White-faced Ibis Study: Focus for Conservation in Eastern Idaho

White-faced ibis (WFIB) is a waterbird designated as a Species of Greatest Conservation Need in Idaho, primarily due to its dependence on relatively few protected marsh sites for breeding. Recently, the Idaho Bird Observatory and the Idaho Department of Fish and Game conducted a study of ibis foraging behavior in eastern Idaho.

White-faced ibis returning to Market Lake, Idaho.

Two colonies at Market Lake and Mud Lake Wildlife Management Areas (WMAs) in eastern Idaho currently comprise the largest breeding concentration of WFIB throughout their range. In fact, a recent effort to inventory all western colonial waterbirds by the U.S. Fish and Wildlife Service revealed that these two colonies comprise about 25% of the known breeding population of WFIB in the western United States.

Conservation of ibis populations relies as much on the protection of foraging habitat as it does nesting areas. WFIB are known to forage and nest extensively in agricultural habitats, but the degree to which they depend on farmlands or prefer different crops and irrigation regimes had not yet been quantified in Idaho.

Researchers designed a study to examine foraging behavior and habitat use patterns of WFIB within a 22 km radius around both breeding colonies. They combined driving surveys with surveys of random, spatially balanced selections of agricultural fields from late April through July 2012. The study benefited greatly from a dedicated field assistant, Kathryn Brenner, and 18 enthusiastic Master Naturalist volunteers from the Upper Snake Naturalists Chapter.

Surveyors collected 210 observations of foraging ibis flocks in the study areas (flock sizes ranged from one to 700 birds). WFIB were observed foraging predominantly in flood-irrigated agricultural fields (78%), but also in wetland habitats (11%), and flood-irrigated edges of center-pivot fields (8%). The data showed that ibis use shallow natural wetlands and flood-irrigated fields in a much higher frequency than what is available in the agricultural landscape. Also, foraging ibis within the 22 km radius of the Market Lake colony were observed almost exclusively to the south and southeast side of the colony, which is closer to the flood-irrigated pastures in the area.

White-faced ibis at Market Lake.

The results of this study identify the importance of flood-irrigated agriculture, as well as natural wetlands, to sustaining the remarkable wildlife values of east Idaho WMAs. These results also suggest that ibis are an excellent focal species for landscape-scale conservation due to their reliance on expansive foraging habitat on private lands surrounding WMAs.

Future conservation efforts around Mud and Market Lakes should focus on a combination of protecting and restoring shallow wetlands and maintaining flood irrigation on private lands around protected colony marshes. Since study completion the partnership has grown to include the Natural Resources Conservation Service, Pheasants Forever, Ducks Unlimited, and the IWJV, and is now focused on developing conservation delivery tools to work with private landowners.

Read this study here.



Also in the Spring, 2013 issue of Conservation Roundup: