The Blue-and-yellow Tanager accepts parasitic eggs but does not successfully raise parasitic nestlings

LUCIANO N. SEGURA; EXEQUIEL GONZÁLEZ; MONGES, VIRGINIA; ANA PAULA CHIRAMBERRO; GERSTMAYER, PAULA A.; COLOMBO, MARTÍN A.; JAUREGUI, ADRIÁN

Gramado

Congreso; Second Ornithological Congress of the Americas; 2023

Neotropical Ornithological Society & Association of Field Ornithologists

Brood parasites reduce host breeding success and favor the evolution of antiparasitic defenses, such as the parasitic egg/nestling recognition and rejection. The Shiny Cowbird Molothrus bonariensis is a Neotropical generalist brood parasite and the Blue-and-yellow Tanager Rauenia bonariensis has been listed as its host. We monitored 82 host nests (2013-2019) in central-east Argentina and found that 35% were parasitized. Parasitic eggs were accepted in 92% of the nests and hatched in 78.5% of the nests that completed the incubation stage (alone in 18% of the nests, with a single host sibling in 27%, and with two host siblings in 55%). No parasitic nestling survived (92% due to apparent starvation between the second and sixth day of age and 8% due to predation). When the parasitic nestling shared the nest with a host sibling, we only observed the death of the parasitic nestling. In parallel, we videotaped 11 non-parasitized and seven parasitized nests during the nestling stage and observed that hosts delivered exclusively fruits (never insects). Although the ability to recognize and discriminate parasitic nestlings has been suggested as an effective antiparasitic defense mechanism, our results indicate that the null nestling parasite success was more linked to the type of food delivered. Our finding also highlights on the controversial strategies of parasitism of the Shiny Cowbird in terms of host selection, since although our host did not successfully rear any parasitic nestling, the occurrence of parasitism was high, suggesting that there would be little or no host selection by the parasite.