Foraging strategies of red squirrels (Sciurus vulgaris L.) in a Scots pine (Pinus sylvestris L.) plantation
Red squirrels (Sciurus vulgaris) returned repeatedly to particular trees (defined as patches) within a Scots Pine (Pinus sylvestris) plantation to feed on pine seed endosperm which they extracted from within the cones (defined as the prey). The present study tested a hypothesis that such Favoured Trees (FTs) allowed faster ingestion of seed endosperm than trees which were avoided. Cone morphometrics and their variability differed markedly amongst trees and FTs had different sized cones than Randomly Selected Trees (RTs). Cones from FTs had markedly more viable seed within them than cones of the same length from RTs. There was more seed in larger cones. Squirrels took longer to extract seed from larger cones. Non-adults took much longer to strip a cone of a given length than did adults, and this difference became significantly greater with increasing cone length. FTs had twice as many cones as RTs but this had a weak effect on the efficiency of finding each cone. However, search efficiency was higher in trees where more cones were eaten in one meal, particularly in spring and summer when feeding was concentrated in trees with lower than average proportions of split cones. A seasonal pattern of cone size selection repeated itself in successive crops which showed adult squirrels preferred trees with middle sized cones but avoided very small and very large cones. Non-adult squirrels selected smaller cones than adults. Avoidance of small cones by adults and the differences between age groups were as predicted by the maximisation of ingestion rate hypothesis, but avoidance of the largest cones by adults was inconsistent with the hypothesis. Inclusion of the increased energetic costs of holding and manipulating larger cones might explain the latter discrepancy. All the other findings of the thesis were consistent with the hypothesis.