Hazardous duty pay and the foraging cost of predation

Abstract

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.

An island-wide predator manipulation reveals immediate and long-lasting matching of risk by prey

“…Our findings suggest that mice are indeed cognizant of the abundance of their fox predators, and that the way mice respond to this increase in fox foraging depends upon environmental context. Moreover, our longterm time series provides support for changes in behaviour predicted by theory and smaller scale studies [32]: within the range of resources provided in our foraging trays (i.e. 4.73 g of seeds), anti-predator behaviour of mice is asymptotic ( figure 2).…”

“…First, we considered the log-transformed difference in rodent foraging between sheltered and exposed trays as a response variable, including sampling session and the interaction of session with day of sampling within a session and sampling site as random effects and fox abundance (log-transformed), risky versus safe night (night) and the interaction of fox abundance and night as fixed effects. The log-transformed difference between sheltered and exposed micohabitats reflects the change in foraging attributable to predation risk [32] and is thought to be less sensitive to changes in rodent density [35], as confirmed by our analyses (see Results; see also the electronic supplementary material). Second, we also considered the absolute value of seeds remaining in each tray as a response variable, with fox abundance, microhabitat (sheltered versus exposed) and the interaction of fox abundance and microhabitat as fixed effects, and the same random effects as above.…”

“…On nights when clear weather likely made foraging more risky for mice, the difference in rodent foraging between sheltered and exposed microhabitats is expected to increase as fox abundance (and thus predation risk) increases because rodents should spend more time foraging in safe microhabitats relative to risky ones [31,32]. On nights when overcast conditions, low moon illumination, or precipitation made foraging less risky for mice, we would expect reduced differences between sheltered and exposed trays, because overall foraging conditions are expected to be equalized between these habitats on safe nights.…”

Predation in bird populations

“…Animals always pay a cost to reduce predation risk when they can (Brown et al 1999;Brown and Kotler 2004). Costs arise from behaviours that enhance short term survival in the presence of the predator, but that decrease long term fitness, such as body condition or reproductive potential (see Preisser et al 2005).…”

Assessing habitat quality of farm-dwelling house sparrows in different agricultural landscapes

“…Reduced habitat heterogeneity at multiple spatial scales, resulting from this 46 agricultural intensification, has been suggested to be the general cause of the decline of farmland 47 6 energy. The driving factor that determines how animals respond to the quality of the 110 environment, thereby influencing GUDs, is often the food availability in the area ( predation, that a certain habitat imposes on a forager (for a review, see Brown and Kotler 2004). 120…”