Nest predation and breeding success in Common Treecreepers nesting in boxes and natural cavities

Abstrakti

Most long-term studies of passerine life-history evolution have been based on species that breed readily in nest-boxes . Very few papers deal with data from natural holes. Here we compare the breeding success ofthe Common Treecreeper (Certhia familiaris) between special nest-boxes (southern Finland; 61°N) and natural nesting sites (Lithuania 55°N). The nest-boxes and natural nest sites did not differ in laying date or the frequency of the second clutches . Significant differences were found in clutch size, number of fledglings per breeding attempt and frequency of the replacement clutches . The reproductive rate was lower in natural sites than in nest-boxes, because of the higher nest predation in natural cavities (37% vs . 8% in nest-boxes). The higher predation in natural cavities led to greater frequency of replacement clutches in natural holes. This increased the clutch size, because the Treecreeper lays the largest clutches in the middle of its breeding period . The proportion of nests suffering predation did not vary seasonally . The observed difference in predation may bias conclusions regarding life-history evolution drawn from nest-box studies alone.