Gary L. Krapu

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.

Survival of Mallard Broods in South-Central North Dakota

-Survival characteristics of 25 broods of Mallards (Anas platyrhynchos) were determined on a study area in the Missouri Coteau of south-central North Dakota in 1976-1977. Radio-equipped Mallard hens fledged at least one duckling in 7 of 16 (44%) broods produced in 1976, 5 of 9 (55%) in 1977, and 12 of 25 (48%) for both years combined. Of the 13 broods in which all young were lost, 11 (85%) were lost within the first two weeks after hatching. All losses of entire broods occurred in wetlands; few ducklings and no entire broods were lost during overland travel. Predation by mink (Mustela vison) was apparently the principal cause of duckling mortality. The magnitude and pattern of brood mortality are key factors in the reproductive ecology of waterfowl. Measurement of brood survival is essential for calculating recruitment from nesting data (Cowardin and Johnson 1979). Yet, survival and mortality patterns during the prefledging period are poorly understood. Most duckling mortality in Mallards (Anas platyrhynchos) occurs before young are three weeks old (Dzubin and Gollop 1972, Ball et al. 1975), but the specific mortality factors of ducklings are largely unknown. Predation, accidents, and losses due to scattering or exhaustion are often cited as potential agents of mortality, but little direct evidence has been presented in the literature. Some workers have suggested that overland travel is particularly hazardous to survival of ducklings (Bellrose 1953, Keith 1961, Odum 1970, Dzubin and Gollop 1972). However, Evans and Black (1956) found no evidence that mobile broods suffered more mortality than sedentary broods in prairie wetland habitat. This paper describes survival characteristics of Mallard broods on a study area in southcentral North Dakota as determined by radio telemetry and observation. To identify factors contributing to duckling mortality, we studied the effects of overland movement, predation, and hen-brood bonds on the survival of Mal-

Feeding ecology of mallards wintering in Nebraska

Food use by mallards (Anas platyrhynchos) wintering on the Platte River in south central Nebraska was determined from mid-December to early March 1978-80. Mallards foraged in river channels, irrigation drainage canals, and agricultural areas. Plant matter formed 97% of the diet (dry weight) and diets did not vary between sexes (P > 0.05). Waste corn was the principal food consumed and formed 46 and 62% of the diets of males and females, respectively. Milo, common duckweed (Lemna minor), smartweed (Polygonum spp.), and barnyardgrass (Echinochloa muricata) composed most of the remaining plant matter ingested. Mallards fed intensively in riparian wetland habitat to obtain invertebrates, but few were consumed because of limited abundance. Dietary protein was lower than reported among mallards wintering in Louisiana. Field feeding occurred primarily in grazed corn stubble and cattle feedlots. The distances traveled to feed, and the duration and timing of feeding varied with snow cover and season phenology. Competition for food was markedly higher during the cold winter of 1979 when heavy snow cover was present. J. WILDL. MANAGE. 47(4):1044-1053 The migrational and wintering patterns of mallards in North America have changed during the 20th century. This change is particularly evident in the central and northwestern United States where water development projects have created reservoirs and canals, and altered flow characteristics of rivers, attracting wintering populations of mallards to sites previously unoccupied (Wagar 1946, Horn 1949, Buller 1975, Hobaugh and Teer 1981). Although the mallard has been intensively studied, its winter ecology at northern nontraditional winter-use sites in the midcontinent region has not been adequately documented. Several studies (e.g., McAtee 1918, Martin and Uhler 1939, Stoudt 1944, Bossenmaier and Marshall 1958, Anderson 1959, Wright 1959) have reported the foods consumed by postbreeding mallards at different localities in Canada and the northern United States. However, detailed information on feeding ecology during winter has been lacking for much of the midcontinent region, particularly the central and northern Great Plains. This study was undertaken to develop a better understanding of mallard winter ecology under rigorous climatic conditions that are characteristic of numerous wintering sites now used by the species. The objectives were to describe: (1) mallard foraging sites and food habits during winter along the Platte River in south central Nebraska, (2) food selection in relation to nutritional requirements, and (3) winter activity patterns and foraging behavior. We thank J. Cochnar, M. Hay, D. Janke, and G. Lingle for field assistance; T. Frank and D. Johnson for help in data analysis; and R. Kologiski, L. Korschgen, and C. Lefever for assisting with seed identification. We are grateful to J. Longcore and K. Reinecke for reviewing an earlier draft of this manuscript. STUDY AREA AND METHODS Information on mallard feeding ecology was collected in winter-use areas along the Platte River between Lexington and I Present address: College of Forest Resources, 240 Nutting Hall, University of Maine, Orono, ME 04469. 1044 J. Wildl. Manage. 47(4):1983 This content downloaded from 157.55.39.209 on Sat, 14 May 2016 05:48:59 UTC All use subject to http://about.jstor.org/terms FEEDING ECOLOGY OF MALLARDS * Jorde et al. 1045 Gibbon, Nebraska, from early December to mid-March 1978-79 and 1979-80 (Jorde 1981). Mallards roosted and foraged in open areas of river channel and drainage canals and made daily feeding flights to cropland. The river remained open for several km in the Overton area even during periods of extreme cold because of heated power generation return flows from the Canaday Steam Plant. Flows in the Platte River have been drastically altered in modern times as a result of upstream water developments (Krapu et al. 1982). Approximately 5,000 and 25,000 mallards overwintered on the study area in 1979 and 1980, respectively. Canada geese (Branta canadensis) were the only other species of waterfowl occurring in significant numbers on the study area; several thousand roosted in open areas of channel and foraged in cropland. Land use in the Platte River Valley is devoted primarily to corn and livestock production. Cropland formed 56% of a 35,000ha area used by mallards wintering between Elm Creek and Lexington. Cornfields accounted for about 95% of the cropland area; other crops included milo, 1%; wheat, 1%; soybeans, <1%; and unidentified, 2%. Food use was determined by examining the esophagi of mallards collected from 3 principal habitats: river channels, irrigation canals, and cropland. Birds were collected during daylight between 0600 and 2000 hours. Those collected after 1700 hours were returning from foraging in cornfields. When possible, birds using aquatic habitats were observed feeding for 10 minutes before collection. Esophageal samples were frozen until analysis. Gizzard contents were not included in the analysis to minimize a potential sampling bias resulting from differential digestion rates among food items consumed (Swanson and Bartonek 1970). Esophageal contents were sorted, identified, counted, and weighed wet; dry weights were obtained after drying at 55 C for 24 hours; volume of each sample was determined by water displacement. A composite winter diet was estimated from the foods consumed by the 68 mallards sampled during the study. The diet was based upon the foods consumed by 22 males and 9 females collected between 0600 and 1700 hours and 21 males and 16 females taken between 1700 and 2000 hours. Feeding pairs were collected simultaneously when feasible to minimize sex-related differences in diet attributable to sampling patterns. A proximate analysis for the composite winter diet was conducted at Raltech Scientific Services, Inc., Madison, Wisconsin. Statistical significance of dietary comparisons was examined using t tests with significance at the 95% confidence interval. From 16 January to 22 February 1980, the daily feeding flights of 2 randomly selected radio-marked mallards were monitored. The transmitters and harness design were similar to those used by Dwyer (1975). Preand post-flight locations and 1 or more foraging sites were recorded along with time of day, habitat, time in flight (TIF), time in field (TIH), additional time in flight (ATIF), and weather. TIF was defined as the time spent in flight between aquatic roost sites and agricultural lands, ATIF as the cumulative time spent in flight within the boundaries of the grainfield being used, and TIH as the total time, including ATIF, spent within the boundaries of a grainfield. Open water areas used by wintering mallards were sampled for invertebrates by sweeping a 20 X 45-cm aquatic dip net through the upper 30 cm of water column over a surface distance of 1 m. In addition, the bottom sediment was sampled to an average depth of 14 cm with a 1,000ml graduated cylinder bottom sampler J. Wildl. Manage. 47(4):1983 This content downloaded from 157.55.39.209 on Sat, 14 May 2016 05:48:59 UTC All use subject to http://about.jstor.org/terms 1046 FEEDING ECOLOGY OF MALLARDS * Jorde et al. (62-mm diam.). The availability of waste corn was measured along transects by counting the number of exposed corn kernels in 1-m2 plots. Snow depth between and within stubble rows was measured and presence of cattle was noted. Weather data, time budget information, and age, sex, and pair status of collected and observed mallards were determined by methods described by Jorde (1981). Percent ice cover on the Platte River was estimated monthly in 1979 and every 2 weeks in 1980 during aerial surveys of mallard distribution. RESULTS AND DISCUSSION Habitat Characteristics at

Effects of harness transmitters on behavior and reproduction of wild mallards

Radio telemetry has been an important research tool in waterfowl studies for >20 years, yet little effort has been made to evaluate potential effects of transmitters on the birds that carry them. As part of a 4-year mallard (Arras platyrhynchos) study in the prairie pothole region of North Dakota and Minnesota, we compared radio-marked and unmarked female mallards in terms of percent time observed feeding, resting, and preening; nest initiation date; and clutch size and egg volume. Radio-marked females carried a 23-g back-mounted transmitter attached with a 2-loop harness (Dwyer 1972). On average, radio-marked females tended to feed less, rest and preen more, initiate nests later, and lay smaller clutches and eggs than unmarked females

Age Determination of Mallards

A technique for distinguishing adult from yearling wild mallards (Anas platyrhynchos), from late winter through the nesting season, was developed by applying discriminant analysis procedures to selected wing feather characters of 126 yearlings and 76 adults (2-year-olds) hand-reared from wild eggs during 1974, 1975, and 1977. Average values for feather characters generally increased as the birds advanced from yearlings to adults. Black-white surface area of greater secondary covert 2 was the single most reliable aging character identified during the study. The error rate was lowest in females (3%) when discriminant functions were used with measurements of primary 1 weight and black-white area cf greater secondary covert 2 and in males (9%) when the functions were used with black-white area of greater secondary coverts 1, 2, and 3. Methodology precludes aging of birds in the field during capture operations. J. WILDL. MANAGE. 43(2):384-393 Although the mallard has been studied widely, only limited information has been published on age-related aspects of its life cycle, especially age-related productivity. This paucity of information can be attributed, in part, to the lack of a reliable aging technique applicable during the nesting season. Although keys have been developed on the basis of certain wing feather characters to determine age of mallards during the fall and winter (Carney and Geis 1960, Carney 1964), the reliability of these characters during the breeding season is diminished because of feather replacement and wear before and during the nesting season. The present study was undertaken to develop a technique for reliably separating yearling from older (adult) mallards from late winter to the onset of wing molt in late summer. Several feather measurements were chosen for establishing discriminant functions for each group. Wing feathers were selected on the basis of observed patterns of variation in feather characters, with knowledge of age-related feather variation based on published 1 Present address: Division of Wildlife Research, U.S. Fish and Wildlife Service, Washington, DC 20240. literature, and on the basis of pattern and timing of molt. Variation in primary feather lengths of yearlings and adults was recognized in blue-winged teal, Anas discors (Dane 1968), and redhead, Aythya americana (Dane and Johnson 1975). Wing covert markings were used to age yearlings of certain species, including gadwall, Anas strepera (Oring 1968); common merganser, Mergus merganser (Anderson and Timken 1971); redhead (Smart 1962, Dane and Johnson 1975); and blue-winged teal (Dane 1968). We thank C. W. Shaiffer, who made most of the measurements; B. A. Hanson for assistance in data collection; T. J. Dwyer for his encouragement and help during development of the study; D. C. McGlauchlin, Manager, Audubon National Wildlife Refuge, for support in obtaining mallard eggs for aging studies; F. B. Lee for supervising the rearing of known-age mallards; and R. J. Greenwood for critically reviewing the manuscript.

Habitat use by migrant sandhill cranes in Nebraska

The principal spring staging areas of the midcontinent population of sandhill cranes (Grus can- adensis) are along the Platte and North Platte rivers in south-central Nebraska. Most of these lands are privately owned and managed for corn and cattle production. Diurnal habitat use by radio-tagged cranes was primarily in cropland (55%), native grassland (28%), and tame hayland (15%). Ninety-nine percent of the cropland use was in cornfields; 55% as grazed stubble, 36% as disced, cultivated, and plowed stubble, 7% as ungrazed stubble, and 1% unclassified. Grazed pastures accounted for 93% of the grassland locations and mowed alfalfa fields 77% of the tame hayland locations. Other habitats were seldom used. Time budget analyses indicated that cranes, while in croplands, grasslands, and haylands, spent 35, 36, and 50% of the time foraging, respectively Cranes roosted in the shallows and on nearby sandbars of about 111 km of river channel. Cranes usuallv roosted where the channel was at least 150 m wide and avoided stretches narrower than 50 m. Height of woody vegetation along shorelines and on islands influenced where cranes roosted when unobstructed channel width was less than 150 m; bridges or roads adjacent to the channel also reduced use by about half. Management recommendations are made for maintaining suitable habitat for sandhill cranes on their staging areas in Nebraska. J. WILDL. MANAGE. 48(2):407-4 17 Approximately one-half million sand- hill cranes (four-fifths of the continental population) gather annually along the Platte and North Platte rivers in Nebraska during March and early April while en route to their breeding grounds in central and arctic Canada, Alaska, and Siberia (US. Fish and Wildl. Serv., unpubl. data). Water developments in the upper Platte River Basin during this century have dras- tically reduced flows, causing major changes in channel width in the Big Bend reach (Williams 1978) where most of the cranes gather. Extensive encroachment by woody vegetation has accompanied chan- nel shrinkage (Currier 1982), and pro- posed developments would cause addi- tional habitat degradation and loss (Krapu et al. 1982), raising concern for the well-

Foods of breeding pintails in North Dakota

Food habits of breeding pintails (Anas acuta) were studied relative to sex, land use, and reproductive condition during the spring and summer of 1969, 1970, and 1971 in eastern North Dakota. Hens and drakes, respectively, consumed 79.2 percent and 30.0 percent animal matter on nontilled wetlands and consumed 16.6 percent and 1.1 percent animal matter on tilled wetlands. Aquatic dipterans (primarily larval forms), snails, fairy shrimp, and earthworms accounted for 71 percent of the diet of hens on nontilled wetlands, while barnyard grass (Echinochloa crusgalli) seeds formed 71 percent of the diet of hens on tilled wetlands. Cereal grain seeds formed 84 percent of the diet of 10 hens feeding on cropland. The diet of hens was influenced by reproductive status. Animal foods were predominant during the laying period (77.1 percent) but were less important in the postlaying diet (28.9 percent). Invertebrates formed 83.9 percent of the diet of renesting hens; 61.0 percent were dipteran larvae and snails. High consumption of animal foods during egg formation presumably is related to invertebrates being superior to plants in providing certain nutrients required for production of viable eggs. Research findings suggest that food requirements of prairie-nesting pintails can be met most effectively by providing pairs access to shallow, nontilled wetland habitat subject to periodic drawdowns. J. WILDL. MANAGE. 38(3):408-417 Information on food habits of breeding pintails is scant. Studies of the food habits of the North American pintail have dealt almost exclusively with nonbreeding pintails and have shown this species to be primarily vegetarian (Anderson 1959, Chamberlain 1959, Glasgow and Bardwell 1962, Mabbott 1920, Martin et al. 1951, McGilvrey 1966, McMahan 1970, Munro 1944). Recent food habit investigations on other species of breeding waterfowl have indicated that invertebrates consistently account for a greater proportion of the diet of hens than drakes (Perret 1962, Bartonek and Hickey 1969, Swanson and Nelson 1970). Their findings provided an impetus for determining the magnitude of invertebrate consumption by pintails during the breeding period. The present study was initiated to determine the diet of drake and hen pintails in three major foraging habitats used during spring and early summer. These foraging habitats were nontilled shallow wetland, tilled wetland, and cropland. Information on reproductive condition of foraging hens was gathered concurrently to provide an assessment of dietary needs associated with reproduction and the capability of selected foraging habitats to provide these needs. This study was supported by the U. S. Fish and Wildlife Service at the Northern Prairie Wildlife Research Center. I am indebted to M. W. Weller, G. A. Swanson, and H. K. Nelson for useful advice and constructive criticism throughout the study, and to P. F. Springer and J. C. Bartonek for critical review of the manuscript.

Less waste corn, more land in soybeans, and the switch to genetically modified crops: trends with important implications for wildlife management

Abstract American agriculture has provided abundant high-energy foods for migratory and resident wildlife populations since the onset of modern wildlife management. Responding to anecdotal evidence that corn residues are declining in cropland, we remeasured waste corn post-harvest in the Central Platte River Valley (CPRV) of Nebraska during 1997 and 1998 to compare with 1978. Post-harvest waste corn averaged 2.6% and 1.8% of yield in 1997 and 1998, respectively. After accounting for a 20% increase in yield, waste corn in 1997 and 1998 was reduced 24% and 47% from 1978. We also evaluated use of soybeans by spring-staging sandhill cranes (Grus canadensis) and waterfowl during spring 1998 and 1999. Despite being widely available in the CPRV, soybeans did not occur in esophageal contents of sandhill cranes (n= 174), northern pintails (Anas acuta, n= 139), greater white-fronted geese (Anser albifrons, n= 198), or lesser snow geese (Chen caerulescens, n = 208) collected with food in their esophagi. Lack of soybean consumption by cranes and waterfowl in Nebraska in early spring builds upon previously published findings, suggesting that soybeans are poorly suited for meeting nutrient needs of wildlife requiring a high-energy diet. Given evidence that high-energy food and numerous populations of seed-eating species found on farmland are declining, and the enormous potential risk to game and nongame wildlife populations if high-energy foods were to become scarce, a comprehensive research effort to study the problem appears warranted. Provisions under the Conservation Security subtitle of The Farm Security and Rural Investment Act of 2002 offer a potential mechanism to encourage producers to manage cropland in ways that would replace part of the high-energy foods that have been lost to increasing efficiency of production agriculture.

Feeding ecology of sandhill cranes during spring migration in Nebraska

We studied the food habits of midcontinent sandhill cranes (Grus canadensis) during spring 1978 and 1979 at their primary staging area along the Platte River and compared population food and foraging habitat requirements with availability. Crane diets varied among the 3 principal foraging habitats, but not between sexes, ages, or years. Cranes feeding in cornfields ate >99% corn (total dry wt); those feeding in native grasslands and alfalfa fields consumed 79-99% invertebrates. The composite diet of cranes was 97% corn and 3% invertebrates, including 2% earthworms, 0.5% snails, and 0.5% insects. Presumably, corn provided energy, whereas invertebrates from grasslands and alfalfa fields provided supplemental nutrients to compensate for protein and calcium deficiencies in corn. The mean density of waste corn decreased (P 50%. Management by burning, haying, and grazing is compatible with crane use of grasslands, and reduced-till farming could benefit cranes by increasing invertebrate populations. J. WILDL. MANAGE. 50(1):71-79 A growing awareness of the impact of water resource development on spring staging habitat of sandhill cranes in the Platte River Valley of Nebraska has stimulated private, state, and federal conservation efforts (Krapu et al. 1982). Depletion of flows in the river has increased development of native wet meadows for crop production and reduced the width of river channels. This has concentrated cranes in restricted reaches of the river and caused concern that food resources needed to meet energy and nutrient requirements of the population may become inadequate. In particular, the role of grasslands in the feeding ecology of cranes needs more study (Wheeler and Lewis 1972, Reinecke and Krapu 1979). Our research was part of a larger investigation of sandhill crane staging ecology (U.S. Fish and Wildl. Serv. 1981) that provided necessary background information to assess the management implications of population food and energy requirements. The objectives of our study were to: (1) relate qualitative aspects of food use t foraging habitat, (2) calculate daily and seasonal population food requirements, and (3) estimate food availability for comparison with projected requirements. We thank C. R. Frith and R. J. Wicht for assistance in contacting landowners and the landowners of the Platte River Valley for access to their properties. D. Janke and D. Jenson contributed to our corn sampling project. B. A. Hanson assisted with insect taxonomy and, along with D. G. Jorde, R. E. Atkins, and G. R. Lingle, collected crane specimens. Molluscs and earthworms were identified by F. M. Uhler and W. N. Beyer, respectively. D. H. Johnson and A. M. Frank supervised the statistical analyses, and T. J. Dwyer and C. E. Korschgen reviewed the manuscript.

Wetland use, settling patterns, and recruitment in mallards

The correlation between number of May ponds in the Prairie Pothole Region (PPR) of North America and size of the continental mallard (Anas platyrhynchos) breeding population the following spring weakened from the 1950s to the 1980s, suggesting possible changes in suitability of prairie ponds for meeting reproductive needs. We studied wetland use and preferences of radioequipped female mallards by reproductive stage (1988-90) in eastern North Dakota and westcentral Minnesota and evaluated effect of land use on pair distribution in eastern North Dakota (1987-91). May pond density varied among years and study areas, with changes in number of temporary and seasonal ponds accounting for 93% of variation in total ponds. During all reproductive stages, semipermanent basins were used most by females, but temporary and seasonal ponds were preferred during prenesting and egg production. Accounting for number of relocations, number of ponds used varied by year, by reproductive stage and with pond density during egg production. Numbers of breeding mallard pairs in stratum 46 in eastern North Dakota increased as May ponds increased from 1963 to 1985, but 33,659 fewer breeding pairs on average were present in 1971-85 than in 1963-70. Number of breeding pairs declined relative to May ponds from the 1960s to the 1980s, probably because fewer pairs settle in temporary and seasonal ponds as the percent of landscape in cropland increases. Waterfowl managers in the PPR should target efforts to increase duck production on landscapes where non-cropped temporarily and seasonally flooded wetland habitats are plentiful, thereby increasing cost effectiveness of management actions taken to increase nest success rate.