Ecological determinants of American crow mortality due to West Nile virus during its North American sweep

We examined the ecological factors influencing population declines in American crows (Corvus brachyrhynchos) as they were initially exposed to West Nile virus (WNV), a pathogen first detected in the US in 1999 that has since become one of North America’s most prevalent vector-borne pathogens. The strongest effects were initial crow population density (denser populations were more likely to suffer declines), avian species diversity (populations in areas with high diversity were less likely to suffer a decline), human population density (populations were more likely to decline in more urban areas), and time since the pathogen’s introduction to the US (populations exposed to the pathogen later in its North American sweep were less likely to suffer declines than those exposed earlier). Variables that played only a minor role included rainfall, mean maximum temperature, and total number of birds, used as a proxy for the overall reservoir competence of the community. These findings indicate that WNV declined in virulence during its rapid 5-year sweep and support the importance of the ‘dilution effect’ whereby a diverse host community dampens pathogen transmission and potentially slows its rate of spread. Results underscore the need for considering the entire community when trying to understand the factors shaping disease risk.     

Using Avian Surveillance in Ecuador to Assess the Imminence of West Nile Virus Incursion to Galápagos

Infectious disease emergence represents a global threat to human, agricultural animal and wildlife health. West Nile virus (WNV) first emerged in the Americas in 1999 following its introduction to New York from the Old World. This flavivirus rapidly spread across much of North America, causing human, equine and avian mortalities and population declines of multiple wild bird species. It has now spread to Central and South America, and there is concern that the virus will reach the Galápagos Islands, a UNESCO World Heritage Site famous for its unique biodiversity, with potentially catastrophic results. Here, we use wild bird surveillance to examine the current WNV status in the Galapagos Islands and around the Ecuadorian city of Guayaquil (the main air and sea port serving Galápagos). We conducted serosurveys of wild birds on three Galápagos Islands (Baltra, San Cristobal and Santa Cruz) with direct transport links to the South American continent. In addition, dead birds killed by car collisions on Santa Cruz were tested for WNV infection. On mainland Ecuador, serosurveys of wild birds were conducted at three sites around Guayaquil. No evidence of WNV seropositivity or infection was detected. Although wider testing is recommended on the mainland, the study highlights a limit of WNV spread within South America. Our results indicate the continued absence of WNV on Galápagos and suggest the current likelihood of human-mediated transport of WNV to Galápagos to be low. The risk of emergence will almost certainly increase over time, however, and stringent biosecurity and surveillance measures should be put in place to minimise the risk of the introduction of WNV (and other alien pathogens) to Galápagos.     

Polymorphic microsatellite loci from the West Nile virus vector Culex tarsalis

Since its introduction in 1999, West Nile virus (WNV) has spread across North America. Culex tarsalis is a highly efficient WNV vector species. Many traits such as virus susceptibility, autogeny and host preference vary geographically and temporally in C. tarsalis. Culex tarsalis genomic libraries were developed and were highly enriched for microsatellite inserts (42–96%). We identified 12 loci that were polymorphic in wild C. tarsalis populations. These microsatellites are the first DNA‐based genetic markers developed for C. tarsalis and will be useful for investigating population structure and constructing genetic maps in this mosquito.     

Population genetic data suggest a role for mosquito‐mediated dispersal of West Nile virus across the western United States

After introduction, West Nile virus (WNV) spread rapidly across the western United States between the years 2001 and 2004. This westward movement is thought to have been mediated by random dispersive movements of resident birds. Little attention has been placed on the role of mosquito vectors in virus dispersal across North America. The mosquito vector largely responsible for WNV amplification and transmission of WNV in the western USA is Culex tarsalis. Here we present population genetic data that suggest a potential role for C. tarsalis in the dispersal of WNV across the western USA. Population genetic structure across the species range of C. tarsalis in the USA was characterized in 16 states using 12 microsatellite loci. structure and geneland analyses indicated the presence of three broad population clusters. Barriers to gene flow were resolved near the Sonoran desert in southern Arizona and between the eastern Rocky Mountains and High Plains plateau. Small genetic distances among populations within clusters indicated that gene flow was not obstructed over large portions of the West Coast and within the Great Plains region. Overall, gene flow in C. tarsalis appears to be extensive, potentially mediated by movement of mosquitoes among neighbouring populations and hindered in geographically limited parts of its range. The pattern of genetic clustering in C. tarsalis is congruent with the pattern of invasion of WNV across the western United States, raising the possibility that movement of this important vector may be involved in viral dispersal.     

Isolation and characterization of microsatellite loci in a cooperatively breeding corvid,the American crow (Corvus brachyrhynchos)

We describe 11 microsatellite loci isolated from the American crow (Corvus brachyrhynchos), the most wide‐spread cooperatively breeding bird in North America. Polymorphism at these loci ranged from four to 43 alleles, and observed heterozygosities from 0.53 to 0.92. Genetic parentage analyses using these markers will allow us to describe the mating system of this common but socially complex species, and to interpret their behavioural interactions in light of relatedness.     

A decade of hibernating bat communities along the periphery of a region of white-nose syndrome

Long-term monitoring programs are necessary to assess populations for conservation planning and management decisions. Hibernating bats in North America have declined because of numerous natural and human-induced disturbances. White-nose syndrome (WNS) has become the most serious threat to North American cave-dwelling bats, leading to significant population declines in several species. We examined trends in hibernating bat populations at 11 hibernacula in northern Georgia and Alabama, USA, from 2013–2022, beginning when WNS was first detected in the region. Although we observed interannual variation in numbers of the federally endangered gray bat (Myotis grisescens), mean counts remained stable over time. In contrast, the tricolored bat (Perimyotis subflavus) and the federally endangered northern long-eared bat (M. septentrionalis) declined by >90% in the first 5 years after WNS detection in the region. Although no northern long-eared bats have been reported since 2019, tricolored bat counts stabilized following initial declines. Understanding changes in bat populations as WNS continues to spread, and determining the extent of population declines, is necessary for making appropriate management decisions. Our findings elucidate the status of cave-dwelling bat species along the periphery of the white-nose syndrome endemic region and highlight the importance of monitoring bat communities on a regional scale to develop effective conservation strategies.     

The genotyping of the West Nile virus in birds in the far eastern region of Russia in 2002-2004

Samples from 20 species of trapped and dead birds were collected in the Far Eastern Region in 2002-2004 and were analyzed by the anti-WNV MAb-modified immunoenzyme assay for antigen detection and RT-PCR for viral RNA detection. Five positive samples from cinereous vultures (Aegypius monachus) and two positive samples from cattle egret (Bubulcus ibis) were found in both tests. The sequencing of the 322 bp fragments of protein E gene showed 99-99.67% homology with the strain WNV/LEIV-VlgOO-27924 of the WNV isolated in Volgograd, Russia, 2000. Additionally, five positive samples from birds (Pica pica, Corvus macrorhynchos, Larus crossirostris, Parus minor, Emberiza spodocephala) collected in autumn 2004 were found during screening with anti-WNV MAb-modified ELISA. These results confirm that the WNV is circulating in the Far Eastern Region of Russia and outbreaks of WN fever in humans may be possible. This demonstrates that the genotype 1a of the West Nile virus could spread in the southern regions of the Far East by migrating birds and introduction of the WNV into other southern regions of the Asian part of Russia are probably.     

Evidence for Co-evolution of West Nile Virus and House Sparrows in North America

West Nile virus (WNV) has been maintained in North America in enzootic cycles between mosquitoes and birds since it was first described in North America in 1999. House sparrows (HOSPs; Passer domesticus) are a highly competent host for WNV that have contributed to the rapid spread of WNV across the U.S.; however, their competence has been evaluated primarily using an early WNV strain (NY99) that is no longer circulating. Herein, we report that the competence of wild HOSPs for the NY99 strain has decreased significantly over time, suggesting that HOSPs may have developed resistance to this early WNV strain. Moreover, recently isolated WNV strains generate higher peak viremias and mortality in contemporary HOSPs compared to NY99. These data indicate that opposing selective pressures in both the virus and avian host have resulted in a net increase in the level of host competence of North American HOSPs for currently circulating WNV strains.     

Factors affecting nest predation on forest songbirds in North America

Nest predation is an important factor in the ecology of passerines and can be a large source of mortality for birds. I provide an overview of factors affecting nest predation of passerines in North America with the goal that it may provide some insight into the ecology and management of woodland birds in the United Kingdom. Although several factors influence productivity, nest success is perhaps the most widely measured demographic characteristic of open-cup-nesting birds, and nest predation is usually the largest cause of nest failure. The identity of predator species, and how their importance varies with habitat and landscape factors, must be known for managers and scientists to design effective conservation plans and place research on nest predation in the appropriate context. Recent studies using video surveillance have made significant contributions to our understanding of the relative importance of different predator taxa in North America. Spatial and temporal variation in nest predation can be better understood when landscapes are placed in a biogeographical context and local habitat and nest-site effects are placed in a landscape context. Low productivity resulting from high nest predation is one of several potential causes of bird population declines in North America and the UK. Although the 'forest fragmentation paradigm' from the eastern US may not apply directly to the UK, thinking about avian demographics from a multiscale perspective, and consideration of factors affecting nest predation with knowledge of the dominant predator species, may provide insight into population declines.     

Long-billed curlew nest site selection and success in the Intermountain West

Grassland birds have experienced steeper population declines between 1966 and 2015 than any other bird group on the North American continent, and migratory grassland birds may face threats in all stages of their annual cycle. The grassland-associated long-billed curlew (Numenius americanus) is experiencing population declines in regional and local portions of their North American breeding range. The nesting period is an important portion of the annual cycle when curlews may face demographic rate limitations from a suite of threats including predators and anthropogenic disturbance. We compared nest sites to random sites within breeding territories to examine nest site selection, and modeled correlates of nesting success for 128 curlew nests at 5 Intermountain West sites. Nest sites were 6 times more likely than random sites to be situated adjacent to existing cowpies. Additionally, curlews selected nest sites with shorter vegetation, and less bare ground, grass, and shrub cover than at random sites within their territories. Nest success varied widely among sites and ranged from 12% to 40% in a season with a mean of 27% for all nests during the 2015 and 2016 seasons. Higher nest success probability was associated with higher curlew densities in the area, greater percent cover of conspicuous objects (cowpies, rocks) near the nest, and higher densities of black-billed magpies (Pica hudsonia) and American crows (Corvus brachyrhynchos) at the site. We also found increased probability of nesting success with increased distance from a nest to the nearest potential perch in that territory. Given the central role of working lands to curlews in much of the Intermountain West, understanding limitations to nesting success in these diverse landscapes is necessary to guide adaptive management strategies in increasingly human-modified habitats. We suggest some grazing and irrigation practices already provide suitable nesting conditions for curlews, and others may require only minor temporal shifts to improve compatibility. © 2019 The Wildlife Society.     

Towards the Conservation of Endangered Avian Species: A Recombinant West Nile Virus Vaccine Results in Increased Humoral and Cellular Immune Responses in Japanese Quail (Coturnix japonica)

West Nile Virus (WNV) arrived in North America in 1999 and is now endemic. Many families of birds, especially corvids, are highly susceptible to WNV and infection often results in fatality. Avian species susceptible to WNV infection also include endangered species, such as the Greater Sage-Grouse (Centrocercus uropbasianuts) and the Eastern Loggerhead Shrike (Lanius ludovicianus migrans). The virus has been shown to contribute towards the likelihood of their extinction. Although a clear and present threat, there exists no avian WNV vaccine available to combat this lethal menace. As a first step in establishing an avian model for testing candidate WNV vaccines, avian antibody based reagents were assessed for cross-reactivity with Japanese quail (Coturnix japonica) T cell markers CD4 and CD8; the most reactive were found to be the anti-duck CD8 antibody, clone Du-CD8-1, and the anti-chicken/turkey CD4 antibody, clone CT4. These reagents were then used to assess vaccine performance as well as to establish T cell populations in quail, with a novel population of CD4/CD8 double positive T cells being identified in Japanese quail. Concurrently, non-replicating recombinant adenoviruses, expressing either the WNV envelope or NS3 ‘genes’ were constructed and assessed for effectiveness as avian vaccines. Japanese Quail were selected for testing the vaccines, as they provide an avian model that parallels the population diversity of bird species in the wild. Both the level of WNV specific antibodies and the number of T cells in vaccinated birds were increased compared to unvaccinated controls. The results indicate the vaccines to be effective in increasing both humoral and cellular immune responses. These recombinant vaccines therefore may find utility as tools to protect and maintain domestic and wild avian populations. Their implementation may also arrest the progression towards extinction of endangered avian species and reduce the viral reservoir that potentiates infection in humans.     

Brains, tools, innovation and biogeography in crows and ravens

ABSTRACT: BACKGROUND: Crows and ravens (Passeriformes: Corvus) are large-brained birds with enhanced cognitive abilities relative to other birds. They are among the few non-hominid organisms on Earth to be considered intelligent and well-known examples exist of several crow species having evolved innovative strategies and even use of tools in their search for food. The 40 Corvus species have also been successful dispersers and are distributed on most continents and in remote archipelagos. RESULTS: This study presents the first molecular phylogeny including all species and a number of subspecies within the genus Corvus. We date the phylogeny and determine ancestral areas to investigate historical biogeographical patterns of the crows. Additionally, we use data on brain size and a large database on innovative behaviour and tool use to test whether brain size (i) explains innovative behaviour and success in applying tools when foraging and (ii) has some correlative role in the success of colonization of islands. Our results demonstrate that crows originated in the Palaearctic in the Miocene from where they dispersed to North America and the Caribbean, Africa and Australasia. We find that relative brain size alone does not explain tool use, innovative feeding strategies and dispersal success within crows. CONCLUSIONS: Our study supports monophyly of the genus Corvus and further demonstrates the direction and timing of colonization from the area of origin in the Palaearctic to other continents and archipelagos. The Caribbean was probably colonized from North America, although some North American ancestor may have gone extinct, and the Pacific was colonized multiple times from Asia and Australia. We did not find a correlation between relative brain size, tool use, innovative feeding strategies and dispersal success. Hence, we propose that all crows and ravens have relatively large brains compared to other birds and thus the potential to be innovative if conditions and circumstances are right.     

Prevalence of west Nile virus antibodies in a breeding population of American Kestrels (Falco sparverius) in Pennsylvania

West Nile virus (WNV) has been identified in nearly 300 species of wild birds, including raptors, in North America since its introduction in New York City in 1999. American Kestrels (Falco sparverius) are susceptible to WNV infection, and the numbers of these birds have declined along the Atlantic coast in recent years. We examined the population biology and WNV exposure of kestrels breeding in the area surrounding Hawk Mountain Sanctuary in Kempton, Pennsylvania, USA. The reproductive biology of kestrels in this area was studied from 1992 until 2004. The number of kestrels breeding in nestboxes in 2004 was only 44% of the 6-yr mean observed prior to 1999. During the 2004 nesting season (study period: 8 June through 22 July 2004), adult kestrels were trapped near the site of their nestboxes. Blood samples were obtained, and serum antibodies specific to WNV were quantified using a plaque reduction neutralization test. Of 22 birds tested, 21 exhibited serum antibodies to WNV, suggesting that most (95%) of the adult kestrels in the population had been exposed to WNV.     

Recent advances in the molecular biology of west nile virus

Since the mid-1990s, West Nile virus (WNV) has emerged as a significant agent of arboviral encephalitis in several regions of the world. In 1999, WNV was introduced into the northeastern United States and was associated with an outbreak of encephalitis affecting humans, birds and horses. Subsequently, the virus has spread across the country, and across southern Canada, and in 2002 and 2003 was associated with the largest outbreaks of arboviral encephalitis recorded in the Western hemisphere. Interestingly, the more recent spread of WNV into Mexico, Central America and the Caribbean has not been associated with the high levels of clinical disease observed in North America. This review addresses the most recent results from studies investigating the molecular biology and evolution of WNV, as well as progress in the development of diagnostic and therapeutic reagents.     

Differences in spatial synchrony and interspecific concordance inform guild‐level population trends for aerial insectivorous birds

Many animal species exhibit spatiotemporal synchrony in population fluctuations, which may provide crucial information about ecological processes driving population change. We examined spatial synchrony and concordance among population trajectories of five aerial insectivorous bird species: chimney swift Chaetura pelagica, purple martin Progne subis, barn swallow Hirundo rustica, tree swallow Tachycineta bicolor, and northern rough‐winged swallow Stelgidopteryx serripennis. Aerial insectivores have undergone severe guild‐wide declines that were considered more prevalent in northeastern North America. Here, we addressed four general questions including spatial synchrony within species, spatial concordance among species, frequency of declining trends among species, and geographic location of declining trends. We used dynamic factor analysis to identify large‐scale common trends underlying stratum‐specific annual indices for each species, representing population trajectories shared by spatially synchronous populations, from 46 yr of North American Breeding Bird Survey data. Indices were derived from Bayesian hierarchical models with continuous autoregressive spatial structures. Stratum‐level spatial concordance among species was assessed using cross‐correlation analysis. Probability of long‐term declining trends was compared among species using Bayesian generalized linear models. Chimney swifts exhibited declining trends throughout North America, with less severe declines through the industrialized Mid‐Atlantic and Great Lakes regions. Northern rough‐winged swallows exhibited declining trends throughout the west. Spatial concordance among species was limited, the proportion of declining trends varied among species, and contrary to previous reports, declining trends were not more prevalent in the northeast. Purple martins, barn swallows, and tree swallows exhibited synchrony across smaller spatial scales. The extensive within‐species synchrony and limited concordance suggest that population trajectories of these aerial insectivores are responding to large‐scale but complex and species‐ and region‐specific environmental conditions (e.g. climate, land use). A single driver of trends for aerial insectivores as a guild appears unlikely.     

Effects of Connectivity and Regional Dynamics on Restoration of Small Mammal Communities in Midwestern Grasslands

Grasslands are among the most imperiled North American ecosystems. State Acres for Wildlife Enhancement (SAFE) is a national conservation program that converts agricultural fields into grasslands mainly to improve habitat for high priority wildlife species. To provide a broader assessment of the contribution of the SAFE program to biodiversity in the Midwest region of North America, we evaluated local and landscape constraints to restoration of small mammal communities. We livetrapped small mammals during three summers (2009–2011) on plots that were recently seeded, seeded 1–4 years prior to sampling, or established references (>10 years old). Restoration trajectories for small mammal communities included a shift over time from dominance by the habitat generalist Peromyscus maniculatus (deer mouse) to communities dominated by grassland Microtus species (prairie voles and meadow voles). Vole abundance during the first year following restoration depended on spatial connectivity provided by linear habitats (roadside ditches and grass waterways) within 300 m of the restored grassland. Patch size and seeding type (cool‐season versus warm‐season grasses) were not predictors of early restoration success. In 2011, voles experienced a severe regional decline consistent with multi‐year population cycles. During the crash, most remaining voles occurred on restored SAFE grasslands, but not on established grasslands. This surprising outcome suggests young restoration plots could function as refuges for voles during population declines in agricultural landscapes.     

Multiscale model of regional population decline in little brown bats due to white‐nose syndrome

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European green crabs (Carcinus maenas) in the northeastern Pacific: genetic evidence for high population connectivity and current-mediated expansion from a single introduced source population

Aim The European green crab (Carcinus maenas) expanded dramatically after its introduction to the west coast of North America, spreading over 1000 km in < 10 years. We use samples of Carcinus maenas collected over time and space to investigate the genetic patterns underlying the species’ initial establishment and spread, and discuss our findings in the context of the species’ life history characteristics and demography. Location The central west coast of North America, encompassing California, Oregon, and Washington (USA) and British Columbia (Canada). Methods We collected 1040 total samples from 21 sites representing the major episodes of population establishment and expansion along the west coast of North America. Microsatellite markers were used to assess genetic diversity and structure at different time points in the species’ spread, to investigate connectivity between embayments and to estimate both short‐term effective population sizes and the number of original founders. Assignment testing was performed to determine the likely source of the introduction. Results Carcinus maenas in western North America likely derived from a single introduction of a small number of founders to San Francisco Bay, CA from the east coast of North America. Throughout its western North American range, the species experiences periodic migration between embayments, resulting in a minor loss of genetic diversity in more recently established populations versus the populations in the area of initial establishment. Main conclusions Low genetic diversity has not precluded the ability of C. maenas to successfully establish and spread on the west coast of North America. An efficient oceanographic transport mechanism combined with highly conducive life history traits are likely the major drivers of C. maenas spread. Evidence for a single introduction underscores the potential utility of early detection and eradication of high‐risk invasive species.     

The demography of extinction in eastern North American birds

Species are being lost at an unprecedented rate during the Anthropocene. Progress has been made in clarifying how species traits influence their propensity to go extinct, but the role historical demography plays in species loss or persistence is unclear. In eastern North America, five charismatic landbirds went extinct last century, and the causes of their extinctions have been heavily debated. Although these extinctions are most often attributed to post-colonial human activity, other factors such as declining ancestral populations prior to European colonization could have made these species particularly susceptible. We used population genomic data from these extinct birds and compared them with those from four codistributed extant species. We found extinct species harboured lower genetic diversity and effective population sizes than extant species, but both extinct and non-extinct birds had similar demographic histories of population expansion. These demographic patterns are consistent with population size changes associated with glacial–interglacial cycles. The lack of support for overall population declines during the Pleistocene corroborates the view that, although species that went extinct may have been vulnerable due to low diversity or small population size, their disappearance was driven by human activities in the Anthropocene.