Nest Mass Variation over the Nesting Cycle in the Pied Flycatcher ( Ficedula Hypoleuca )

Abstract

Nest parameters are most commonly measured only once during the nesting cycle. However, the condition of a nest is not constant but can substantially change from one nesting stage to the other, especially between incubation and nestling periods. These temporal changes may drive modifications in nest characteristics. We investigated the change in nest fresh mass between the early stage of incubation and shortly after the nestlings fledged and examined whether nest dry mass measured after the completion of the nesting cycle, which is commonly used in avian studies, is correlated with initial and final nest fresh mass in a small migratory passerine – the Pied Flycatcher. Nest fresh mass after the nestlings fledged constituted 180% of the initial fresh mass and the magnitude of mass increase was dependent on the number of fledglings and probably was partly associated with increasing water content in nesting material. Nest dry mass was strongly correlated with nest fresh mass measured both at the beginning of incubation and after the nestlings fledged, and also with the number of fledglings. Because in the Pied Flycatcher changes in the nest fresh mass are dependent on brood characteristics, in order to obtain the most reliable estimate of the initial nest fresh mass, we recommend weighing the nest shortly after its completion, taking care to make the measurement when the humidity of the habitat is rather low.