Data from: Does sun glare increase antipredator behaviour in prey?

As the sun gradually lowers over the horizon, prey species with more sun in their eyes should have more difficulty in visually monitoring their surroundings for threats and thus experience a higher predation risk. In a unique setting, I could examine changes in antipredator behaviour in a prey species, the semipalmated sandpiper (Calidris pusilla), facing attacks by peregrine falcons (Falco peregrinus), which originated from the general direction of the lowering sun. I predicted gradual changes in antipredator behaviour as sun glare becomes more problematic later in the day. As the day progressed, sandpipers occurred in sparser groups when the sun glared but not when clouds obscured the sun, suggesting that fewer individuals engaged in risky foraging. Pecking rate and foraging success decreased later in the day when the sun glared but not otherwise implying an increase in vigilance at the expense of foraging. When more sun hit their eyes, sandpipers also moved faster suggesting increased skittishness. The sun glare effect might be relevant to any species foraging in open areas not only when the sun sets but also when it rises especially if predators can target prey species at these vulnerable times. The temporal gradient in predation risk that the sun glare effect creates might thus apply broadly and have important consequences for antipredator vigilance, foraging efficiency, and habitat use.

当太阳逐渐沉落地平线时，眼部受阳光直射更多的猎物物种，在视觉监控周遭环境以侦测威胁时会面临更大困难，因此遭遇捕食的风险也更高。在一项独特的实验场景中，我得以研究一种猎物物种——半蹼滨鹬（Calidris pusilla）——在面对来自落日方向的游隼（Falco peregrinus）袭击时，其反捕食行为的变化。我预测，随着当日晚些时候阳光眩光问题愈发严重，反捕食行为会逐渐发生改变。随着当日时间推移，当阳光产生眩光时，滨鹬的群体规模会更稀疏；而当云层遮蔽太阳时则无此现象，这表明参与风险觅食的个体数量有所减少。当阳光产生眩光时，滨鹬的啄食速率与觅食成功率会在当日晚些时候下降；反之则无此变化，这意味着它们以牺牲觅食效率为代价，提升了警戒水平。当眼部受阳光直射更多时，滨鹬的移动速度也会加快，这表明它们变得更加易受惊。阳光眩光效应可能对任何在开阔区域觅食的物种都具有影响，不仅在日落时分，在日出时分亦是如此——尤其是当捕食者能够在这些脆弱时段对猎物发起袭击时。因此，阳光眩光效应所构建的捕食风险时间梯度，可能具有广泛的适用性，并会对反捕食警戒、觅食效率以及栖息地利用产生重要影响。