Advantages in Mathematically Weighting Waterfowl Food Habits Data

Abstract

The relative importance of various foods occurring in the diet of blue-winged teal (Anas discors), pintail (A. acuta), and gadwall (A. strepera) breeding in south-central North Dakota and lesser scaup (Aythya affinis) breeding in the vicinity of Great Slave Lake, Northwest Territories, are compared by the aggregate volume and aggregate percent methods. Advantages of the aggregate percent method are discussed in relation to the information presented. J. WILDL. MANAGE. 38(2):302-307 Recent investigations of the foods consumed by breeding and immature ducks inhabiting prairie and subarctic wetlands of North America have emphasized the value of using the esophageal contents rather than the gizzard for this purpose (Perret 1962; Bartonek and Hickey 1969a, 1969b; Dirschl 1969; Sugden 1969; Bartonek and Murdy 1970; Swanson and Bartonek 1970; Swanson and Nelson 1970; Krapu 1972; Swanson and Sargeant 1972). This change was implemented primarily through improved sampling procedures which provided birds containing substantial amounts of food in their esophagi. The trend toward utilizing the esophagus of waterfowl somewhat paralleled an earlier and similar change that occurred in food habit studies of upland game birds (Martin et al. 1946; Martin et al. 1951). The purpose of this paper is to reevaluate two existing methods of presenting either volumetric or weight data in light of the current use of the esophagus as a source of information. The data that form the basis for these comparisons were gathered to support feeding ecology studies of blue-winged teals, pintails, and gadwalls in south-central North Dakota and lesser scaups in the Northwest Territories. Appreciation is extended to P. F. Springer for critically reviewing the manuscript.