Landscape and field characteristics affecting winter waterfowl grazing damage to agricultural perennial forage crops on the lower Fraser River delta, BC, Canada

Abstract

The lower Fraser River delta is an important waterfowl staging area on the lower coast of British Columbia, Canada. Since the early 1980s, wintering waterfowl have been causing economically significant damage to perennial forage fields (hay, pasture and silage). We examined the effect of farm management practices and landscape attributes on the extent of grazing damage on a total of 196 perennial forage fields between 2001 and 2005. Multiple regression analysis and an information-theoretic model comparison approach were used to identify field and landscape parameters that account for variation in damage. Rather than limit our evaluation to single-species use of forage crops, we considered the combined grazing impact of a complex of wintering waterfowl, including lesser snow goose (Chen caerulescens), American wigeon (Anas americana), mallard (Anas platyrhynchos), northern pintail (Anas acuta), and trumpeter swan (Cygnus buccinator) and identified which management practices might mitigate overall grazing damage. Forage species composition and availability of alternative feeding areas had an effect on waterfowl grazing damage to perennial forage fields. Fields with higher proportions of orchard grass showed higher levels of grazing damage; and damage was lower in years when abundant alternative feeding areas (AFAs) in the form of unharvested potatoes were available. Although these factors were found to be important in explaining variation in damage to perennial forage fields, our best model accounted for only 13% of the variation in damage. Mitigation efforts must be comprehensive and consider a wide range of factors that influence damage to perennial forage fields. Although manipulation of field characteristics and management of AFAs can contribute to waterfowl grazing damage mitigation, strategic geographic distribution of AFAs and management of human disturbance in designated AFA areas would further mitigate damage.