Host Use by Generalist and Specialist Brood Parasitic Cowbirds at Population and Individual Levels

MARIA CECILIA DE MARSICO; BETTINA MAHLER; MANUELA CHOMNALEZ; ALEJANDRO G. DI GIACOMO; JUAN CARLOS REBOREDA

ADVANCES IN THE STUDY OF BEHAVIOR

ELSEVIER ACADEMIC PRESS INC

Año: 2010 p. 83 - 121

0065-3454

We analyzed host use at population and individual levels in the host-generalist shiny cowbird (Molothrus bonariensis) and in the host-specialist screaming cowbird (M. rufoaxillaris). At the population level shiny cowbirds were less generalists than previously assumed and host use varied considerably among regions. There was, however, no clear preference for host species, since we found no associations between frequency of parasitism and host’s body mass, type of nest or genetic distance between host and parasite. Regarding screaming cowbirds, frequency and intensity of parasitism varied among host populations. Parasitic eggs and chicks were equally successful in the primary and secondary hosts, but they experienced high mortality rates when transferred to other suitable, but unused hosts. Screaming and shiny cowbirds overlapped little in host use and had no apparent effect on each other’s success when reared together in a common host. At the individual level, there was an association between mtDNA haplotypes of shiny and screaming cowbird chicks and the hosts in whose nests they were found, indicating that nest choice by parasitic females is not random. We discuss how host imprinting by females can lead to the formation of host specific races and how the occurrence of recognition errors and social learning can lead to the colonization of new hosts.Molothrus bonariensis) and in the host-specialist screaming cowbird (M. rufoaxillaris). At the population level shiny cowbirds were less generalists than previously assumed and host use varied considerably among regions. There was, however, no clear preference for host species, since we found no associations between frequency of parasitism and host’s body mass, type of nest or genetic distance between host and parasite. Regarding screaming cowbirds, frequency and intensity of parasitism varied among host populations. Parasitic eggs and chicks were equally successful in the primary and secondary hosts, but they experienced high mortality rates when transferred to other suitable, but unused hosts. Screaming and shiny cowbirds overlapped little in host use and had no apparent effect on each other’s success when reared together in a common host. At the individual level, there was an association between mtDNA haplotypes of shiny and screaming cowbird chicks and the hosts in whose nests they were found, indicating that nest choice by parasitic females is not random. We discuss how host imprinting by females can lead to the formation of host specific races and how the occurrence of recognition errors and social learning can lead to the colonization of new hosts.