We review the concepts and research associated with measuring fear and its consequences for foraging. When foraging, animals should and do demand hazardous duty pay. They assess a foraging cost of predation to compensate for the risk of predation or the risk of catastrophic injury. Similarly, in weighing foraging options, animals tradeoff food and safety. The foraging cost of predation can be modelled, and it can be quantitatively and qualitatively measured using risk titrations. Giving-up densities (GUDs) in depletable food patches and the distribution of foragers across safe and risky feeding opportunities are two frequent experimental tools for titrating food and safety. A growing body of literature shows that: (i) the cost of predation can be big and comprise the forager's largest foraging cost, (ii) seemingly small changes in habitat or microhabitat characteristics can lead to large changes in the cost of predation, and (iii) a forager's cost of predation rises with risk of mortality, the forager's energy state and a decrease in its marginal value of energy. In titrating for the cost of predation, researchers have investigated spatial and temporal variation in risk, scale-dependent variation in risk, and the role of predation risk in a forager's ecology. A risk titration from a feeding animal often provides a more accurate behavioural indicator of predation risk than direct observations of predator-inflicted mortality. Titrating for fear responses in foragers has some well-established applications and holds promise for novel methodologies, concepts and applications. Future directions for expanding conceptual and empirical tools include: what are the consequences of foraging costs arising from interference behaviours and other sources of catastrophic loss? Are there alternative routes by which organisms can respond to tradeoffs of food and safety? What does an animal's landscape of fear look like as a spatially explicit map, and how do various environmental factors affect it? Behavioural titrations will help to illuminate these issues and more.

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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.

Communities of granivorous desert rodents may be influenced by either predation risk or resources. To examine the influence of these factors, I manipulated illumination, using lanterns, and resources, using seeds. Foraging behavior is responsive to changes in predation risk; increased illumination reduces foraging in open areas without cover. Foraging behavior is also affected by resource enrichments. Differences among species in habitat selection are correlated with specific abilities to detect and avoid predators. The least vulnerable species, Dipodomys deserti, foraged heavily in the open and was largely unaffected by treatments; the other species of kangaroo rats and kangaroo mice (Dipodomys merriami, Dipodomys microps, and Microdipodops pallidus) also prefer the open, but responded to both risk and resource manipulations; highly vulnerable Peromyscus maniculatus was restricted to bushes, even under the best of circumstances; Perognathus longimembris was displaced from preferred microhabitats by the presence of kangaroo rats. A correlation between auditory bullar volume and use of open habitat by the various species in this community suggests that predation risk provides an axis along which habitat segregation occurs.Predation can structure communities of mobile prey when risk differs among habitats. Animals specializing in predator avoidance and in exploitation of risky environments have reduced interactions with superior competitors; this promotes coexistence.

Researchers have documented microhabitat partitioning among the heteromyid rodents of the deserts of North America that may result from microhabitat specific predation rates; large/bipedal species predominate in the open/risky microhabitat and small/quadrupedal species predominate in the bush/safer microhabitat. Here, we provide direct experimental evidence on the role of predatory risk in affecting the foraging behavior of three species of heteromyid rodents: Arizona pocket mouse (Perognathus amplus; small/quadrupedal), Bailey's pocket mouse (P. baileyi; large/quadrupedal), and Merriam's kangaroo rat (Dipodomys merriami; large/bipedal). Both kangaroo rats and pocket mice are behaviorally flexible and able to adjust their foraging behavior to nightly changes in predatory risk. Under low levels of perceived predatory risk the kangaroo rat foraged relatively more in the open microhabitat than the two pocket mouse species. In response to the presence of barn owls, however, all three species shifted their habitat use towards the bush microhabitat. In response to direct measures of predatory risk, i.e. the actual presence of owls, all three species reduced foraging and left resource patches at higher giving up densities of seeds. In response to indirect indicators of predatory risk, i.e. illumination, there was a tendency for all three species to reduce foraging. The differences in morphology between pocket mice and kangaroo rats do appear to influence their behavioral responses to predatory risk.