Collective behaviour in vertebrates: a sensory perspective

Abstract

Collective behaviour models can predict behaviours of schools, flocks, and herds. However, in many cases, these models make biologically unrealistic assumptions in terms of the sensory capabilities of the organism, which are applied across different species. We explored how sensitive collective behaviour models are to these sensory assumptions. Specifically, we used parameters reflecting the visual coverage and visual acuity that determine the spatial range over which an individual can detect and interact with conspecifics. Using metric and topological collective behaviour models, we compared the classic sensory parameters, typically used to model birds and fish, with a set of realistic sensory parameters obtained through physiological measurements. Compared with the classic sensory assumptions, the realistic assumptions increased perceptual ranges, which led to fewer groups and larger group sizes in all species, and higher polarity values and slightly shorter neighbour distances in the fish species. Overall, classic visual sensory assumptions are not representative of many species showing collective behaviour and constrain unrealistically their perceptual ranges. More importantly, caution must be exercised when empirically testing the predictions of these models in terms of choosing the model species, making realistic predictions, and interpreting the results.

Keywords: collective animal behaviour; sensory system; visual acuity; visual field.

Figure 1.

MM and TM outputs comparing the group properties: (a) group polarity, (b) number of groups, (c) average group size and (d) average nearest neighbour distance (NND) for the classic and realistic visual assumptions in the European starling.

Figure 2.

MM and TM outputs comparing the group properties: (a) group polarity, (b) number of groups, (c) average group size and (d) average nearest neighbour distance (NND) for the classic and realistic visual assumptions in the red-winged blackbird.

Figure 3.

MM and TM outputs comparing the group properties: (a) group polarity, (b) number of groups, (c) average group size and (d) average nearest neighbour distance (NND) for the classic and realistic visual assumptions in the golden shiner.

Figure 4.

MM and TM outputs comparing the group properties: (a) group polarity, (b) number of groups, (c) average group size and (d) average nearest neighbour distance (NND) for the classic and realistic visual assumptions in the zebrafish.

Figure 5.

Spatial map illustrating the probability of neighbour presence surrounding an individual (i.e. warmer colours indicate high probability, cooler colours indicate low probability). Values detail the averages per each species represented throughout the entire stimulus duration (3600 time steps).

Figure 6.

Overlap of the visual space of the visual coverage (measured ophthalmoscopically) and interaction distance (derived from the minimum visual acuity and converted into units of body length) comparing the classic parameters used for birds and fish and the realistic visual parameters of the animals used in this study (European starling (EUST), red-winged blackbird (RWBL), golden shiner (GOSH) and zebrafish (ZBFI)). Additionally, we have included other realistic estimates of bird species for which both the visual field and visual acuity information has been measured (American goldfinch (AMGO), American robin (AMRO), Carolina chickadee (CACH), common grackle (COGR), dark-eyed junco (DEJU), and white-crowned sparrow (WCSP)).