Food Consumption in Relation to Habitat in Breeding Chickadees

IN 1959 Dr. W. H. Drury, Jr., Director of the Hatheway School of Conservation Education at Drumlin Farm, invited me to come to Massachusetts to carry out some ornithological investigations in behalf of the Massachusetts Audubon Society. The Black-capped Chickadee (Parus atricapillus) was chosen for this study because it is easy to watch and because it would be possible to compare its biology with that of European tits, which I have studied for many years (Kluyver, 1950, 1951, 1952, 1957; Kluyver and Tinbergen, 1953). Both European deciduous and coniferous woods are inhabited by tits (Parus species), and each species has a typical habitat. One species, the Great Tit (Parus major), although mainly adapted to deciduous woods, will also inhabit pine woods, where insects suitable for its food (in spring mainly caterpillars, as these larvae are large enough for feeding nestlings) are relatively scarce. Moreover, in European pine woods the Great Tit meets serious food competition from other species of tits, whose methods of hunting insects are better adapted to pine-wood conditions. Pine wood is, therefore, a marginal habitat for this species, with reproduction being lower and mortality higher than in deciduous woods. Because it is the only species of Parus in eastern Massachusetts, the Black-capped Chickadee does not meet with any competition from allied species and lives in both types of wood. Natural mixed woods probably are its favorite habitat, where it hunts insects in both broadleaved trees and pines. It nests, at least in Massachusetts, primarily in dead birches. From my European experience I expected deciduous woods to contain more preferred food insects (both species and individuals) than pine. The object of my study was to investigate if and to what extent some of the factors that control population densityespecially reproduction and nestling mortality-are influenced by the availability of caterpillars and other food resources. Moreover, I wanted to study details of nest building and breeding biology, as well as dispersal of adults and young in the postreproductive season.