Evolution of avian visual systems in species with different degrees of sociality

Background

Information provides fitness benefits to organisms because it allows them to assess alternative environmental conditions (relative to food, predators, mates, etc.) before making decisions that will affect their survival and reproduction. For visually oriented vertebrates information is usually obtained through the eyes, which are optical devices that capture and produce an image of the environment where information extraction begins. Birds show a remarkably high inter-specific variability in eye form, shape, optical design, and position in the skull, which leads to different types of visual systems.

A central question is the relative role of anti-predator and food finding behaviors in explaining specializations of avian eyes. This is a relevant evolutionary problem because visual systems specialized in a particular type of prey could constrain the ability to obtain visual information about predation. This creates a potential trade-off in gathering information relevant to different fitness components that is poorly understood, because of the scarcity of comparative data on the different elements of the avian visual systems.

I am particularly interested in the differences in the use of visual information by solitary and social species. Both types of species rely on personal information (obtained through trail-and-error interactions with the environment or experience) to make foraging and anti-predator decisions. However, social species also use social information (obtained through monitoring others’ interactions with the environment) to make similar decisions; thus, their visual environments become more complex. The degree of sociality could affect the sensory trade-off between foraging and predation depending on the relative role personal and social information play in species living in different habitat types.

Goal

To assess the role of different ecological factors (e.g., foraging technique, predation, etc.) in the evolution of avian vision in species with different degrees of sociality

Model species

I focus on the Order Passeriformes, and in particular diurnal species, to minimize phylogenetic noise due to differences in visual systems between orders and the confounding effects of adaptations to night vision.

Methodological approaches

Main contributions (for more details see my papers)

(I) Incorporating inter-specific differences in the configuration of visual fields into classic social foraging models (e.g., producer-scrounger) affects qualitatively and quantitatively their predictions. This suggests that empirical studies should test assumptions as to how model organisms gather visual cues (Trends in Ecology and Evolution 19: 25-31).

(II) Coordination of vigilance in foraging groups has been proposed as a mechanism to reduce the time allocated to visual monitoring and to increase the time spent foraging, which would benefit exploitation of resources in groups. However, coordinated vigilance is favored only when animals have a low probability of detecting predators when head-down (e.g., narrow visual fields), but a high probability of being warned when another member of the group detects a predator (e.g., alarm calls). For other combinations of personal and social information, coordinated vigilance has little value and may even have a negative value, which supports the lack of empirical support for this vigilance pattern in loose foraging aggregations (Behavioral Ecology 15: 898-906).

(III) The effects of the distance between group mates on individual scanning and foraging strategies are similar to those of group size variations in foraging aggregations, which suggest that both factors may be affecting the ‘group-size’ effect simultaneously (Behavioral Ecology 15: 371-379).

(IV) Information about conspecific's behavior can be gathered from head-down postures in species with wide-visual fields, contrary to the assumptions of many theoretical models (Animal Behaviour 69: 73-81).

(V) Individuals are sensitive to differences in the behavior of conspecifics foraging in groups. The intensity of this response increases with the number of conspecifics behaving in a particular way (e.g., an increasing proportion of time scanning or foraging), and decreases with the distance between neighbors due to a reduction in visual contrast and resolution (Behavioral Ecology and Sociobiology 55: 502-511).

(VI) High light intensity (sunlit patches) can negatively affect the transmission of visual information about predator attacks between group members by reducing the ability of individuals to detect subtle changes in the behavior of conspecifics displaying anti-predator responses due to disability glare. This effect could vary the suitability of foraging patches depending on light conditions (In revision).

Plans

(a) To assess how two key visual capacities (visual acuity and the extent of the visual fields) affect social interactions (flock size and neighbor distance) that are associated to anti-predator strategies while animals forage in groups.

(b) To study the visual sensory mechanisms (gaze following, hierarchical representation of visual social stimuli) birds with different levels of sociality use to gather visual social information.