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Diet composition of wintering Wilson's Snipe.

Article Excerpt
Studies of Wilson's Snipe (Gallinago delicata) suggest that animal foods are a significant portion of their winter diet (Erickson 1941, Whitehead 1965, White and Harris 1966, Owens 1967, Booth 1968, Jirovec 1971, Tuck 1972). Most studies suggest aquatic insects and mollusks are the primary animal foods consumed by snipe and discount the importance of earthworms (Oligochaeta). Owens (1967) found earthworms in 50% of the birds he collected in wet cattle pastures in Louisiana, but they accounted for only 21.6% of the total animal volume in the diet. Previous studies stimulated debate over the importance of plant foods in the diet of wintering Wilson's Snipe. Whitehead (1965), Owens (1967), and Booth (1968) found the dry mass of plant materials comprised ~41, 50, and 62% of the diet of wintering snipe, respectively. In contrast, White and Harris (1966) and Jirovec (1971) reported that plant foods accounted for [greater than or equal to] 20% of the dry mass in the diet.

Inconsistencies between these studies and the conclusion that earthworms are relatively unimportant in the diet of wintering snipe probably occurred because they included gizzard contents in diet composition analysis. This approach biases diet composition toward hard food items (i.e., plant foods or hard animal parts) because the grinding action of the gizzard quickly renders soft foods (e.g., earthworms) unrecognizable (Rundle 1982). This bias can be avoided by examining only the contents of the esophagus and proventriculus (Swanson and Bartonek 1970, Reinecke and Owen 1980, Rundle 1982).

Snipe have long bills with a prehensile tip used to probe moist soils in search of invertebrates (Arnold 1994). Winter habitats used by Wilson's Snipe typically have wet ground (i.e., wet pastures, plowed and fallow rice fields, and coastal marshes) (Arnold 1994), and soil moisture is a primary variable regulating earthworm abundance and distribution (Curry 1998). Our objective was to quantify the diet of wintering Wilson's Snipe based solely on examination of upper digestive tract contents.

METHODS

We conducted this study in the rice prairies and coastal marshes along the central Gulf Coast of Texas from October 1997 through April 1998. Collection sites included five different habitat types: harvested rice fields, fallow rice fields, mud fiats (i.e., recently disked fallow rice fields), drained impoundments, and coastal marshes. Vegetation communities and land use practices associated with the study area were described by McCloskey (1999).

We collected Wilson's Snipe (n = 372) by shooting, systematically alternating between habitat types throughout the non-breeding period. We typically collected four birds per day allocated throughout the day. We examined diet composition by analyzing the contents of the upper digestive tract (UDT) (i.e., esophagus and proventriculus). Each specimen was injected with 2-3 ml of 80% ethanol into their UDT immediately after collection to prevent post-mortem digestion of food items. The UDT contents were...

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