Animals that feed socially can sometimes better locate prey, often by transferring information about food that is patchy, dense, and temporally and spatially unpredictable. Information transfer is a potential benefit of living in breeding colonies where unsuccessful foragers can more readily locate successful ones and thereby improve feeding efficiency. Most studies on social foraging have been short term, and how long-term environmental change affects both foraging strategies and the associated benefits of coloniality is generally unknown. In the colonial Cliff Swallow (Petrochelidon pyrrhonota), we examined how social foraging, information transfer, and feeding ecology changed over a 40-year period in western Nebraska. Relative to the 1980s, Cliff Swallows in 2016–2022 were more likely to forage solitarily or in smaller groups, spent less time foraging, were more successful as solitaries, fed in more variable locations, and engaged less in information transfer at the colony site. The total mass of insects brought back to nestlings per parental visit declined over the study. The diversity of insect families captured increased over time, and some insect taxa dropped out of the diet, although the three most common insect families remained the same over the decades. Nestling Cliff Swallow body mass at 10 days of age and the number of nestlings surviving per nest declined more sharply with colony size in 2015–2022 than in 1984–1991 at sites where the confounding effects of ectoparasites were removed. Adult body mass during the provisioning of nestlings was lower in more recent years, but the change did not vary with colony size. The reason(s) for the reduction in social foraging and information transfer over time is unclear, but the consequence is that colonial nesting may no longer offer the same fitness advantages for Cliff Swallows as in the 1980s. The results illustrate the flexibility of foraging behavior and dynamic shifts in the potential selective pressures for group living.

中文翻译：

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40 年来，悬崖燕子的群居觅食和群居带来的好处不断减少

群居性进食的动物有时可以更好地定位猎物，通常是通过传递不完整、密集且在时间和空间上不可预测的食物信息。信息传递是生活在繁殖群体中的一个潜在好处，在那里，不成功的觅食者可以更容易地找到成功的觅食者，从而提高饲养效率。大多数关于社会觅食的研究都是短期的，长期环境变化如何影响觅食策略和殖民性的相关利益通常是未知的。在殖民时期的悬崖燕子 ( Petrochelidonpyrrhonota ) 中，我们研究了内布拉斯加州西部 40 年来社会觅食、信息传递和摄食生态的变化。与 1980 年代相比，2016-2022 年的悬崖燕子更有可能单独或以较小的群体形式觅食，花费更少的时间觅食，作为独居者更成功，在更多可变的地点进食，并且较少在栖息地进行信息传递。在这项研究中，每次父母拜访时带回雏鸟的昆虫总量有所下降。随着时间的推移，捕获的昆虫科的多样性不断增加，尽管三个最常见的昆虫科在几十年来保持不变，但一些昆虫类群已从饮食中消失。与 1984-1991 年相比，在消除了外寄生虫混杂影响的地点，2015 年至 2022 年，崖燕雏鸟 10 日龄体重和每个巢中存活的雏鸟数量随群体规模的下降幅度大于 1984 年至 1991 年。近年来，在提供雏鸟期间，成体体重较低，但这种变化并不随蜂群大小而变化。随着时间的推移，社会觅食和信息传递减少的原因尚不清楚，但其后果是，群体筑巢可能不再为悬崖燕提供与 20 世纪 80 年代相同的健康优势。结果说明了觅食行为的灵活性以及群体生活潜在选择压力的动态变化。