title: Host switching in cowbird brood parasites: how often does it occur?
abstract: Avian obligate brood parasites lay their eggs in nests of host species, which provide all parental care. Brood parasites may be host specialists, if they use one or a few host species, or host generalists, if they parasitize many hosts. Within the latter, strains of host-specific females might coexist. Although females preferentially parasitize one host, they may occasionally successfully parasitize the nest of another species. These host switching events allow the colonization of new hosts and the expansion of brood parasites into new areas. In this study, we analyse host switching in two parasitic cowbirds, the specialist screaming cowbird (Molothrus rufoaxillaris) and the generalist shiny cowbird (M. bonariensis), and compare the frequency of host switches between these species with different parasitism strategies. Contrary to expected, host switches did not occur more frequently in the generalist than in the specialist brood parasite. We also found that migration between hosts was asymmetrical in most cases and host switches towards one host were more recurrent than backwards, thus differing among hosts within the same species. This might depend on a combination of factors including the rate at which females lay eggs in nests of alternative hosts, fledging success of the chicks in this new host and their subsequent success in parasitizing it.
authors.affiliation: Departamento de Ecología, Genética y Evolución, and IEGEBA-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: M
authors.initials: M
authors.lastname: Domínguez
authors.affiliation: Departamento de Ecología, Genética y Evolución, and IEGEBA-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: M A
authors.initials: MA
authors.lastname: de la Colina
authors.affiliation: Departamento de Conservación, Aves Argentinas/Asociación Ornitológica del Plata, Buenos Aires, Argentina.
authors.forename: A G
authors.initials: AG
authors.lastname: Di Giacomo
authors.affiliation: Departamento de Ecología, Genética y Evolución, and IEGEBA-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: J C
authors.initials: JC
authors.lastname: Reboreda
authors.affiliation: Departamento de Ecología, Genética y Evolución, and IEGEBA-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: B
authors.initials: B
authors.lastname: Mahler
mesh_terms: D063147:Animal Distribution; D025041:Animal Migration; D000818:Animals; D003163:Competitive Behavior; D051456:Gene Flow; D005819:Genetic Markers; D014644:Genetic Variation; D006239:Haplotypes; D006801:Humans; D008969:Molecular Sequence Data; D009425:Nesting Behavior / Q000502:physiology*; D010058:Oviposition; D046109:Passeriformes / Q000235:genetics / Q000502:physiology*; D013045:Species Specificity
chemical_list: D005819:Genetic Markers
keywords: genetic differentiation; host switches; migration rate; screaming cowbird; shiny cowbird