Explore the vast range of titles available.

Much attention has been paid to the impacts of plastics and other debris on marine organisms, but the effects of plastic on terrestrial organisms have been largely ignored. Detrimental effects of terrestrial plastic could be most pronounced in intensively human-modified landscapes (e.g., urban and agricultural areas), which are a source of much anthropogenic debris. Here, we examine the occurrence, types, landscape associations, and consequences of anthropogenic nest material in the American crow (Corvus brachyrhynchos), a North American species that breeds in both urban and agricultural landscapes. We monitored 195 nestlings in 106 nests across an urban and agricultural gradient in the Sacramento Valley, California, USA. We found that 85.2% of crow nests contained anthropogenic material, and 11 of 195 nestlings (5.6%) were entangled in their nests. The length of the material was greater in nests in agricultural territories than in urban territories, and the odds of entanglement increased 7.55 times for each meter of anthropogenic material in the nest. Fledging success was significantly lower for entangled than for unentangled nestlings. In all environments, particularly urban, agricultural, and marine, careful disposal of potential hazards (string, packing and hay bale twine, balloon ribbon, wire, fishing line) could reduce the occurrence of entanglement of nestling birds.

There is growing concern that infectious disease can impair the cognitive performance of wild animals, but the mechanisms by which this may occur are unclear. Here, we examined the apparent contributions of cognitive and motivational factors to the poor performance on a string-pulling task among American crows ( Corvus brachyrhynchos ) infected with a common bacterial pathogen ( Campylobacter spp.). In a sample of 57 crows, of which 65% were infected with Campylobacter , we found that infected crows were significantly less likely to solve a string-pulling task with a food reward and took longer to solve it after engaging with the task. However, their poor performance appeared largely motivational. Infected birds exhibited longer latency to attempt the task (9.0 ± 2.8 vs. 22.8 ± 3.4 min when uninfected vs. infected, respectively). They also had a slower attempt rate after initial engagement (lower persistence) than uninfected crows: on average, the attempt rate of infected birds was 61% lower than for uninfected birds. Anorexia may have played a role in this lower motivation, as infected crows consumed significantly fewer calories when food was provided ad libitum than uninfected crows: birds with the highest apparent infection intensity ate 43.4% fewer calories/day than uninfected birds. Our study provides a framework for distinguishing among the potential mechanisms underlying impaired performance on a problem-solving task among infected individuals. It also sheds light on some of the potential downstream fitness and survival consequences for animals exhibiting disease-linked changes in behavior and cognitive performance.

Numerous studies have correlated the advancement of lay date in birds with warming climate trends, yet the fitness effects associated with this phenological response have been examined in only a small number of species. Most of these species--primarily insectivorous cavity nesters in Europe--exhibit fitness declines associated with increasing asynchrony with prey. Here, we use 25 years of demographic data, collected from 1986 to 2010, to examine the effects of spring temperature on breeding initiation date, double brooding, and annual fecundity in a Nearctic-Neotropical migratory songbird, the black-throated blue warbler (Setophaga caerulescens). Data were collected from birds breeding at the Hubbard Brook Experimental Forest, New Hampshire, USA, where long-term trends toward warmer springs have been recorded. We found that black-throated blue warblers initiated breeding earlier in warmer springs, that early breeders were more likely to attempt a second brood than those starting later in the season, and that double brooding and lay date were linked to higher annual fecundity. Accordingly, we found selection favored earlier breeding in most years. However, in contrast to studies of several other long-distance migratory species in Europe, this selection pressure was not stronger in warmer springs, indicating that these warblers were able to adjust mean lay date appropriately to substantial inter-annual variation in spring temperature. Our results suggest that this North American migratory songbird might not experience the same fecundity declines as songbirds that are unable to adjust their timing of breeding in pace with spring temperatures.

Background Although American crows are a key indicator species for West Nile virus (WNV) and mount among the highest viremias reported for any host, the importance of crows in the WNV transmission cycle has been called into question because of their consistent underrepresentation in studies of Culex blood meal sources. Here, we test the hypothesis that this apparent underrepresentation could be due, in part, to underrepresentation of crow nesting habitat from mosquito sampling designs. Specifically, we examine how the likelihood of a crow blood meal changes with distance to and timing of active crow nests in a Davis, California, population. Methods Sixty artificial mosquito resting sites were deployed from May to September 2014 in varying proximity to known crow nesting sites, and Culex blood meal hosts were identified by DNA barcoding. Genotypes from crow blood meals and local crows (72 nestlings from 30 broods and 389 local breeders and helpers) were used to match mosquito blood meals to specific local crows. Results Among the 297 identified Culex blood meals, 20 (6.7%) were attributable to crows. The mean percentage of blood meals of crow origin was 19% in the nesting period (1 May–18 June 2014), but 0% in the weeks after fledging (19 June–1 September 2014), and the likelihood of a crow blood meal increased with proximity to an active nest: the odds that crows hosted a Culex blood meal were 38.07 times greater within 10 m of an active nest than > 10 m from an active nest. Nine of ten crow blood meals that could be matched to a genotype of a specific crow belonged to either nestlings in these nests or their mothers. Six of the seven genotypes that could not be attributed to sampled birds belonged to females, a sex bias likely due to mosquitoes targeting incubating or brooding females. Conclusion Data herein indicate that breeding crows serve as hosts for Culex in the initial stages of the WNV spring enzootic cycle. Given their high viremia, infected crows could thereby contribute to the re-initiation and early amplification of the virus, increasing its availability as mosquitoes shift to other moderately competent later-breeding avian hosts. Graphical Abstract

Campylobacter jejuni is the most common foodborne pathogen in industrialized countries. Most human infections come from contaminated poultry, but wild birds are also known to harbor C. jejuni. Wild birds are often described as asymptomatic carriers, but this assumption is based on domestic poultry research. We studied the effects of C. jejuni infection on body condition and survival of adult and nestling American crows Corvus brachyrhynchos in Davis, California. Previous work demonstrated that more than half of the crows in this population are infected with C. jejuni and that at least some of the isolates carried by crows are similar to those found in domestic animals and humans. In this study, we compared the body condition of infected and uninfected individuals at the time of capture among adults (n = 44; 52% infected) and nestlings (n = 97; 77% infected). We subsequently monitored these banded individuals for up to 3 yr and used mark–recapture survival analysis to estimate relationships between infection status and later survival. We found that adult crows infected with C. jejuni were in poor condition relative to uninfected adults: average body mass of infected birds was 12% lower, whereas average body size did not differ between the two groups. Likewise, apparent survival probability was lower for infected adults. In contrast, nestling body condition, fledging success, and survival did not differ by infection status. This is the first study to document adverse effects of C. jejuni infection in a free-living, wild bird. If these effects are widespread, C. jejuni exposure may be a cause of conservation concern for some species, especially when human activities increase exposure to infections or introduce novel strains to wild bird populations. Our results add to the growing body of work demonstrating hidden long-term costs of seemingly mild infections in wild populations.

A key characteristic of MHC genes is the persistence of allelic lineages over macroevolutionary periods, often through multiple speciation events. This phenomenon, known as trans-species polymorphism (TSP), is well documented in several major taxonomic groups, but has less frequently been observed in birds. The order Passeriformes is arguably the most successful terrestrial vertebrate order in terms of diversity of species and ecological range, but the reasons for this success remain unclear. Passerines exhibit the most highly duplicated MHC genes of any major vertebrate taxonomic group, which may generate increased immune response relative to other avian orders with fewer MHC loci. Here, we describe phylogenetic patterns of the MHC IIB in the passerine family Corvidae. Our results indicate wide-spread TSP within this family, with at least four supported MHC IIB allelic lineages that predate speciation by many millions of years. Markov chain Monte Carlo simulations indicate that divergence of these lineages occurred near the time of the divergence of the Passeriformes and other avian orders. We suggest that the current MHC diversity observed in passerines is due in part to the multiple duplication of a single MHC locus, DAB1, early in passerine evolution and that subsequent duplications of these paralogues have contributed to the enormous success of this order by increasing their ability to recognize and mount immune responses to novel pathogens.

The ‘social distancing’ that occurred in response to the COVID-19 pandemic in humans provides a powerful illustration of the intimate relationship between infectious disease and social behaviour in animals. Indeed, directly transmitted pathogens have long been considered a major cost of group living in humans and other social animals, as well as a driver of the evolution of group size and social behaviour. As the risk and frequency of emerging infectious diseases rise, the ability of social taxa to respond appropriately to changing infectious disease pressures could mean the difference between persistence and extinction. Here, we examine changes in the social behaviour of humans and wildlife in response to infectious diseases and compare these responses to theoretical expectations. We consider constraints on altering social behaviour in the face of emerging diseases, including the lack of behavioural plasticity, environmental limitations and conflicting pressures from the many benefits of group living.We also explore the ways that social animals can minimize the costs of disease-induced changes to sociality and the unique advantages that humans may have in maintaining the benefits of sociality despite social distancing.

The idea that extrapair paternity (EPP) in birds is part of a mixed reproductive strategy driven primarily by females is controversial. In cooperatively breeding American crows, we compared predictions of four female benefits hypotheses—the genetic diversity, good genes, genetic compatibility, and direct benefits hypotheses—to our predictions if EPP was primarily male driven. We found that genetically diverse broods were not more successful, extrapair young were not in better condition and did not have a higher survival probability, and, contrary to prediction, offspring sired by within‐group extrapair males were more inbred than within‐pair offspring. There was evidence of direct benefits, however: provisioning rate and number of surviving offspring were higher in groups containing within‐group extrapair sires. Females therefore derived no apparent benefits from extragroup extrapair males but both direct benefits and genetic costs from within‐group extrapair males. We suggest that males and females both influence the distribution of EPP in this system.

Perfluorooctane sulfonic acid (PFOS) is an anthropogenic chemical found in aqueous film-forming foams (AFFFs) and many consumer products. Despite its environmental ubiquity and persistence, little is known about the effects of PFOS on stress levels in wild animals. Here, we examined PFOS bioaccumulation and correlations between PFOS exposure and oxidative stress in snapping turtles ( Chelydra serpentina ) downstream of Griffiss Air Force Base in Rome, New York, a known source of AFFF contamination. Maximum concentrations of PFOS were extrapolated as 41.7 ppb and 498 ppb in water and turtle samples, respectively; in comparison, the proposed United States national advisory concentration of PFOS in drinking water is currently 0.00002 ppb. PFOS concentrations declined with distance downstream from the base and were lower in other local water bodies. Indices of oxidative stress were positively correlated with plasma PFOS concentrations in snapping turtles. These data illuminate the potential for bioaccumulation and increasing oxidative stress levels associated with PFOS contamination in a wild population of aquatic turtles.

An animal's social behaviour both influences and changes in response to its parasites. Here we consider these bidirectional links between host social behaviours and parasite infection, both those that occur from ecological vs evolutionary processes. First, we review how social behaviours of individuals and groups influence ecological patterns of parasite transmission. We then discuss how parasite infection, in turn, can alter host social interactions by changing the behaviour of both infected and uninfected individuals. Together, these ecological feedbacks between social behaviour and parasite infection can result in important epidemiological consequences. Next, we consider the ways in which host social behaviours evolve in response to parasites, highlighting constraints that arise from the need for hosts to maintain benefits of sociality while minimizing fitness costs of parasites. Finally, we consider how host social behaviours shape the population genetic structure of parasites and the evolution of key parasite traits, such as virulence. Overall, these bidirectional relationships between host social behaviours and parasites are an important yet often underappreciated component of population-level disease dynamics and host–parasite coevolution.