West Nile Virus and California Breeding Bird Declines

Since it was first detected in 1999, West Nile virus (WNV) quickly spread, becoming the dominant vector-borne disease in North America. Sometimes fatal to humans, WNV is even more widespread among birds, with hundreds of species known to be susceptible to WNV infection in North America alone. However, despite considerable mortality and local declines observed in American crows (Corvus brachyrhynchos), there has been little evidence of a large regional association between WNV susceptibility and population declines of any species. Here we demonstrate a correlation between susceptibility to WNV measured by large-scale testing of dead birds and two indices of overall population change among bird species following the spread of WNV throughout California. This result was due primarily to declines in four species of Corvidae, including all species in this family except common ravens (Corvus corax). Our results support the hypothesis that susceptibility to WNV may have negative population consequences to most corvids on regional levels. They also provide confirmation that dead animal surveillance programs can provide important data indicating populations most likely to suffer detrimental impacts due to WNV.     

Combining Breeding Bird Survey and Christmas Bird Count Data to Evaluate Seasonal Components of Population Change in Northern Bobwhite

Abstract Annual surveys of wildlife populations provide information about annual rates of change in populations but provide no information about when such changes occur. However, by combining data from 2 annual surveys, conducted in different parts of the year, seasonal components of population change can be estimated. We describe a hierarchical model for simultaneous analysis of 2 continent-scale monitoring programs. The Christmas Bird Count is an early winter survey, whereas the North American Breeding Bird Survey is conducted in June. Combining information from these surveys permits estimation of seasonal population variance components and improves estimation of long-term population trends. The composite analysis also controls for survey-specific sampling effects. We applied the model to estimation of population change in northern bobwhites (Colinus virginianus). Over the interval 1969–2004, bobwhite populations declined, with trend estimate of −3.56% per year (95% CI = [−3.80%, −3.32%]) in the surveyed portion of their range. Our analysis of seasonal population variance components indicated that northern bobwhite populations changed more in the winter and spring portion of the year than in the summer and fall portion of the year. (JOURNAL OF WILDLIFE MANAGEMENT 72(1):44–51; 2008)     

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.     

Interspecific competition between introduced house finch populations and two associated passerine species

Summary House Finches (Carpodacus mexicanus), natives of western North America, have expanded their range in the eastern United States since their 1940 release in New York City. Range and the relation of House Finch population growth to the population dynamics of House Sparrows (Passer domesticus) and Purple Finches (Carpodacus purpureus) were examined, using data from the Breeding Bird Survey and the Christmas Bird Count. The House Finch population grew exponentially throughout its eastern range. Significant negative relationships in population density, relative to spatial and temporal control populations, were found between House Finches and House Sparrows in summer and winter, and between House Finches and Purple Finches in summer. Purple Finch and House Sparrow populations outside of the House Finch range appeared to have no effect on each other throughout the study. Neither changes in 74 weather variables, nor changes in forest, field or developed habitat explained the observed trends in population density. The results indicate that House Finches compete with these two species, but winter migration complicates the picture.     

The Effect of West Nile Virus Perceptions and Knowledge on Protective Behavior and Mosquito Breeding in Residential Yards in Upstate New York

A knowledge, attitudes, and practices (KAP) questionnaire combined with entomological surveys of residential mosquito-breeding sites were conducted in two Upstate New York neighborhoods. We tested the hypothesis that “correct” West Nile virus (WNV) knowledge and perceptions correspond with the use of practices that prevent mosquitoes from breeding and biting. Our results demonstrate that perceptions of WNV relate to the number of positive containers in yards and the use of mosquito preventive measures. In contrast, WNV knowledge was not related. Culex pipiens and Cx. restuans were common species found breeding in containers. Aedes japonicus was the most abundant species in 77% of positive containers (buckets, flower pots, and birdbaths). This new, invasive mosquito together with the Culex species identified in this study represent significant potential as vectors of WNV and other arboviruses affecting human and animal health. We conclude that more training and education programs should focus on WNV control strategies and recognizing mosquito breeding in residential yards. This is the first study to directly investigate the relationship between KAP and breeding of WNV vectors in residential yards.     

Conservation Status of North American Birds in the Face of Future Climate Change

Human-induced climate change is increasingly recognized as a fundamental driver of biological processes and patterns. Historic climate change is known to have caused shifts in the geographic ranges of many taxa and future climate change is expected to result in even greater redistributions of species. As a result, predicting the impact of climate change on future patterns of biodiversity will greatly aid conservation planning. Using the North American Breeding Bird Survey and Audubon Christmas Bird Count, two of the most comprehensive continental datasets of vertebrates in the world, and correlative distribution modeling, we assessed geographic range shifts for 588 North American bird species during both the breeding and non-breeding seasons under a range of future emission scenarios (SRES A2, A1B, B2) through the end of the century. Here we show that 314 species (53%) are projected to lose more than half of their current geographic range across three scenarios of climate change through the end of the century. For 126 species, loss occurs without concomitant range expansion; whereas for 188 species, loss is coupled with potential to colonize new replacement range. We found no strong associations between projected climate sensitivities and existing conservation prioritizations. Moreover, species responses were not clearly associated with habitat affinities, migration strategies, or climate change scenarios. Our results demonstrate the need to include climate sensitivity into current conservation planning and to develop adaptive management strategies that accommodate shrinking and shifting geographic ranges. The persistence of many North American birds will depend on their ability to colonize climatically suitable areas outside of current ranges and management actions that target climate adaptation.     

A Hierarchical Model for Estimating Change in American Woodcock Populations

Abstract The Singing-Ground Survey (SGS) is a primary source of information on population change for American woodcock (Scolopax minor). We analyzed the SGS using a hierarchical log-linear model and compared the estimates of change and annual indices of abundance to a route regression analysis of SGS data. We also grouped SGS routes into Bird Conservation Regions (BCRs) and estimated population change and annual indices using BCRs within states and provinces as strata. Based on the hierarchical model–based estimates, we concluded that woodcock populations were declining in North America between 1968 and 2006 (trend = −0.9%/yr, 95% credible interval: −1.2, −0.5). Singing-Ground Survey results are generally similar between analytical approaches, but the hierarchical model has several important advantages over the route regression. Hierarchical models better accommodate changes in survey efficiency over time and space by treating strata, years, and observers as random effects in the context of a log-linear model, providing trend estimates that are derived directly from the annual indices. We also conducted a hierarchical model analysis of woodcock data from the Christmas Bird Count and the North American Breeding Bird Survey. All surveys showed general consistency in patterns of population change, but the SGS had the shortest credible intervals. We suggest that population management and conservation planning for woodcock involving interpretation of the SGS use estimates provided by the hierarchical model.     

Potential transmission of West Nile virus in the British Isles: an ecological review of candidate mosquito bridge vectors

West Nile virus (WNV) transmitted by mosquitoes (Diptera: Culicidae) infects various vertebrates, being pathogenic for birds, horses and humans. After its discovery in tropical Africa, sporadic outbreaks of WNV occurred during recent decades in Eurasia, but not the British Isles. WNV reached New York in 1999 and spread to California by 2003, causing widespread outbreaks of West Nile encephalitis across North America, transmitted by many species of mosquitoes, mainly Culex spp. The periodic reappearance of WNV in parts of continental Europe (from southern France to Romania) gives rise to concern over the possibility of WNV invading the British Isles. The British Isles have about 30 endemic mosquito species, several with seasonal abundance and other eco-behavioural characteristics predisposing them to serve as potential WNV bridge vectors from birds to humans. These include: the predominantly ornithophilic Culex pipiens L. and its anthropophilic biotype molestus Forskal; tree-hole adapted Anopheles plumbeus Stephens; saltmarsh-adapted Ochlerotatus caspius Pallas, Oc. detritus Haliday and Oc. dorsalis (Meigen); Coquillettidia richiardii Ficalbi, Culiseta annulata Schrank and Cs. morsitans (Theobald) from vegetated freshwater pools; Aedes cinereus Meigen, Oc. cantans Meigen and Oc. punctor Kirby from seasonal woodland pools. Those underlined have been found carrying WNV in other countries (12 species), including the rarer British species Aedes vexans (Meigen), Culex europaeus Ramos et al., Cx. modestus Ficalbi and Oc. sticticus (Meigen) as well as the Anopheles maculipennis Meigen complex (mainly An. atroparvus van Thiel and An. messeae Falleroni in Britain). Those implicated as key vectors of WNV in Europe are printed bold (four species). So far there is no proof of any arbovirus transmission by mosquitoes in the British Isles, although antibodies to Sindbis, Tahyna, Usutu and West Nile viruses have been detected in British birds. Neighbouring European countries have enzootic WNV and human infections transmitted by mosquito species that are present in the British Isles. However, except for localized urban infestations of Cx. pipiens biotype molestus that can be readily eliminated, there appear to be few situations in the British Isles where humans and livestock are exposed to sustained risks of exposure to potential WNV vectors. Monitoring of mosquitoes and arbovirus surveillance are required to guard the British Isles against WNV outbreaks and introduction of more anthropophilic mosquitoes such as Stegomyia albopicta (Skuse) and Ochlerotatus japonicus (Theobald) that have recently invaded Europe, since they transmit arboviruses elsewhere.     

Economic conditions predict prevalence of West Nile virus

Understanding the conditions underlying the proliferation of infectious diseases is crucial for mitigating future outbreaks. Since its arrival in North America in 1999, West Nile virus (WNV) has led to population-wide declines of bird species, morbidity and mortality of humans, and expenditures of millions of dollars on treatment and control. To understand the environmental conditions that best explain and predict WNV prevalence, we employed recently developed spatial modeling techniques in a recognized WNV hotspot, Orange County, California. Our models explained 85-95% of the variation of WNV prevalence in mosquito vectors, and WNV presence in secondary human hosts. Prevalence in both vectors and humans was best explained by economic variables, specifically per capita income, and by anthropogenic characteristics of the environment, particularly human population and neglected swimming pool density. While previous studies have shown associations between anthropogenic change and pathogen presence, results show that poorer economic conditions may act as a direct surrogate for environmental characteristics related to WNV prevalence. Low-income areas may be associated with higher prevalence for a number of reasons, including variations in property upkeep, microhabitat conditions conducive to viral amplification in both vectors and hosts, host community composition, and human behavioral responses related to differences in education or political participation. Results emphasize the importance and utility of including economic variables in mapping spatial risk assessments of disease.     

An Integrative Eco-Epidemiological Analysis of West Nile Virus Transmission

West Nile disease, caused by the West Nile virus (WNV), is a mosquito-borne zoonotic disease affecting humans and horses that involves wild birds as amplifying hosts. The mechanisms of WNV transmission remain unclear in Europe where the occurrence of outbreaks has dramatically increased in recent years. We used a dataset on the competence, distribution, abundance, diversity and dispersal of wild bird hosts and mosquito vectors to test alternative hypotheses concerning the transmission of WNV in Southern France. We modelled the successive processes of introduction, amplification, dispersal and spillover of WNV to incidental hosts based on host–vector contact rates on various land cover types and over four seasons. We evaluated the relative importance of the mechanisms tested using two independent serological datasets of WNV antibodies collected in wild birds and horses. We found that the same transmission processes (seasonal virus introduction by migratory birds, Culex modestus mosquitoes as amplifying vectors, heterogeneity in avian host competence, absence of ‘dilution effect’) best explain the spatial variations in WNV seroprevalence in the two serological datasets. Our results provide new insights on the pathways of WNV introduction, amplification and spillover and the contribution of bird and mosquito species to WNV transmission in Southern France.     

The consistency and stability of abundance-occupancy relationships in large-scale population dynamics

1. Abundance-occupancy relationships comprise some of the most general and well-explored patterns in macro-ecology. The theory governing these relationships predicts that species will exhibit a positive interspecific and intraspecific relationship between regional occupancy and local abundance. Abundance-occupancy relationships have important implications in using distributional surveys, such as atlases, to understand and document large-scale population dynamics and the consequences of environmental change. A basic need for interpreting such data bases is a better understanding of whether changes in regional occupancy reflect changes in local abundance across species of varying life-history characteristics. 2. Our objective was to test the predictions of the abundance-occupancy rule using two independent data sets, the New York State Breeding Bird Atlas and the North American Breeding Bird Survey. The New York State Breeding Bird Atlas consists of 5332 25-km(2) survey blocks and is one of the first atlases in the USA to be completed for two time periods (1980-85 and 2000-05). The North American Breeding Survey is a large-scale annual survey intended to document the relative abundance and population change of songbirds throughout the USA. 3. We found that regional occupancy was positively correlated with relative abundance across 98 (beta = 0.60 +/- 0.11 SE, P < 0.001, R(2) = 0.60) and 85 species (beta = 0.67 +/- 0.06 SE, P < 0.001, R(2) = 0.57) in two separate time periods. This relationship proved stable over time and was notably consistent between breeding habitat groups and migratory guilds. 4. Between 1980 and 2005, changes in regional occupancy were highly correlated with long-term abundance trend estimates for 75 species (beta = 5.73 +/- 0.24 SE, P < 0.001, R(2) = 0.88). Over a 20-year period, woodland and resident birds showed an increase in occupancy while grassland species showed the greatest decline; these patterns were mirrored by changes in local abundance. 5. Although exceptions existed, we found most changes in occupancy parallel changes in local abundance. These findings support the basic predictions of the abundance-occupancy rule and demonstrate its consistency and stability in species and groups of varying life-history characteristics.     

Multimodality in the individual size distributions of bird communities

Aim Body size often plays a significant role in community assembly through its impacts on the life history and ecological attributes of species. Insight into the importance of size in structuring communities can be gained by examining the distribution of sizes of individuals [i.e. the individual size distribution (ISD) or size spectrum] in a community. ISDs have been studied extensively in aquatic and tree communities, but have received little attention in terrestrial animal communities. Here, we conduct the first macroecological analysis of ISDs in terrestrial animal communities to determine whether they show broad‐scale consistency in shape. Location North America, north of Mexico. Methods Using likelihood‐based methods and Gaussian mixture modelling, coupled with data from the Breeding Bird Survey and Christmas Bird Count, we determine whether the ISDs for thousands of breeding and wintering North American bird communities are: (1) monotonically decreasing, (2) unimodal or (3) multimodal. Results We find that avian ISDs are consistently multimodal, with most characterized by more than five modes in both breeding and wintering communities from local to continental scales. In addition, the positions of these modes along the size axis are remarkably consistent. Main conclusions The striking consistency in the ISD within bird communities, as with tree and aquatic communities, indicates that the ISD is an important and informative characterization of resource utilization within an ecological assemblage. The differences in shape of the ISD among these groups also suggest that differences in body size‐related constraints affect interactions within a group and with the environment. Our results confirm that avian assemblages do exhibit structure along the body size axis, and therefore it will be fruitful to explore this pattern in greater detail.     

Vector competence of northern and southern European Culex pipiens pipiens mosquitoes for West Nile virus across a gradient of temperatures

In Europe, West Nile virus (WNV) outbreaks have been limited to southern and central European countries. However, competent mosquito vectors and susceptible bird hosts are present in northern Europe. Differences in temperature and vector competence of mosquito populations may explain the absence of WNV outbreaks in northern Europe. The aim of the present study was to directly compare vector competence of northern and southern European Culex pipiens (Cx. p.) pipiens mosquitoes for WNV across a gradient of temperatures. WNV infection and transmission rates were determined for two Cx. p. pipiens populations originating from The Netherlands and Italy, respectively. Mosquitoes were orally exposed by providing an infectious bloodmeal, or by injecting WNV (lineage 2) in the thorax, followed by 14‐day incubation at 18, 23, or 28 °C. No differences in infection or transmission rates were found between the Cx. p. pipiens populations with both infection methods, but WNV transmission rates were significantly higher at temperatures above 18 °C. The absence of WNV outbreaks in northern Europe cannot be explained by differences in vector competence between Cx. p. pipiens populations originating from northern and southern Europe. This study suggests that low temperature is a key limiting factor for WNV transmission.     

Ornithology and bird conservation in North America – a Canadian perspective

Capsule A comparison between North American and European ornithology shows many differences between the two.

While local knowledge was developed over millennia in Europe, in North America much was originally learned from the indigenous people. Knowing the food value of wild game was essential to survival and led to a strong tradition of wildlife management in North America. However, there was also systematic exploration of the local avifauna by museum-based collectors. This dual origin of ornithology is still detectable today. North American ornithology, particularly through the introduction of the Migratory Birds Convention Act of 1917, is strongly influenced by federal, state and provincial governments who have a statutory responsibility for the protection of wild birds. Because the USA and Canada, and more recently Mexico, are responsible for the administration of the Act, many initiatives in bird conservation involve international co-operation, starting initially with the North American Waterfowl Management Plan, but now extended to all species of birds. Many partnerships involving government, professional and amateur ornithologists (e.g. Bird Studies Canada) have resulted in monitoring of bird populations similar to that done by the BTO. However, there still seems to be a paucity of population studies and survey information in the mainstream ornithological journals in North America.     

Energetic determinants of abundance in winter landbird communities

There is increasing evidence that individual energetics constrain macroecological patterns. Here we model total abundance within winter landbird communities as a function of (1) energy supply, as measured by ecosystem net primary productivity, and (2) energy use of individuals, as influenced by body mass and ambient temperature. Using data from the North American Christmas Bird Count, we find that total abundance increases with productivity to the 0.61 power, and decreases with body mass and environmental temperature as predicted by metabolic theory when individuals are below their thermoneutral zone. We note a negative relationship between ambient temperature and average body mass, and suggest that this community‐level pattern, reminiscent of Bergmann's Rule, is related to a tendency for small species to be less‐abundant or absent from cold locations. Results from this study emphasize the importance of individual‐level metabolism for understanding large‐scale ecological patterns.     

West Nile Virus Surveillance in 2013 via Mosquito Screening in Northern Italy and the Influence of Weather on Virus Circulation

West Nile virus (WNV) is a recently re-emerged health problem in Europe. In Italy, an increasing number of outbreaks of West Nile disease, with occurrences of human cases, have been reported since 2008. This is particularly true in northern Italy, where entomological surveillance systems have been implemented at a regional level. The aim of this study was to use, for the first time, all the entomological data collected in the five regions undergoing surveillance for WNV in northern Italy to characterize the viral circulation (at a spatial and temporal scale), identify potential mosquito vectors, and specify relationships between virus circulation and meteorological conditions. In 2013, 286 sites covering the entire Pianura Padana area were monitored. A total of 757,461 mosquitoes were sampled. Of these, 562,079 were tested by real-time PCR in 9,268 pools, of which 180 (1.9%) were positive for WNV. The largest part of the detected WNV sequences belonged to lineage II, demonstrating that, unlike those in the past, the 2013 outbreak was mainly sustained by this WNV lineage. This surveillance also detected the Usutu virus, a WNV-related flavivirus, in 241 (2.6%) pools. The WNV surveillance systems precisely identified the area affected by the virus and detected the viral circulation approximately two weeks before the occurrence of onset of human cases. Ninety percent of the sampled mosquitoes were Culex pipiens, and 178/180 WNV-positive pools were composed of only this species, suggesting this mosquito is the main WNV vector in northern Italy. A significantly higher abundance of the vector was recorded in the WNV circulation area, which was characterized by warmer and less rainy conditions and greater evapotranspiration compared to the rest of the Pianura Padana, suggesting that areas exposed to these conditions are more suitable for WNV circulation. This observation highlights warmer and less rainy conditions as factors able to enhance WNV circulation and cause virus spillover outside the sylvatic cycle.     

Evolving Management Strategies for a Recently Discovered Exotic Forest Pest: The Pine Shoot Beetle, Tomicus Piniperda (Coleoptera)

Established populations of the Eurasian pine shoot beetle (Tomicus piniperda (L.); Coleoptera: Scolytidae) were first discovered in North America in Ohio in 1992. As of 31 December 2000, T. piniperda was found in 303 counties in 12 US states (Illinois, Indiana, Maine, Maryland, Michigan, New Hampshire, New York, Ohio, Pennsylvania, Vermont, West Virginia, and Wisconsin) and in 43 counties in 2 Canadian provinces (Ontario and Quebec). A federal quarantine imposed in November 1992 regulates movement of pine (Pinus) trees, logs, and certain pine products from infested to uninfested areas within US. The forest products, Christmas tree, and nursery industries are affected by the quarantine. This paper summarizes information on the discovery and spread of T. piniperda in North America, survey efforts, recent interception history, development and changes in the federal quarantine, development of a national compliance management program, and extension and research efforts.