Selection of food patches by sympatric herbivores in response to concealment and distance from a refuge

Abstract

Small herbivores face risks of predation while foraging and are often forced to trade off food quality for safety. Life history, behaviour, and habitat of predator and prey can influence these trade-offs. We compared how two sympatric rabbits (pygmy rabbit, Brachylagus idahoensis; mountain cottontail, Sylvilagus nuttallii) that differ in size, use of burrows, and habitat specialization in the sagebrush-steppe of western North America respond to amount and orientation of concealment cover and proximity to burrow refuges when selecting food patches. We predicted that both rabbit species would prefer food patches that offered greater concealment and food patches that were closer to burrow refuges. However, because pygmy rabbits are small, obligate burrowers that are restricted to sagebrush habitats, we predicted that they would show stronger preferences for greater cover, orientation of concealment, and patches closer to burrow refuges. We offered two food patches to individuals of each species during three experiments that either varied in the amount of concealment cover, orientation of concealment cover, or distance from a burrow refuge. Both species preferred food patches that offered greater concealment, but pygmy rabbits generally preferred terrestrial and mountain cottontails preferred aerial concealment. Only pygmy rabbits preferred food patches closer to their burrow refuge. Different responses to concealment and proximity to burrow refuges by the two species likely reflect differences in perceived predation risks. Because terrestrial predators are able to dig for prey in burrows, animals like pygmy rabbits that rely on burrow refuges might select food patches based more on terrestrial concealment. In contrast, larger habitat generalists that do not rely on burrow refuges, like mountain cottontails, might trade off terrestrial concealment for visibility to detect approaching terrestrial predators. This study suggests that body size and evolutionary adaptations for using habitat, even in closely related species, might influence anti-predator behaviors in prey species.

Keywords: Brachylagus idahoensis; Sylvilagus nuttallii; burrow; concealment cover; mountain cottontail; predation risk; pygmy rabbit; sagebrush‐steppe.

Figure 1

Rabbit species used in our experiments included (A) pygmy rabbit (Brachylagus idahoensis) in front of an 8‐cm diameter plastic tube, and (B) mountain cottontail (Sylvilagus nuttallii) in front of a 10‐cm diameter plastic tube. Plastic tubes were used as artificial burrow refuges in experiments.

Figure 2

A free‐ranging coyote (Canis latrans) looking into the outdoor experimental arenas used in experiment 3, to examine patch choice by pygmy rabbits (Brachylagus idahoensis) and mountain cottontails (Sylvilagus nuttallii). Rabbits were never at risk of mortality in these experiments, but we controlled for behavioral variation from exposure to natural predator cues, such as the sight, smell, or sound of this coyote, by randomizing the order in which individual rabbits received treatments in each of the feeding experiments.

Figure 3

Transparencies placed on the five sides of clear acrylic boxes to create feeding patches that varied in the total amount or orientation of concealment cover. Areas shown in black were opaque, and areas shown in white were transparent, and squares within panels were randomly arranged. For 0%, 25%, 50%, 75%, and 100% concealment cover, the top panel was identical to the four side panels. For the terrestrial concealment, the top panel and upper 17 cm of the side panels were completely transparent, and the lower 27 cm of the side panels were opaque black. For aerial concealment, the top panel and upper 17 cm of the side panels were opaque black.

Figure 4

The average proportion of food consumed by pygmy rabbits (Brachylagus idahoensis) and mountain cottontails (Sylvilagus nuttallii) from the food patch with greater total concealment for each paired concealment cover combination. Both pygmy rabbits and mountain cottontails consumed proportions >0.5 from the most concealed patch across concealment combinations with α = 0.05 and different letters denote significant differences in mean proportions among concealment combinations. Pygmy rabbits and mountain cottontails did not differ in proportions consumed from more concealed patches (P = 0.56) nor was there a species × concealment combination interaction (P = 0.36).

Figure 5

The proportion of food pygmy rabbits (Brachylagus idahoensis) and mountain cottontails (Sylvilagus nuttallii) consumed from the food patch with 50% terrestrial‐only (T) or aerial‐only (A) concealment cover when paired with (A) another patch with 50% concealment cover arranged in a different orientation (i.e., T, A, or R [50% random cover over entire box]) and (B) another patch with either 0% or 100% concealment. Capital letters denote significant differences in mean proportion consumed among concealment combinations for pygmy rabbits, and lower case letters denote differences for mountain cottontails. An asterisk denotes proportions that were significantly different from 0.5 for each species with α = 0.05.

Figure 6

The proportion of food pygmy rabbits (Brachylagus idahoensis) and mountain cottontails (Sylvilagus nuttallii) consumed from the closer food patch when paired with another patch at close (1.5 m), moderate (5 m) or far (8.5 m) distances from the burrow refuge. Paired patches in the close versus moderate and moderate versus far combinations were 3.5 m apart and patches in the close versus far combination were 7 m apart. Different letters denote significant differences among the main effect of distance combinations across rabbit species (i.e., the distance × species combination was not significant). Asterisks denote mean proportions by species and distance combination that were >0.5 with α = 0.05. The proportion consumed in the closer food patch was greater for pygmy rabbits than cottontails for all distance combinations (P < 0.0001).