The visual fields of two ground‐foraging birds, House Finches and House Sparrows, allow for simultaneous foraging and anti‐predator vigilance

Abstract

In birds, differences in the extent and position of the binocular visual field reflect adaptations to varying foraging strategies, and the extent of the lateral portion of the field may reflect anti-predator strategies. The goal of this study was to describe and compare the visual fields of two ground-foraging passerines, House Finch Carpodacus mexicanus and House Sparrow Passer domesticus . We found that both species have a binocular field type that is associated with the accurate control of bill position when pecking. Both species have eye movements of relatively large amplitude, which can produce substantial variations in the configuration of the binocular fields. We propose that in these ground foragers, their relatively wide binocular fields could function to increase foraging efficiency by locating multiple rather than single food items prior to pecking events. The lateral fields of both species are wide enough to facilitate the detection of predators or conspecifics while head-down foraging. This suggests that foraging and scanning are not mutually exclusive activities in these species, as previously assumed. Furthermore, we found some slight, but significant, differences between species: House Sparrow binocular fields are both wider and vertically taller, and the blind area is wider than in House Finches. These differences may be related to variations in the degree of eye movements and position of the orbits in the skull.

The subtlety of simple eyes: the tuning of visual fields to perceptual challenges in birds

“…Frequently, the perceptual challenges associated with moving, foraging and exposure to predation will occur simultaneously, or there may be rapid switching between them. For example, a foraging bird may require information to guide the detection of a food object while at the same time needing information on predatory dangers [46,47]. It may also instantaneously require information to control flight once a predator has been detected.…”

“…For example, in a particular species, the gaining of specific information to optimize the detection of food may not optimize the way information is gained for the detection of predators. Indeed, it has often been assumed that because these informational demands are so dissimilar, the tasks of foraging and of predator detection cannot be conducted simultaneously and require a bird to switch between discrete behaviours in order to carry them out [46,48,49]. As well as different tasks providing conflicting demands for different information, it is also possible that the optimal solutions for gaining information for the conduct of a particular task may pose apparently insurmountable problems when birds are faced with a new set of tasks.…”

Tolerance of disturbance by humans in long-time resident and recent colonist urban doves

“…First, some species' visual fields probably permit surveillance for predators during head-down foraging (Fernández-Juricic et al 2008), although this may be less of an issue when, as here, closely-related species (which probably have similar visual fields) are being compared. Second, even when species' proportional vigilance time allocations are similar, differences in scanning regime structure may nonetheless result in disparate predator detection efficacies (Fernández-Juricic 2012).…”

First to Flush: The Effects of Ambient Noise on Songbird Flight Initiation Distances and Implications for Human Experiences with Nature

“…Most birds rely on vision for both foraging and vigilance and can maintain vigilance while searching for food through peripheral vision and frequent movement of the head and eyes to maximize the visual field (Lima and Bednekoff, 1999;Fernández-Juricic et al, 2008). These behaviors, as well as adapted visual fields, are thought to be primarily determined by feeding ecology (Martin, 2007).…”

“…These behaviors, as well as adapted visual fields, are thought to be primarily determined by feeding ecology (Martin, 2007). Ground foraging birds generally have wide lateral visual fields and engage in frequent head movements to compensate for time spent head-down looking for food (Fernández-Juricic et al, 2008, 2010. Thus, we hypothesize that ground foraging species rely heavily on acoustic cues for threat detection while foraging and predict that they are more susceptible to the effects of masking in noisy conditions and will exhibit decreasing FIDs as noise increases (Figure 1).…”