Changes of nest mass in relation to nesting stages in the Great Tit Parus major

Abstract

ABSTRACT Capsule Nest mass of the Great Tit Parus major increases over the course of the nesting cycle and the magnitude of the increase between incubation and post-fledging stage is positively correlated with brood size. Aims To investigate whether, in the Great Tit, fresh nest mass changes over the course of the nesting cycle, is correlated with dry nest mass assessed after the nestlings have fledged, and whether temporal variation in fresh nest mass is associated with clutch or brood size. Methods Fresh nest mass was measured at the beginning of egg laying, the beginning of incubation and shortly after the nestlings fledged. Dry nest mass was measured after subjecting nests collected at the end of the nesting cycle to a drying procedure. Results Between the onset of egg laying and early incubation nest mass increased by 14.1%, and between early incubation and post-fledging stage by 69.7%. The magnitude of the increase over the late nesting stage correlated positively with the number of 14 day-old nestlings. Nest dry mass and post-fledging fresh nest mass, but not mass at the early stages of the nesting cycle (egg laying and incubation), were positively correlated with clutch and brood sizes. There was no variation among the nests in the pattern of mass change between the egg laying and incubation stages, while this pattern varied widely between the incubation and post-fledging stages. Conclusions While nests are most commonly weighed after the nestlings have fledged, we suggest that in order to obtain the most reliable estimate of investment in nest building, nests should be weighed during the early stages of the nesting cycle, preferably at the onset of incubation, to avoid brood size-dependent changes in their masses.