The exaggerated begging behaviour of an obligate avian brood parasite is shared with a nonparasitic close relative

TitleThe exaggerated begging behaviour of an obligate avian brood parasite is shared with a nonparasitic close relative
Publication TypeJournal Article
Year of Publication2013
AuthorsRivers, JW, Blundell, MA, Loughin, TM, Peer, BD, Rothstein, SI
JournalAnimal Behaviour
Pagination529 -536
Accession NumberKNZ001591
KeywordsAgelaius phoeniceus, begging, brood parasitism, brown-headed cowbird, Molothrus ater, offspring signalling, red-winged blackbird

Offspring signalling models predict that the begging displays of obligate brood parasites are more intense than nonparasitic species because parasitic young are never reared by their genetic parents and often compete against unrelated host young during development. The brown-headed cowbird, Molothrus ater, has been described as having exaggerated begging relative to nonparasitic species, but an effective test of this idea is lacking because previous studies have not controlled for evolutionary history while simultaneously standardizing rearing conditions. We quantified the begging intensity of cowbirds and the closely related, nonparasitic red-winged blackbird, Agelaius phoeniceus, when both species experienced identical rearing conditions in two distinct nest environments: reared alone by a small cowbird host, or reared with two host young by a moderate-sized cowbird host. Against theoretical predictions, we found that in both nest environments four components of the cowbird begging display were similar to (or less intense than) blackbird begging displays (i.e. latency to beg, begging score, call rate and call amplitude) when nestlings were tested across a gradient of short-term need. Our results provide the first experimental evidence that a closely related, yet nonparasitic, species shares an exaggerated begging display with a brood-parasitic species when reared under conditions typically experienced by parasitic offspring. We discuss three nonexclusive explanations for our findings: (1) relatedness among cowbird nestmates reduced cowbird begging intensity (kin selection hypothesis), (2) reduced body condition of blackbirds elevated their begging intensity (body condition hypothesis) and (3) intense competition in blackbird nest environments led to increased blackbird begging intensity (competitive environment hypothesis).