diurnal time-activity budgets of wintering canvasbacks in louisiana

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River exceeds flood stage about 25% of the year. ... search (e.g., preparation for diving, diving and tipping-up), capture and handling; resting- inactive birds with ...
Wilson Bull., 102(4), 1990, pp. 645-654

DIURNAL

TIME-ACTIVITY CANVASBACKS WILLIAM

L. HOHMAN

BUDGETS OF WINTERING IN LOUISIANA AND DAVID

P. RAVE'

Ansmcr.We determined diurnal time-activity budgets of Canvasbacks (Aythya vu& sineriu) at Catahoula Lake and at the Mississippi River Delta, Louisiana, from December 1987 to March 1988. Canvasback feeding, resting, locomotory, and comfort activities varied by month and location with a month-location interaction. Moreover, the percentage of time spent feeding varied by sex with a month-sex interaction. Study site differences in the timeactivity budgets of wintering Canvasbacks may be related to characteristics of their foods, foraging mode, disturbance level, and physical features of habitats at the two study sites. Canvasbacks wintering in Louisiana generally spent less time feeding and more time resting during the day than they did in Mississippi or coastal South Carolina. Levels of agonistic behavior were lower than those observed in South Carolina. We found no evidence of male dominance of female Canvasbacks in Louisiana. Received 14 Dec. 1989, accepted 22 Mar. 1990.

Over-winter and annual survival probabilities of waterfowl may be influenced by their relative body condition in winter (Haramis et al. 1986, Hepp et al. 1986). Further, it has been suggested that waterfowl recruitment is correlated with winter body condition (Heitmeyer and Fredrickson 198 1, Kaminski and Gluesing 1986). Energy relationships between a bird and its habitat, as reflected in its body condition relative to other individuals, are mediated through the time-activity budget of the bird (Paulus 1988). Whereas many aspects of the behavior (Alexander and Hair 1979; Alexander 1980, 1987), nutritional ecology (Perry 1982, Perry et al. 1986, Lovvom 1987), and population biology (Nichols and Haramis 1980a, b; Haramis et al. 1985) of Canvasbacks (Aythyu vulisineriu) wintering in the Atlantic Flyway have been investigated, Canvasbacks wintering elsewhere, especially in the Gulf of Mexico region, have been inadequately studied. Louisiana is a major wintering area for Canvasbacks, providing habitat since 1985 for >25% of the continental population (U.S. Fish and Wildlife Service [USFWS], Office of Migratory Bird Management, unpubl. data). We report here on time-activity budgets of wintering Canvasbacks at two sites in Louisiana. Canvasback activities are compared among wintering populations and between the wintering and migration periods.

’ U.S. Fish and Wildlife Service,National Wetlands ResearchCenter,BatonRougeField ResearchStation, % Center for Wetland Resources,Louisiana State Univ., Baton Rouge, Lmisiana 70803-7500. (Present addressDPR: 409 Walnut Street, Grand Forks, North Dakota 58201.)

645

646

THE WILSON

BULLETIN

STUDY

l

Vol. 102, No. 4, December 1990

AREAS AND METHODS

This study was conducted at Catahoula Lake (CL) in central Louisiana (3 lo1 SN, 92“OO’W) and at the Mississippi River Delta (MRD) in southeastern Louisiana (29”15’N, 89’15’W). These two sites were selected from nine that traditionally are used by wintering Canvasbacks because of their locations (inland vs coastal) and high use. Sixty-eight to 74% of all Canvasbacks observed on monthly statewide surveys in winter 1987-1988 were recorded on these two sites (D. W. Woolington, USFWS, unpubl. data). Maximum numbers of Canvasbacks censused were 58,000 on CL and 14,000 on the MRD. CL is a large (12,150 ha), swallow basin in the Mississippi River floodplain. The lake is drained in the summer to stimulate plant growth and flooded in the fall to provide waterfowl habitat and hunting opportunity (Zwank et al. 1985). Local rainfall or flooding of the Mississippi River caused by major runoff events upstream may produce abrupt changes in lake levels. For example, in winter 1987-1988, lake levels increased 3.9 mm in four days following locally heavy rains. Water depth at the center of the lake ranged from 0.2 m to 5.5 m and averaged 3.1 + 0.22 m (X + SE) during the study. The deltaic plain of the Mississippi River is a highly dynamic and complex wetland system (Bahr et al. 1983). Water levels in the marsh change daily and seasonally. Marsh flooding is directly influenced by tidal changes and stages of the Mississippi River. The Mississippi River exceeds flood stage about 25% of the year. River stage is generally highest in late winter and lowest in summer. High and low tides occur once each day with a maximum range of 0.3 m. Wind also exerts a major influence on water levels in the marsh. Onshore winds may impede river flow and cause back-flooding into the marsh, whereas sustained offshore winds tend to reduce marsh water levels. Feeding sites used by Canvasbacks at the two study locations differed markedly from each other and from those used elsewhere by wintering Canvasbacks (e.g., San Francisco Bay, Chesapeake Bay, coastal North Carolina). At CL, open water feeding sites as deep as 6 m were used by Canvasbacks, but at the MRD, birds used deltaic splays (i.e., accreting mudflats receiving shallow, intermittent flooding) almost exclusively. Deltaic splays were pitted with shallow depressions generally

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