Foraging pigs alter their behaviour in response to exploitation

Abstract

When food finders are exploited by others, but cannot themselves switch to scrounging or leave their foraging group, other behavioural adaptations should be favoured. Tactical deception in primates and foraging at the periphery of the group in ground-feeding birds have been suggested as two such responses. We show that exploited individuals may also respond by adjusting their foraging behaviour to the concurrent behaviour of the scroungers. We investigated the foraging strategies of exploited subordinate domestic pigs, Sus scrofa. Pairs of pigs were tested in competitive foraging trials. We trained the subordinate pig in each pair to use a producing tactic in competitive pair trials by informing it about the location of hidden food during a preceding search trial in which it foraged alone. The dominant pig was naı̈ve about the food location in the competitive trials but able to displace the subordinate from the food source. We have shown previously that the dominants scrounged on their coforagers in these competitive trials by following them and displacing them from the food source. In the present study, logistic regression analyses show that the food-finding subordinates altered their foraging behaviour depending on the current behaviour of the dominants. Overall, the subordinates were more likely to show food-directed behaviour when the chances of arriving at the food source ahead of their exploiters were higher. The foraging behaviour of individual subordinates was related to their exploitation experience. Individuals subjected to higher exploitation pressure showed more varied strategies. These behavioural strategies are most simply interpreted as attempts by the exploited food finders to increase the time they can spend at the food source before the scroungers arrive. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.