Title: Environmental correlates of diurnal and nocturnal foraging patterns of nonbreeding shorebirds
Abstract: -Knowledge of abiotic factors influencing the foraging ecology of nonbreeding shorebirds (Charadriiformes: Charadrii) is based on research conducted almost exclusively during the day. Consequently, we examined the relative contributions of environmental variables to diurnal and nocturnal foraging patterns (presence/absence) of nonbreeding shorebirds at Humboldt Bay, California, USA from January 1992 to January 1993. The influence of environmental variables on foraging patterns differed between day and night. Most notably, the diurnal presence of birds increased with: (1) shorter daylength [Black-bellied Plover (Pluvialis squatarola), dowitchers (Limnodromus spp.), and small sandpipers (Calidris mauri and C. minutilla)]; and (2) shorter durations of mud flat exposure [American Avocet (Recurvirostra americana), Marbled Godwit (Limosa fedoa), and Dunlin (Calidris alpina)]. By contrast, the nocturnal presence of most species increased during the fall [Marbled Godwit, dowitchers, Black-bellied Plover, Semipalmated Plover (Charadrius semipalmatus), and Dunlin] and on nights with a visible moon [Marbled Godwit, Willet (Catoptrophorus semipalmatus), dowitchers, Semipalmated Plover, and Dunlin]. Our results suggest that interspecific variation in diurnal and nocturnal feeding patterns of shorebirds is associated mostly with variation in tidal, seasonal, and moonlight conditions. Furthermore, our findings suggest that nocturnal foraging by most shorebird species at a northern temperate, intertidal site did not increase during periods of short daylength. Received 28 July 1997, accepted 13 Jan. 1998. Nonbreeding distributions of shorebirds in coastal habitats are influenced by numerous environmental factors, especially tides and weather (see Burger 1984), which influence the availability of food resources. Tides predictably alter the amount of available foraging habitat, and variation in temperature, wind, and daylength further influence the availability of intertidal prey (Evans 1976). These generalizations, however, are based largely on research conducted during the day despite the growing body of literature (e.g., McNeil 1991, Dodd and Colwell 1996, McNeil and Rodriguez S. 1996) documenting nocturnal foraging by shorebirds. Consequently, the environmental correlates of nocturnal foraging by shorebirds remain poorly understood. Only one study (Robert et al. 1989) has quantified environmental influences of both diurnal and nocturnal distributions of shorebirds. Most studies (e.g., Heppleston 1971, Zwarts et al. 1990, Evans and Harris 1994, Thibault and McNeil 1994) have evaluated the contributions of one environmental factor (moonlight) to nocturnal foraging by shorebirds. Furthermore, with the exception of Robert and coworkers (1989) and Zwarts and coworkers (1990), most researchers have focused on a single species. Findings from these studies suggest that the nocturnal foraging ecology of shorebirds is influenced by variation in tides (Robert et al. 1989), moonlight (Heppleston 1971, Robert et al. 1989, Zwarts et al. 1990, Evans and Harris 1994, Thibault and McNeil 1994), and season (Rompre and McNeil 1994, Dodd and Colwell 1996). In this paper, we examine the relative contributions of environmental variables to diurnal and nocturnal foraging by eight shorebird species at Humboldt Bay, California, USA, an important Pacific Coast estuary for nonbreeding shorebirds (Colwell 1994). Elsewhere (Dodd and Colwell 1996), we showed that shorebirds at North Humboldt Bay foraged principally during the day, although diurnal and nocturnal distributions varied both among seasons and species. STUDY AREA AND METHODS We studied shorebirds (Charadriiformes: Charadrii) from 10 January 1992-10 January 1993 at the Arcata Marsh Project in North Humboldt Bay, Humboldt Co., California, USA. North Humboldt Bay is the largest of three basins comprising Humboldt Bay with approximately 12.2 km2 of exposed tidal mud flat at mean low tide (Costa and Stork 1984). Local tides are I Deptartment of Wildlife, Humboldt State Univ.,
Publication Year: 1998
Publication Date: 1998-01-01
Language: en
Type: article
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Cited By Count: 35
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