Intertidal and farmland habitats of ducks in the Puget Sound region: A landscape perspective

Abstract

In managing coastal ecosystems, adjacent uplands have been considered mainly as sources of materials affecting littoral environments, and not as parts of an integrated system of habitats directly used by semiaquatic fauna. Agriculture is often viewed as detrimental to coastal habitats, but many waterbirds use both marine and farmland habitats on a daily and seasonal basis. We investigated the importance to dabbling ducks (Anatini) of the juxtaposition of farmland and intertidal habitats in the Puget Sound region of USA and Canada. When feeding in intertidal areas of the Fraser River Delta in British Columbia, wintering dabbling ducks ate mainly the exotic eelgrass Zostera japonica and appeared to avoid the native Zostera marina. Biomass of Z. japonica leaves was insufficient to support herbivorous American wigeon Anas americana throughout winter. Intertidal invertebrates might be adequate to support omnivorous northern pintail A. acutus, mallard A. platyrhynchos and green-winged teal A. crecca, but invertebrate biomass declined substantially in winter. A switch by these ducks from feeding in intertidal areas in autumn to farmland in winter might have resulted from inadequate or much reduced food resources in intertidal areas. Throughout the Puget Sound region, intertidal habitats with adjacent farmland supported about 75% of wigeon, 94% of pintail, 93% of mallard and 92% of teal, and few sites that lacked farmland supported substantial numbers of these species throughout winter. Radio-tagged wigeon and pintail moved among coastal sites even in a mild winter, and temperature patterns over 60 years suggest that ice cover on marine bays and flooded farmland forces dabbling ducks to leave the Fraser Delta in about 13% of all winters to seek alternative sites. For dabbling ducks in this region, it appears that farmland adjacent to intertidal areas is an important component of coastal habitat complexes, and a system of alternative sites should be included in regional landscape plans.