Breeding phenology in Great and Blue Tits (Parus spp.): are urban populations more resistant to climate change than rural ones?

Abstrakti

Urbanization and climate change are two environmental factors that have most prominently affected breeding phenology of birds during recent decades. We examined such relationships in rural, suburban and urban nest box populations of Great Tits Parus major and Blue Tits P. caeruleus in the capital region of Finland in the 1980s and 1990s. We expected that mild winters and high spring temperatures may advance the breeding season of tits, but less so in urban habitats, where breeding should in any case start earlier than elsewhere. On average, Blue Tits began egg laying a few days earlier in spring than Great Tits. Contrary to expectations, tits bred later in the urban parks of the city than in other habitats, whereas breeding was earliest in suburban areas. It seems that these intermediate habitats, in some way, offer the advantages of both rural and urban habitats. During the study period, the timing of breeding in tits showed advancing temporal trends in rural habitats, and in the Blue Tit also in urban habitats. The effect of increasing winter temperatures on laying dates was mainly minor, but a significant delay emerged in urban Great Tits. The main effect of increasing April temperatures on laying dates was a significant advancement. In urban habitats, however, the advancing effect was in Great Tits significantly stronger and in Blue Tits significantly weaker than in other habitats. The results suggest that breeding of tits may advance also with warming climate but some urban populations might be more resistant to climate change than rural ones.