Reduced dietary conservatism in a wild bird in the presence of intraspecific competition

The presence of intraspecific competitors can increase foraging costs through exploitation of resources. Optimal foraging theory suggests that when the cost of pursuing one food type increases, alternative resources should be accepted. Accepting novel foods readily might put a competitor at an advantage over its more conservative rivals in the race for sufficient sustenance, but also opens it to the danger of poisoning by chemically protected food. Dietary conservatism is a foraging behaviour characterised by a prolonged avoidance of novel foods, long after neophobia (initial fear of novel objects) has been overcome, and so might be seen as a disadvantage to foragers in a competitive situation. There are two stable foraging strategies found within forager populations: 1) adventurous consumers (AC) which rapidly accept novel foods and 2) foragers showing dietary conservatism (DC). The expression of these two strategies may also vary with environmental conditions. The aim of this study was to investigate the effect of intraspecific competition on the levels of dietary conservatism displayed among wild caught blue tits Cyanistes caeruleus . Blue tits were offered items of both novel and familiar foods under two conditions: with a competitor and without. Our results showed that individuals who experienced competition incorporated the novel items into their diet faster than those who did not experience competition. This study demonstrates, for the first time, the degree of plasticity in the expression of the DC trait using wild birds in laboratory conditions. This plasticity represents a significant adaptation to reduce the costs of foraging conservatively when novel alternative resources should be accepted.