Cognitive Ecology in brood parasites: brain, memory and space use

JUAN C. REBOREDA; ROMINA C. SCARDAMAGLIA

Iguazú

Congreso; Ornithological Congress of the Americas; 2017

The adaptive specialization hypothesis proposes that the brain and cognition are adaptively specialized to solve specific ecological problems. Brood parasites such as cowbirds exploit the parental care of other species (hosts) by dumping their eggs in their nests. This parasitic behaviour imposes special demands on information processing: cowbirds should locate host nests, remember their location and return to those nests when they are ready to lay eggs. This cowbird's demand for remembering the precise location and nesting stage of multiple host nests correlates with a relative enlargement of the hippocampus, a brain region involved with spatial information processing in all vertebrates. This enlargement is present in the sex that locates host nests: females of Brown-headed (Molothrus ater) and Shiny Cowbirds (M. bonariensis) and females and males of Screaming Cowbirds (M. rufoaxillaris). We studied the use of space (including daily ranges, communal roost use and host-nest visitation pattern) in radio-tagged Shiny and Screaming Cowbirds and examined comparative aspects of cognition and memory under natural circumstances. Females of both species visited host nests prior to laying and flew directly from the communal roost to target nests around dawn, supporting the hypothesis that they remember their location from previous prospecting behaviour. Daily ranges in females of Shiny Cowbirds and both sexes of Screaming Cowbirds were constant, which is consistent with nest monitoring behavior. Our results illustrate how cognitive adaptations can be studied in the context of field behavioural ecology.