Host community-wide patterns of post-fledging behavior and survival of obligate brood parasitic brown-headed cowbirds

Abstract

The antagonistic arms races between obligate brood parasites and their hosts provide critical insights into coevolutionary processes and constraints on the evolution of life history strategies. In avian brood parasites—a model system for examining host–parasite dynamics—research has primarily focused on the egg and nestling stage, while far less is known about the behavior and ecology of fledgling and juvenile brood parasites. To provide greater insights into the post-fledging period of generalist brood parasites, we used handheld and automated telemetry systems to examine the behavior and survival of fledgling brown-headed cowbirds (Molothrus ater). Our host community-wide analysis (data on cowbirds fledged from different host species were pooled) shows that fledgling cowbirds’ follow patterns of movement and survival found across the post-fledging literature on parental passerine species. Cowbird fledgling survival was lowest during the first 3 days post-fledging, whereas daily rates of survival neared 100% after about 16 days post-fledging. Cowbird daytime post-fledging activity rates, perch heights, and distance from the natal area all increased with fledging age and young generally gained independence from host parents at 3–4 weeks post-fledging, with approximately the same latency as has been observed in studies on fledglings of cowbird host species. Our research demonstrates how automated telemetry systems can overcome past methodological limitations in post-fledging research and provides an important foundation for future studies examining adaptations that cowbirds and other brood parasites use to exploit hosts during the post-fledging period.