Institute of Vertebrate Biology, Czech Academy of Sciences, Brno, Czech Republic.
Department of Psychology, University of Essex, Colchester, UK.
Anim Cogn. 2022 Aug;25(4):991-1002. doi: 10.1007/s10071-022-01646-0. Epub 2022 Jul 1.
Egg rejection is a crucial defence strategy against brood parasitism that requires the host to correctly recognise the foreign egg. Rejection behaviour has, thus, evolved in many hosts, facilitated by the visual differences between the parasitic and host eggs, and driving hosts to rely on colour and pattern cues. On the other hand, the need to recognise non-egg-shaped objects to carry out nest sanitation led birds to evolve the ability to discriminate and eject objects using mainly shape cues. However, little is known regarding the evolutionary significance of rejection behaviour in general and the cognitive processes underlying it. Here, we investigated the response of the barn swallow (Hirundo rustica) during pre-laying and laying stages to four objects types that differed in shape (eggs vs stars) and colour/pattern (mimetic vs non-mimetic) to investigate (1) what cognitive mechanisms are involved in object discrimination and (2) whether egg rejection is a direct defence against brood parasitism, or simply a product of nest sanitation. We found that swallows ejected stars more often than eggs in both stages, indicating that swallows possess a template for the shape of their eggs. Since the effect of colour/pattern on ejection decisions was minor, we suggest that barn swallows have not evolved a direct defence against brood parasitism but instead, egg ejection might be a product of their well-developed nest sanitation behaviour. Nonetheless, the fact that mimetic eggs were ejected especially in the pre-laying stage shows that nest sanitation could be an effective defence against poorly timed brood parasitism.
卵的排斥是一种针对巢寄生的关键防御策略，宿主需要正确识别外来卵。因此，在许多宿主中，通过寄生卵和宿主卵之间的视觉差异，以及驱使宿主依赖颜色和图案线索，排斥行为得到了进化。另一方面，为了识别非卵形物体以进行巢清洁，鸟类进化出了主要使用形状线索来区分和排出物体的能力。然而，对于排斥行为的一般进化意义及其背后的认知过程，我们知之甚少。在这里，我们研究了在产卵前和产卵阶段，仓鸮（Hirundo rustica）对四种形状不同（卵与星）和颜色/图案不同（拟态与非拟态）的物体类型的反应，以调查（1）物体识别涉及哪些认知机制，（2）卵的排斥是否是针对巢寄生的直接防御，还是仅仅是巢清洁的产物。我们发现，在两个阶段，仓鸮排出的星比卵多，这表明仓鸮对其卵的形状有一个模板。由于颜色/图案对排出决策的影响较小，我们认为仓鸮没有进化出针对巢寄生的直接防御，而是卵的排出可能是其发达的巢清洁行为的产物。尽管如此，拟态卵尤其是在产卵前阶段被排出的事实表明，巢清洁可能是针对时机不佳的巢寄生的有效防御。
