A review of agricultural land use by shorebirds with special reference to habitat conservation in the Fraser River Delta, British Columbia

Many estuaries worldwide are important habitats for shorebirds. Agricultural fields adjacent to food-rich intertidal areas can provide roosting and feeding habitat, particularly at high tide. The Fraser River Delta (FRD) contains rich agricultural land and is Canada's most important non-breeding site for shorebirds. We review and synthesize recent studies that have investigated agricultural land as non-breeding habitat for shorebirds in the FRD using radio-tracking, day-time and night-time surveys, stable isotope analysis of blood samples, examination of prey in stomach and faecal samples, and farmer surveys regarding field management. The three primary shorebirds studied in the FRD were dunlin (Calidris alpina pacifica), black-bellied plover (Pluvialis squatarola), and killdeer (Charadrius vociferus). Field use is mainly nocturnal for dunlin, but diurnal for black-bellied plovers and killdeer. Dunlin and black-bellied plovers mainly use bare or winter cover crop fields, preferring short cover. Killdeer mainly use berry and winter vegetable fields. All species prefer fields recently manured, fertilized, or laser levelled. Day length and precipitation influenced field use. Stable isotope analysis (delta C-13, delta N-15) of dunlin blood indicates that approximately 38% of dunlin diet is obtained from agricultural habitat. Younger birds have a higher terrestrial contribution to diet (similar to 43%) than adults (similar to 35%). Dunlin prey includes agricultural pest species such as leatherjacket (Tipulidae) larvae and wireworm (Agriotes spp.). Coastal agricultural land with diverse crop types benefits shorebirds, and its loss may negatively impact fitness, especially for juveniles. Research conducted in the FRD shows the importance of farmland for wintering shorebirds and suggests conservation and management strategies to preserve and enhance the wildlife value of this agricultural habitat.