Factors Affecting Gerbil Foraging Behavior and Rates of Owl Predation

Abstract

We experimented on how illumination, habitat structure, and three different species of owls affected the foraging behavior of Gerbillus allenbyi and G. pyramidum, two gerbil species that coexist on sand dune habitats in the Negev Desert, Israel. We also tested how illumination and habitat structure affected rates of predation by owls on the two gerbil species. In a large aviary, we manipulated presence and absence of owls, owl species, presence and absence of illumination, and shrub cover. In response to the presence of owls or to increased illumination, gerbils foraged less, shifted foraging activity to the bush microhabitat, and quit patches at a higher giving—up density of resources. In accord with moonlight avoidance, both gerbil species suffered higher predation rates under illumination than in the absence of illumination. In addition, G. pyramidum distinguished among owl species, as indicated by changes in patch use and habitat selection. Habitat structure also affected foraging behavior and rates of predation. Gerbils foraged less in the open than in the bush microhabitat, foraged less when there was no cover present, and foraged less in the bush microhabitat when patches were encumbered by entangling branches. In accord with avoidance of open areas, both gerbil species suffered higher rates of predation when shrub cover was 0% than when shrub cover was 10%. With 0% cover, G. allenbyi suffered higher predation rates than G. pyramidum, but with 10% cover, rates of owl predation did not differ between gerbil species. Rates of owl predation on the two species corresponded to their natural patterns of macro— and microhabitat partitioning; relative to G. allenbyi, G. pyramidum predominates on open sand dunes and biases its behavior toward the open microhabitat. The results suggest that predation interacts with resource competition to determine the distribution and habitat separation of G. allenbyi and G. pyramidum.

Moonlight avoidance in gerbils reveals a sophisticated interplay among time allocation, vigilance and state-dependent foraging

“…There, gerbils visit fewer resource patches in response to risk factors such as open microhabitat, moonlight, and the presence of predators (e.g. Kotler et al 1991Kotler et al , 1993bBrown et al 1994) and exploit those resource patches less thoroughly (e.g. Kotler et al 1991).…”

“…Examples among other taxa include prairie rattlesnakes (Clarke et al 1996), nocturnal sea birds (Mougoet & Bretagnolle 2000), Galapagos fur seals (Archocephalus galapagoensis; see Trillmich & Mohren 1980) and lake-inhabiting zooplankton (Zaret & Suffern 1976). Moonlight probably makes organisms more conspicuous to their predators (Kotler et al 1991). All may represent examples of the interplay of foraging, risk management and state.…”

“…Increased illumination appears to aid predators such as owls and foxes more than it aids their rodent prey (Kotler et al 1988(Kotler et al , 1991Longland & Price 1991). From the rodent's point of view, it is better that the predator does not encounter the prey, but this is more difficult on bright nights.…”

Chronobiology by moonlight

“…The effect of moonlight as an indirect cue for predation risk for rodents received considerable attention during the last decades [4,[58][59][60]. Rodents are preyed upon by owls and mammalian predators, whose predation efficiency increases during full Moon nights [4,59,61 -64]; consequently, many rodent species reduce activity or shift it to more sheltered habitats [58,65 -70].…”

Relaxation of risk-sensitive behaviour of prey following disease-induced decline of an apex predator, the Tasmanian devil

“…Similar behaviour has been observed in other medium-sized mammals, including free-ranging domestic goats [35], where low, dense vegetation can reduce landscape surveillance and predator detection [13,35]. This contrasts with many small terrestrial prey species such as rodents having higher GUDs in open habitats, which represent higher risk of predation from visual predators such as owls and cats [30,36,37].…”