Foraging mode shift in varying environmental conditions by dunlin Calidris alpina

Abstract

Predators may have a series of alternative foraging modes. Under the food resource maximization hypothesis, predators are expected to shift between foraging modes such that they attain the highest intake rate in response to prey availability and constraints varying with environmental conditions. To test this hypothesis, we measured foraging action rate (actions per unit time), capture rate (captures per unit time), and intake rate (amount of energy and nutrients per unit time) for 2 foraging modes, pecking (feeding on epifauna at the sediment surface) and probing (feeding on infauna by inserting the bill into the sediment), in dunlin Calidris alpina on an intertidal sandflat. The birds chose their foraging mode to attain higher feeding success, i.e. individuals that obtained higher capture and intake rates by pecking allocated a higher proportion of foraging effort to pecking, and vice versa. The birds shifted foraging mode from probing to pecking with increased time after emersion. The shift may be related to decreasing efficiency of probing due to increases in the costs of energy and time caused by decreasing sediment penetrability (increasing hardness) with time after emersion. Our in situ study empirically suggests that, while environmental constraints reduce the predators' foraging mode flexibility, the birds show individual-based appropriate adjustments in their foraging mode to attain a higher intake rate at a given time and patch. This extends the ideal forager model for patch choice into foraging mode choice. KEY WORDS: Decision making · Feeding ecology · Foraging behavior · Intertidal ecosystems · ShorebirdsResale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESS

Shifts in foraging behavior of wintering Hooded Cranes (Grus monacha) in three different habitats at Shengjin Lake, China

“…We used the relative importance of each AIC and their weight, w i (i = 1, … 16) for drawing inferences from each model. To calculate the relative importance of each explanatory variable in a candidate model, we added the weights of all explanatory variables contained in each candidate model (Kuwae et al 2010).…”

Effects of variation in food resources on foraging habitat use by wintering Hooded Cranes (Grus monacha)

“…Fortunately, the cranes adjusted with a spatial redistribution and made trips to mediate its effects while searching further afield for alternative food items. Positive relationships between wader foraging habitat use and food abundance have also been found in other studies (Backwell et al 1998;Folmer et al 2010;Kuwae et al 2010), while Lantz et al (2011) and Beerens et al (2011) argue that food accessibility is also important. It is more profitable for cranes to raise the benefits/cost ratio of food accessibility simultaneously while avoiding deeper food items and harder sediment (Kuwae et al 2010;Baschuk et al 2012;Clausen et al 2012).…”

Effect of water level fluctuations on temporal-spatial patterns of foraging activities by the wintering Hooded Crane (Grus monacha)

“…The survey results from each 20 min period were used as an independent sample from which we calculated the foraging frequency (changes in behavior per unit of time), length of foraging time (the total time of foraging bouts) and foraging time budget [26,42,44]. Foraging success was quantified by analyzing the recordings of foraging birds and budgeting their time in foraging bouts [4].…”

“…variation in food availability, waterbirds have to change their wintering habitats and behavior patterns in order to obtain sufficient energy for wintering [1,4]. For many waterbirds, fluctuations in water levels change birdperched micro-habitats [5] and directly affect the length of exposure to and availability of food in these habitats [6,7].…”