Have brood parasitic cowbird nestlings caused the evolution of more intense begging by host nestlings?

Please cite this article in press as: Rivers, J.W host nestlings?, Animal Behaviour (2010), d Obligate avian brood parasites rely entirely on host species to raise their offspring, a unique behaviour that has made them an ideal group for a wide variety of ecological and evolutionary topics (Rothstein 1990; Davies 2000). Because brood parasites are raised by heterospecific parents and often share the nest with unrelated host nestlings (Rothstein 1990; Davies 2000), they are typically influenced only by the direct costs of begging (i.e. predation and growth costs; Dearborn 1999; Chappell & Bachman 2002; Haskell 2002; Johnstone & Godfray 2002) and have served as a model for studies of parental care, parenteoffspring conflict and nestling begging behaviour. Theory predicts that brood parasitic offspring should evolve more exaggerated begging displays than nonparasitic species for a given level of need (Harper 1986; Motro 1989; Holen et al. 2001), and a number of investigations have confirmed that parasitic nestlings show exaggerated begging vocalizations and postures relative to host species (Davies et al.