Patterns of parental care and movement in divided broods of golden-winged warblers

Abstract

Post-fledging brood division is a poorly understood, yet widespread suite of avian behaviours that includes both division of parental care and spatial division of a brood. For most species, the differences in parental care between adult males and females and the behavioural mechanisms explaining spatial patterns of brood division are unknown. We studied brood division in golden-winged warblers Vermivora chrysoptera to describe the spatial and behavioural characteristics of brood division and assess hypotheses describing the potential benefits of brood division. Female golden-winged warblers are known to travel farther from their nests than males within the post-fledging period, although the mechanism resulting in this spatial pattern is unknown. From 2010 to 2012, we monitored radio-marked golden-winged warbler fledglings from fledging until independence from adult care at three sites in the western Great Lakes region of North America. We observed no significant differences in provisioning, parental attendance, daily distance traveled and fledgling begging between male- and female-reared sub-broods. We also did not observe a relationship between parental sex and fledgling sex or mass. However, female-reared sub-broods exhibited a unique period of relatively consistent directional movement on days 8–10 after fledging, which resulted in females traveling farther from the nests than males. Our observations were not fully consistent with any previously proposed hypotheses about the benefits of brood division. Brood division is a complex behaviour that may have a suite of benefits, including predation defense and provisioning efficiency, that are not fully understood.