Eye size across avian lineages covaries with participation in a specialized foraging behavior

Foraging ecology and visual ability are often strongly related across
animal lineages, as many organisms identify food sources by sight. Birds
particularly rely upon vision to seek out prey or other food items,
leading to the correlated evolution of eye size and foraging behavior.
Here, we focus on a specialized foraging tactic termed ‘disturbance
foraging’, whereby a responding species exploits prey items flushed by a
disturbing species. Using global databases of disturbance-responder
species and eye size measurements from museum specimens, we tested the
prediction that relative eye size accounting for body mass allometry (a
proxy for visual acuity and sensitivity) would be larger in disturbance
foragers that require enhanced visual performance to locate escaping prey
(N = 463) compared to other species (N = 2840). As predicted, disturbance
foragers possessed larger relative eye sizes. Residual eye size was
correlated with a gradient in avian foraging behavior, such that species
with the smallest and largest relative eye sizes were near-sighted and
far-sighted non-disturbance foragers, respectively, while disturbance
foragers had intermediate eye sizes. Birds appeared to invest similarly in
acuity and sensitivity in relation to foraging behavior as measured by
their respective anatomical proxies (residual axial length (AL) and cornea
diameter (CD)), although there was partial evidence that some species
groups invested more in acuity based upon the eye shape ratio (CD/AL).
These patterns imply that even highly specialized behavioral tactics may
evolve in concert with their respectively linked neurological and sensory
systems.

在各动物类群中，觅食生态与视觉能力往往存在强关联——诸多生物均通过视觉识别食物来源。鸟类尤为依赖视觉搜寻猎物或其他食物，这使得眼球尺寸与觅食行为产生协同演化。
本研究聚焦于一种被称为干扰觅食（disturbance foraging）的特化觅食策略：即响应物种利用被干扰物种惊起的猎物。我们借助全球干扰-响应物种数据库与博物馆标本的眼球尺寸测量数据，验证了如下假设：相较于其他物种（N=2840），依赖增强视觉性能以定位逃逸猎物的干扰觅食者（N=463），其校正体重异速生长的相对眼球尺寸（作为视觉敏锐度与敏感度的替代指标）更大。
正如假设所示，干扰觅食者的相对眼球尺寸确实更大。残差眼球尺寸与鸟类觅食行为的梯度存在显著关联：相对眼球尺寸最小的物种为近视型非干扰觅食者，最大的则为远视型非干扰觅食者，而干扰觅食者的眼球尺寸处于中间水平。
从解剖学替代指标（残差眼轴长度（axial length, AL）与角膜直径（cornea diameter, CD））来看，鸟类在视觉敏锐度与敏感度上的投入似乎与觅食行为相匹配；不过亦有部分证据表明，部分类群基于眼形比率（CD/AL）更多地投入于视觉敏锐度的提升。
上述研究结果表明，即便是高度特化的行为策略，也可能与其关联的神经与感觉系统协同演化。