The retrieval of food hoarded by red squirrels inhabiting an urban park

Abstract

Food hoarding is a useful evolutionary adaptation which strongly affects animal fitness. However, its effectiveness depends on the trade-off between costs of gathering supplies and the benefits of using them by a hoarder when other food is hardly available. A field experiment conducted between November and April in a large urban park in Warsaw (Poland) showed that the survival rate of hazelnuts Corylus avellana hoarded by red squirrels Sciurus vulgaris was very low – about half of nuts disappeared from caches within one day, and after 50 days the probability of nut survival was 0.01. The survival rate of hazelnuts cached by squirrels was lower than these hidden in control caches. This difference suggests that squirrel-made caches were recovered by caching individuals and/or robbed by pilferers, both conspecific and heterospecific, more successfully than man-made caches. Moreover, survival rates of nuts deployed in control caches in clumps of trees were lower than in the open space areas avoided by squirrels. The probability of nut survival in a squirrel cache and in the control cache increased with the increasing proportion of days with frost as frozen soil limit squirrel access to cached nuts. The probability of nut survival in a squirrel cache and in control cache in the clumps of trees increased over the study period. We discuss whether food hoarding in the environmental conditions of an urban park where animals are oversupplied with food by humans is beneficial for squirrels or if it is an unimportant imprinted behaviour which does not increase their fitness.