George A. Swanson

Advantages in Mathematically Weighting Waterfowl Food Habits Data

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.

Feeding Ecology of Breeding Blue-Winged Teals

A 5-year investigation of factors influencing the selection of foods consumed by blue-winged teals (Anas discors) during the breeding season in the glaciated prairie region of south-central North Dakota showed that birds first arriving on the breeding grounds consumed a diet consisting of 45 percent invertebrates. The proportion of animal foods in the diet increased to 95 percent at the onset of the nesting season. The quality and quantity of foods selected at any given time were influenced by the biological demands and morphological adaptations of the bird, the behavior and ecology of the invertebrates selected as foods, and the general nature of the aquatic ecosystems as determined by the hydrology and geology of the area and modified by land use and weather. Feeding activities changed significantly when food availability within the aquatic ecosystem changed. During the spring and early summer, temporary and seasonal wetlands, if not severely disturbed, were of paramount importance to breeding blue-winged teals since they provided abundant and readily available, high protein, animal foods. Later in the summer when seasonal wetlands began to dry up, insects began to emerge in the semipermanent ponds and lakes, and feeding intensity shifted to these more permanent waters. This trend, however, was often reversed temporarily during the early summer following heavy precipitation that refilled shallow water areas and again stimulated invertebrate development. J. WILDL. MANAGE. 38(3):396-407 Information concerning foods consumed by blue-winged teals during the breeding season is scarce. Early studies concentrated primarily on fall and winter collections (Mabbott 1920, Bennett 1938, Martin and Uhler 1939, Kortright 1943). The data presented here describe the foods selected by breeding blue-winged teals over a 5year period (1967-71) and are part of a larger study designed to provide information to assess the significance of changes occurring in waterfowl breeding habitat on the prairies. The blue-winged teal is the most abundant breeding duck in North Dakota; the statewide population in 1967 was estimated to contain 680,000 breeding pairs (Stewart and Kantrud 1972a). The various aspects of the life history of the blue-winged teal have been described by Bent (1923), Bennett (1938), Kortright (1943), Delacour (1956), and Johnsgard (1965). The first birds generally arrive in south-central North Dakota during April and nesting is usually initiated by mid-May. Attempts by unsuccessful females to renest are generally terminated in early July. Appreciation is extended to J. C. Bartonek for encouragement and sincere interest; and to V. A. Adomaitis and J. A. Shoesmith for chemical analysis; D. H. Johnson and D. A. Davenport for aid in statistical analysis; and V. A. Adomaitis, H. F. Duebbert, F. B. Lee, R. E. Stewart, and P. F. Springer for critically reviewing the manuscript.

Foods consumed by breeding mallards on wetlands of South-Central North Dakota

Foods consumed by 117 mallards (Anas platyrhynchos) collected on the breeding grounds of south-central North Dakota during spring and summer 1974-80 were examined. Animal foods accounted for 38 and 37% of the diet of paired males and nonlaying females, respectively (N = 80). The diet of laying females consisted of 72% animal foods, which differed significantly from that of paired males and nonlaying females. Insects, gastropods, crustaceans, annelids, and seeds made up 27.1, 16.4, 12.9, 12.8, and 24.8% of the diet, respectively, of laying females (N = 37). J. WILDL. MANAGE. 49(1):197-203 The prairie pothole region of North America contains a high density of shallow wetland basins with biotic communities that have developed under the influence of glaciation and a semiarid climate. Annual moisture deficits vary in magnitude and are accompanied by changes in water levels and dissolved salts (Stewart and Kantrud 1971, Swanson et al. 1974b). Plant and animal communities continually change in response to fluctuations in water level and salt content, and periodic droughts produce major changes in wetland biotic communities (Swanson and Meyer 1977). The dynamic nature of this water regime, and the periodic changes in the biota that it produces, is a dominant factor influencing the food base available to breeding waterfowl. Superimposed on the dynamic water regime of the prairie pothole region are tillage practices that can alter seasonally flooded wetlands annually and semipermanent wetlands during drought years. Tillage alters the food base of low prairie, wet meadow, and shallow marsh zones and is a major factor interacting with hydrology to influence biotic succession and, consequently, food availability. The high rate of nest destruction experienced by ground-nesting ducks in the prairie pothole region (Kirsch 1969, Higgins 1977) requires persistent renesting by mallard females if they are to achieve reproductive success. With each renesting effort and subsequent loss in body reserves, the food base available to breeding females increases in importance (Swanson et al. 1979). Foods consumed by laying mallards on the breeding grounds have not been identified. Perret (1962) described foods consumed by mallard females, but the reproductive status of the birds was not reported. Some preliminary results of foods consumed by laying mallards were discussed by Swanson et al. (1979). Studies of wetland ecology, mallard feeding ecology, and mallard renesting characteristics were undertaken concurrently in the prairie pothole region of south-central North Dakota to assess the ecological relation between breeding birds and their aquatic habitats. The purpose of the present paper is to describe foods consumed by laying female mallards on the breeding grounds of south-central North Dakota and compare these with foods of paired nonlaying females, paired males, and birds in

Benthic Sampling for Waterfowl Foods in Emergent Vegetation

Foods selected by dabbling ducks (Anatinae) on breeding grounds have recently been investigated to define the ecological and physiological factors that influence waterfowl production (Drobney and Fredrickson 1979, Swanson et al. 1979, Reinecke and Owen 1980). One of the major obstacles encountered in feeding ecology studies of breeding dabbling ducks has been a lack of quantitative sampling gear that will function in the seasonally flooded aquatic habitats attractive to dabbling ducks. Standard grab samplers such as the Ekman, Petersen, and Ponar will not function in highly vegetated substrates, and considerable effort is required to penetrate this type of substrate with a standard core sampler. Sampling benthic organisms in dense stands of emergent vegetation requires specialized equipment capable of rapid and deep penetration of the substrate. Greater penetration is required to compensate for the binding effect of dense root masses and rhizomes that can remove

Diel Food Selection by Anatinae on a Waste-Stabilization System

Diel food selection by 33 adult and immature surface-feeding ducks (Anatinae), collected on a North Dakota waste-stabilization system during the spring and summer of 1967-75, demonstrated high invertebrate consumption (98 percent by volume). Midges (Chironomidae: Diptera) and Cladocera (primarily Daphnia magna) each accounted for 44 percent of the diet. Adult insects accounted for 89 percent of the diet of birds collected between sunset and midnight, Cladocera represented 76 percent of the diet between midnight and sunrise, and immature midges and Cladocera made up 93 percent of the diet between sunrise and sunset. Pairs and broods of mallards (Anas platyrhynchos) and gadwalls (Anas strepera) contributed most of the use on the impoundments. J. WILDL. MANAGE. 41(2):226-231 Although it has been generally recognized that migrant waterfowl, breeding pairs, and females with broods are attracted to waste-stabilization ponds (Uhler 1956, 1964, Dornbush and Anderson 1964, Dodge and Low 1972, Willson 1975) or other enriched aquatic habitats (Benson 1964:111, Lee et al. 1964:72, McKnight and Low 1969), there is a paucity of information concerning foods that are consumed by ducks on these areas. The attraction of waterfowl to an organically-enriched, wastestabilization system is of interest because vascular plants associated with waterfowl food consumption (Martin and Uhler 1939) are by design eliminated or discouraged. Vascular plants interfere with efficient breakdown of waste products (Barsom 1973) or harbor insects capable of disease transmission (Myklebust and Harmston 1962). The purpose of this paper is to describe the foods consumed by anatids using an organically enriched aquatic system and to relate this information to other aquatic ecosystems that are attractive to breeding waterfowl. The data presented are part of a study of feeding ecology designed to assess the significance of changes occurring in aquatic habitats utilized by breeding waterfowl on the prairies. Appreciation is extended to J. R. Serie and M. I. Meyer for aid in the field and laboratory and to F. B. Lee, D. S. Gilmer, H. F. Duebbert, J. T. Lokemoen, and A. D. Kruse for critical review of the manuscript.

Limnological conditions influencing duckling use of saline lakes in south-central North Dakota

The distribution of ducklings on North Dakota saline lakes and their tolerance of these waters under controlled conditions were investigated. Sulfates dominated the anions and sodium, magnesium, and potassium the cations of the lakes investigated. Salt concentrations are altered by changes in water volume and construction-induced hydrologic barriers that change the natural water flow and mixing. Hydrologic characteristics of saline lakes dictate the limnological conditions that influence duckling use by controlling salt concentrations, the availability of fresh water, and aquatic foods. Ducklings were closely associated with fresh inflow from spring seepages or adjacent wetlands of low salt content. Ducklings that used sheltered bays with chemically stratified water were able to feed on fresh water. Ducklings <1-3 days of age experienced some mortality at 16 mmhos/cm and could not tolerate salt concentrations in prairie lakes that exceeded 20 mmhos/cm unless fresh water was also available. Salt concentrations of 17 mmhos/cm significantly reduced growth. High levels of magnesium and sulfates may cause greater stress on birds than equivalent concentrations of sodium chloride that are processed by the supraorbital salt glands. J. WILDL. MANAGE. 48(2):340-349 The prairie pothole region of North America contains a high density of shallow wetland basins that were formed by glaciation and developed under the influence of a semiarid climate. The hydrologic regimes of these basins dictate their chemical characteristics and subsequently the plant and invertebrate communities they support (Stewart and Kantrud 1971, Swanson et al. 1974). Lakes in south-central North Dakota that contain elevated salt levels function as hydrologic sumps, occur in low-lying basins, and are usually associated with glacial outwash or meltwater channels. The prairie pothole region supports a major segment of the annual continental waterfowl population, however, little is known of the response of breeding ducks to its saline lakes (Serie and Swanson 1976). Waterfowl are attracted to saline lakes where they feed on a variety of salt-tolerant invertebrates, vascular plants, and filamentous algae (Swanson et al. 1974, Serie and Swanson 1976, Krapu and Swanson 1978). Although adults are known to fly between freshwater sites and saline lakes where they feed, little information exists on the suitability of this type of habitat for ducklings. Female dabbling ducks nest on islands in permanent saline lakes (Duebbert et al. 1983) but the fate of the broods that they produce has not been determined. Current interest in the use of wastewater derived from irrigation return flows and geothermal effluent to develop waterfowl habitat requires more knowledge about waterfowl response to saline waters. Land-use practices can also increase salt levels of natural wetlands by initiating hydrologic changes. The objective of this study was to identify the limnological conditions that influence duck brood use of saline lakes. This paper details: (1) a description of the chemical characteristics of saline lakes in south-central North Dakota; (2) a survey 340 J. Wildl. Manage. 48(2):1984 This content downloaded from 157.55.39.132 on Thu, 15 Sep 2016 06:06:12 UTC All use subject to http://about.jstor.org/terms DUCKLING DISTRIBUTION * Swanson et al. 341 of their use by duck broods; and (3) exposure of incubator-hatched ducklings to their waters. Appreciation is extended to M. G. Barron, P. F. Springer, and J. F. Wolf for assistance in the field; D. H. Johnson for aid in statistical analysis; and H. F. Duebbert, A. B. Sargeant, and T. C. Winter for reviewing the manuscript.

Renesting Characteristics of Captive Mallards on Experimental Ponds

Renesting characteristics of captive wild-strain mallards (Anas platyrhynchos) were investigated on experimental ponds in southcentral North Dakota during the breeding seasons of 1976-81. Renesting efforts and egg production increased during the 1st 3 years. Post-yearling females that experienced clutch loss during early incubation produced 3 clutches of eggs during the breeding season. All of the birds produced 4 clutches and 50% produced 5 during the study. Birds provided with an unlimited food supply produced an average of 10.36 ? 1.03 (SD), 9.97 ? 1.09 (SD), 9.59 ? 0.91 (SD), 8.47 ? 0.94 (SD), and 8.50 ? 0.50 (SD) eggs during each successive nesting attempt. Clutch size differed (P < 0.01) among birds, ages, and nesting attempts. Renesting intervals for mallard females on unlimited food averaged 7.13 ? 1.24 (SD) days and ranged from 5 to 10 days. Intervals differed (P < 0.01) among birds and interval sequences. When food availability was reduced, renesting intervals increased and clutch size decreased. J. WILDL. MANAGE. 50(1):32-38 Ground-nesting waterfowl lose many nests to severe weather, predators (Kirsch 1969, Higgins 1977), and agricultural practices such as tillage and haying. Females compensate for such egg losses through renesting (Swanson et al. 1985). The importance of renesting by groundnesting birds to annual production has been shown by numerous authors (Gates 1962, Pospahala et al. 1974, Donham et al. 1976, Nilsson 1983). The characteristics of renesting ducks, however, are not well documented (Sowls 1955, Coulter and Miller 1968, Cowardin and JohnThis content downloaded from 157.55.39.253 on Wed, 08 Jun 2016 04:55:22 UTC All use subject to http://about.jstor.org/terms J. Wildl. Manage. 50(1):1986 MALLARD RENESTING * Swanson et al. 33 son 1979). Renesting has been demonstrated with wild marked birds, but the proportion of females that renest after their clutch is destroyed is not known (Sowls 1955, Keith 1961, Gates 1962, Strohmeyer 1967, Coulter and Miller 1968). Renesting is difficult to document because nests destroyed during early laying usually are not found, and renesting can occur outside of a study area. Early-nesting species, such as mallards, initiate laying soon after arrival on the breeding grounds, can establish several nests through continuous laying (Gates 1962), and may continue to renest into late June and early July (Swanson et al. 1985). Birds captured during the early stages of laying often abandon their nests and, as a result, the 1st attempt may not be documented. Here we describe the characteristics of renesting, wild-strain mallards on experimental ponds. Appreciation is extended to D. H. Johnson for aid in statistical analysis, and H. F. Duebbert and A. T. Klett for critically reviewing the manuscript.

Mercury residues in pintails breeding in North Dakota

Livers of 42 pintail hens (Anas acuta) breeding in eastern North Dakota during the spring and early summer of 1969 and 1970 were analyzed for total mercury by the neutron activation technique. Mercury content on a wet weight basis ranged from 0.055 ppm to 9.512 ppm and averaged 0.888 +/- 1.796 ppm (sd). Liver mercury levels of hens collected in early spring (prior to planting of crops) were significantly lower than those of hens taken late in the nesting season (P 0.05). Albumen mercury residue was correlated with liver mercury content (r = 0.756, P < 0.05). Mercury content in livers of five wild juveniles averaged 0.123 +/- 0.074 ppm. 11 references, 1 figure, 3 tables.

A Telemetry Technique for Monitoring Diel Waterfowl Activity

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Multiple tube sampler for benthic and pelagic invertebrates in shallow wetlands

Sampling devices that minimize bias and function in aquatic habitats used by waterfowl are needed. We devised a multiple tube sampling device for quantitative sampling of small (<3 cm) aquatic invertebrates in wetlands. The sampler reduced bias associated with sampling macroinvertebrates that utilize the benthic-pelagic interface because it simultaneously collects benthic and water column invertebrates. The sampler was statistically superior to other sampling devices because each sampling effort provided 4 subsamples and a within-sample variance that could be estimated. The devices also was durable and reasonably inexpensive to construct