The cognitive-buffer hypothesis proposes that more harsh and unpredictable environments favour animals with larger brains and resulting greater cognitive skills. Comparisons across taxa have supported the hypothesis, but it has rarely been tested within a species. We measured brain size, as inferred from head dimensions, for 1141 cliff swallow specimens collected in western Nebraska, 1982–2018. Cliff swallows starving to death during unusual late-spring cold snaps had significantly smaller brains than those dying from other causes, suggesting that brain size in this species can affect foraging success and that greater cognitive ability may confer advantages when conditions exceed normal environmental extremes. Brain size declined significantly with the size of the breeding colony from which a specimen came. Larger brains may be favoured in smaller colonies that represent more unpredictable and more challenging social environments where there is less public information on food sources and less collective vigilance against predators, even in relatively normal conditions. Our results provide intraspecific support for the cognitive-buffer hypothesis and emphasize the potential evolutionary impact of rare climatic events.

认知缓冲假说提出，更恶劣和不可预测的环境有利于大脑更大，认知能力更高的动物。整个分类单元的比较都支持该假设，但很少在一个物种中进行过测试。我们从头颅尺寸推算出了1982-2018年间在内布拉斯加州西部采集的1141份悬崖燕子标本的大脑大小。悬崖燕子在异常的春季寒风中饿死，其大脑比其他原因死亡的燕子要小得多，这表明该物种的大脑大小会影响觅食的成功，而当条件超过正常的极端环境时，更大的认知能力可能会带来优势。脑大小随样本来源的繁殖群体的大小而显着下降。较大的大脑可能在较小的殖民地受到青睐，较小的殖民地代表着更加不可预测和更具挑战性的社会环境，在这些环境中，即使在相对正常的条件下，有关食物来源的公共信息较少，对掠食者的集体警惕性也较低。我们的结果为认知缓冲假说提供了种内支持，并强调了罕见气候事件的潜在进化影响。