The begging of the parasitic Shiny Cowbird (Molothrus bonariensis) chick increases the predation of nests of the host Chalk-browed Mockingbird (Mimus saturninus)

Obligate avian brood parasites chicks may increase the predation risks of the nest in which they are by making it more detectable through their intense begging or by increasing the visit rate of the adult host to the nest. We studied the effect of the presence of the Shiny Cowbird (Molothrus bonariensis) chick on the predation rate of Chalk-browed Mockingbird (Mimus saturninus) nests. This study was carried out at Reserve El Destino (Magdalena-Buenos Aires). In the first experiment (seasons 2011-12 and 2012-13), the clutches were manipulated to beconformed by twomockingbirdand one cowbird chicks or by two mockingbird chicks. Predation rate was higher in the parasitized nests and correlated with a higher proportion of time of total begging produced in those nests. The intensity of begging of cowbird chicks was higher thanintensity of begging of mockingbird chicks, although there was no difference in the rate of feeding visits of the adults to the nest. In a second experiment (seasons 2015-16 and 2016-17), clutches made up of three mockingbird chicks and clutches with two mockingbird and one cowbird chicks were compared. Predation rate was higher in parasitized nests, although the proportion of time of total begging and the feeding rate of adults to the nest was similar between treatments. However, the begging intensity of the shiny cowbird chick was greater than the begging of host chicks. In conclusion, the begging intensity of the parasite chicks increases the predation of the Chalk-browed Mockingbirds nests.