Conformity to Bergmann's rule in birds depends on nest design and migration

Ecogeographical rules attempt to explain large-scale spatial patterns in biological traits. One of the most enduring examples is Bergmann's rule, which states that species should be larger in colder climates due to the thermoregulatory advantages of larger body size. Support for Bergmann's rule, however, is not consistent across taxonomic groups, raising questions about what factors may moderate its effect. Behavior may play a crucial, yet so far underexplored, role in mediating the extent to which species are subject to environmental selection pressures in colder climates. Here, we tested the hypothesis that nest design and migration influence conformity to Bergmann's rule in a phylogenetic comparative analysis of the birds of the Western Palearctic, a group encompassing dramatic variation in both climate and body mass. We predicted that migratory species and those with more protected nest designs would conform less to the rule than sedentary species and those with more exposed nests. We find that sedentary, but not short- or long-distance migrating, species are larger in colder climates. Among sedentary species, conformity to Bergmann's rule depends, further, on nest design: Species with open nests, in which parents and offspring are most exposed to adverse climatic conditions during breeding, conform most strongly to the rule. Our findings suggest that enclosed nests and migration enable small birds to breed in colder environments than their body size would otherwise allow. Therefore, we conclude that behavior can substantially modify species' responses to environmental selection pressures.

Colonial, more widely distributed and less abundant bird species undergo wider population fluctuations independent of their population trend

Understanding temporal variability in population size is important for conservation biology because wide population fluctuations increase the risk of extinction. Previous studies suggested that certain ecological, demographic, life-history and genetic characteristics of species might be related to the degree of their population fluctuations. We checked whether that was the case in a large sample of 231 European breeding bird species while taking a number of potentially confounding factors such as population trends or similarities among species due to common descent into account. When species-specific characteristics were analysed one by one, the magnitude of population fluctuations was positively related to coloniality, habitat, total breeding range, heterogeneity of breeding distribution and natal dispersal, and negatively related to urbanisation, abundance, relative number of subspecies, parasitism and proportion of polymorphic loci. However, when abundance (population size) was included in the analyses of the other parameters, only coloniality, habitat, total breeding range and abundance remained significantly related to population fluctuations. The analysis including all these predictors simultaneously showed that population size fluctuated more in colonial, less abundant species with larger breeding ranges. Other parameters seemed to be related to population fluctuations only because of their association with abundance or coloniality. The unexpected positive relationship between population fluctuations and total breeding range did not seem to be mediated by abundance. The link between population fluctuations and coloniality suggests a previously unrecognized cost of coloniality. The negative relationship between population size and population fluctuations might be explained by at least three types of non-mutually exclusive stochastic processes: demographic, environmental and genetic stochasticity. Measurement error in population indices, which was unknown, may have contributed to the negative relationship between population size and fluctuations, but apparently only to a minor extent. The association between population size and fluctuations suggests that populations might be stabilized by increasing population size.

Bioenergy and biodiversity: Intensified biomass extraction from hedges impairs habitat conditions for birds

Biomass is increasingly used as an alternative source for energy in Europe. Woody material cut from hedges is considered to provide a suitable complement to maize and oilseed rape, which are currently the dominant biomass sources. Since shrubs and trees are also important habitats for birds, however, coppicing of hedges at the landscape scale may adversely affect the diversity of the avifauna. To evaluate this risk, we estimated the response of hedge birds to three management scenarios differing in cutting intensity and hedge selection. The analysis was done using hedge data of the Lautertal municipality (n = 339 hedges; Vogelsberg area, Hesse, Germany). It focused on 25 bird species, which are all listed in the hedge programme of the German Ornithological Stations. Information on the preferences of these birds for certain hedge features such as height or width was gathered by an extensive literature review. A cluster analysis on the consolidated literature data allowed us to identify three groups of birds according to their preference for certain hedge attributes. Two groups, which included Yellowhammer (Emberiza citrinella L.) (i) and Blackbird (Turdus merula L.) (ii), favoured trees located in hedges, but differed in their preference for hedge shape, with (i) being attracted by long and broad hedges and (ii) by high hedges. The third group, which included the Whitethroat (Sylvia communis L.), preferred small hedges with gaps and medium vegetation density. Spatially explicit suitability models based on these data allowed us to predict the status quo of hedge suitability for these species groups. Field surveys proved the accuracy of the predictions to be sufficient, since the hedge suitability predicted was significantly and positively correlated to the occurrence of 9 out of the 12 testable focal species. Our models predicted biomass extraction to almost always reduce hedge suitability for the three bird groups. Concerning the Yellowhammer and the Blackbird group, a high level of biomass extraction reduced hedge suitability by approximately 20%. We thus conclude that intensively extracting biomass can significantly reduce hedge suitability for birds, despite considerable differences in habitat requirements. Considering the variable response of the bird groups to our scenarios as well as the variation in habitat occupancy by birds, however, cutting woody material from hedges nevertheless provides an option to reduce adverse effects of bioenergy production on biodiversity at the landscape scale, as long as hedge management is based on the best knowledge available.

Genetic diversity, temporal dynamics, and host specificity in blood parasites of passerines in north China

Avian blood parasites have been preliminarily studied in East Asia, but no data are available from long-term monitoring. The aim of this study was to evaluate the prevalence, genetic diversity, and temporal dynamics of Plasmodium, Haemoproteus, and Leucocytozoon in two passerine communities (one forest and one urban) in north China from 2008 to 2013, as well as the association between infected lineages and host specificities. Out of 633 birds from 40 species, 157 individuals (24.8 %) were infected; overall prevalence was 26.7 % and 16.8 % in two sites, respectively. The dominant avian blood parasite genus in the forest park changed yearly between Plasmodium and Haemoproteus, while the Leucocytozoon maintained a low infection level. Forty-four haplotypes were identified by sequencing a 432-bp fragment of the cytochrome b (cyt b) gene; more than 70 % were novel (six Plasmodium lineages, 16 Haemoproteus lineages, and nine Leucocytozoon lineages). Based on our data gathered over consecutive years, we found that the highly observed lineages of Haemoproteus showed higher host diversities than those of Plasmodium, and the most infected lineage EMEL01 (100 % identity with SGS1) take on the highest host diversity but low temporal diversity of the two genera, implying that this lineage infected a great diversity of species in certain years, but maintained a lower infection level or even disappeared in other years. The results suggest that genetic diversity of avian blood parasites in East Asia is high and provides scope for further research. In addition, compared with overall analysis, yearly prevalence monitoring is important in uncovering the temporal dynamic and host specificity variations over time.

Biological consequences of global change for birds

Climate is currently changing at an unprecedented rate; so also human exploitation is rapidly changing the Earth for agriculture, forestry, fisheries and urbanization. In addition, pollution has affected even the most remote ecosystems, as has the omnipresence of humans, with consequences in particular for animals that keep a safe distance from potential predators, including human beings. Importantly, all of these changes are occurring simultaneously, with increasing intensity, and further deterioration in both the short and the long-term is predicted. While the consequences of these components of global change are relatively well studied on their own, the effects of their interactions, such as the combined effects of climate change and agriculture, or the combined effects of agriculture through nutrient leakage to freshwater and marine ecosystems and fisheries, and the effects of climate change and urbanization, are poorly understood. Here, I provide a brief overview of the effects of climate change on phenology, diversity, abundance, interspecific interactions and population dynamics of birds. I address whether these effects of changing temperatures are direct, or indirect through effects of climate change on the phenology, distribution or abundance of food, parasites and predators. Finally, I review interactions between different components of global change.

Brood parasitism correlates with the strength of spatial autocorrelation of life history and defensive traits in Magpies

Environmental characteristics of neighboring locations are generally more similar than those of distant locations. Selection pressures due to parasitism and other environmental conditions shape life history traits of hosts; thus, the probability of parasitism should be associated with the strength of spatial autocorrelation in life history and defensive traits of their hosts. Here we test this hypothesis in three different subpopulations of Magpie (Pica pica) parasitized by the Great Spotted Cuckoo (Clamator glandarius) during three breeding seasons. In some of the years and study plots, we found evidence of positive spatial autocorrelations for clutch size and parasitism rate, but not for laying date. As predicted, brood parasitism was associated with the strength of these spatial autocorrelations. Magpies that bred close to each other in areas of high risk of parasitism responded similarly to experimental parasitic eggs. Moreover, an elevated risk of parasitism eliminated the spatial autocorrelation for clutch size, which became randomly distributed. We discuss possible mechanisms explaining these associations, which may have important consequences for estimating evolutionary responses of hosts to parasitic infections and, therefore, for epidemiological, ecological, and evolutionary studies of host-parasite relationships.

Migratory divides and their consequences for dispersal, population size and parasite-host interactions

Populations of migratory birds differ in their direction of migration with neighbouring populations often migrating in divergent directions separated by migratory divides. A total of 26% of 103 passerine bird species in Europe had migratory divides that were located disproportionately often along a longitudinal gradient in Central Europe, consistent with the assumption of a Quaternary glacial origin of such divides in the Iberian and Balkan peninsulas followed by recolonization. Given that studies have shown significant genetic differentiation and reduced gene flow across migratory divides, we hypothesized that an absence of migratory divides would result in elevated rates of gene flow and hence a reduced level of local adaptation. In a comparative study, species with migratory divides had larger population sizes and population densities and longer dispersal distances than species without migratory divides. Species with migratory divides tended to be habitat generalists. Bird species with migratory divides had higher richness of blood parasites and higher growth rates of Staphylococcus on their eggs during the incubation period. There was weaker cell-mediated immunity in adults and stronger cell lysis in species with migratory divides. These findings may suggest that migratory divides constitute barriers to dispersal with consequences for ecology and evolution of distributions, population sizes, habitats and parasite-host interactions. They also suggest that migratory divides may play a role in local adaptation in host-parasite interactions.