Central place foraging in a human‐dominated landscape: how do common cranes select feeding sites?

Abstract

Human infrastructure and disturbance play an important role when animals select resources in human‐modified landscapes. Theory predicts that animals trade food intake against costs of movement or disturbance to optimize net energy gain and fitness, but other necessary resources may also constrain the decisions, e.g. when animals repeatedly need to return to a central location, such as a nest, waterhole or night roost. Central place foraging theory states that the probability of occurrence of an animal decreases with the distance to the central location while selectivity for food items or foraging sites providing high net energy gain should increase with distance. We studied foraging patterns of common cranes Grus grus feeding in an agricultural landscape adjacent to a wetland to which they return for night roost. We used availability of spilled grains on harvested fields and distance to human settlement as proxy for site quality (i.e. increased likelihood of increased net energy gain with increased food availability and less disturbance). As predicted by theory, our results clearly show that cranes were more likely (more than twice as high resource selection function scores) to select foraging sites close to roosts. However, contrary to predictions, the selection of high quality sites in terms of high food availability decreased with distance to roost sites. Nevertheless, our results indicate that cranes were more likely to select sites with low risk of human disturbance far from roost sites, and were more tolerant to disturbance close to roost sites. How different species respond to the local and environmental conditions will increase the understanding of the species’ resource requirement, and also where in the landscape to prioritize conservation or management actions (e.g. mitigation of human disturbance and crop damage prevention to sustain agricultural production).

Influences of submerged plant collapse on diet composition, breadth, and overlap among four crane species at Poyang Lake, China

“…Cranes may increasingly depend upon agricultural fields around Poyang Lake, which may, in turn, cause significant crop damage and economic losses. This is especially true on agricultural fields surrounding protected wetlands where waterbirds concentrate in high numbers [ 116 , 117 ]. At Poyang Lake, cranes mainly fed on post-harvest remains of rice seeds and lotus rhizomes; thus, crop damage and economic loss were limited.…”

Selection of a diversionary field and other habitats by large grazing birds in a landscape managed for agriculture and wetland biodiversity

“…Our study was, however, limited to the growing season and to one diversionary field, consequently we could not analyse additional factors known to influence the use and selection of the landscape and consequent variation in damage risk to arable land (e.g. seasonality, distance to roost site, disturbance, agricultural practices, crop nutrient content; Nilsson et al., 2016, 2020; Fox et al., 2017).…”

“…Moreover, additional landscape characteristics (e.g. distance to forest edge, roads, settlements) may affect field selection by large grazing birds and should thus also be considered to maximise use of birds of diversionary fields (Jensen et al., 2017; Nilsson et al., 2020). Knowledge about how large grazing birds respond to the combined strategy of scaring and diversionary fields is limited, but it has been shown that low refuge availability reduced the effectiveness of diversionary feeding and scaring, and that diversionary feeding may cause habitat shift and reduction in activity areas for common cranes (Pekarsky et al., 2021).…”

“…Moreover, additional landscape characteristics (e.g. distance to forest edge, roads, settlements) may affect field selection by large grazing birds and should thus also be considered to maximise use of birds of diversionary fields (Jensen et al, 2017;Nilsson et al, 2020). Knowledge 2).…”

So many choices, so little time: Food preference and movement vary with the landscape of fear

“…Thus, movement is affected by three components: potential energy gain of foraging, energetic losses through movement (and foraging) itself, and potential energy loss through predation risk avoidance. To both maximize gain and minimize risk, the forager could forage closer to its shelter or refuge (i.e., safe place to rest), as described in the central‐place foraging theory (foragers first exploit patches near the central location, except if distant patches have high quality and profitable resources; Bakker et al, 2005; Fryxell, 1999, Nilsson et al, 2020; Orians & Pearson, 1979; Schoener, 1979).…”