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Geology topics

Douglas H. Johnson

Publications and source records attributed to Douglas H. Johnson.

At least 217 records · Page 12Linked to original sources
USGS1985

An evaluation of condition indices for birds

A Lipid Index, the ratio of fat to fat-free dry weight, is proposed as a measure of fat stores in birds. The estimation of the index from field measurements of live birds is illustrated with data on the sandhill crane ( Grus canadensis) and greater white-fronted goose ( Anser albifrons ). Of the various methods of assessing fat stores, lipid extraction is the most accurate but also the most involved. Water extraction is a simpler laboratory method that provides a good index to fat and can be calibrated to serve as an estimator. Body weight itself is often inadequate as a condition index, but scaling by morphological measurements can markedly improve its value.

Journal of Wildlife Management↗
USGS1984

Habitat use by migrant sandhill cranes in Nebraska

The principal spring staging areas of the midcontinent population of sandhill cranes ( Grus canadensis ) 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 usually 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.

Nebraska↗
USGS1984

Effects of weather on breeding ducks in North Dakota

The present report quantifies relations between weather and several aspects of the breeding biology of four duck species: mallard (Anas platyrhynchos), gadwall (A. strepera), blue-winged teal (A. discors), and redhead (Aythya americana). Data were obtained from two locations in North Dakota,--the J. Clark Salyer National Wildlife Refuge, intermittently during 1936-68, and the Northern Prairie Wildlife Research Center's Woodworth Station during 1965-77. Arrival dates varied with mean temperature before and during the usual arrival period; early-arriving species were affected by early-season temperatures, and later-arriving species by temperatures later in spring. After temperature effects were accounted for, first arrivals were seen at the more southern Woodworth Station a few days earlier than at Salyer. High spring temperatures also seemed to induce early nesting. The mallard, which nested earliest, was most affected by temperatures during April whereas the other species were most affected by temperatures during late April and May. Peak hatching dates were also earlier in years with higher temperatures in May. Earlier peaks were associated with early first nests, so it was difficult to separate the effects of weather and date of initial nesting. Peaks at Woodworth occurred earlier than at Salyer, after temperature differences were taken into account. The period of most active nesting was longest for the early-nesting mallard, shortest for the late-nesting gadwall, and intermediate for the blue-winged teal and redhead. For two species, precipitation during the breeding season may have prolonged nesting activities. We also found that late nesting seasons tend to be compressed. Productivity at Salyer, measured by the brood to pair ratio, was generally greater in years with higher temperatures during 23 April-3 June. Effects were more pronounced among early-nesting species. Average brood size for Classes I and II tended to decline during the 1947-62 period at Salyer; pair populations generally increased. Consequently, it was nearly impossible to distinguish the effects of pair density on brood size from those of yearly trend. In addition, Class II broods were smaller in years when temperatures were higher during late May and June.

Fish and Wildlife Technical Report↗
USGS1982

Variability in nest survival rates and implications to nesting studies

We used four reasonably large samples (83-213) of Mallard ( Anas platyrhynchos ) and Blue-winged Teal ( A. discors ) nests on an interstate highway right-of-way in southcentral North Dakota to evaluate potential biases in hatch-rate estimates. Twelve consecutive, weekly searches for nests were conducted with a cable-chain drag in 1976 and 1977. Nests were revisited at weekly intervals. Four methods were used to estimate hatch rates for the four data sets: the Traditional Method, the Mayfield Method, and two modifications of the Mayfield Method that are sometimes appropriate when daily mortality rates of nests are not constant. Hatch rates and the average age of nests at discovery declined as the interval between searches decreased, suggesting that mortality rates were not constant in our samples. An analysis of variance indicated that daily mortality rates varied with the age of nests in all four samples. Mortality was generally highest during the early laying period, moderately high during the late laying period, and lowest during incubation. We speculate that this relationship of mortality to nest age might be due to the presence of hens at nests or to differences in the vulnerability of nest sites to predation. A modification of the Mayfield Method that accounts for age-related variation in nest mortality was most appropriate for our samples. We suggest methods for conducting nesting studies and estimating nest success for species possessing similar nesting habits.

The Auk↗
USGS1982

Population modeling for furbearer management

The management of furbearers has become increasingly complex as greater demands are placed on their populations. Correspondingly, needs for information to use in management have increased. Inadequate information leads the manager to err on the conservative side; unless the size of the 'harvestable surplus' is known, the population cannot be fully exploited. Conversely, information beyond what is needed becomes an unaffordable luxury. Population modeling has proven useful for organizing information on numerous game animals. Modeling serves to determine if information of the right kind and proper amount is being gathered; systematizes data collection, data interpretation, and decision making; and permits more effective management and better utilization of game populations. This report briefly reviews the principles of population modeling, describes what has been learned from previous modeling efforts on furbearers, and outlines the potential role of population modeling in furbearer management.

Book chapter↗
USGS1981

Improved population estimates through the use of auxiliary information

When estimating the size of a population of birds, the investigator may have, in addition to an estimator based on a statistical sample, information on one of several auxiliary variables, such as: (1) estimates of the population made on previous occasions, (2) measures of habitat variables associated with the size of the population, and (3) estimates of the population sizes of other species that correlate with the species of interest. Although many studies have described the relationships between each of these kinds of data and the population size to be estimated, very little work has been done to improve the estimator by incorporating such auxiliary information. A statistical methodology termed 'empirical Bayes' seems to be appropriate to these situations. The potential that empirical Bayes methodology has for improved estimation of the population size of the Mallard (Anas platyrhynchos) is explored. In the example considered, three empirical Bayes estimators were found to reduce the error by one-fourth to one-half of that of the usual estimator.

Book chapter↗
USGS1980

The comparison of usage and availability measurements for evaluating resource preference

Modern ecological research often involves the comparison of the usage of habitat types or food items to the availability of those resources to the animal. Widely used methods of determining preference from measurements of usage and availability depend critically on the array of components that the researcher, often with a degree of arbitrariness, deems available to the animal. This paper proposes a new method, based on ranks of components by usage and by availability. A virtue of the rank procedure is that it provides comparable results whether a questionable component is included or excluded from consideration. Statistical tests of significance are given for the method. The paper also offers a hierarchical ordering of selection processes. This hierarchy resolves certain inconsistencies among studies of selection and is compatible with the analytic technique offered in this paper.

Ecology↗