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At least 1,297 records · Page 72Linked to original sources
USGS2025

Trends in richness and occupancy of Ugandan birds and relation to local tree cover

Changes in vegetation cover are occurring across sub-Saharan Africa and can have substantial effects on ecological communities, but limited data make understanding status and trends difficult for many taxa. We surveyed birds for several decades across Uganda using point counts. Using time-to-detection analysis in a trait-informed Bayesian multi-species occupancy framework, we model bird species richness as a function of year and local tree cover across 28 sites. We test for trends in richness and occupancy, and for the relationship between these and local and landscape-scale tree cover. Species richness increased at 75% of sites through the study period, and generalist bird species were most likely to be increasing in occupancy. Forest specialist bird species, and to a lesser extent generalists, responded positively to tree cover. Woody cover is changing across Uganda, with declines most pronounced in areas with the highest tree cover. This is likely to be causing declines in forest specialist species while favouring generalists. When tree cover decline is caused by conversion to croplands, rather than transitions to grasslands, grassland specialists are unlikely to benefit. Effects of climate and land use change and population pressure are likely to continue to alter woody plant cover and thus affect East African bird communities.

African Journal of Ecology↗
USGS2011

The population crash of the white-rumped vulture, and its struggle to recover

The white-rumped vulture Gyps bengalensis was once the most abundant bird of prey on the Indian sub-continent. This species easily adapted to life in urban settings; thriving as a keystone species that maintained an ecological balance between the living and the dead. Dead livestock comprised the bulk of the white-rumped vulture diet and was ultimately responsible for its catastrophic population crash. Within ten years of the first documented population declines more than 99% of the white-rumped vultures were lost. The white-rumped vulture was listed as critically endangered in 2000 and has since remained at high risk for extinction.

The Falconer↗
USGS1988

Conservation of North American rallids

The Rallidae are a diverse group in their habitat selection, yet most North American species occur in or near wetlands As a consequence, most species are subject to habitat enhancement or perturbation from waterfowl management programs. The overall effects of these management programs relative to rallid conservation have been assessed for few species, and there is a need for synthesis of such information. In the cases of some species or raves, population status is not known, and suggested directions for conservation and management are needed. Rare, endangered, or status undetermined species or races often occur in areas where related species are classified as game birds, and the effects of such hunting on rarer forms are not known. Their generally secretive nature, the endangered status of several races and populations, and continued loss of habitat and threats to present habitat, warrant an examination of the conservation status of the North American taxa in this group. In 1977, a committee of the International Association of Fish and Wildlife Agencies summarized available information on management and biology of American Coots ( Fulica americana ), rails, and gallinules in North America (Holliman 1977). That summary was intended to provide relatively complete information on conservation of these species, and also to provide guidance for research within the U.S. Fish and Wildlife Service's (FWS) Accelerated Research Program for Webless Migratory Shore and Upland Game Birds (ARP). Subsequently, a number of rallid studies were funded under this program. The program was eliminated in 1982, following substantial research activities on North American rallids. Since the demise of the ARP, additional research on rallids in North America has focused on an area the International Association of Fish and Wildlife Agencies report failed to cover in detail--that of endangered rallids in the U.S. and their possessions. Most of these studies have been of threatened and endangered taxa in western coastal marshes. This report updates and summarizes information on North American rallids since the ARP report and identifies the major conservation problems of this group with the intent of focusing future efforts on these priority issues. Consideration of island forms occurring within U.S. possessions is beyond the scope of this report, mainly because of the special conservation problems associated with their insular distribution. The major topics include habitat requirements, effects of habitat and hunting management techniques currently practiced on wetland areas, and conservation of endangered and threatened populations. Research needs are identified. Habitats of the American Coot are similar to those of several waterfowl species, and the biology of coots is considered only as it is typical of rails in general.

The Wilson Bulletin↗
USGS2009

Variability in population abundance is associated with thresholds between scaling regimes

Discontinuous structure in landscapes may result in discontinuous, aggregated species body-mass patterns, reflecting the scales of structure available to animal communities within a landscape. The edges of these body-mass aggregations reflect transitions between available scales of landscape structure. Such transitions, or scale breaks, are theoretically associated with increased biological variability. We hypothesized that variability in population abundance is greater in animal species near the edge of body-mass aggregations than it is in species that are situated in the interior of body-mass aggregations. We tested this hypothesis by examining both temporal and spatial variability in the abundance of species in the bird community of the Florida Everglades sub-ecoregion, USA. Analyses of both temporal and spatial variability in population abundance supported our hypothesis. Our results indicate that variability within complex systems may be non-random, and is heightened where transitions in scales of process and structure occur. This is the first explicit test of the hypothetical relationship between increased population variability and scale breaks. ?? 2009 by the author(s).

Ecology and Society↗
USGS2021

Diverse patterns of migratory timing, site use, and site fidelity by Alaska-breeding Whimbrels

Birds that conduct long-distance migrations exhibit varied patterns of consistency in migratory timing and site use. Understanding variation in these traits among populations can help uncover mechanisms driving migratory behaviors and identify potential population threats. Whimbrels ( Numenius phaeopus ) are long-distance migratory shorebirds with a Holarctic breeding distribution, and recent studies have documented population-specific migrations that vary in duration (short to long) and frequency of stops (none/few to multiple). Factors driving these population-specific differences are unclear. We studied the migration ecology of Whimbrels breeding in Alaska, USA, using satellite transmitters deployed from 2006 to 2010 and tracked through 2015. Whimbrels moved entirely within the Pacific Americas Flyway, and some conducted nonstop flights that exceeded seven days across ~ 8700 km. Birds dispersed across numerous sites throughout the flyway, often using agriculture or aquaculture habitats. Whimbrels generally exhibited fidelity to breeding and non-breeding sites, but typically only exhibited fidelity to staging sites used prior to long, nonstop migratory flights. The duration of migration for Whimbrels at more southern non-breeding locations was longer than for those at more northern non-breeding sites, and birds at more southern sites also terminated southbound migration later and initiated northbound migration earlier than birds at more northern sites. Alaska-breeding Whimbrels exhibited greater variation in migratory behaviors than those in other populations in the species’ range. We attribute this within-population diversity to the extensive breadth of non-breeding distributions (~ 70° latitude across ~ 8600 km), a range that naturally shaped individual responses to unequal migratory demands.

Alaska↗
USGS1980

Estimating the size and trend of the California condor population, 1965-1978

During 1965-1978, three principal methods were used to measure the size and trend of the California Condor (Gymnogyps californianus) population. An October survey conducted by as many as 136 observers had limited value because daily activity patterns of condors were unpredictable and because analysis of results could not be standardized. Evaluation of 4,381 condor observations by cooperators, and results of comparative surveys done in 1970-1971 and 1977-1978 show declines in numbers of condor sightings, numbers of condors per sighting, and in the numbers of sightings including more than one immature-plumaged bird. The data cannot be evaluated statistically, but they suggest a marked decline in the condor population between 1965 and 1978. Future refinements of survey techniques are dependent on having individually recognizable condors in the population.

California Fish and Game↗
USGS2018

Landscape genetics identifies streams and drainage infrastructure as dispersal corridors for an endangered wetland bird

Anthropogenic alterations to landscape structure and composition can have significant impacts on biodiversity, potentially leading to species extinctions. Population‐level impacts of landscape change are mediated by animal behaviors, in particular dispersal behavior. Little is known about the dispersal habits of rails (Rallidae) due to their cryptic behavior and tendency to occupy densely vegetated habitats. The effects of landscape structure on the movement behavior of waterbirds in general are poorly studied due to their reputation for having high dispersal abilities. We used a landscape genetic approach to test hypotheses of landscape effects on dispersal behavior of the Hawaiian gallinule ( Gallinula galeata sandvicensis ), an endangered subspecies endemic to the Hawaiian Islands. We created a suite of alternative resistance surfaces representing biologically plausible a priori hypotheses of how gallinules might navigate the landscape matrix and ranked these surfaces by their ability to explain observed patterns in genetic distance among 12 populations on the island of O`ahu. We modeled effective distance among wetland locations on all surfaces using both cumulative least‐cost‐path and resistance‐distance approaches and evaluated relative model performance using Mantel tests, a causal modeling approach, and the mixed‐model maximum‐likelihood population‐effects framework. Across all genetic markers, simulation methods, and model comparison metrics, surfaces that treated linear water features like streams, ditches, and canals as corridors for gallinule movement outperformed all other models. This is the first landscape genetic study on the movement behavior of any waterbird species to our knowledge. Our results indicate that lotic water features, including drainage infrastructure previously thought to be of minimal habitat value, contribute to habitat connectivity in this listed subspecies.

Hawai`i↗
USGS2021

Temperature‐associated decreases in demographic rates of Afrotropical bird species over 30 years

Tropical mountains harbor globally significant levels of biodiversity and endemism. Climate change threatens many tropical montane species, yet little research has assessed the effects of climate change on the demographic rates of tropical species, particularly in the Afrotropics. Here, we report on the demographic rates of 21 Afrotropical bird species over 30 years in montane forests in Tanzania. We used mark–recapture analyses to model rates of population growth, recruitment, and apparent survival as functions of annual mean temperature and annual precipitation. For over one‐half of focal species, decreasing population growth rates were associated with increasing temperature. Due to the trend in temperature over time, we substituted a time covariate for the temperature covariate in top‐ranked population growth rate models. Temperature was a better explanatory covariate than time for 6 of the 12 species, or 29% of all focal species. Population growth rates were also lower for species found further below their elevational midpoint and for smaller‐bodied species. Changes in population growth rates were more closely tied to changes in recruitment than to changes in apparent survival. There were no consistent associations between demographic rates and precipitation. This study demonstrates temperature‐associated demographic impacts for 6 (29%) of 21 focal species in an Afrotropical understory bird community and highlights the need to incorporate the impacts of climate change on demographic rates into conservation planning across the tropics.

Global Change Biology↗
USGS2012

Molecular detection of hematozoa infections in tundra swans relative to migration patterns and ecological conditions at breeding grounds

Tundra swans ( Cygnus columbianus ) are broadly distributed in North America, use a wide variety of habitats, and exhibit diverse migration strategies. We investigated patterns of hematozoa infection in three populations of tundra swans that breed in Alaska using satellite tracking to infer host movement and molecular techniques to assess the prevalence and genetic diversity of parasites. We evaluated whether migratory patterns and environmental conditions at breeding areas explain the prevalence of blood parasites in migratory birds by contrasting the fit of competing models formulated in an occupancy modeling framework and calculating the detection probability of the top model using Akaike Information Criterion (AIC). We described genetic diversity of blood parasites in each population of swans by calculating the number of unique parasite haplotypes observed. Blood parasite infection was significantly different between populations of Alaska tundra swans, with the highest estimated prevalence occurring among birds occupying breeding areas with lower mean daily wind speeds and higher daily summer temperatures. Models including covariates of wind speed and temperature during summer months at breeding grounds better predicted hematozoa prevalence than those that included annual migration distance or duration. Genetic diversity of blood parasites in populations of tundra swans appeared to be relative to hematozoa prevalence. Our results suggest ecological conditions at breeding grounds may explain differences of hematozoa infection among populations of tundra swans that breed in Alaska.

Alaska↗
USGS1994

Are more North American species decreasing than increasing?

Population trends for North American species are calculated for 1966-'91 and 1982-'91 using Nonh American Breeding Bird Survey data. Species are grouped into 3 systems of guild classifications representing migration status, breeding habitat and nesting substrate. Trends for these groups are summarized by time period, bioregion and physiographic region. At the continental level, declines approximately equalled increases. There are slightly more declines during the last 10 years. Prairie populations declined more than expected, while western populations increased. Scrub and grassland nesting species declined significantly in several bioregions while woodland species increased. Most guilds did not depart significantly from a ratio of 50:50 increases to decreases or have opposing trends in different bioregions. Guild group changes are usually clustered geographically. Guild and other analyses that search for patterns among population trend estimates offer an excellent means of identifying critical conservation issues.

Book chapter↗
USGS2021

Endangered Australian top predator is frequently exposed to anticoagulant rodenticides

Anticoagulant rodenticides (ARs) used to control mammalian pest populations cause secondary exposure of predatory species throughout much of the world. It is important to understand the drivers of non-target AR exposure patterns as context for assessing long-term effects and developing effective mitigation for these toxicants. In Australia, however, little is known about exposure and effects of ARs on predators. We detected AR residues in 74% of 50 opportunistically collected carcasses of the Tasmanian wedge-tailed eagle ( Aquila audax fleayi ), an endangered apex predator. In 22% of birds tested, or 31% of those exposed, liver concentrations of second generation ARs (SGARs) were >0.1 mg/kg ww. Eagles were exposed to flocoumafen, a toxicant only available from agricultural suppliers, at an exceptionally high rate (40% of birds tested). Liver SGAR concentrations were positively associated with the proportion of agricultural habitat and human population density in the area around where each eagle died. The high exposure rate in a species not known to regularly prey upon synanthropic rodents supports the hypothesis that apex predators are vulnerable to SGARs. Our results indicate that AR exposure constitutes a previously unrecognized threat to Tasmanian wedge-tailed eagles and highlight the importance of efforts to address non-target AR exposure in Australia.

Tasmania↗
USGS2021

Migration efficiency sustains connectivity across agroecological networks supporting sandhill crane migration

Preserving avian flyway connectivity has long been challenged by our capacity to meaningfully quantify continental habitat dynamics and bird movements at temporal and spatial scales underlying long-distance migrations. Waterbirds migrating hundreds or thousands of kilometers depend on networks of wetland stopover sites to rest and refuel. Entire populations may rely on discrete wetland habitats, particularly in arid landscapes where the loss of limited stopover options can have disproportionately high impacts on migratory cost. Here, we examine flyway connectivity in water-limited ecosystems of western North America using 108 GPS tagged greater sandhill cranes. Bird movements were used to reconstruct wetland stopover networks across three geographically unique sub-populations spanning 12 US-Mexican states and Canadian provinces. Networks were monitored with remote sensing to identify long-term (1988-2019) trends in wetland and agricultural resources supporting migration and evaluated using network theory and centrality metrics as a measure of stopover site importance to flyway connectivity. Sandhill crane space-use was analyzed in stopover locations to identify important ownership and landscape factors structuring bird distributions. Migratory efficiency was the primary mechanism underpinning network function. A small number of key stopover sites important to minimizing movement cost between summering and wintering locations were essential to preserving flyway connectivity. Localized efficiencies were apparent in stopover landscapes given prioritization of space-use by birds where the proximity of agricultural food resources and flooded wetlands minimized daily movements. Model depictions showing wetland declines from 16-18% likely reflect a new normal in landscape drying that could decouple agriculture-waterbird relationships as water scarcity intensifies. Sustaining network resilience will require conservation strategies to balance water allocations preserving agricultural and wetlands on private lands that accounted for 67-96% of habitat use. Study outcomes provide new perspectives of agroecological relationships supporting continental waterbird migration needed to prioritize conservation of landscapes vital to maintaining flyway connectivity.

western North America↗
USGS2018

Variation in inbreeding rates across the range of Northern Spotted Owls (Strix occidentalis caurina): Insights from over 30 years of monitoring data

Inbreeding has been difficult to quantify in wild populations because of incomplete parentage information. We applied and extended a recently developed framework for addressing this problem to infer inbreeding rates in Northern Spotted Owls ( Strix occidentalis caurina ) across the Pacific Northwest, USA. Using pedigrees from 14,187 Northern Spotted Owls, we inferred inbreeding rates for 14 types of matings among relatives that produce pedigree inbreeding coefficients of F = 0.25 or F = 0.125. Inbreeding was most common in the Washington Cascades, where an estimated 15% of individuals are inbred. Inbreeding was lowest in western Oregon (3.5%) and northern California (2.7%), and intermediate for the Olympic Peninsula of Washington (6.1%). Estimates from the Olympic Peninsula were likely underestimates because of small sample sizes and the presence of few pedigrees capable of resolving inbreeding events. Most inbreeding resulted from matings between full siblings or half siblings, although a high rate of inbreeding from mother–son pairs was identified in the Olympic Peninsula. Geographic variation in inbreeding rates may reflect population declines and bottlenecks that have been detected in prior investigations. We show that there is strong selection against inbred birds. Only 3 of 44 inbred birds were later identified as parents (6.8%), whereas 2,823 of 10,380 birds that represented a comparable cross section of the data were later seen as reproducing parents (27.2%). Habitat loss and competition with Barred Owls ( S. varia ) remain primary threats to Northern Spotted Owls. However, given the negative consequences of inbreeding, Spotted Owl populations in Washington with suitable habitat and manageable numbers of Barred Owls may benefit from translocations of individuals from Oregon and California to introduce new genetic variation and reduce future inbreeding events.

California, Oregon, Washington↗
USGS2006

Feral Pigs, Introduced Mosquitoes, and the Decline of Hawai'i's Native Birds

The introduction of mosquitoes, avian pox, and avian malaria to the Hawaiian Islands has had a profound effect on the geographical distribution and population number of highly susceptible Hawaiian honeycreepers, and likely contributed to the extinction of several species. While the mosquito vector (disease-carrier) is most closely associated with human activity, in remote Hawaiian rain forests, feral pigs may be pivotally important to the disease system. Since 1991, USGS scientists have taken a leadership position in identifying the role these diseases continue to play in the decline and extinction of native Hawaiian forest birds and in finding ways to mitigate their impacts.

Hawai'i↗
USGS2023

Application of a catch multiple survey analysis for Atlantic horseshoe crab Limulus polyphemus in the Delaware Bay

Objective This paper applies a catch multiple survey analysis (CMSA) to Atlantic horseshoe crabs Limulus polyphemus in the Delaware Bay to generate robust population estimates for harvest management. Currently, horseshoe crabs along the U.S. Atlantic coast are harvested as bait for other fisheries and collected for their blood, which is used in a biomedical industry. The Delaware Bay is home to the largest population of horseshoe crabs and is a significant stopover for shorebirds to rebuild energy by consuming horseshoe crab eggs prior to completing their northward migration. To address this interrelationship, the Adaptive Resource Management (ARM) Framework has been used since 2013 to ensure that horseshoe crab harvest within the region takes into account the forage needs of migratory birds. Since its inception, the ARM Framework has used a single trawl survey's swept area-based population estimates of horseshoe crab relative abundance and a theoretical population model developed primarily from literature-derived values. With more data collected in the region in recent years and other sources of mortality that can now be quantified, a catch survey model can provide horseshoe crab population estimates going forward. Methods A CMSA was used to estimate male and female horseshoe crab population size for 2003–2021 using all quantifiable sources of mortality and three fishery-independent indices of abundance. Result The CMSA results indicated that adult abundance of male and female horseshoe crabs was stable from 2003 to 2013 and then began to increase through 2017, a result that is consistent with stock rebuilding following a period of harvest restrictions as recommended by the ARM Framework. Population estimates were lower in recent years but remained above the levels estimated before implementation of the ARM Framework. In 2021, the CMSA estimated that there were over 6 million mature females and nearly 16 million mature male horseshoe crabs in the region. Conclusion The CMSA provides the best and most comprehensive population estimates of horseshoe crabs in Delaware Bay and will improve modeling efforts within the ARM Framework going forward.

Delaware, Maryland, New Jersey↗
USGS1977

The decline of brown pelicans on the Louisiana and Texas Gulf Coast

Before 1920, native populations of brown pelicans (Pelecanus occidentalis carolinensis) were estimated at 50,000 to 85,000 birds in Louisiana and 5,000 in Texas. By 1958, brown pelicans had vanished from two wintering areas in each state, and wintering and breeding birds disappeared from additional areas between 1959 and 1961. By 1963, the disappearance of the brown pelican from Louisiana was complete, and in Texas only about 100 birds were observed annually. Mortality before 1939, particularly in Texas, was attributed mostly to hunters and fishermen. Losses in both states were attributed to hurricanes, disease, and extended periods of freezing weather. Pesticides may also have contributed significantly. Widespread endrin-caused fish mortality was documented between 1958 and 1964 in Louisiana. Pelicans undoubtedly were exposed to endrine through eating the fish. Significant levels of DDE were found in Texas fishes in the late 1960's. DDE residues in pelican eggs were high enough to be responsible for nesting failure. Shell thinning averaged 10% in Texas pelican eggs collected in 1970, 1972, and 1974, but in earlier years greater thinning was associated with the collapse and loss of eggs. Poor reproductive success during recent years was believed due to (1) failure of many adult pelicans to nest and (2) a high rate of nestling mortality in the few pairs that did nest and hatch young. The remnant population of brown pelicans on the Texas Coast will disappear unless reproductive success improves, because recruitment is presently insufficient to offset mortality.

Louisiana, Texas↗
USGS2006

Species richness and patterns of invasion in plants, birds, and fishes in the United States

We quantified broad-scale patterns of species richness and species density (mean # species/km 2 ) for native and non-indigenous plants, birds, and fishes in the continental USA and Hawaii. We hypothesized that the species density of native and non-indigenous taxa would generally decrease in northern latitudes and higher elevations following declines in potential evapotranspiration, mean temperature, and precipitation. County data on plants ( n = 3004 counties) and birds ( n =3074 counties), and drainage (6 HUC) data on fishes ( n = 328 drainages) showed that the densities of native and non-indigenous species were strongly positively correlated for plant species ( r = 0.86, P < 0.0001), bird species ( r = 0.93, P <0.0001), and fish species ( r = 0.41, P <0.0001). Multiple regression models showed that the densities of native plant and bird species could be strongly predicted (adj. R 2 = 0.66 in both models) at county levels, but fish species densities were less predictable at drainage levels (adj. R 2 = 0.31, P <0.0001). Similarly, non-indigenous plant and bird species densities were strongly predictable (adj. R 2 = 0.84 and 0.91 respectively), but non-indigenous fish species density was less predictable (adj. R 2 = 0.38). County level hotspots of native and non-indigenous plants, birds, and fishes were located in low elevation areas close to the coast with high precipitation and productivity (vegetation carbon). We show that (1) native species richness can be moderately well predicted with abiotic factors; (2) human populations have tended to settle in areas rich in native species; and (3) the richness and density of non-indigenous plant, bird, and fish species can be accurately predicted from biotic and abiotic factors largely because they are positively correlated to native species densities. We conclude that while humans facilitate the initial establishment, invasions of non-indigenous species, the spread and subsequent distributions of non-indigenous species may be controlled largely by environmental factors.

Biological Invasions↗