Nest size is positively correlated with fledging success in Corsican Blue Tits (Cyanistes caeruleus) in an insular oak-dominated habitat mosaic

Avian nests function to provide a safe environment for parents, eggs and nestlings. Positive associations between nest size and other components of breeding performance are expected in two conditions. First, larger nests protect nest occupants better against environmental fluctuations (e.g., weather) than smaller nests. This implies that nest size is a determinant of survival in nest occupants. Second, if reproduction is physically costly, “stronger” parents are expected to be able to build both larger nests and rear more offspring. Here we present the findings of a 17-year correlative nest box study in Corsican Blue Tits ( Cyanistes caeruleus ogliastrae ) that examined the associations between nest size and different aspects of breeding success. We found that females with larger nests produced more fledglings, but did not produce more hatchlings or heavier nestlings than females with smaller nests. The analyses involving nest size controlled for other female characteristics (first-egg date, clutch size, female age) and environmental factors (oak habitat type, weather during the nestling stage) which we assumed could influence aspects of breeding success. Our findings concerning associations between the size of the nest and breeding success differ from those reported in previous studies in other geographic regions, perhaps because the costs that are associated with reproduction or the local environmental conditions that influence breeding performance are population specific. Our correlative study illustrates that avian studies of niche construction may benefit from long-term multi-factor investigations.