driving these differences, we evaluated variation in timing of nesting of eight Arctic-breeding shorebird species at 18 sites over a 23-year period. We used the Normalized Difference Vegetation Index as a proxy to determine the start of spring (SOS) growing season and quantified relationships between SOS and nest initiation dates as a measure of phenological responsiveness. Among species, we tested four life history traits (migration distance, seasonal timing of breeding, female body mass, expected female reproductive effort) as species-level predictors of responsiveness. For one species (Semipalmated Sandpiper), we also evaluated whether responsiveness varied across sites. Although no species in our study completely tracked annual variation in SOS, phenological responses were strongest for Western Sandpipers, Pectoral Sandpipers, and Red Phalaropes. Migration distance was the strongest additional predictor of responsiveness, with longer-distance migrant species generally tracking variation in SOS more closely than species that migrate shorter distances. Semipalmated Sandpipers are a widely distributed species, but adjustments in timing of nesting relative to variability in SOS did not vary across sites, suggesting that different breeding populations of this species were equally responsive to climate cues despite differing migration strategies. Our results unexpectedly show that long-distance migrants are more sensitive to local environmental conditions, which may help them to adapt to ongoing changes in climate.

Ecological correlates of alternative reproductive tactics: conspecific brood parasitism rates vary with nest predation and seasonal effects influenced by climate change

Ecological and social factors shape individual reproductive strategies. Climate change has wide‐ranging effects on the timing of reproduction and availability of nesting sites for many birds. Ecological factors such as season length or predation rate could in turn affect the relative success rates of alternative reproductive tactics (ARTs). A new article by Pöysä (2024) featuring a long‐term study of common goldeneyes Bucephala clangula highlights the role of climate change in altering rates of conspecific brood parasitism (CBP) by affecting nest initiation dates and season length. While some authors have emphasized the effects of spatial and temporal aggregation of nests in promoting tactics of reproductive interference, few studies have addressed the effects of environmental variables on rates of CBP and other ARTs. I review some of the evidence for a relationship between population‐level nest predation rate and rates of CBP, principally in ducks and rails, and suggest a role for high rates of nest loss from all sources in the evolution of CBP and host responses. There is a need for further studies that examine environmental correlates of ARTs. Long‐term studies have the highest potential to reveal how shifts in phenology and life history variables may respond to environmental perturbations. Comparative studies of similar species in remote geographic locations can add perspective of how different ecological variables affect the prevalence of ARTs.

Consequences of drought for grassland songbird reproduction

AbstractAbiotic stressors can be major sources of selection, resulting in diverse demographic responses operating via multiple direct and indirect mechanisms. However, unusual weather events are notoriously difficult to study due to their spatial and temporal unpredictability. A severe drought affected the Flint Hills of Kansas in 2018, occurring during the ongoing population‐level studies of three species of declining grassland songbirds: Eastern Meadowlarks (Sturnella magna), Grasshopper Sparrows (Ammodramus savannarum), and Dickcissels (Spiza americana). We compared nest survival, nest initiation date, and potential behavioral drivers of reproductive differences (i.e., nest orientation, investment) between the 2018 drought year and 2–6 years of average‐to‐wet years. Nest initiation in the drought year was concentrated early in the season, suggesting that birds did not renest or attempt second broods. The two species that build domed nests shifted the orientation of nest entrances away from early morning sun and toward the direction of prevailing winds in the drought year. Multiple nest‐level metrics of investment and success were similar in drought and nondrought years. These results suggest that demographic changes during droughts can reflect both direct responses and may also involve biotically mediated trophic consequences.

Forest management, forest vegetation, and climate influence nesting ecology of a focal bird species in the western USA

Landscape-scale forest restoration aims to restore ecological structure and function and provide habitat for wildlife. However, forest management likely has varying impacts across wildlife life stages, with consequences for population persistence. Using 10 years of nest (n = 294) survey data for a focal bird species, white-headed woodpecker (Dryobates albolarvatus), we assessed how forest management (tree removal and prescribed burning) at two spatial scales (stand [2.25 ha] and landscape [314 ha]), forest vegetation variables at three spatial scales (nest tree, local [0.4 ha], and landscape [314 ha]), and climate influenced nest initiation date, egg production, egg survival, and nestling survival. We applied Bayesian hierarchical mixed effects models to these data to identify and compare drivers at each life stage. None of the variables we considered influenced egg production; white-headed woodpeckers laid an average of four eggs. As the extent of the landscape with tree removal increased, nests initiated later. Egg survival was higher in nests with prescribed burning at the stand scale. Nestling survival was higher in sites that had been managed with burning and tree removal at the stand scale, but the relationship with burning switched to negative at the landscape scale. Only nestling survival was shaped by attributes of the nest cavity itself. Egg survival increased with increased variation in forest patch sizes at the landscape scale. Woodpeckers initiated nests earlier under warmer conditions, with previous August and September temperatures being particularly influential. Both egg and nestling survival increased with cumulative precipitation. While increased temperatures decreased egg survival, nestling survival peaked at an optimal maximum temperature (∼32 °C). This study illustrates how forest management, forest vegetation, and climate factors affecting nesting ecology vary throughout the nesting season. Additionally, effects that switch directions (positive versus negative) across spatial scales indicate spatially dependent ecological processes (e.g., nest suitability versus adult foraging). This study provides a model for assessing the effects of forest management on bird population persistence by considering the nesting season as stages with distinct ecological limitations linked to spatially-dependent factors.

Evaluation of fall‐seeded cover crops for grassland nesting waterfowl in eastern South Dakota

AbstractThe Prairie Pothole Region (PPR) is the primary breeding ground for many species of North American waterfowl. The PPR was historically dominated by mixed and tallgrass prairies interspersed with wetlands, but >70% of the native grassland area has been lost due to widespread conversion to croplands. Cover cropping is a reemerging farming technique that may provide suitable nesting cover for grassland nesting waterfowl in active croplands, but waterfowl nest survival in fall cover‐cropped fields has not been evaluated. We studied use (nest abundance and density) and nest survival of breeding waterfowl in fall‐seeded cover crops and perennial cover during 2018 and 2019. We searched 2,094 ha of cover crops and 1,604 ha of perennial cover and found 123 and 304 duck nests, respectively, in each cover type. Estimated nest success (34‐day interval) was 3.7% and 16.6% in cover crops during 2018 and 2019, respectively, versus 22.1% in 2018 and 24.9% in 2019 in perennial cover, with increased success of cover‐crop fields in 2019 resulting from precipitation that prevented most fields from being planted to row crops. In a model that included effects of planting, daily nest survival in perennial cover was 0.944 (SD = 0.026) in 2018 and 0.960 (SD = 0.019) in 2019. Estimated daily nest survival was 0.912 (SD = 0.040) in 2018 and 0.960 (SD = 0.019) in 2019 during intervals when planting did not occur, but was only 0.417 (SD = 0.124) in 2018 and 0.612 (SD = 0.117) in 2019 on the day that planting occurred. Estimated nest densities in 2018 and 2019, adjusted for nests that failed prior to discovery, were 5.1 (SE = 1.1) and 11.0 (SE = 3.1) nests 100‐ha−1 in perennial cover, but only 2.1 (SE = 0.8) and 2.6 (SE = 0.7) in cover crops, respectively. Based on observed nest initiation and planting dates, about 70% of duck nests in cover crops would experience planting events in a typical growing season. Our results suggest that under current management techniques, fall‐seeded cover crops offer poor nesting habitat for waterfowl; however, the important benefits cover crops provide to soil health, water quality, and other ecosystem services remain.

Minimal shift of eastern wild turkey nesting phenology associated with projected climate change

Climate change may induce mismatches between wildlife reproductive phenology and temporal occurrence of resources necessary for reproductive success. Verifying and elucidating the causal mechanisms behind potential mismatches requires large-scale, longer-duration data. We used eastern wild turkey (Meleagris gallopavo silvestris) nesting data collected across the southeastern U.S. over eight years to investigate potential climatic drivers of variation in nest initiation dates. We investigated climactic relationships with two datasets, one inclusive of successful and unsuccessful nests (full dataset) and another of just successful nests (successfully hatched dataset), to determine whether successfully hatched nests responded differently to weather changes than all nests did. In the full dataset, each 10 cm increase in January precipitation was associated with nesting occurring 0.46–0.66 days earlier, and each 10 cm increase in precipitation during the 30 days preceding nesting was associated with nesting occurring 0.17–0.21 days later. In the successfully hatched dataset, a 10 cm increase in March precipitation was associated with nesting occurring 0.67–0.74 days earlier, and an increase of one unit of variation in February maximum temperature was associated with nesting occurring 0.02 days later. We combined the results of these modeled relationships with multiple climate scenarios to understand potential implications of future climate change on wild turkey nesting phenology; results indicated that mean nest initiation date is projected to change by <0.1 day by 2040–2060. Wild turkey nesting phenology did not track changes in spring green-up timing, which could result in phenological mismatch between the timing of nesting and the availability of resources critical for successful reproduction.

Waterfowl distribution and productivity in the Prairie Pothole Region of Canada: tools for conservation planning

AbstractSpecies conservation requires an understanding of the factors and interactions affecting species distribution and behavior, habitat availability and use, and corresponding vital rates at multiple temporal and spatial scales. Opportunities to investigate these relationships across broad geographic regions are rare. We combined long‐term waterfowl population surveys, and studies of habitat use and breeding success, to develop models that identify and incorporate these interactions for upland‐nesting waterfowl in the Prairie Pothole Region (PPR) of Canada. Specifically, we used data from the annual Waterfowl Breeding Population and Habitat Survey (1961–2009) at the survey segment level and associated habitat covariates to model and map the long‐term average duck density across the Canadian PPR. We analyzed nest location and fate data from approximately 25,000 duck nests found during 3 multi‐year nesting studies (1994–2011) to model factors associated with nest survival and habitat selection through the nesting season for the 5 most common upland nesting duck species: mallard (Anas platyrhynchos), gadwall (Mareca strepera), blue‐winged teal (Spatula discors), northern shoveler (Spatula clypeata), and northern pintail (Anas acuta). Duck density was highly variable across the Canadian PPR, reflecting positive responses to local wetland area and count, and amounts of cropland and grassland, a regional positive response to latitude, and a negative response to local amounts of tree cover. Nest survival was affected by temporal and spatial variables at multiple scales. Specifically, nest survival demonstrated interactive effects among species, nest initiation date, and nesting cover type and was influenced by relative annual wetness, population density, and surrounding landscape composition at landscape scales, and broad geographic gradients (east‐west and north‐south). Likewise, species‐specific probability of nest habitat selection was influenced by timing of nest initiation, population density, relative annual wetness, herbaceous cover, and tree cover in the surrounding landscape, and location within the Canadian PPR. We combined these models, with estimates of breeding effort (nesting, renesting, and nest attempts) from existing literature, in a stochastic conservation planning model that estimates nest distribution and success given spatiotemporal variation in duck density, habitat availability, and influential covariates. We demonstrate the use of this model by examining various conservation planning scenarios. These models allow estimation of local, landscape, and regional influence of conservation investments and other landscape changes on the productivity of breeding duck populations across the PPR of Canada. These models lay the groundwork for the incorporation of conservation delivery costs for full return‐on‐investment analyses and scenario analyses of climate, habitat, and land use change in regional and continental population models.

Reproductive senescence and mating tactic interact and conflict to drive reproductive success in a passerine.

An understanding of the drivers of individual fitness is a fundamental component of evolutionary ecology and life-history theory. Reproductive senescence, mate and mating tactic choice and latent heterogeneity in individual quality interact to affect individual fitness. We sought to disentangle the effects of these fitness drivers, where longitudinal data are required to understand their respective impacts. We used reproductive allocation and success data from a long-term (1989-2018) study of white-throated dippers Cinclus cinclus in Switzerland to simultaneously examine the effects of female and male age, mating tactic, nest initiation date and individual heterogeneity on reproductive performance. We modelled quadratic and categorical effects of age on reproductive parameters. The probability of polygyny increased with age in both sexes before declining in older age classes. Similarly, hatching probability in monogamous pairs and the number of nestlings hatched in both monogamous and polygynous pairs increased with female age before declining later in life. As predicted, offspring survival in monogamous pairs increased with male age before declining in older age classes, but male age had no effect on offspring survival in polygynous nesting attempts. Our results demonstrate that parental age, mating tactic and individual heterogeneity all affect reproductive success, and that the impacts of senescent decline are expressed across different demographic components as a function of sex-specific senescent decline and mating tactic.

Reproductive Success of Red-Billed Tropicbirds (Phaethon aethereus) on St. Eustatius, Caribbean Netherlands

The daily nest-survival rates of Red-billed Tropicbirds (Phaethon aethereus) were estimated over six breeding seasons on St. Eustatius in the Caribbean. We analyzed 338 nesting attempts between 2013 and 2020. The daily survival rate (DSR) of tropicbird nests was modeled as a function of nest initiation date, sea surface temperature (SST), elevation, vegetation in front of the nest, and year. Yearly nest survival rates (± SE) of the best fitting models ranged from 0.21 ± 0.06–0.74 ± 0.13 (n = 338 nests). DSR of the most parsimonious models averaged 0.39 ± 0.04 during the incubation period, 0.83 ± 0.05 during the chick-rearing period, and 0.30 ± 0.04 during the nesting period (incubation through fledging) when data were pooled across all years. Models with linear and quadratic trends of nest initiation date combined with SST and elevation received strong support in the incubation and nesting periods. Nests initiated in peak nesting season, when SSTs were lower, had higher DSR estimates than nests initiated early or late in the season. Compared to studies of the same species from Saba and the Gulf of California, survival probability on St. Eustatius was lower during the incubation stage but higher during the chick-rearing period. Similar to populations in the Gulf of California, tropicbird reproduction differed and laying date varied among years, and survival was influenced by SST. Our results are consistent with a study on White-tailed Tropicbirds (Phaethon lepturus) in Bermuda which found that survival was affected by temporal factors rather than physical site characteristics. Our study contributes to a better understanding of the factors that influence Red-billed Tropicbird survival on a small Caribbean island.

Early nest initiation and vegetation density enhance nest survival in Wild Turkeys

Abstract The theory of adaptive habitat selection suggests resource selection by animals should reflect underlying quality, such that individual selection confers an adaptive advantage via increased fitness. Using resource selection functions and nest survival models, we demonstrated that visual obstruction at the nest site was adaptively significant but timing of nest initiation had the greatest effect on nest survival for eastern Wild Turkeys (Meleagris gallopavo silvestris). Predation risk is a selective pressure, and if individuals can perceive predation risk, they may respond by altering the selection of nest site characteristics based on prior experience. We evaluated patterns in nest site selection of 387 Wild Turkeys and the consequences of selection on reproductive success across the southeastern United States from 2014 to 2019. We monitored 549 nest sites and found that nest initiation date had the strongest effect on daily nest survival rates, wherein adult females at our earliest nest initiation date were ~4 times more likely to successfully nest than females at our latest nest initiation date. Selection of nest sites with greater visual obstruction also increased daily nest survival rates, and females were 1.17 (95% CI: 1.100–1.234) and 1.37 (95% CI: 1.258–1.486) times more likely to select sites for every 10-cm increase in visual obstruction and maximum vegetation height, respectively. Collectively, our results indicate that nest initiation date is likely the critical parameter driving Wild Turkey nest success, whereas vegetative conditions play a lesser role in influencing nest success. Females nesting earlier may be in better body condition and show increased nest attentiveness, which may mediate nest success more than vegetation conditions around nest sites. Our work indicates that increasing the reproductive success of Wild Turkeys may hinge on females being able to nest as early as possible within the reproductive season.

Variation in eastern wild turkey nesting phenology at their northern range limit

AbstractLimiting the potential for disturbance of wild turkey (Meleagris gallopavo) breeding and nesting is often stated as a concern for management, particularly when associated with the spring hunting season. The timing of wild turkey nesting has been shown to vary with latitude, with spring phenology, and among individuals, but local information on nesting timing is needed to fully evaluate local harvest regulations. Our objectives were to characterize wild turkey nesting phenology and identify overlap with current hunting season timing and hunter effort in Maine, USA. We also identified sources of variation related to land cover and individual female characteristics such as body condition and pathogen infection status. Finally, we compared the temporal distributions of nest initiation across the 2 years of our study. We assessed nesting phenology of eastern wild turkeys (M. g. silvestris) in Penobscot, Hancock, and Cumberland counties, Maine, by monitoring females for nesting activity using VHF and GPS transmitters. During April–July 2018 and 2019, we located 69 nests from radiomarked females and 3 nests from unmarked females. Of the nests discovered, 56 were presumed first attempts, 12 were second attempts, and one was a third attempt. The median date of nest initiation (i.e., date first egg was laid) for first nests was April 27 in 2018 and May 5 in 2019. Females that nested in areas with greater residential and urban development initiated nests earlier than females that used more rural agricultural land covers. Despite a delay in the onset of nesting in 2019, the distribution of nest initiation among females did not change throughout the season. Our results indicate that the majority of male harvest occurred concurrently with egg laying. Thus, current hunting season timing likely limits risks associated with disturbance of mating. Given that Maine's wild turkey population is thought to be stable or increasing, our data support maintaining the current hunting season structure. However, breeding and nesting phenology of wild turkeys should continue to be monitored in relation to changing environmental conditions, trends in the turkey population, hunter numbers, and spring harvest, so that future changes can be incorporated into harvest management and decision making.

Does hatch date set the clock? Timing of post‐fledging movements for families of a colonially breeding, long‐distance migratory songbird

Factors that influence the development of migration timing in juvenile songbirds have implications for the ability of individuals to respond positively to rapid environmental changes. We investigated the impacts of nest timing on the post‐breeding movement timing of juveniles and adults of a migratory songbird. We tested whether first egg date and environmental factors predicted the initiation of post‐breeding stages: fledge date for juveniles, and colony departure date for both adults and juveniles. At breeding colonies of purple martin Progne subis in southern Ontario, Canada, we monitored nests to determine the date of nest initiation (‘first egg date') and deployed 122 coded radio‐frequency tracking tags on young and adults to determine the timing of post‐breeding stages. We found that first egg date, the number of nestmates, and age of parents were the main predictors of fledge date. Of these three factors, only first egg date carried through post‐breeding to influence colony departure date for juvenile birds, but this relationship weakened between first egg date and departure date. Nestmates tended to fledge together (range 0–4 days) but exhibited greater variation in colony departure timing (range 0–11 days). Further, while first egg influenced departure date, increasing variation between fledging and departure led to some birds departing breeding colonies at a younger age, suggesting influence of local environmental factors (e.g. social or photoperiod change) in departure decisions. The timing of adult colony departure date was independent of first egg dates. In sum, our results suggest a role for first egg dates in setting timing of post‐breeding movements, but with variation introduced between fledge and departure dates. Experimental manipulations of photoperiod in a wild setting are needed and future research should investigate whether the timing of movement driven by nesting timing, holds across the rest of migration or even the lifetime of bird.

Nest survival and cause-specific nest mortality in the San Clemente Bell’s Sparrow

Nest monitoring and the use of camera systems can provide researchers with reproductive data integral to the successful management and recovery of threatened and endangered avian species. From 2012 to 2019, we used cameras to monitor 110 nests of the threatened San Clemente Bell’s Sparrow (<i>Artemisiospiza belli clementeae</i>) to identify nest predators and evaluate threats to their recovery on San Clemente Island (SCI). We evaluated the effects of winter precipitation, nest initiation date, and nest substrate on nest survival rates. We also used cameras to identify and estimate cause-specific mortality rates from native and non-native nest predators. We did not observe significant impacts of precipitation or nest initiation date on nest survival. Nests in California boxthorn (<i>Lycium californicum</i>) had significantly lower survival rates than nests in other substrates. The native San Clemente Island fox (<i>Urocyon littoralis clementae</i>) was the most common nest predator, followed by non-native black rats (<i>Rattus rattus</i>). Overall, nests were much more likely to be predated by native than non-native predators. This suggests that San Clemente Bell’s Sparrows could achieve recovery despite the presence of non-native predators. Our findings help describe and quantify the breeding ecology of San Clemente Bell’s Sparrows, providing necessary information for data-driven management and recovery efforts.

Hydrology management influences nest survival but not clutch size in Lesser Scaup

Components of reproductive success such as clutch size and nest survival may greatly affect avian population growth rates. Understanding how environmental conditions influence temporal variation in these demographic parameters could thus provide valuable insight into best management practices for species of concern. One such species that could benefit from a better understanding of such processes is Lesser Scaup (<em>Aythya affinis</em>), whose overall abundance in North America has declined since the early 1980s. We used a long-term study (2005–2019) of Lesser Scaup demography at Red Rock Lakes National Wildlife Refuge in southwestern Montana, USA, to examine how the management of wetland conditions influenced within- and across-year temporal variation in clutch size and nest survival. Predicted clutch size varied more across nest initiation dates (6.18–10.05 eggs) within years than it did across years (7.51–8.38 eggs), and none of the covariates we examined were significantly related to clutch size across years. Nest daily survival rates varied substantially across days within breeding seasons (e.g., 2018: 0.38–0.985), and annual mean nest survival varied greatly across years (0.27–0.58). Furthermore, seasonal chronology of managed wetland water levels influenced nest survival such that years when water levels gradually rose to a maximum late in the breeding season, relative to mean nest initiation date, resulted in the highest nest survival. These findings collectively suggest that when flows can be manipulated with water control structures, efforts to manage the chronology of water levels at watershed and local wetland scales could improve nest survival, whereas such management efforts will not likely affect clutch sizes.

Life-history attributes of Arctic-breeding birds drive uneven responses to environmental variability across different phases of the reproductive cycle.

Animals exhibit varied life‐history traits that reflect adaptive responses to their environments. For Arctic‐breeding birds, traits related to diet, egg nutrient allocation, clutch size, and chick growth are predicted to be under increasing selection pressure due to rapid climate change and increasing environmental variability across high‐latitude regions. We compared four migratory birds (black brant [Branta bernicla nigricans], lesser snow geese [Chen caerulescens caerulescens], semipalmated sandpipers [Calidris pusilla], and Lapland longspurs [Calcarius lapponicus]) with varied life histories at an Arctic site in Alaska, USA, to understand how life‐history traits help moderate environmental variability across different phases of the reproductive cycle. We monitored aspects of reproductive performance related to the timing of breeding, reproductive investment, and chick growth from 2011 to 2018. In response to early snowmelt and warm temperatures, semipalmated sandpipers advanced their site arrival and bred in higher numbers, while brant and snow geese increased clutch sizes; all four species advanced their nest initiation dates. During chick rearing, longspur nestlings were relatively resilient to environmental variation, whereas warmer temperatures increased the growth rates of sandpiper chicks but reduced growth rates of snow goose goslings. These responses generally aligned with traits along the capital‐income spectrum of nutrient acquisition and altricial–precocial modes of chick growth. Under a warming climate, the ability to mobilize endogenous reserves likely provides geese with relative flexibility to adjust the timing of breeding and the size of clutches. Higher temperatures, however, may negatively affect the quality of herbaceous foods and slow gosling growth. Species may possess traits that are beneficial during one phase of the reproductive cycle and others that may be detrimental at another phase, uneven responses that may be amplified with future climate warming. These results underscore the need to consider multiple phases of the reproductive cycle when assessing the effects of environmental variability on Arctic‐breeding birds.

Individual heterogeneity in fitness in a long-lived herbivore.

Heterogeneity in the intrinsic quality and nutritional condition of individuals affects reproductive success and consequently fitness. Black brant (Branta bernicla nigricans) are long‐lived, migratory, specialist herbivores. Long migratory pathways and short summer breeding seasons constrain the time and energy available for reproduction, thus magnifying life‐history trade‐offs. These constraints, combined with long lifespans and trade‐offs between current and future reproductive value, provide a model system to examine the role of individual heterogeneity in driving life‐history strategies and individual heterogeneity in fitness. We used hierarchical Bayesian models to examine reproductive trade‐offs, modeling the relationships between within‐year measures of reproductive energy allocation and among‐year demographic rates of individual females breeding on the Yukon‐Kuskokwim Delta, Alaska, using capture–recapture and reproductive data from 1988 to 2014. We generally found that annual survival tended to be buffered against variation in reproductive investment, while breeding probability varied considerably over the range of clutch size‐laying date combinations. We provide evidence for relationships between breeding probability and clutch size, breeding probability and nest initiation date, and an interaction between clutch size and initiation date. Average lifetime clutch size also had a weak positive relationship with apparent survival probability. Our results support the use of demographic buffering strategies for black brant. These results also indirectly suggest associations among environmental conditions during growth, fitness, and energy allocation, highlighting the effects of early growth conditions on individual heterogeneity, and subsequently, lifetime reproductive investment.

The Influence of Biological Factors on Haematological Values in Wild Marsh Harrier (Circus aeruginosus) Nestlings.

Simple SummaryHaematological examination can be used to address the health state of birds. The present study aimed to investigate how hatching order, brood size, and nest initiation date influence the haemoglobin level, red blood cell count, white blood cell count, and glucose level in the blood of raptor nestlings in which brood reduction occurs during nestling rearing. Blood samples were collected to assess the health status of wild marsh harrier nestlings in the agricultural landscape of eastern Poland. Statistical analyses revealed that hatching order, but not brood size or nest initiation date, had an impact on the haematological data of nestlings. Hatching order affected these data in that haemoglobin levels and red blood cell counts gradually decreased, whereas glucose levels and white blood cell counts increased, from the first- to the last-hatched nestlings. The poor condition of the youngest nestlings reflected in these indices may increase the likelihood of their perishing, and consequently, of brood reduction.Marsh harrier (Circus aeruginosus) is a species with obligatory cainism, in which hatching asynchrony creates a pronounced size hierarchy in nestlings. The size-related competitive advantage of older nestlings means that they tend to dominate the younger ones, and brood reduction occurs in most nests. The aim of the study was to reference values and carry out a haematological examination in order to evaluate the physiological status and health of nestlings with respect to hatching order, brood size, and nest initiation date. To do so, we examined 19 nests with a total of 58 nestlings from a free-living population of this species located in fishpond complexes in the agricultural landscape of eastern Poland. Repeated blood samples (118 in all) were collected from nestlings. The following parameters were measured using fresh full blood: red blood cell count (RBC), haemoglobin level (Hb), white blood cell count (WBC), and plasma glucose level (Glu). The data were analysed using generalized linear mixed models and linear mixed models ((G)LMM). The study revealed that hatching order, but not brood size or nest initiation date, affected the physical condition of marsh harrier nestlings. Hb levels and RBC counts gradually decreased, whereas Glu levels and WBC counts increased from the first- to the last-hatched nestlings. This result points to the generally poorer condition of the youngest nestlings compared with their older siblings. The poor physiological condition of the youngest nestlings may consequently increase the likelihood of their perishing, and hence, of brood reduction.

Agriculture is adapting to phenological shifts caused by climate change, but grassland songbirds are not.

Migratory birds time their migration based on cues that signal resource availability for reproduction. However, with climate change, the timing of seasonal events may shift, potentially inhibiting the ability of some species to use them as accurate cues for migration. We studied the relationship between phenological shifts and reproduction by long‐ and short‐distance migratory songbirds—Bobolinks (Dolichonyx oryzivorus) and Savannah Sparrows (Passerculus sandwichensis). Our study population breeds in hayfields and pastures in Vermont, USA, where farmers are also changing management activities in response to climate change. From 2002 to 2019, we monitored nest initiation dates to quantify correlations with environmental factors and the timing of nest initiation. We collected historical and projected precipitation and temperature data for the breeding grounds, and their respective wintering and stopover sites, the North Atlantic Oscillation (NAO) and the El Niño Southern Oscillation (ENSO). We predicted that winter conditions experienced by the short‐distance migrant, the Savannah Sparrow, but not the long‐distance migrant, the Bobolink, would explain the timing and success of nesting, however that this timing would be misaligned with changes in agricultural practices by hay farmers. Nest initiation dates did not show significant directional change for either species, but did vary among years. Interannual variation in Savannah Sparrow nest initiation dates was best explained by the interaction between precipitation on the breeding grounds and average wintering site (Wilmington, North Carolina). For Bobolinks, interannual variation in nest initiation dates was best explained by the interaction between breeding ground precipitation and average temperature in their fall stopover site (Barquisimieto, Venezuela). However, first haying dates in Vermont advanced by ~10 days over 18 years. These results suggest that the conflict between the timing of hay harvests and grassland songbird reproduction will increase, further threatening population processes for these species, as early harvests notably decrease annual productivity.

American Black Duck Nesting Ecology in North Carolina

ABSTRACTNorth Carolina, USA, is the southernmost extent of the American black duck's (Anas rubripes) breeding range; however, little is known about their nesting ecology in this region. We located and monitored 140 nesting black ducks over 2 years (2017–2018) to quantify preferred nesting habitat and assess nesting productivity within coastal North Carolina. We located nests in brackish marshes (75%) and man‐made dredge spoil islands (25%) at a density of 1 nest/22 ha. Black ducks selected high marsh and nested an average of 21.81 m from open water at a mean elevation of 1.36 m. In preferred nesting habitat, visual obstruction readings were 0.50 m with a maximum mean vegetation height of 0.81 m and land cover consisted largely of grasses (84.6%). Apparent nest success rates varied from 31% (2017) to 63% (2018) across years. The majority (72.2%) of variability in nest success was best predicted by nest location (mainland marsh, natural island, or spoil island), vegetation density, maximum vegetation height, and year. Management for breeding black ducks in coastal North Carolina should focus on promoting selected nesting habitat and reducing nest predators. Prescribed burns, used to set back succession on spoil islands and in brackish marshes should be conducted in the winter or in the early growing season not to exceed the twenty‐fifth quantile date of black duck nest initiation (2 Apr). © 2021 The Wildlife Society.