Timing of breeding in subarctic passerines in relation to food availability

Abstract

We studied timing of breeding in four species of hole-nesting passerines, the Siberian tit (Poecile cinctus), great tit (Parus major), pied flycatcher (Ficedula hypoleuca), and redstart (Phoenicurus phoenicurus), and the abundance of the arthropods in their diet (ground-dwelling spiders, winged insects, foliage-feeding lepidopteran and hymenopteran larvae) in Finnish Lapland for 6-12 years. Densities of the invertebrate groups varied considerably, both seasonally and annually. All the bird species started to breed in early summer, when weather conditions were often poor. At the beginning of the breeding season all species relied on ground-dwelling spiders, whose abundances peaked early and were less variable over the years than those of insects. Abundances and timing of emergence of caterpillars in birch and pine canopies (the major food sources for foliage-gleaners) were highly variable, but each year their abundances peaked in July or August, after the nestling period of the birds. This contrasts with r...