The value of agricultural wetlands as invertebrate resources for wintering shorebirds

Agricultural landscapes have received little recognition for the food resources they provide to wintering waterbirds. In the Willamette Valley of Oregon, modest yet significant populations of wintering shorebirds (Charadriiformes) regularly use hundreds of dispersed wetlands on agricultural lands. Benthic invertebrates are a critical resource for the survival of overwintering shorebirds, yet the abundance of invertebrate resources in agricultural wetlands such as these has not been quantified. To evaluate the importance of agricultural wetlands to a population of wintering shorebirds, the density, biomass, and general community composition of invertebrates available to birds were quantified at a sample of Willamette Valley sites during a wet (1999-2000) and a dry winter (2000-2001). Invertebrate densities ranged among wetlands from 173 to 1925 (mean ± S.E.: 936 ± 106) individuals/m2 in the wet winter, and from 214 to 3484 (1028 ± 155) individuals/m2 in the dry winter. Total invertebrate estimated biomass among wetlands ranged from 35 to 652 (mean ± S.E.: 364 ± 35) mg/m2 in the wet winter, and from 85 to 1405 (437 ± 62) mg/m2 in the dry winter. These estimates for food abundance were comparable to that observed in some other important freshwater wintering regions in North America.