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Geology topics

Gary L. Krapu

Publications and source records attributed to Gary L. Krapu.

At least 55 records · Page 3Linked to original sources

Modified transmitter attachment method for adult ducks

The value of radio telemetry for waterfowl research depends on the availability of suitable methods of attaching transmitters. In previous studies, external transmitters attached to adult Mallards (Anas platyrhynchos) with sutures and glue did not stay on birds reliably. In an attempt to improve transmitter retention, a method of attachment was tested in which 4-g transmitters were attached mid-dorsally with sutures and with a stainless steel anchor-shaped wire inserted subcutaneously (anchor transmitters). Field tests indicated that all of 26 female Mallards and 63 of 65 female Gadwalls (Anas strepera) retained their anchor transmitters during 4369 bird-days of monitoring during nesting and brood rearing. Survival rates of females with anchor transmitters compared favorably with those reported from other studies. In this study, females with and without anchor transmitters did not differ with respect to survival rates of their ducklings. The anchor transmitter may be suitable for a variety of field studies on numerous species.

Journal of Field Ornithology↗

Communal roosting and foraging behavior of staging sandhill cranes

Each spring more than 300,000 Sandhill Cranes (Grus canadensis) roost communally at night in river channels in the Platte River Valley of Nebraska and disperse at dawn to forage in agricultural fields. Cranes with central roosts had activity ranges double the size of those with peripheral roosts; 42% of the birds changed activity ranges prior to the onset of migration. Minimum daily flight distance generally increased during the staging period. Cranes used native grassland and planted hayland more often than expected, relative to their percentage of occurrence, and fed longest there; cornfields were underutilized. These differences probably reflect, in part, (1) limited distribution of grasslands and haylands resulting in a greater energy expenditure to acquire protein in the form of macroinvertebrates and (2) wider distribution of cornfields with adequate energyrich foods but limited protein. Cranes probably forage more efficiently and conserve energy by following conspecifics from communal roosts to local feeding grounds, by settling in fields where foraging flocks are already present, and by establishing diurnal activity centers. Alert behavior varied with flock size but not as predicted from group size, presumably because predation of staging adult cranes is inconsequential.

The Wilson Bulletin↗

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 (Anas 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. Thus, behavioral and reproductive data from ducks marked with back-mounted harness-attached transmitters may be biased. We recommend that new designs of radio packages be field tested and caution that effects may be masked under extreme environmental conditions.

Journal of Wildlife Management↗

Habitat use, survival, and causes of mortality among mallard broods hatched near the James River in North Dakota

Habitat use and survival by nine mallard (Anas platyrhynchos) broods from nests on the James River floodplain and adjacent drift plain were monitored during summer 1987. Radio-marked broods were relocated an average of 22% of the time in the river channel, 22% in oxbow ponds, 43% in a large sewage lagoon complex, and 13% in basin wetlands. Four of the six broods hatched on the floodplain stayed primarily in riverine wetlands throughout the brood-rearing period. Seven of nine broods fledged at least one young; a total of 27 ducklings survived to fledging of the 82 that hatched. The seven hens that fledged young used an average of two wetlands each from hatching to fledging. Mink and raptor predation and adverse weather conditions were the principal identified causes of mortality. Potential effects on waterfowl production of planned downstream irrigation, a part of the Reformulated Garrison Diversion Unit, are discussed and recommendations are made to reduce adverse impacts to wildlife.

Prairie Naturalist↗

Conditioning of sandhill cranes during fall migration

Body mass of adult female and male sandhill cranes (Grus canadensis) increased an average of 17 and 20%, respectively, from early September to late October on staging areas in central North Dakota and varied by year. Increases in body mass averaged 550 and 681 g among female and male G. c. canadensis, respectively, and 616 and 836 g among female and male G. c. rowani. Adult and juvenile G. c. rowani were lean at arrival, averaging 177 and 83 g of fat, respectively, and fat reserves increased to 677 and 482 g by mid-October. Fat-free dry mass increased by 12% among juveniles, reflecting substantial growth, but remained constant among adults. The importance of fall staging areas as conditioning sites for sandhill cranes, annual variation in body mass, and vulnerability of cranes to habitat loss underscore the need to monitor status of fall staging habitat in the northern plains region and to take steps to maintain suitable habitat where necessary.

Journal of Wildlife Management↗

Prairie basin wetlands of the Dakotas: a community profile

This description of prairie basin wetlands of the Dakotas is part of a series of community profiles on ecologically important wetlands of national significance. The shallow wetlands of the Dakotas form the bulk of the portion of the Prairie Pothole Region lying within the United States. This region is famous as the producer of at least half of North America's waterfowl and an unknown, but large, proportion of other prairie-dwelling marsh and aquatic birds.The wetlands described here lie in relatively small, shallow basins that vary greatly in their ability to maintain surface water, and in their water chemistry, which varies from fresh to hypersaline. These wetlands occur in a wide variety of hydrological settings, in an area where annual and seasonal precipitation varies greatly in form and amount. Thus the presence of surface water in these wetlands is largely unpredictable. Superimposed on these phenomena are the effects of a variety of land uses, including pasture, cultivation, mechanical forage removal, idle conditions and burning. All those factors greatly affect the plant and animal communities found in these basins.This profile covers lacustrine and palustrine basins with temporarily flooded, seasonally flooded, and semipermanently flooded water regimes. Basins with these water regimes compose about 90% of the basins in the Prairie Pothole Region of the Dakotas. This profile outlines the wetland subsystems, classes and subclasses that occur in these basins, and provides a useful reference to their geologic, climatic, hydrologic, and pedologic setting.Detailed information on the biotic environment of the wetlands dealt with in this profile will be useful to scientists and resource managers. Special recognition is paid to the macrophyte and invertebrate communities, which have dynamic qualities found in few other of the world's wetland ecosystems.The most noteworthy animal inhabitants of these basins are waterfowl, which are a resource of international concern. Because of the importance of this resource, much research on the habitat use and feeding ecology of breeding waterfowl has been conducted in the region. These topics receive special attention in this profile.The Prairie Pothole Region is a major world supplier of cereal grains. Consequently, wetlands in the region are often drained for crop production or otherwise cropped when water conditions permit. These practices degrade the value of wetlands for most species of wildlife and conflict with the aims of conservationists. The subject of human uses and impacts to prairie wetlands is thus an important part of this profile.

Biological Report↗

The influence of diet quality on clutch size and laying pattern in mallards

We measured the effect of diet quality on variation in the seasonal pattern of Mallard ( Anas platyrhynchos ) reproduction. Twenty wild-strain hens, consisting of 10 sibling pairs, were maintained in captivity. One sib of each pair was fed an enriched diet, and the other was fed wheat. The wheat diet resulted in reduced clutch size, egg size, laying rate, number of nesting attempts, and total eggs laid. Diet did not affect laying initiation, duration, or the seasonal pattern of change in clutch and egg size with each renest. We believe the variation and pattern observed are adaptations to a highly variable prairie environment where the probability of reproductive success decreases as the season progresses.

The Auk↗

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 < 0.05) from 399 kg/ha in November, to 205 kg/ha in early March, to 128 kg/ha after departure of the cranes. Simulations of population energetics indicated that 450,000-550,000 cranes would consume 20-25% of the waste corn available in the Platte River Valley during spring. Corn availability is unlikely to affect crane use of staging areas unless cropping practices or fall tillage reduce the acreage of harvested cornfields by >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.

Nebraska↗

Winter ecology of bald eagles in southcentral Nebraska

Approximately 200 bald eagles wintered along a 370-km section of the Platte and North Platte rivers in Nebraska during the winters of 1978-79 and 1979-80. A preponderance of the wintering eagles were adults, with the adult:subadult ratio highest during the harsh winter of 1978-79. Nocturnal roosts were located primarily in tree plantings near the river, with mean tree age at the roosts ranging from 39 to 84 years. Bald eagles utilized a diverse prey base that included fish, birds, and mammals. Remains of 56 prey species were identified from pellets; 76% of pellets contained birds, 34% mammals, and 11% fish. Eagles foraged principally on fish when ice covered less than 80% of channels and water levels were moderate to low. Waterfowl and mammals dominated the diet when the river was almost entirely frozen or water levels were high. Mallards, eastern cottontails, and carp were the principal avian, mammalian, and piscine prey, respectively. Eagles traveled long distances from the river to feed on field-feeding waterfowl when alternate prey were not available. Fish were underrated in pellets because body components are more digestible than other major prey consumed.

Nebraska↗