Region-specific neuron recruitment in the hippocampus of brown-headed cowbirds Molothrus ater (Passeriformes: Icteridae)

Avian brood parasites do not raise their own young. Rather, they leave eggs and offspring in nests of other species. Finding potential nests to parasitize is mostly up to the female and requires enhanced spatial memory as the female must remember nest locations as well as whether each located nest is in the nest building, incubation or offspring provisioning stage. In many cases, enhancement of ecologically relevant spatial memory is associated with larger hippocampal volume compared to the sex, or a species, that does not have similar demand for spatial memory. Female brown-headed cowbirds (Molothrus ater), a parasitic species ubiquitous across North America, have greater hippocampus volume and new neuron recruitment as compared to male cowbirds and non-parasitic species. The present study reveals female cowbirds display greater new neuron recruitment compared to males specifically in the rostral hippocampal subdivision. It is still unclear, however, whether the function of new cells in the rostral hippocampus is related to sex differences in spatial memory. These data reveal the avian hippocampus exhibits subdivisions in new cell recruitment but it remains unclear whether these subdivisions serve distinct functions in spatial memory and other hippocampal functions.