The Role of Touch in Prey Density Estimation By Calidris Alba

Abstract

We observed the performances and behaviour of Calidris alba while the birds searched in wet sand for the polychaete Nerine cirratulus by touch alone. The mechanism by which the birds determine the potentially most profitable area so quickly was investigated. The amount of tactile information sampled, was calculated to be far too small to have directed the search of C. alba, if it was assumed that the mechanoreceptors of the bill-tip organ function only, when they are in direct contact with prey. So, as the next logical step, touch perception of remote prey was introduced in the model and a minimal detection distance of 2 cm around the inserted bill tip was calculated. We inferred that remote perception of prey by touch is a common phenomenon in the Calidris genus and probably in some other wader genera too. Therefore, in addition to the definition of hunting types as formulated by Pienkowski (1981, 1982) a third category is proposed: The Plover type (visual), the Sandpiper type (remote touch) and the Oystercatcher type (direct touch). The eco-behavioural data provided us with constraints for the construction of the bill tip organ in a morphological sense by a quantification of the distance of detection.