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At least 1,693 records · Page 94Linked to original sources
USGS2007

Selection for rapid embryo development correlates with embryo exposure to maternal androgens among passerine birds

Greater offspring predation favors evolution of faster development among species. We hypothesized that greater offspring predation exerts selection on mothers to increase levels of anabolic androgens in egg yolks to achieve faster development. Here, we tested whether (1) concentrations of yolk androgens in passerine species were associated with offspring predation and (2) embryo and nestling development rates were associated with yolk androgen concentrations. We examined three androgens that increase in potency along the synthesis pathway: androstenedione (A4) to testosterone (T) to 5??- dihydrotestosterone (5??-DHT). Concentrations of none of these steroids were related to clutch size; only A4 was allometrically related to egg volume. Species that experience greater predation showed higher yolk concentrations of T and 5??-DHT. Higher concentrations of T and particularly 5??-DHT were strongly correlated with faster development during the embryo period and less so during the nestling period. Development rates were most strongly correlated with 5??-DHT, suggesting that potency increases along the androgen synthesis pathway and that effects are mediated by the androgen receptor pathway. These results are consistent with the hypothesis that selection for faster development by time-dependent offspring mortality may be achieved epigenetically by varying embryo exposure to maternal anabolic steroids. ?? 2007 by The University of Chicago. All rights reserved.

American Naturalist↗
USGS2019

Brood size affects future reproduction in a long-lived bird with precocial young

Estimation of trade-offs between current reproduction and future survival and fecundity of long-lived vertebrates is essential to understanding factors that shape optimal reproductive investment. Black brant geese (Branta bernicla nigricans) fledge more goslings, on average, when their broods are experimentally enlarged to be greater than the most common clutch size of four eggs. Thus, we hypothesized that the lesser frequency of brant clutches exceeding four eggs results, at least partially, from a future reduction in survival, breeding probability, or clutch size for females tending larger broods. We used an eight-year mark-recapture dataset (Barker robust design) with five years of clutch and brood manipulations to estimate long-term consequences of reproductive decisions in brant. We did not find evidence of a trade-off between reproductive effort and true survival or future initiation date and clutch size. Rather, future breeding probability was maximized (0.92 ± 0.03 [se]) for manipulated females tending broods of four goslings and lower for females tending smaller (one gosling; 0.63 ± 0.09 [se]) or larger broods (seven goslings; 0.52 ± 0.15 [se]). Our results suggest that demographic trade-offs for female brant tending large broods may reduce the fitness value of clutches larger than four and, therefore, contribute to the paucity of larger clutches. The lack of a trade-off between reproductive effort and survival provides evidence that survival, to which fitness is most sensitive in long-lived animals, is buffered against temporal variation in brant.

American Naturalist↗
USGS2019

Higher nest predation favors rapid fledging at the cost of plumage quality in nestling birds

Life-history theory predicts that rapid growth comes at a cost to offspring quality and adult longevity. However, trade-offs have been examined primarily based on proximate variation within species rather than evolved differences across species. Evolved differences are important to examine because species may co-evolve mechanisms to reduce long-term costs of rapid growth. For example, trade-offs associated with fast growth and short development time might be expressed in ephemeral traits because costs associated with these traits are paid for only a short duration. We explored this idea using nestling body feathers, an ephemeral trait, and examined whether shorter development time yielded lower quality feathers. We found a strong trade-off whereby nestlings that spend more time in the nest produced higher quality plumage across 123 temperate and tropical species. Using a subset of these species (n=67), we found that plumage quality was lower in species with higher rates of nest predation, which favors rapid nestling growth and short development times. Our results suggest that evolution of more rapid growth may co-evolve with other mechanisms whereby long-term costs are reduced by shifting costs of allocational trade-offs to ephemeral traits that are short-lived.

The American Naturalist↗
USGS2019

Proximity to unconventional shale gas infrastructure alters breeding bird abundance and distribution

Unconventional shale gas development is a rapidly expanding driver of forest loss and fragmentation in the central Appalachian region. We evaluated the relationship between breeding passerine abundances and distance from shale gas development at a long-term (2008–2017) study site in northern West Virginia, USA. We examined responses of 27 species within 3 habitat guilds: forest interior, early successional, and synanthropic. More than half of the species evaluated showed sensitivity to distance from unconventional shale gas infrastructure (e.g., well pads, access roads, pipelines). Five forest interior species occurred in greater abundances farther from shale gas development, whereas 3 forest interior gap specialists increased in abundance closer to shale gas. Early successional and synanthropic species, including the nest-parasitic Brown-headed Cowbird ( Molothrus ater ), generally occurred in greater abundances closer to shale gas infrastructure. We used interpolated distributions of 4 focal species to assess their spatial response to unconventional shale gas development over time. Our results indicate that breeding passerine distributions and community composition are changing with forest disturbance driven by unconventional shale gas energy development.

West Vigninia↗
USGS2021

The demographic contributions of connectivity versus local dynamics to population growth of an endangered bird

Conservation and management increasingly focus on connectivity, because connectivity driven by variation in immigration rates across landscapes is thought to be crucial for maintaining local population and metapopulation persistence. Yet, efforts to quantify the relative role of immigration on population growth across the entire range of species and over time have been lacking. We assessed whether immigration limited local and range‐wide population growth of the endangered snail kite Rostrhamus sociabilis in Florida, USA, over 18 years using multi‐state, reverse‐time modelling that accounts for imperfect detection of individuals and unobservable states. Demographic contributions of immigration varied depending on the dynamics and geographic position of the local populations, were scale‐dependent and changed over time. By comparing the relative contributions of immigration versus local demography for periods of significant change in local abundance, we found empirical evidence for a disproportionately large role of immigration in facilitating population growth of a centrally located population—a connectivity ‘hub’. The importance of connectivity changed depending of the spatial scale considered, such that immigration was a more important driver of population growth at small versus large spatial scales. Furthermore, the contribution of immigration was much greater during time periods when local population size was small, emphasizing abundance‐dependent rescue effects. Our findings suggest that efforts aimed at improving local breeding habitat will likely be most effective at increasing snail kite population growth. More broadly, our results provide much needed information on the role of connectivity for population growth, suggesting that connectivity conservation may have the greatest benefits when efforts focus on centrally located habitat patches and small populations. Furthermore, our results highlight that connectivity is highly dynamic over time and that interpreting the effects of connectivity at local scales may not transfer to region‐wide dynamics.

Florida↗
USGS2026

Spatially concentrating logging could mitigate climate-magnified fragmentation risks to a globally endangered bird

1. Rising timber demand is transforming forest structure globally, profoundly affecting biodiversity and climate resilience. Logging-driven fragmentation is potentially a major driver of biodiversity loss in production landscapes, yet its interactions with escalating climate stressors remain poorly understood. 2. We combine two decades of Landsat-derived habitat metrics with 29,000 surveys of the marbled murrelet ( Brachyramphus marmoratus )—an iconic Pacific Northwest old-forest specialist seabird affecting management of >10 million hectares. Controlling for habitat amount and detection probability, increasing landscape-scale forest edge amount sharply reduces murrelet occupancy, with impacts worsening under unfavourable climate-driven ocean conditions. 3. Comparing alternative landscape-scale timber harvest strategies, spatially concentrated logging consistently supports higher murrelet populations than fragmented approaches producing equivalent wood volumes, with benefits amplified under adverse ocean conditions. However, historical harvesting policies in the Pacific Northwest have instead driven severe habitat fragmentation, which we show is eroding the value of core set-aside forests on federal and conservation lands and ultimately rendering murrelets more vulnerable to climate change. 4. Synthesis and applications : We map key opportunities to boost populations by reducing edginess around remaining nesting habitat and investigate these opportunities' spatial distribution across land ownership and timber productivity gradients. Concentrating logging could be critical for mitigating fragmentation and climate threats for murrelets and potentially other forest-dependent species amid rising timber demand.

California, Oregon, Washington↗
USGS2020

Limitations, lack of standardization, and recommended best practices in studies of renewable energy effects on birds and bats

Increasing global energy demand is fostering the development of renewable energy as an alternative to fossil fuels. However, renewable energy facilities may adversely affect wildlife. Facility siting guidelines recommend or require project developers complete pre‐ and postconstruction wildlife surveys to predict risk and estimate effects of proposed projects. Despite this, there are no published studies that have quantified the types of surveys used or how survey types are standardized within and across facilities. We evaluated 628 peer‐reviewed publications, unpublished reports, and citations, and we analyzed data from 525 of these sources (203 facilities: 193 wind and 10 solar) in the United States and Canada to determine the frequency of pre‐ and postconstruction surveys and whether that frequency changed over time; frequency of studies explicitly designed to allow before‐after or impact‐control analyses; and what types of survey data were collected during pre‐ and postconstruction periods and how those data types were standardized across periods and among facilities. Within our data set, postconstruction monitoring for wildlife fatalities and habitat use was a standard practice ( n = 446 reports), but preconstruction estimation of baseline wildlife habitat use and mortality was less frequently reported ( n = 84). Only 22% ( n = 45) of the 203 facilities provided data from both pre‐ and postconstruction, and 29% ( n = 59) had experimental study designs. Of 108 facilities at which habitat‐use surveys were conducted, only 3% estimated of detection probability. Thus, the available data generally preclude comparison of biological data across construction periods and among facilities. Use of experimental study designs and following similar field protocols would improve the knowledge of how renewable energy affects wildlife.

Conservation Biology↗
USGS2025

Waterfowl endozoochory: Traits drive plant-bird dispersal interactions in North America

Plant biogeography and ongoing changes in plant distributions are influenced by long-distance dispersal (LDD) of seeds, and migratory waterfowl (Anatidae: Ducks, geese and swans) are particularly important for the dispersal of plants in and around wetlands through gut passage (endozoochory). However, this dispersal is not contemplated by classical dispersal syndromes; hence, currently we have limited understanding of what angiosperm traits predict seed dispersal by waterfowl and any differences due to avian trait variation among waterfowl species. We conducted a literature search for data on the presence of seeds in the alimentary canal or faeces of North American waterfowl as a proxy for dispersal interactions, since an important fraction of these seeds survives gut passage. We present a list of North American flowering plant species ( N = 536) from 95 families potentially dispersed by 38 waterfowl species, together with traits of these plants and their vectors. Owing largely to limited sampling effort, 47% of plant species and 35% of plant genera recorded were only found in a single waterfowl species. A suite of analytical approaches revealed major differences in the traits of plants whose seeds are ingested and likely dispersed between foraging groups (guilds) and in relation to other waterfowl traits. Diving ducks and sea ducks are associated with sublittoral plants that have submerged or floating leaves, and hence with the classical hydrochory syndrome. Dabbling ducks and herbivorous waterfowl (notably geese) are associated with terrestrial herbaceous plants, and also with the unspecialised dispersal syndrome common in terrestrial plants. Plants with larger seeds or of greater height are more likely to be dispersed by dabbling ducks, whereas shorter plants are more likely to be dispersed by geese than by other waterfowl. Network analyses of interactions between waterfowl species and plant traits were generally consistent with these results, but also provided evidence that not all geese, dabbling ducks, or sea duck species are alike in their interactions with plants along the terrestrial–aquatic gradient, but instead occupy distinct dispersal niches. The traditional classification of waterfowl into guilds therefore does not accurately reflect their differing roles in the ingestion and dispersal of plant seeds. Aquatic plant species had more vector species than terrestrial ones. Detailed studies of waterfowl endozoochory and more trait determinations for North American plants are needed to facilitate predictions of LDD as waterfowl population sizes and migration patterns vary in the future with climate change.

Freshwater Biology↗
USGS2009

A spatial model of bird abundance as adjusted for detection probability

Modeling the spatial distribution of animals can be complicated by spatial and temporal effects (i.e. spatial autocorrelation and trends in abundance over time) and other factors such as imperfect detection probabilities and observation-related nuisance variables. Recent advances in modeling have demonstrated various approaches that handle most of these factors but which require a degree of sampling effort (e.g. replication) not available to many field studies. We present a two-step approach that addresses these challenges to spatially model species abundance. Habitat, spatial and temporal variables were handled with a Bayesian approach which facilitated modeling hierarchically structured data. Predicted abundance was subsequently adjusted to account for imperfect detection and the area effectively sampled for each species. We provide examples of our modeling approach for two endemic Hawaiian nectarivorous honeycreepers: 'i'iwi Vestiaria coccinea and 'apapane Himatione sanguinea. ?? 2009 Ecography.

Ecography↗