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USGS2026

Bird breeding success in restored grasslands compared to croplands and natural grasslands: A meta-analysis

Reproductive success is central to long-term population persistence, yet it is rarely assessed in ecosystem restoration. We performed a multilevel meta-analysis to assess whether bird breeding success increases from croplands to restored grasslands or from restored grasslands to natural grasslands. We quantified five comparisons of two breeding success variables between croplands and restored grasslands in three species, and 228 comparisons of nine variables between natural and restored grasslands in 22 species using 14 datasets from North America and Europe. For the few grassland birds that nest in croplands, clutch size was higher in restored fields than in croplands. Most importantly, breeding success did not differ between restored and natural grasslands in nine species and for all species combined. In 13 species, breeding success differed between restored and natural grasslands, and it was often higher in restored grasslands during early breeding stages, but higher in natural grasslands during later stages. Eight species did better in restored grasslands (Clay-colored Sparrow, Dickcissel, Eastern Meadowlark, Lesser Prairie-chicken, Mourning Dove, Red-winged Blackbird, Sprague's Pipit, Western Meadowlark), whereas four species did better in natural grasslands (Baird's Sparrow, Common Nighthawk, Lark Bunting, Savannah Sparrow). Our results suggest that bird breeding success can be as high in restored grasslands as in natural ones, and certainly higher than in croplands. While restored grasslands differ widely by geography, climate, method and management, our results offer hope for ecosystem restoration. However, the differences found also imply that species requirements should be considered in grassland ecosystem restoration and management.

Biological Conservation↗

USGS2022

New frontiers in bird migration research

Bird migrations are impressive behavioral phenomena, representing complex spatiotemporal strategies to balance costs of living while maximizing fitness. The field of bird migration research has made great strides over the past decades, yet fundamental gaps remain. Technologies have sparked a transformation in the study of bird migration research by revealing remarkable insights into the underlying behavioral, cognitive, physiological and evolutionary mechanisms of these diverse journeys. Here, we aim to encourage broad discussions and promote future studies by highlighting research fields that are characterized by major knowledge gaps or conflicting evidence, namely the fields of navigation, social learning, individual development, energetics and conservation. We approach each topic by summarizing the current state of knowledge and provide a future outlook of ideas and state-of-the-art methods to further advance the field. Integrating knowledge across these disciplines will allow us to understand the adaptive abilities of different species and to develop effective conservation strategies in a rapidly changing world.

Current Biology↗

USGS2013

Effects of drought on birds and riparian vegetation in the Colorado River Delta, Mexico

The riparian corridor in the delta of the Colorado River in Mexico supports internationally important bird habitat. The vegetation is maintained by surface flows from the U.S. and Mexico and by a high, non-saline aquifer into which the dominant phreatophytic shrubs and trees are rooted. We studied the effects of a regional drought on riparian vegetation and avian abundance and diversity from 2002 to 2007, during which time surface flows were markedly reduced compared to the period from 1995 to 2002. Reduced surface flows led to a reduction in native tree cover but an increase in shrub cover, mostly due to an increase in Tamarix spp., an introduced halophytic shrub, and a reduction in Populus fremontii and Salix gooddingii trees. However, overall vegetation cover was unchanged at about 70%. Overall bird density and diversity were also unchanged, but riparian-obligate species tended to decrease in abundance, and generalist species increased. Although reduction in surface flows reduced habitat value and negatively impacted riparian-obligate bird species, portions of the riparian zone exhibited resilience. Surface flows are required to reduce soil salt levels and germinate new cohorts of native trees, but the main source of water supporting this ecosystem is the aquifer, derived from underflows from irrigated fields in the U.S. and Mexico. The long-term prospects for delta riparian habitats are uncertain due to expected reduced flows of river water from climate change, and land use practices that will reduce underflows to the riparian aquifer and increase salinity levels. Active restoration programs would be needed if these habitats are to be preserved for the future.

Colorado River↗

USGS2024

Bird community response to one decade of riparian restoration along the Colorado River delta in Mexico

We assessed the response of breeding birds to one decade of riparian restoration in the Colorado River delta including active vegetation management since 2010 and various environmental water deliveries since 2014. Bird surveys were conducted from 2002 to 2021 at 230 bird count stations distributed along five river reaches with different hydrogeomorphic characteristics, across 7 routes in actively revegetated (“restored”) sites, and 20 routes in non-actively revegetated (“control”) sites. Both restored and control sites could be affected by environmental flows/water deliveries. We examined the temporal trajectories of four community-aggregated metrics for 53 breeding species, and the number of detections (counts) for the 30 most frequently detected among the 53 species at the restored and control sites, using generalized linear mixed-effects models. Diversity and richness of the 53 breeding species were highest in the wettest river reach, but higher than in control sites in only one restored site within one of the driest river reaches. The avian community was recovering in control sites, ameliorating a long-term declining trend, perhaps indicating indirect positive effects of active restoration. The response to restoration of the 30 most common species was species-specific. Ten of the 16 riparian forest specialist species had more detections in restored sites of the wettest reach (vs. only two in the driest reach). Species with preference for agricultural fields and generalists had the highest counts along the entire delta. Generalists generally decreased following revegetation, which was another positive restoration effect. Our results will be used to help guide future restoration efforts.

Ecological Engineering↗

USGS2014

Bird migration and avian influenza: a comparison of hydrogen stable isotopes and satellite tracking methods

Satellite-based tracking of migratory waterfowl is an important tool for understanding the potential role of wild birds in the long-distance transmission of highly pathogenic avian influenza. However, employing this technique on a continental scale is prohibitively expensive. This study explores the utility of stable isotope ratios in feathers in examining both the distances traveled by migratory birds and variation in migration behavior. We compared the satellite-derived movement data of 22 ducks from 8 species captured at wintering areas in Bangladesh, Turkey, and Hong Kong with deuterium ratios (δD) in the feathers of these and other individuals captured at the same locations. We derived likely molting locations from the satellite tracking data and generated expected isotope ratios based on an interpolated map of δD in rainwater. Although δD was correlated with the distance between wintering and molting locations, surprisingly, measured δD values were not correlated with either expected values or latitudes of molting sites. However, population-level parameters derived from the satellite-tracking data, such as mean distance between wintering and molting locations and variation in migration distance, were reflected by means and variation of the stable isotope values. Our findings call into question the relevance of the rainfall isotope map for Asia for linking feather isotopes to molting locations, and underscore the need for extensive ground truthing in the form of feather-based isoscapes. Nevertheless, stable isotopes from feathers could inform disease models by characterizing the degree to which regional breeding populations interact at common wintering locations. Feather isotopes also could aid in surveying wintering locations to determine where high-resolution tracking techniques (e.g. satellite tracking) could most effectively be employed. Moreover, intrinsic markers such as stable isotopes offer the only means of inferring movement information from birds that have died as a result of infection. In the absence of feather based-isoscapes, we recommend a combination of isotope analysis and satellite-tracking as the best means of generating aggregate movement data for informing disease models.

Ecological Indicators↗

USGS2017

Importance of scale, land cover, and weather on the abundance of bird species in a managed forest

Climate change and habitat loss are projected to be the two greatest drivers of biodiversity loss over the coming century. While public lands have the potential to increase regional resilience of bird populations to these threats, long-term data are necessary to document species responses to changes in climate and habitat to better understand population vulnerabilities. We used generalized linear mixed models to determine the importance of stand-level characteristics, multi-scale land cover, and annual weather factors to the abundance of 61 bird species over a 20-year time frame in Chippewa National Forest, Minnesota, USA. Of the 61 species modeled, we were able to build final models with R-squared values that ranged from 26% to 69% for 37 species; the remaining 24 species models had issues with convergence or low explanatory power (R-squared < 20%). Models for the 37 species show that stand-level characteristics, land cover factors, and annual weather effects on species abundance were species-specific and varied within guilds. Forty-one percent of the final species models included stand-level characteristics, 92% included land cover variables at the 200 m scale, 51% included land cover variables at the 500 m scale, 46% included land cover variables at the 1000 m scale, and 38% included weather variables in best models. Three species models (8%) included significant weather and land cover interaction terms. Overall, models indicated that aboveground tree biomass and land cover variables drove changes in the majority of species. Of those species models including weather variables, more included annual variation in precipitation or drought than temperature. Annual weather variability was significantly more likely to impact abundance of species associated with deciduous forests and bird species that are considered climate sensitive. The long-term data and models we developed are particularly suited to informing science-based adaptive forest management plans that incorporate climate sensitivity, aim to conserve large areas of forest habitat, and maintain an historical mosaic of cover types for conserving a diverse and abundant avian assemblage.

Minnesota↗

USGS2023

Illegal shooting is now a leading cause of death of birds along power lines in the western USA

Human actions, both legal and illegal, affect wildlife in many ways. Inaccurate diagnosis of cause of death undermines law enforcement, management, threat assessment, and mitigation. We found 410 dead birds collected along 196 km of power lines in four western USA states during 2019 – 2022. We necropsied these carcasses to test conventional wisdom suggesting that electrocution is the leading cause of death of birds at electrical infrastructure. Of 175 birds with a known cause of death, 66% died from gunshot. Both raptors and corvids were more likely to die from gunshot than from other causes, along both transmission and distribution lines. Past mitigation to reduce avian deaths along power lines has focused almost exclusively on reducing electrocutions or collisions. Our work suggests that, although electrocution and collision remain important, addressing illegal shooting now may have greater relevance for avian conservation.

Idaho, Montana. Nevada, Oregon, Utah, Wyoming↗

USGS2010

Field detection of avian influenza virus in wild birds: evaluation of a portable rRT-PCR system and freeze-dried reagents

Wild birds have been implicated in the spread of highly pathogenic avian influenza (HPAIV) of the H5N1 subtype, prompting surveillance along migratory flyways. Sampling of wild birds is often conducted in remote regions, but results are often delayed because of limited local analytical capabilities, difficulties with sample transportation and permitting, or problems keeping samples cold in the field. In response to these challenges, the performance of a portable real-time, reverse transcriptase-polymerase chain reaction (rRT-PCR) unit (RAPID(Registered), Idaho Technologies, Salt Lake City, UT) that employed lyophilized reagents (Influenza A Target 1 Taqman; ASAY-ASY-0109, Idaho Technologies) was compared to virus isolation combined with real-time RT-PCR conducted in a laboratory. This study included both field and experimental-based sampling. Field samples were collected from migratory shorebirds captured in northern California, while experimental samples were prepared by spiking fecal material with an H6N2 AIV isolate. Results indicated that the portable rRT-PCR unit had equivalent specificity to virus isolation with no false positives, but sensitivity was compromised at low viral titers. Use of portable rRT-PCR with lyophilized reagents may expedite surveillance results, paving the way to a better understanding of wild bird involvement in HPAIV H5N1 transmission.

Journal of Virological Methods↗

USGS2013

Landscape factors and hydrology influence mercury concentrations in wading birds breeding in the Florida Everglades, USA

The hydrology of wetland ecosystems is a key driver of both mercury (Hg) methylation and waterbird foraging ecology, and hence may play a fundamental role in waterbird exposure and risk to Hg contamination. However, few studies have investigated hydrological factors that influence waterbird Hg exposure. We examined how several landscape-level hydrological variables influenced Hg concentrations in great egret and white ibis adults and chicks in the Florida Everglades. The great egret is a visual “exploiter” species that tolerates lower prey densities and is less sensitive to hydrological conditions than is the white ibis, which is a tactile “searcher” species that pursues higher prey densities in shallow water. Mercury concentrations in adult great egrets were most influenced by the spatial region that they occupied in the Everglades (higher in the southern region); whereas the number of days a site was dry during the previous dry season was the most important factor influencing Hg concentrations in adult ibis (Hg concentrations increased with the number of days dry). In contrast, Hg concentrations in egret chicks were most influenced by calendar date (increasing with date), whereas Hg concentrations in ibis chicks were most influenced by chick age, region, and water recession rate (Hg concentrations decreased with age, were higher in the southern regions, and increased with positive water recession rates). Our results indicate that both recent (preceding two weeks) hydrological conditions, and those of the prior year, influence Hg concentrations in wading birds. Further, these results suggest that Hg exposure in wading birds is driven by complex relationships between wading bird behavior and life stage, landscape hydrologic patterns, and biogeochemical processes.

Florida↗

USGS2022

Genomically diverse carbapenem resistant Enterobacteriaceae from wild birds provide insight into global patterns of spatiotemporal dissemination

Carbapenem resistant Enterobacteriaceae (CRE) are a threat to public health globally, yet the role of the environment in the epidemiology of CRE remains elusive. Given that wild birds can acquire CRE, likely from foraging in anthropogenically impacted areas, and may aid in the maintenance and dissemination of CRE in the environment, a spatiotemporal comparison of isolates from different regions and timepoints may be useful for elucidating epidemiological information. Thus, we characterized the genomic diversity of CRE from fecal samples opportunistically collected from gulls ( Larus spp.) inhabiting Alaska (USA), Chile, Spain, Turkey, and Ukraine and from black kites ( Milvus migrans ) sampled in Pakistan and assessed evidence for spatiotemporal patterns of dissemination. Within and among sampling locations, a high diversity of carbapenemases was found, including Klebsiella pneumoniae carbapenemase (KPC), New Delhi metallo-beta-lactamase (NDM), oxacillinase (OXA), and Verona integron Metallo beta-lactamase (VIM). Although the majority of genomic comparisons among samples did not provide evidence for spatial dissemination, we did find strong evidence for dissemination among Alaska, Spain, and Turkey. We also found strong evidence for temporal dissemination among samples collected in Alaska and Pakistan, though the majority of CRE clones were transitory and were not repeatedly detected among locations where samples were collected longitudinally. Carbapenemase-producing hypervirulent K. pneumoniae was isolated from gulls in Spain and Ukraine and some isolates harbored antimicrobial resistance genes conferring resistance to up to 10 different antibiotic classes, including colistin. Our results are consistent with local acquisition of CRE by wild birds with spatial dissemination influenced by intermediary transmission routes, likely involving humans. Furthermore, our results support the premise that anthropogenically-associated wild birds may be good sentinels for understanding the burden of clinically-relevant antimicrobial resistance in the local human population.

Science of the Total Environment↗

USGS2003

Influences of roads and development on bird communities in protected Chihuahuan Desert landscapes

Our objective was to improve knowledge about effects of broad-scale road and development variables on bird communities in protected desert landscapes. Bird species richness and the relative abundance or probability of occurrence of many species were significantly associated with total length of roads within each of two spatial extents (1- and 2-km radii), distance to the nearest road, distance to the nearest development, or the two-way interactions of these variables. Regression models reflected non-linear relations, interaction effects, spatial-extent effects, and interannual variation. Road and development effects warrant special attention in protected areas because such places may be important sources of indigenous bird communities in a region.

Biological Conservation↗

USGS1997

Spatial and temporal heterogeneity in metallic elements in industrialized aquatic bird habitat

This study examined the potential for exposure of migratory aquatic birds to contaminants in highly industrialized habitats at Baltimore Harbor, Maryland. Seven nearshore, benthic sites were sampled every 3 or 6 months from June 1987 to December 1988. Twenty metallic elements were measured in composites (i.e. annelids, amphipods, and isopods were pooled), clams, and sediments. Elevated concentrations were widespread throughout the sites, depending on the element. Most concentrations in composites were lowest at sites innermost and outside the harbor. Higher concentrations in composites were not related to season. Most concentrations were higher in composites than in sediments or clams, but they varied by element for clams and sediments. The largest flock of wintering waterfowl frequented the site exhibiting the highest concentrations of most elements ( p < 0.0001). Average concentrations of known toxic elements were probably not harmful to aquatic birds or their prey, but the highest detected concentrations of eight elements warrant caution. At least eight other elements exceeded background concentrations, but toxicity to birds or their prey are unknown.

Maryland↗

USGS2015

Estimating mercury exposure of piscivorous birds and sport fish using prey fish monitoring

Methylmercury is a global pollutant of aquatic ecosystems, and monitoring programs need tools to predict mercury exposure of wildlife. We developed equations to estimate methylmercury exposure of piscivorous birds and sport fish using mercury concentrations in prey fish. We collected original data on western grebes ( Aechmophorus occidentalis ) and Clark’s grebes ( Aechmophorus clarkii ) and summarized the published literature to generate predictive equations specific to grebes and a general equation for piscivorous birds. We measured mercury concentrations in 354 grebes (blood averaged 1.06 ± 0.08 μg/g ww), 101 grebe eggs, 230 sport fish (predominantly largemouth bass and rainbow trout), and 505 prey fish (14 species) at 25 lakes throughout California. Mercury concentrations in grebe blood, grebe eggs, and sport fish were strongly related to mercury concentrations in prey fish among lakes. Each 1.0 μg/g dw (&sim;0.24 μg/g ww) increase in prey fish resulted in an increase in mercury concentrations of 103% in grebe blood, 92% in grebe eggs, and 116% in sport fish. We also found strong correlations between mercury concentrations in grebes and sport fish among lakes. Our results indicate that prey fish monitoring can be used to estimate mercury exposure of piscivorous birds and sport fish when wildlife cannot be directly sampled.

Environmental Science & Technology↗

USGS2001

Perfluorooctane sulfonate in fish-eating water birds including bald eagles and albatrosses

Perfluorooctane sulfonate (PFOS) was measured in 161 samples of liver, kidney, blood, or egg yolk from 21 species of fish-eating water birds collected in the United States including albatrosses from Sand Island, Midway Atoll, in the central North Pacific Ocean. Concentrations of PFOS in the blood plasma of bald eagles collected from the midwestern United States ranged from 13 to 2220 ng/mL (mean: 330 ng/mL), except one sample that did not contain quantifiable concentrations of PFOS. Concentrations of PFOS were greater in blood plasma than in whole blood. Among 82 livers from various species of birds from inland or coastal U.S. locations, Brandt's cormorant from San Diego, CA, contained the greatest concentration of PFOS (1780 ng/g, wet wt). PFOS was also found in the sera of albatrosses from the central North Pacific Ocean at concentrations ranging from 3 to 34 ng/mL. Occurrence of PFOS in birds from remote marine locations suggests widespread distribution of PFOS and related fluorochemicals in the environment.

Environmental Science & Technology↗

USGS2013

Marsh wrens as bioindicators of mercury in wetlands of Great Salt Lake: do blood and feathers reflect site-specific exposure risk to bird reproduction?

Nonlethal sampling of bird blood and feathers are among the more common ways of estimating the risk of mercury exposure to songbird reproduction. The implicit assumption is that mercury concentrations in blood or feathers of individuals captured in a given area are correlated with mercury concentrations in eggs from the same area. Yet, this assumption is rarely tested. We evaluated mercury concentrations in blood, feathers, and eggs of marsh wrens in wetlands of Great Salt Lake, Utah, and, at two spatial scales, specifically tested the assumption that mercury concentrations in blood and feather samples from birds captured in a defined area were predictive of mercury concentrations in eggs collected in the same area. Mercury concentrations in blood were not correlated with mercury concentrations in eggs collected within the same wetland unit, and were poorly correlated with mercury concentrations in eggs collected at the smaller home range spatial scale of analysis. Moreover, mercury exposure risk, as estimated via tissue concentrations, differed among wetland units depending upon whether blood or egg mercury concentrations were sampled. Mercury concentrations in feathers also were uncorrelated with mercury concentrations in eggs, and were poorly correlated with mercury concentrations in blood. These results demonstrate the potential for contrasting management actions that may be implemented based solely on the specific avian tissue that is sampled, and highlight the importance of developing avian tissues as biomonitoring tools for assessing local risk of mercury exposure to bird reproduction.

Environmental Science & Technology↗

USGS2000

Geographic analysis of species richness and community attributes of forest birds from survey data in the mid-Atlantic integrated assessment region

Species richness of local communities is a state variable commonly used in community ecology and conservation biology. Investigation of spatial and temporal variations in richness and identification of factors associated with these variations form a basis for specifying management plans, evaluating these plans, and for testing hypotheses of theoretical interest. However, estimation of species richness is not trivial: species can be missed by investigators during sampling sessions. Sampling artifacts can lead to erroneous conclusions on spatial and temporal variation in species richness. Here we use data from the North American Breeding Bird Survey to estimate parameters describing the state of bird communities in the Mid-Atlantic Assessment (MAIA) region: species richness, extinction probability, turnover and relative species richness. We use a recently developed approach to estimation of species richness and related parameters that does not require the assumption that all the species are detected during sampling efforts. The information presented here is intended to visualize the state of bird communities in the MAIA region. We provide information on 1975 and 1990. We also quantified the changes between these years. We summarized and mapped the community attributes at a scale of management interest (watershed units).

Delaware, Maryland, Pennsylvania, Virginia, West V↗

USGS2015

Z chromosome divergence, polymorphism and relative effective population size in a genus of lekking birds

Sex chromosomes contribute disproportionately to species boundaries as they diverge faster than autosomes and often have reduced diversity. Their hemizygous nature contributes to faster divergence and reduced diversity, as do some types of selection. In birds, other factors (mating system and bottlenecks) can further decrease the effective population size of Z-linked loci and accelerate divergence (Fast-Z). We assessed Z-linked divergence and effective population sizes for two polygynous sage-grouse species and compared them to estimates from birds with various mating systems. We found lower diversity and higher F ST for Z-linked loci than for autosomes, as expected. The π Z / π A ratio was 0.38 in Centrocercus minimus, 0.48 in Centrocercus urophasianus and 0.59 in a diverged, parapatric population of C. urophasianus, a broad range given the mating system among these groups is presumably equivalent. The full data set had unequal males and females across groups, so we compared an equally balanced reduced set of C. minimus and individuals pooled from both C. urophasianus subgroups recovering similar estimates: 0.54 for C. urophasianus and 0.38 for C. minimus. We provide further evidence that N eZ / N eA in birds is often lower than expected under random mating or monogamy. The lower ratio in C. minimus could be a consequence of stronger selection or drift acting on Z loci during speciation, as this species differs strongly from C. urophasianus in sexually selected characters with minimal mitochondrial divergence. As C. minimus also exhibited lower genomic diversity, it is possible that a more severe demographic history may contribute to its lower ratio.

Heredity↗

USGS2012

Climate impacts on bird and plant communities from altered animal-plant interactions

The contribution of climate change to declining populations of organisms remains a question of outstanding concern. Much attention to declining populations has focused on how changing climate drives phenological mismatches between animals and their food. Effects of climate on plant communities may provide an alternative, but particularly powerful, influence on animal populations because plants provide their habitats. Here, we show that abundances of deciduous trees and associated songbirds have declined with decreasing snowfall over 22 years of study in montane Arizona, USA. We experimentally tested the hypothesis that declining snowfall indirectly influences plants and associated birds by allowing greater over-winter herbivory by elk (Cervus canadensis). We excluded elk from one of two paired snowmelt drainages (10 ha per drainage), and replicated this paired experiment across three distant canyons. Over six years, we reversed multi-decade declines in plant and bird populations by experimentally inhibiting heavy winter herbivory associated with declining snowfall. Moreover, predation rates on songbird nests decreased in exclosures, despite higher abundances of nest predators, demonstrating the over-riding importance of habitat quality to avian recruitment. Thus, our results suggest that climate impacts on plant–animal interactions can have forceful ramifying effects on plants, birds, and ecological interactions.

Arizona↗