Agriculture, Ecosystems and Environment 102 (2004) 403–407 Short communication Factors affecting rice grain density unconsumed by white-fronted geese in relation to wheat damage Tatsuya Amano ∗ , Katsumi Ushiyama, Go Fujita, Hiroyoshi Higuchi Laboratory of Biodiversity Science, School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan Received 6 January 2003; received in revised form 26 August 2003; accepted 10 September 2003 Abstract Lake Miyajimanuma, in central Hokkaido, is an important stopover site for white-fronted geese (Anser albifrons) wintering in Japan. In this area, increasing numbers of the geese are causing damage to wheat crops. The effects of several factors on the unconsumed density of food resources in rice fields, their main foraging site, were investigated with a view to propose a method for reducing damage. It is shown that unconsumed rice grain density increased with decreasing distance from houses, roads and windbreaks, which seemed to act as disturbance factors. Unconsumed rice density was also affected by the type of harvester used, probably because of the difference in net intake rate between the sites where different types of harvester operated. It is recommended that rice fields be harvested using the current machinery, and located further from houses, roads and windbreaks, wheat fields being located nearer to houses, roads and windbreaks. © 2003 Elsevier B.V. All rights reserved. Keywords: Anser albifrons; Crop damage; Disturbance; Unconsumed food density 1. Introduction Farmers have attempted to reduce crop losses by birds, such as geese, using various visual and acoustic scares or by shooting (e.g. Mason and Clark, 1994; Lane and Nakamura, 1996). An alternative approach to avoid agricultural damage is based on the density of resources present within a patch when a forager ceases foraging. Animals show patch preferences and do not exploit patches equally due to spatial or temporal variation in the condition of feeding sites (Valone and Brown, 1989; Begon et al., 1996; Bowers and Breland, 1996). The following two field management measures, therefore, may be successfully used: (1) vulnerable crops should be located in fields with high densities ∗ Corresponding author. Tel./fax: +81-3-5841-7542. E-mail address: tatsu@es.a.u-tokyo.ac.jp (T. Amano). of left over food resources; (2) fields that provide food of no commercial value for animals should be located in fields with low densities of left over food resources. This study aimed at applying this approach to white-fronted geese (Anser albifrons Scopoli) in Lake Miyajimanuma, central Hokkaido, Japan. In this area, geese feed mainly on post-harvest remains of rice, but include growing wheat in their diets (Lane et al., 1998). The decrease of wetlands and rice fields in Japan has reduced goose habitats to particular areas (Kurechi, 1997), whereas the Asian population of A. albifrons is decreasing sharply and needs conservation measures (Ikeuchi, 1996). There are several factors that potentially affect den- sities of unconsumed food. The sensitivity of geese to disturbance is well documented (Vickery and Gill, 1999), and Gill et al. (1996) showed that the extent to which feeding sites are exploited by pink-footed 0167-8809/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2003.09.021