Data from: 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 sustinance, but also opens it to the danger of poisoning by chemically protected food. Dietary conservatism is 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 plascticty 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.

种内竞争者（intraspecific competitors）可通过资源掠夺提升觅食成本。最优觅食理论（optimal foraging theory）指出，当搜寻某一类食物的成本升高时，觅食者应转而接受替代资源。快速接纳新奇食物的个体，在争夺充足营养的竞争中相较于持保守觅食策略的同类更具优势，但同时也面临摄入具有化学防御机制的食物而中毒的风险。饮食保守性（dietary conservatism）指的是在新物恐惧（neophobia，即对新奇物体的初始恐惧）消退后，仍长期回避新奇食物的觅食行为，因此在竞争环境中可能对觅食者不利。觅食者种群内存在两种稳定的觅食策略：（1）冒险型觅食者（adventurous consumers, AC），可快速接纳新奇食物；（2）表现出饮食保守性的觅食者（dietary conservatism, DC）。这两种策略的表达还会随环境条件发生改变。本研究旨在探究种内竞争对野生捕获青山雀（Cyanistes caeruleus）所表现出的饮食保守性水平的影响。实验设置了有竞争者与无竞争者两种条件，为青山雀提供新奇食物与熟悉食物。结果显示，经历过种内竞争的个体比未经历竞争的个体更快将新奇食物纳入其食谱。本研究首次在实验室条件下利用野生鸟类证实了DC性状表达的可塑性（plasticity）程度。这种可塑性是一项重要的适应策略，可在需要接纳新奇替代资源时，降低保守觅食所带来的成本。