Visual imprinting and auditory-discrimination learning in young of the canvasback and semiparasitic redhead (Anatidae)

Abstract

Laboratory studies were used to determine if visual imprinting and auditory-discrimination learning differ between ducklings of the semiparasitic redhead (Aythya americana) and canvasback (A. valisineria). Both species exhibited visual imprinting, but only canvasbacks exhibited evidence of auditory learning. Brood parasitism in redheads is apparently associated with a reduction in their ability to learn an auditory discrimination, but not in their ability to visually imprint to inanimate models.Canvasback responses were selectively enhanced by calls presented in the absence of a visual-imprinting stimulus. It is suggested that such an enhancement of responses to maternal calls when the parent is heard but not seen could facilitate the maintenance of family units in non-parasitic species like the canvasback. Redheads gave fewer responses to maternal calls than did canvasbacks, and their responses lo calls were virtually unaffected by withdrawal of an accompanying visual stimulus. The reduced auditory responsiveness arid learning in redheads, combined with the reduced effects of visual-stimulus withdrawal, could facilitate the ultimate and biologically necessary separation of these brood parasites from members of the foster species.