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.当太阳逐渐沉至地平线以下时，眼部受阳光直射更多的猎物物种，在通过视觉监测周边环境以识别威胁时会面临更大阻碍，因此其被捕食的风险也将更高。在一项独特的实验场景中，本研究得以考察某一猎物物种——半蹼滨鹬（Calidris pusilla）的反捕食行为变化，该物种会遭受来自落日大致方向的游隼（Falco peregrinus）的袭击。我预测，随着当日晚些时候太阳眩光带来的干扰愈发严重，该物种的反捕食行为会出现渐进式变化。随着时间推移，当太阳出现眩光时，滨鹬的集群密度会降低；而当云层遮蔽太阳时，集群密度则无此变化，这表明参与高风险觅食活动的个体数量有所减少。当日晚些时候出现太阳眩光时，滨鹬的啄食速率与觅食成功率均会下降，而在无眩光的情况下则无此现象，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，这表明其警觉性提升、变得更为易惊。太阳眩光效应可能会对所有在开阔区域觅食的物种产生影响，不仅在日落时段，在日出时段亦是如此——尤其是当捕食者能够在这些脆弱时段袭击猎物时。因此，太阳眩光效应所构建的捕食风险时间梯度可能具有广泛适用性，并会对反捕食警戒、觅食效率以及栖息地选择产生重要影响。