Brown-headed cowbirds are brood parasites. Females, but not males, search for potential host nests in which to lay their eggs. They revisit nests to monitor host egg laying and may even return to nests they have parasitized to determine the fate of their own eggs. We found that females do better than males on spatial navigation tasks but not on touchscreen tests of spatial memory. Females have a larger hippocampus than males but this sex difference also occurs in non-parasitic members of the Icterid family of birds, like red-winged blackbirds. Female brown-headed cowbirds have more hippocampal neurogenesis than males and non-parasitic blackbirds, with a peak in neurogenesis at the end of the breeding season when search for host nests has stopped. Brood parasitism in cowbirds offers a window into the evolutionary modifications of cognition and the brain that accompany specialization in behaviour.
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