Diurnal activity budgets and habitat functions of Northern Pintail Anas acuta wintering in Sinaloa, Mexico RODRIGO MIGOYA, GUYA. BALDASSARRE and MICHAELP. LOSITO We determined the activity budgets and habitat use patterns of Northern Pintail wintering in the Ensenada del Pabellon Coastal System in Sinaloa, Mexico, over the winters of 1989-90,1990-91 and 1991-92. Radio-marked females (n = 47-59/year) were used to lead observers to Pintail flocks, where time budget data were collected. Dominant daytime activities were resting (47%), feeding (20%), preening (17%) and locomoting (13%). Annual variation was high and depended on the availability and functional use of four habitat types. Natural fresh-brackish marshes were used for resting (34-58%), feeding (6-39%), and social activity (0.4-6%). Ephemeral ponds also were used for feeding (743%) and social activity (0.34%) during some wintering periods, but they generally functioned as resting areas (31-71%). Mangrove mudflats were used for resting (51-79%), whereas reservoirs were used for resting (44-54%) and social activity (1-5%), particularly during midwinter. Management recommendations include en- hancing rice availability, but also improving quality of natural marshes via control of Cattail. Keywords: Activity Budget, Habitat, Mexico, Northern Pintail, Sinaloa, Winter Northern Pintail Anas acuta (hereafter Pin- tail) populations are circumpolar through- out the northern hemisphere and, in North America, are considered a species of prior- ity concern under the North American Wa- terfowl Management Plan (United States Fish and Wildlife Service [USFWS] and Canadian Wildlife Service 1986). Breeding populations of Pintail in North America have averaged about two million during the 1990s, which is some 50% below long-term numbers as tallied since 1955 (Dubovosky et al. 1993). Pintail were classified as a pri- ority following this dramatic decline in numbers, which has induced increased management and research attention (Ducks Unlimited 1990). Along the west coast of Mexico, annual aerial surveys on the Upper Mainland West Coast (UMWC) indicated the special signif- icance of this area to wintering waterfowl, particularly Pintail (Kramer & Migoya 1989). For example, annual aerial surveys conducted during January from 1970 through to 1988 indicate that 12-23% of the Pintail population in North America win- ters in Mexico (USFWS, Laurel, Md., unpubl. data). Field studies conducted in the winter of 1987-88 also identified western Mexico as an important wintering habitat for Pintail (Migoya 1989), an observation later corrob- orated by band-return analyses (Hestbeck 134 Wildfowl 45 (1994): 134-000 1993). The Ensenada del Pabellon Coastal System (hereafter Pabellon) in the state of Sinaloa is of particular importance to win- tering Pintail; midwinter surveys have av- eraged >100,000 Pintail since 1965 (USFWS, unpubl. data), and we recorded as many as 1,500,000 Pintail at Pabellon in February 1990. Hence, Pabellon is clearly the major Pintail wintering wetland in Mexico, and among the most important wintering sites on the North American continent. Analyses of band-recovery data identi- fied the Central Valley of California as the most important wintering area for Pintail in North America (Hestbeck 1993). However, the Central Valley has lost 95% of its origi- nal wetlands (Gilmer et al. 1982, Heitmeyer et at. 1989), whereas wetland systems on the UMWC of Mexico are largely pristine because coastal wetlands have not in- curred much drainage from agricultural practices. Therefore, given the deteriora- tion of habitat conditions in California and the continental decline in Pintail numbers, it is increasingly important to determine the functional role of wetlands in the UMWC of Mexico as wintering waterfowl habitat. Pintail are among the first species of wa- terfowl to arrive in large numbers on win- tering grounds and are philopatric to win- tering sites (Hestbeck 1993). Pintail also