Brood parasitism disproportionately increases nest provisioning and helper recruitment in a cooperatively breeding bird

URSINO, CYNTHIA; DE MÁRSICO, MARÍA CECILIA; MARIELA SUED; A. FARALL; REBOREDA, JUAN CARLOS

Cusco

Congreso; IX Congreso de Ornitología Neotropical y VIII Congreso Peruano de Ornitología; 2011

Brood parasitismdisproportionately increases nest provisioning and helper recruitment in acooperatively breeding bird Cynthia A. Ursino1, María C. De Mársico1, MarielaSued2, Andrés Farall3 and Juan C. Reboreda1 1Departamento de Ecología, Genética y Evolución, Facultad de CienciasExactas y Naturales, Universidad de Buenos Aires.2Instituto del Cálculo, Facultad de Ciencias Exactas y Naturales, Universidadde Buenos Aires.3Departamento deCiencias de la Atmósfera y los Océanos, Facultad de Ciencias Exactas yNaturales, Universidad de BuenosAires.e-mail:cynursino@ege.fcen.uba.ar Obligate avian brood parasites like Cowbirds (Molothrus spp.) lay their eggs in nests of other species (hosts),which raise the parasitic young. Parasiticnestlings often exhibit more exaggerated begging displays than host young for agiven hunger level. A few studies in biparental host species showed that suchintense begging may influence host parental behavior. In contrast, little is knownabout the effect of brood parasitism on parental behaviors in hosts that breedcooperatively. In these species parents are assisted by one or more individuals(?helpers?) that contribute tonestling feeding and nest defense. In this study we used a model selection approach to examine theinfluence of brood parasitism on nest provisioning levels in a cooperativehost, the Baywing (Agelaioides badius),parasitized by the Screaming (M. rufoaxillaris)and Shiny Cowbird (M. bonariensis). We monitored nest contents and group size (parent plus helpers) at 128baywing nests at Buenos Aires Province, Argentina between 2006 and 2010. We video recorded feeding visits by cooperative groupsat 23 nests when nestlings were 3-4, 6-7 and 9-10 days of age. The mostparsimonious model indicated that feeding visits increased with nestling age,group size and number of Cowbird nestlings in the brood. In addition, nestsartificially parasitized by Shiny and Screaming Cowbirds recruited more helpersthan unmanipulated nests having only host or Screaming Cowbird young. Ourresults showed that brood parasitism induced changes in brood demand and Baywingsresponded to these changes by adjusting overall provisioning rates or byrecruiting additional helpers. These findings are in agreement with previousresults showing an effect of parasitic nestlings on host?s parental behaviorand indicate that brood parasitism and cooperative breeding may interact indetermining the levels of parental effort in cooperatively breeding hosts.