Data from: Climate change and bird reproduction: warmer springs benefit breeding success in boreal forest grouse

Global warming is predicted to adversely affect 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 – a
support of 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 3
weeks, peak of mating advanced only 4-5 days. Contrasting 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.