Abstract
Global warming is predicted to adversely affect the reproduction of birds, especially in northern latitudes. A recent study in Finland inferred that declining populations of black grouse, Tetrao tetrix, could be attributed to advancement of the time of mating and chicks hatching too early—supporting the mismatch hypothesis. Here, we examine the breeding success of sympatric capercaillie, T. urogallus, and black grouse over a 38-year period in southeast Norway. Breeding season temperatures increased, being most pronounced in April. Although the onset of spring advanced nearly three weeks, the peak of mating advanced only 4–5 days. In contrast to the result of the Finnish study, breeding success increased markedly in both species (capercaillie: 62%, black grouse: 38%). Both brood frequency and brood size increased during the study period, but significantly so only for brood frequency in capercaillie. Whereas the frequency of capercaillie broods was positively affected by rising temperatures, especially during the pre-hatching period, this was not the case in black grouse. Brood size, on the other hand, increased with increasing post-hatching temperatures in both species. Contrary to the prediction that global warming will adversely affect reproduction in boreal forest grouse, our study shows that breeding success was enhanced in warmer springs.
Highlights
A warmer climate is predicted to have pronounced impacts on local fauna and flora [1,2], especially in northern latitudes [3]
In a summary article from a long-term study of the population ecology of capercaillie and black grouse in our study area (Varaldskogen, southeast Norway), we reported that the breeding success of both capercaillie and black grouse increased gradually during a 30-year period from 1979 to 2009 [17]
In a series of regressions, we examined the annual relationships between breeding success and temperature in 13 time periods throughout the breeding season
Summary
A warmer climate is predicted to have pronounced impacts on local fauna and flora [1,2], especially in northern latitudes [3]. In years with high summer temperatures, bilberry will be less exhausted and rebuild their chemical defence quickly, leading to poorer breeding the following year They examined weather records and time-series data on abundances of capercaillie and black grouse and reported an inverse relationship with high summer temperatures during 1 or 2 years before peak bilberry seed production. They predicted that warmer summers would limit grouse reproduction. Expanding the time series to 38 years, we confirm that breeding success was higher—not lower—in warmer springs
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