Indirect risk effects reduce feeding efficiency of ducks during spring

Abstract

Indirect risk effects of predators on prey behavior can have more of an impact on prey populations than direct consumptive effects. Predation risk can elicit more vigilance behavior in prey, reducing the amount of time available for other activities, such as foraging, which could potentially reduce foraging efficiency. Understanding the conditions associated with predation risk and the specific effects predation risk have on prey behavior is important because it has direct influences on the profitability of food items found under various conditions and states of the forager. The goals of this study were to assess how ducks perceived predation risk in various habitat types and how strongly perceived risk versus energetic demand affected foraging behavior. We manipulated food abundance in different wetland types in Illinois, USA to reduce confounding between food abundance and vegetation structure. We conducted focal‐animal behavioral samples on five duck species in treatment and control plots and used generalized linear mixed‐effects models to compare the effects of vegetation structure versus other factors on the intensity with which ducks fed and the duration of feeding stints. Mallards fed more intensively and, along with blue‐winged teal, used longer feeding stints in open habitats, consistent with the hypothesis that limited visibility was perceived to have a greater predation risk than unlimited visibility. The species temporally nearest to nesting, wood ducks, were willing to take more risks for a greater food reward, consistent with an increase in a marginal value of energy as they approached nesting. Our results indicate that some duck species value energy differently based on the surrounding vegetation structure and density. Furthermore, increases in the marginal value of energy can be more influential than perceived risk in shaping foraging behavior patterns. Based on these findings, we conclude that the value of various food items is not solely determined by energy contained in the item but by conditions in which it is found and the state of the forager.

Worth the reward? An experimental assessment of risk‐taking behavior along a life history gradient

“…We conclude that species' life history strategies in addition to other factors (e.g. habitat structure, Behney et al 2018) work to shape the amount of risk female ducks are willing to engage in while foraging.…”

“…The adjacent control plot did not receive any corn. It is unlikely that corn kernels could have spread into control plots and based on 10 food samples taken in each plot at the time of treatment, and again three weeks later (see Behney for details on food sampling), no corn was detected in control plots. Treatment plots received corn treatments once each year and the treatment of plots was staggered throughout the study period to ensure a recently treated plot was always available throughout the study period.…”

“…Random effects included focal sample nested within block and we included site as a fixed effect because we only had two sites. We included flock size (log transformed to facilitate model convergence) in all models due to the abundant literature documenting effects of group size on vigilance (Powell 1974, Caraco 1979a and in our study system, Behney et al (2018) found that flock size was an important predictor of feeding intensity of mallards and wood ducks. We ran models including life history characteristics alone and in additive and interactive relationships with food treatment.…”

Effect of Habitat Management on Duck Behavior and Distribution During Spring Migration in Indiana

“…These factors may result in waterfowl using habitats with lower food densities (Morrison 2002). Predation risk evokes a trade-off between vigilance and feeding behavior in foraging animals (Brown 1999) and during an individual foraging bout, the proportion of time an individual spends feeding relative to being vigilant likely depends on both forage density and perceived predation risk (Schoener 1971;Hill and Ellis 1984;McNamara and Houston 1994;Verdolin 2006;Bednekoff 2007;Behney et al 2018). Because direct assessment of food availability and predation risk is difficult, many birds use habitat characteristics, such as cover, to judge the predation risk and potential food density of a habitat, and therefore the quality of that habitat (van der Wal et al 1998;Rowcliffe et al 1999).…”

“…Because direct assessment of food availability and predation risk is difficult, many birds use habitat characteristics, such as cover, to judge the predation risk and potential food density of a habitat, and therefore the quality of that habitat (van der Wal et al 1998;Rowcliffe et al 1999). Previous research has shown mixed results on the effect of cover on predation risk (Davis 1973;Underwood 1982;Behney et al 2018), and therefore assessing both distribution and behavior can provide insight into perceptions of animals. Behavioral observations may be particularly useful for migratory populations whose numbers are variable and where scheduled bird counts may miss large influxes of birds (Webster et al 2002).…”