Wood warbler population dynamics in response to mast seeding regimes in Europe.

Mast seeding is the episodic, massive production of plant seeds synchronized over large areas. The resulting superabundance of seeds represents a resource pulse that can profoundly affect animal populations across trophic levels. Following years of high seed production, the abundance of both seed consumers and their predators increase. Higher predator abundance leads to increased predation pressure across the trophic web, impacting nonseed consumers such as the wood warbler Phylloscopus sibilatrix through increased nest predation after tree mast years. Over the past 30 years, the frequency of tree seed masts has increased, while wood warbler populations have declined in several regions of Europe. We hypothesized that increasing mast frequencies may have contributed to the observed population declines by creating suboptimal breeding conditions in years after masting. We measured reproductive output in four study areas in central Europe, which was between 0.61 and 1.24 fledglings lower in the years following masting than nonmasting. For each study area, we used matrix population models to predict population trends based on the estimated reproductive output and the local mast frequencies. We then compared the predicted with the observed population trends to assess if the frequency of mast years had contributed to the population dynamics. In Wielkopolska National Park (PL) and Hessen (DE), masting occurred on average only every 4 years and populations were stable or nearly so, whereas in Jura (CH) and Bialowieza National Park (PL), masting occurred every 2 and 2.5 years, respectively, and populations were declining. The simple matrix population models predicted the relative difference among local population trends over the past 10-20 years well, suggesting that the masting frequency may partly explain regional variation in population trends. Simulations suggest that further increases in mast frequency will lead to further declines in wood warbler populations. We show that changes in a natural process, such as mast seeding, may contribute to the decline in animal populations through cascading effects.

Mites inhabiting nests of wood warbler, Phylloscopus sibilatrix (Aves: Passeriformes), in the Wielkopolska National Park in western Poland.

The wood warbler, Phylloscopus sibilatrix (Aves: Passeriformes), is a well-known model organism for studying bird migration, breeding habitat selection and nest predation. The nest acarofauna of this bird species has not been extensively studied so far. To provide a comprehensive report on mite species inhabiting wood warbler nests and to assess infestation parameters (prevalence, intensity, and abundance) for mite species and orders, we collected 45 nests of this bird species in the Wielkopolska National Park in western Poland. Analyses revealed a huge diversity (198 species) of mites inhabiting wood warbler nests. We found individuals belonging to the Mesostigmata, Trombidiformes and Sarcoptiformes. The Trombidiformes, represented in our study only by the Prostigmata, achieved statistically significantly lower intensity and abundance, compared to representatives of other orders. However, the number of recorded prostigmatid species was high (65). The most common were: Stigmaeus sphagneti (22 nests), Stigmaeus longipilis (16), Eupodes voxencollinus (15), Cunaxa setirostris (14), Stigmaeus pilatus (11), and Linopodes sp. 2 (10). The prevalence of Mesostigmata and Sarcoptiformes was equal, reaching 91.1%. Most of Gamasina (Mesostigmata) species found in this study were more characteristic of the soil environment and forest litter than bird nests, but there was also a typical bird parasite, viz. Ornithonyssus sylviarum. None of the observed species of Uropodina (Mesostigmata) or Oribatida (Sarcoptiformes) was typical for bird nests. Among the Uropodina, the highest parameters of nest infestation were achieved by Oodinychus ovalis, whereas among the Oribatida, they were achieved by Metabelba pulverosa. We discuss the importance of wood warbler nests for mite dispersal, survival and reproduction.