Alleviating grazing damage by white‐fronted geese: an optimal foraging approach

Abstract

1.Agricultural damage by wildlife is a serious constraint on the coexistence of humans and wildlife. Understanding the behavioural processes involved in such agricultural damage will inform management actions. In this study, a linear programming model based on optimal foraging theory was used to formulate management strategies designed to reduce wheat damage caused by white-fronted geese Anser albifrons around Lake Miyajimanuma in Japan. 2. Geese feed on rice grains or wheat leaves. Their choice of food is constrained by their daily energy requirement, daily nitrogen requirement, digestive capacity and daily maximum foraging time. With these constraints, we predicted the proportion of geese that should forage on wheat leaves under energy-maximizing, nitrogen-maximizing and timeminimizing strategies, and compared the results with the observed proportion. 3. Our predictions for the energy-maximizing strategy successfully explained the variation in the observed proportion of geese foraging on wheat leaves. It appeared that nitrogen constraints drove the geese to forage on wheat in autumn, but energy considerations drove the geese to forage on wheat plus rice in late spring. 4. Based on these results, we predicted that by increasing the harvest remains of rice by 30%, a large reduction in wheat damage could be achieved both in autumn and in spring. Damage could be reduced further by supplying protein-rich food, such as grass on fallow fields and on ridges of rice fields in autumn, and by leaving geese foraging in rice fields undisturbed. 5. Synthesis and applications. Optimal foraging models that consider foraging goals and constraints have considerable potential for identifying measures for minimizing agricultural damage problems caused by grazing bird species. Specifically, for geese grazing on wheat fields in Japan, we advocate increasing the availability of alternative protein-rich foods, such as rice harvest remains and grass, and minimizing disturbance to geese foraging on rice fields.

Distribution of Barnacle GeeseBranta leucopsisin Relation to Food Resources, Distance to Roosts, and the Location of Refuges

“…Food quality did not seem to affect goose distribution. Indeed, the sites selected by geese were of sufficiently high forage quality (nitrogen concentrations from 2.6% to 5.5%), which was well beyond the limit for Barnacle Geese of 2.4% (Prop & Deerenberg 1991, Amano et al 2004). This lack of food quality effect is different from previous field experimental studies (Bos et al 2005, van der Graaf et al 2007, which demonstrated that fertilized plots were preferred above control plots.…”

“…Small herbivores require a higher nutrient concentration in their diets than large herbivores, as they are less capable of utilizing poor quality plants (Prins & Ydenberg 1985, Durant et al 2004, Prins & van Langevelde 2008. For instance, the Barnacle Goose Branta leucopsis requires food containing more than 15% crude protein to meet nitrogen requirements (Prop & Deerenberg 1991, Amano et al 2004. Furthermore, waterfowl have food retention times as short as a few hours (Prop & Vulink 1992, McKay et al 1994, which is reflected by a high throughput and defecation rate (Owen 1980).…”

Temporal and intrapopulation variation in prey choice of wintering geese determined by stable isotope analysis

“…Hence, when faced with the choice between prey species (all other things being equal), consumers should select the one that will deliver highest energy intake and therefore maximum fitness (Charnov 1976). Although initially thought to be of trivial importance (Pyke, Pulliam & Charnov 1977), recent empirical studies have shown that factors such as nutrient content (McKay, Bishop & Ennis 1994; Hassall, Riddington & Helden 2001), digestibility (Prop & Vulink 1992), or a combination of these factors (Amano et al . 2004; Durant, Fritz & Duncan 2004) may substantially affect resource selection.…”

Habitat use and movement patterns of Northern Pintails during spring in northern Japan: the importance of agricultural lands

“…However, the quality of rice fields as spring habitat for pintails likely depends on how rice is harvested and postharvest treatment of stubble (Shimada 1999, Kross et al 2008). Also, availability of waste rice diminishes with time since harvest (Amano et al 2004, Manley et al 2004). Because spring staging occurred ∼5 mo after most rice had been harvested in Japan, invertebrates and seeds of other moist soil plants in rice fields were likely used by migrating pintails (Stafford et al 2010).…”

“…Because spring staging occurred ∼5 mo after most rice had been harvested in Japan, invertebrates and seeds of other moist soil plants in rice fields were likely used by migrating pintails (Stafford et al 2010). Furthermore, feeding by migrating White‐fronted Geese on the core stopover area in Hokkaido reduced the amount of waste rice available to pintails in spring (Amano et al 2004), likely increasing the importance of other food items.…”