Ecological barriers mediate spatiotemporal shifts of bird communities at a continental scale.

Species' range shifts and local extinctions caused by climate change lead to community composition changes. At large spatial scales, ecological barriers, such as biome boundaries, coastlines, and elevation, can influence a community's ability to shift in response to climate change. Yet, ecological barriers are rarely considered in climate change studies, potentially hindering predictions of biodiversity shifts. We used data from two consecutive European breeding bird atlases to calculate the geographic distance and direction between communities in the 1980s and their compositional best match in the 2010s and modeled their response to barriers. The ecological barriers affected both the distance and direction of bird community composition shifts, with coastlines and elevation having the strongest influence. Our results underscore the relevance of combining ecological barriers and community shift projections for identifying the forces hindering community adjustments under global change. Notably, due to (macro)ecological barriers, communities are not able to track their climatic niches, which may lead to drastic changes, and potential losses, in community compositions in the future.

Farmland practices are driving bird population decline across Europe.

Declines in European bird populations are reported for decades but the direct effect of major anthropogenic pressures on such declines remains unquantified. Causal relationships between pressures and bird population responses are difficult to identify as pressures interact at different spatial scales and responses vary among species. Here, we uncover direct relationships between population time-series of 170 common bird species, monitored at more than 20,000 sites in 28 European countries, over 37 y, and four widespread anthropogenic pressures: agricultural intensification, change in forest cover, urbanisation and temperature change over the last decades. We quantify the influence of each pressure on population time-series and its importance relative to other pressures, and we identify traits of most affected species. We find that agricultural intensification, in particular pesticides and fertiliser use, is the main pressure for most bird population declines, especially for invertebrate feeders. Responses to changes in forest cover, urbanisation and temperature are more species-specific. Specifically, forest cover is associated with a positive effect and growing urbanisation with a negative effect on population dynamics, while temperature change has an effect on the dynamics of a large number of bird populations, the magnitude and direction of which depend on species' thermal preferences. Our results not only confirm the pervasive and strong effects of anthropogenic pressures on common breeding birds, but quantify the relative strength of these effects stressing the urgent need for transformative changes in the way of inhabiting the world in European countries, if bird populations shall have a chance of recovering.

Covariation in population trends and demography reveals targets for conservation action.

Wildlife conservation policies directed at common and widespread, but declining, species are difficult to design and implement effectively, as multiple environmental changes are likely to contribute to population declines. Conservation actions ultimately aim to influence demographic rates, but targeting actions towards feasible improvements in these is challenging in widespread species with ranges that encompass a wide range of environmental conditions. Across Europe, sharp declines in the abundance of migratory landbirds have driven international calls for action, but actions that could feasibly contribute to population recovery have yet to be identified. Targeted actions to improve conditions on poor-quality sites could be an effective approach, but only if local conditions consistently influence local demography and hence population trends. Using long-term measures of abundance and demography of breeding birds at survey sites across Europe, we show that co-occurring species with differing migration behaviours have similar directions of local population trends and magnitudes of productivity, but not survival rates. Targeted actions to boost local productivity within Europe, alongside large-scale (non-targeted) environmental protection across non-breeding ranges, could therefore help address the urgent need to halt migrant landbird declines. Such demographic routes to recovery are likely to be increasingly needed to address global wildlife declines.

Wintering bird communities are tracking climate change faster than breeding communities.

Global climate change is driving species' distributions towards the poles and mountain tops during both non-breeding and breeding seasons, leading to changes in the composition of natural communities. However, the degree of season differences in climate-driven community shifts has not been thoroughly investigated at large spatial scales. We compared the rates of change in the community composition during both winter (non-breeding season) and summer (breeding) and their relation to temperature changes. Based on continental-scale data from Europe and North America, we examined changes in bird community composition using the community temperature index (CTI) approach and compared the changes with observed regional temperature changes during 1980-2016. CTI increased faster in winter than in summer. This seasonal discrepancy is probably because individuals are less site-faithful in winter, and can more readily shift their wintering sites in response to weather in comparison to the breeding season. Regional long-term changes in community composition were positively associated with regional temperature changes during both seasons, but the pattern was only significant during summer due to high annual variability in winter communities. Annual changes in community composition were positively associated with the annual temperature changes during both seasons. Our results were broadly consistent across continents, suggesting some climate-driven restructuring in both European and North American avian communities. Because community composition has changed much faster during the winter than during the breeding season, it is important to increase our knowledge about climate-driven impacts during the less-studied non-breeding season.

Spatially different annual cycles but similar haemosporidian infections in distant populations of collared sand martins.

BACKGROUND: Populations of long-distance migratory birds experience different environments and are consequently exposed to different parasites throughout their annual cycles. Though, specific whereabouts and accompanied host-parasite interactions remain unknown for most migratory passerines. Collared sand martins (Riparia riparia) breeding in the western Palaearctic spend the nonbreeding period in Africa, but it is not yet clear whether specific populations differ in overwintering locations and whether these also result in varying infections with vector-transmitted endoparasites. RESULTS: Geolocator tracking revealed that collared sand martins from northern-central and central-eastern Europe migrate to distant nonbreeding sites in West Africa and the Lake Chad basin in central Africa, respectively. While the ranges of these populations were clearly separated throughout the year, they consistently spent up to 60% of the annual cycle in Africa. Ambient light recorded by geolocators further indicated unsheltered roosting during the nonbreeding season in Africa compared to the breeding season in Europe. We found 5-26% prevalence of haemosporidian parasites in three breeding populations and one migratory passage population that was only sampled but not tracked. In total, we identified seven Plasmodium and nine Haemoproteus lineages (incl. two and seven new lineages, respectively), the latter presumably typical for swallows (Hirundinae) hosts. 99.5% of infections had a low intensity, typical for chronic infection stages, whereas three individuals (0.5%) showed high parasitaemia typical for acute infections during spring migration and breeding. CONCLUSIONS: Our study shows that blood parasite infections are common in several western Palaearctic breeding populations of collared sand martins who spent the nonbreeding season in West Africa and the lake Chad region. Due to long residency at the nonbreeding grounds blood parasite transmissions may mainly occur at host population-specific residences sites in Europe and Africa; the latter being likely facilitated by unsheltered roosting and thus high vulnerability to hematophagous insects. The rare cases of high parasitaemia during spring migration and breeding further indicates either relapses of chronic infection or primary infections which occurred shortly before migration and during breeding.

Older birds have better feathers: A longitudinal study on the long-distance migratory Sand Martin, Riparia riparia.

Feather quality is of critical importance to long-distance migratory birds. Here, we report a series of analyses of a unique data set encompassing known-age individuals of the long-distance migratory Sand Martin (Riparia riparia). Sampling over 17 years along the Tisza River, eastern Hungary, has resulted in the recapture of numerous individuals enabling longitudinal and cross-sectional investigation of the role of adaptation to variable environmental conditions on feather morphology. We show that older individuals tend to possess better quality feathers, measured using bending stiffness, feather length and thickness as proxies. Bending stiffness and feather thickness do not change with individual age, in contrast with increases in feather length and declines in daily feather growth versus age of individual alongside moult duration. Individuals who live to older ages tend to have similar, or higher, feather growth rates and better feather quality than individuals captured at younger ages. Thus, on the basis of strong selection against individuals with slow feather growth, as seen in other species of swallows and martins, which causes a delay in moult completion, the results of this analysis highlight the potential cost of producing better quality feathers when this depends on moult duration. Feather length also does change during the lifetime of the individual and thus enabled us to further investigate influence of individual and environmental conditions during the moult. The results of this analysis provide important insights on the adaptive significance of these traits, and the potential use of physical characteristics in unravelling the reasons why long distance migratory bird populations are in global decline.

Consistent response of bird populations to climate change on two continents.

Global climate change is a major threat to biodiversity. Large-scale analyses have generally focused on the impacts of climate change on the geographic ranges of species and on phenology, the timing of ecological phenomena. We used long-term monitoring of the abundance of breeding birds across Europe and the United States to produce, for both regions, composite population indices for two groups of species: those for which climate suitability has been either improving or declining since 1980. The ratio of these composite indices, the climate impact indicator (CII), reflects the divergent fates of species favored or disadvantaged by climate change. The trend in CII is positive and similar in the two regions. On both continents, interspecific and spatial variation in population abundance trends are well predicted by climate suitability trends.

Assessing the effects of climate on host-parasite interactions: a comparative study of European birds and their parasites.

BACKGROUND: Climate change potentially has important effects on distribution, abundance, transmission and virulence of parasites in wild populations of animals. METHODOLOGY/PRINCIPAL FINDING: Here we analyzed paired information on 89 parasite populations for 24 species of bird hosts some years ago and again in 2010 with an average interval of 10 years. The parasite taxa included protozoa, feather parasites, diptera, ticks, mites and fleas. We investigated whether change in abundance and prevalence of parasites was related to change in body condition, reproduction and population size of hosts. We conducted analyses based on the entire dataset, but also on a restricted dataset with intervals between study years being 5-15 years. Parasite abundance increased over time when restricting the analyses to datasets with an interval of 5-15 years, with no significant effect of changes in temperature at the time of breeding among study sites. Changes in host body condition and clutch size were related to change in temperature between first and second study year. In addition, changes in clutch size, brood size and body condition of hosts were correlated with change in abundance of parasites. Finally, changes in population size of hosts were not significantly related to changes in abundance of parasites or their prevalence. CONCLUSIONS/SIGNIFICANCE: Climate change is associated with a general increase in parasite abundance. Variation in laying date depended on locality and was associated with latitude while body condition of hosts was associated with a change in temperature. Because clutch size, brood size and body condition were associated with change in parasitism, these results suggest that parasites, perhaps mediated through the indirect effects of temperature, may affect fecundity and condition of their hosts. The conclusions were particularly in accordance with predictions when the restricted dataset with intervals of 5-15 years was used, suggesting that short intervals may bias findings.

Collyriclosis in Central European hirundines.

Cutaneous monostome trematode Collyriclum faba (Bremser in Schmalz 1831) is a digenetic flatworm with unknown life cycle. Here, we provide the first compelling evidence that despite low prevalence of the parasite, European hirundines are parasitized by this species. First host record for sand martin (Riparia riparia) and first European host record for barn swallow (Hirundo rustica) is provided. The birds were captured and checked in ten European and Middle Eastern countries, stretching from Ireland to Bahrain, but only samples from Central Europe (Czech Republic, Hungary and Poland) were positive for C. faba. In total, 164,582 sand martins and 100,443 barn swallows were examined, and seven and two birds had cutaneous C. faba cysts. Even though over 40% of the birds captured were juveniles, all but one infected individuals were adults, equally both males and females. The prevalence of the parasite on Central European hirundines were calculated as one in 20,641 for sand martins and one in 4,484 for barn swallows. All the infected birds were captured in close vicinity of water bodies. All the cysts were found close to the vent or on the legs. No adverse effects on its bird hosts were observed.

Factors affecting germline mutations in a hypervariable microsatellite: a comparative analysis of six species of swallows (Aves: Hirundinidae).

Microsatellites mutate frequently by replication slippage. Empirical evidence shows that the probability of such slippage mutations may increase with the length of the repeat region as well as exposure to environmental mutagens, but the mutation rate can also differ between the male and female germline. It has been hypothesized that more intense sexual selection or sperm competition can also lead to elevated mutation rates, but the empirical evidence is inconclusive. Here, we analyzed the occurrence of germline slippage mutations in the hypervariable pentanucleotide microsatellite locus HrU10 across six species of swallow (Aves: Hirundinidae). These species exhibit marked differences in the length range of the microsatellite, as well as differences in the intensity of sperm competition. We found a strong effect of microsatellite length on the probability of mutation, but no residual effect of species or their level of sperm competition when the length effect was accounted for. Neither could we detect any difference in mutation rate between tree swallows (Tachycineta bicolor) breeding in Hamilton Harbour, Ontario, an industrial site with previous documentation of elevated mutation rates for minisatellite DNA, and a rural reference population. However, our cross-species analysis revealed two significant patterns of sex differences in HrU10 germline mutations: (1) mutations in longer alleles occurred typically in the male germline, those in shorter alleles in the female germline, and (2) male germline mutations were more often expansions than contractions, whereas no directional bias was evident in the female germline. These results indicate some fundamental differences in male and female gametogenesis affecting the probability of slippage mutations. Our study also reflects the value of a comparative, multi-species approach for locus-specific mutation analyses, through which a wider range of influential factors can be assessed than in single-species studies.

Age-independent telomere length predicts fitness in two bird species.

Telomeres are dynamic DNA-protein structures that form protective caps at the ends of eukaryotic chromosomes. Although initial telomere length is partly genetically determined, subsequent accelerated telomere shortening has been linked to elevated levels of oxidative stress. Recent studies show that short telomere length alone is insufficient to induce cellular senescence; advanced attrition of these repetitive DNA sequences does, however, reflect ageing processes. Furthermore, telomeres vary widely in length between individuals of the same age, suggesting that individuals differ in their exposure or response to telomere-shortening stress factors. Here, we show that residual telomere length predicts fitness components in two phylogenetically distant bird species: longevity in sand martins, Riparia riparia, and lifetime reproductive success in dunlins, Calidris alpina. Our results therefore imply that individuals with longer than expected telomeres for their age are of higher quality.

Ecological conditions during winter affect sexual selection and breeding in a migratory bird.

Populations of migratory birds have undergone marked declines, although the causes and mechanisms remain unknown. Because environmental effects on population dynamics are mediated by the effects of ecological factors on individuals, understanding changes in individual phenotypes in response to ecological conditions is key to understanding population trends. We show that breeding individuals of a declining population of trans-Saharan migratory barn swallows, Hirundo rustica, were affected by environmental conditions, as estimated from the normalized difference vegetation index (NDVI), reflecting primary production, in their winter quarters. The breeding dates of the same individuals in consecutive breeding seasons were advanced and clutch sizes were larger after winters with high NDVI in the winter quarters. Feather moult was also affected by winter conditions, with consequences for male sexual attractiveness. Length of tail ornament was positively correlated with NDVI during the previous winter, and males with large tail ornaments reproduced earlier and had larger clutches. The mean annual breeding date of the population was earlier and breeding success was increased after favourable winters, but this result was mainly determined by a single winter with very low NDVI. Thus, ecological conditions in Africa influence individual performance and productivity in a barn swallow population.