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Geology topics

Douglas H. Johnson

Publications and source records attributed to Douglas H. Johnson.

At least 199 records · Page 11Linked to original sources
USGS1997

Modeling the population dynamics of Gulf Coast sandhill cranes

The Midcontinental population of sandhill cranes (Grus canadensis) has a large geographic range, contains nearly 500,000 birds, and is hunted in much of its range. The population includes three subspecies; the numbers of two of these are uncertain, and they should be afforded protection from hunting that would be detrimental to their population. The two subspecies of concern tend to concentrate in the eastern part of the Great Plains during fall and spring and to winter along the Gulf Coast in Texas. This paper uses the limited information available about the Gulf Coast subpopulation in a model. We included in the model five input parameters: population size, annual survival rate in absence of hunting, the number of birds taken by hunters, the extent of additivity of hunting mortality, and recruitment rate, measured as the fraction of juveniles in the winter population. Using three widely ranging estimates of each parameter, we examined the general behavior of the simulated population. Realistic population projections occurred with medium (60,000) or large (166,000) population sizes, low (2000) or moderate (4000) harvests, and recruitment rates of 0.07 and 0.11. All values of survival in the absence of hunting and additivity of hunting yielded some realistic projections. Results of modelling suggest that the variables warranting closer monitoring are population size and recruitment rate.

Book chapter↗
USGS1996

Waterfowl communities in the northern plains: Chapter 13

Features that determine the composition of avian communities have received extensive and enthusiastic attention, both empirically and theoretically (e.g., Cody 1974; Strong et al. 1984; Wiens, 1989a,b). Interspecific competition for limited resources is one influence widely regarded as critical, but others include species-specific responses to environmental conditions, predation, parasitism, commensal and mutualistic interactions, disturbance and chance, and historical events (Wiens, 1989b). Despite the attention they have received, the relative importance of the different features remains highly controversial. Certainly the community of birds present in an area will be but a subset of the total population of each constituent species; thus, the total population size of each species is a potential influence on local communities. Since many bird communities in the temperate zone are reconstituted annually with migrants, the geographical location of a site within the breeding range is an important feature; clearly, an avian community outside the normal breeding range of a particular species is unlikely to include that species, irrespective of the suitability of vegetation and other habitat features. Further, suitable habitat encountered earlier in spring migration is more likely to be occupied than is habitat encountered later. And the breeding ranges of birds are known to shift from year to year, depending on climatic conditions, a phenomenon that represents a modification of the general breeding range at a finer scale of resolution. The return of migrant birds to areas from which they fledged or where they previously bred modifies the occupancy of a particular habitat (HildTn 1964); likewise, traditional use of breeding sites by birds can induce species to persist in unsuitable habitat (Wiens 1985). Thus site fidelity can weaken the relationship between habitat quality and number of birds on an area (Wiens 1985). Waterfowl have received less attention from community ecologists than have many other groups of birds despite the importance attributed to waterfowl by biologists more generally, as well as by the public. Exceptions include work by Nudds and colleagues in Canada and by P?ysS and colleagues in Finland (see Nudds 1992 and references contained therein). Further, waterfowl are important ecologically; in much of the prairie of the North American midcontinent, waterfowl are numerically among the most common bird species and are certainly dominant in terms of biomass. This chapter addresses some influences on waterfowl communities in mixed-grass prairie pothole habitat. It takes a temporal perspective, based on annual censuses of breeding ducks for 25 years on a specific study area at Woodworth, North Dakota. Any changes in the structural features of the habitat that may have occurred during this period at the census site were at most gradual. I examine how the waterfowl communities varied in response to influences that did change annually, such as climate, conditions of the wetlands on the study area, the regional populations of birds from which the communities were constituted, and the population at Woodworth during the previous year. The results of the analyses are interpreted relative to individual characteristics of 11 waterfowl species: Mallard ( Anas platyrhynchos ), Gadwall ( Anas strepera ), Green-winged Teal ( Anas crecca ), Blue-winged Teal ( Anas discors ), Northern Pintail ( Anas acuta ), Northern Shoveler ( Anas clypeata ), American Wigeon ( Anas americana ), Canvasback ( Aythya valisineria ), Redhead ( Aythya americana ), Lesser Scaup ( Aythya affinis ), and Ruddy Duck ( Oxyura jamaicensis ).

Book chapter↗
USGS1996

Survival of radiomarked canvasback ducklings in northwestern Minnesota

Duckling survival, an important factor affecting annual recruitment, has not been determined adequately for canvasbacks ( Aythya valisineria ). We investigated the magnitude, timing, and causes of mortality of canvasback ducklings from hatch to fledging at the Agassiz National Wildlife Refuge (NWR) in northwestern Minnesota during 1987-90. During the 4 years, 217 day-old ducklings were radiomarked and released in 52 broods. Another 141 ducklings were radiomarked at ≥ to 4 weeks of age. Survival was estimated with the Kaplan-Meier nonparametric estimator and the Weibull parametric model. Most mortalities occurred within 10 days after hatch. Total brood loss occurred in 18 (85%) of 52 broods released. The primary sources of mortality were predation principally by mink ( Mustela vison ), and exposure to precipitation and cold temperature. For combined years, females had lower survival than males ( P =0.03). If the disparate survival between sexes of canvasbacks observed in this study is representative of canvasbacks in their breeding range, this phenomenon contributes to reduced reproductive potential and the male-biased sex ratio of the species.

Minnesota↗
USGS1996

Long-term declines in nest success of prairie ducks

Increased predation on nests of ducks in prairie uplands, as a result of habitat alteration, has been hypothesized to cause decreased nest success and population sizes. We tested whether, and by how much, nest success declined using data compiled from 37 studies conducted between 1935 and 1992 at 67 sites in the Prairie Pothole Region of Canada and the United States. Nest success declined (P = 0.0002) over time, but time explained only 10% of the variation; precipitation ( P = 0.79) did not account for additional variation in nest success. Nest success declined at similar ( P = 0.13) rates among 5 species, but late nesters (gadwall [Anas strepera], blue-winged teal [ A. discors ] and northern shoveler [ A. clypeata ]) had higher success ( P = 0.004) than early nesters (mallard [ A. platyrhynchos ] and northern pintail [ A. acuta ]). Populations of gadwalls and northern shovelers, however, have not declined, indicating that declines in nest success may not be related causally to population change. Long-term population declines in blue-winged teal, northern pintails, and mallards coincide with large-scale temporal declines in nest success. Declines in nest success were parallel in parkland and grassland regions, suggesting a causal agent (or agents) that act(s) at a broad scale, despite inherent differences in the composition of the predator communities and habitats between regions.

Prairie Pothole Region↗
USGS1996

Management of northern prairies and wetlands for the conservation of neotropical migratory birds

Grasslands and wetlands of the northern prairies provide important breeding habitat for a number of birds. Deciding which species deserve most attention in managing those habitats depends, in part, on the importance of the area to the species. Many species in northern prairies are more common elsewhere and need no special consideration in that area. Several species, however, are critically dependent on the prairies. These species merit particular attention if protection of biodiversity is a goal. Both grasslands and wetlands in the northern prairies have been extensively converted for agricultural use, which has reduced the value of these habitats for breeding birds. Most land-use changes took place before monitoring programs for birds began, so quantitative assessments of changes in avian populations are lacking. This paper discusses the status of bird populations in the northern prairies, key upland and wetland habitats, effects of common management practices, and issues that specifically result from a landscape perspective. Most management practices are employed for other objectives; consequences to nongame birds are incidental, but vitally important to some species.

General Technical Report↗
USGS1996

An introduction to the Woodworth Study Area

The Woodworth Study Area (WSA) was purchased by the U.S. Fish and Wildlife Service (FWS) during the early 1960's as a waterfowl production area. Unlike most such areas, its primary purpose was not to provide waterfowl breeding habitat directly, but instead it was dedicated for use as a research area to develop information for better management of upland and wetland habitats. This article provides some history of the area and background information about biological monitoring and research that have been conducted on the WSA. Unless otherwise stated, information included in derived from (1) or unpublished data on file at the Northern Prairie Science Center (NPSC).

North Dakota↗
USGS1995

Statistical sirens: The allure of nonparametrics

Although nonparametric statistical methods have a role to play in the analysis of data, often their virtues are overstated and their deficiencies overlooked. A recent Special Feature in Ecology advocated nonparametric methods because of an erroneously stated advantage that they require no assumptions regarding the distribution underlying the observations. The present paper points out some often—ignored feature of nonparametric tests comparing two means, and advocates parameter estimation as a preferred alternative to hypothesis testing in many situations.

Ecology↗
USGS1995

Using known populations of pronghorn to evaluate sampling plans and estimators

Although sampling plans and estimators of abundance have good theoretical properties, their performance in real situations is rarely assessed because true population sizes are unknown. We evaluated widely used sampling plans and estimators of population size on 3 known clustered distributions of pronghorn ( Antilocapra americana ). Our criteria were accuracy of the estimate, coverage of 95% confidence intervals, and cost. Sampling plans were combinations of sampling intensities (16, 33, and 50%), sample selection (simple random sampling without replacement, systematic sampling, and probability proportional to size sampling with replacement), and stratification. We paired sampling plans with suitable estimators (simple, ratio, and probability proportional to size). We used area of the sampling unit as the auxiliary variable for the ratio and probability proportional to size estimators. All estimators were nearly unbiased, but precision was generally low (overall mean coefficient of variation [CV] = 29). Coverage of 95% confidence intervals was only 89% because of the highly skewed distribution of the pronghorn counts and small sample sizes, especially with stratification. Stratification combined with accurate estimates of optimal stratum sample sizes increased precision, reducing the mean CV from 33 without stratification to 25 with stratification; costs increased 23%. Precise results ( x̄ CV = 13) but poor confidence interval coverage (83%) were obtained with simple and ratio estimators when the allocation scheme included all sampling units in the stratum containing most pronghorn. Although areas of the sampling units varied, ratio estimators and probability proportional to size sampling did not increase precision, possibly because of the clumped distribution of pronghorn. Managers should be cautious in using sampling plans and estimators to estimate abundance of aggregated populations.

North Dakota↗
USGS1995

Factors associated with duck nest success in the prairie pothole region of Canada

Populations of some dabbling ducks have declined sharply in recent decades and information is needed to understand reasons for this. During 1982-85, we studied duck nesting for 1-4 years in 17 1.6 by 16.0-km, high-density duck areas in the Prairie Pothole Region (PPR) of Canada, 9 in parkland and 8 in prairie. We estimated nest-initiation dates, habitat preferences, nest success, and nest fates for mallards ( Anas platyrhynchos ), gadwalls ( A. strepera ), blue-winged teals ( A. discors ), northern shovelers ( A. clypeata ), and northern pintails ( A. acuta ). We also examined the relation of mallard production to geographic and temporal variation in wetlands, breeding populations, nesting effort, and hatch rate. Average periods of nest initiation were similar for mallards and northern pintails, and nearly twice as long as those of gadwalls, blue-winged teals, and northern shovelers. Median date of nest initiation was related to presence of wet wetlands (contained visible standing water), spring precipitation, and May temperature. Length of initiation period was related to presence of wet wetlands and precipitation in May, June temperature, and nest success; it was negatively related overall to drought that prevailed over much of Prairie Canada during the study, especially in 1984. Mallards, gadwalls, and northern pintails nested most often in brush in native grassland, blue-winged teals in road rights-of-way, and northern shovelers in hayfields and small (< 2 ha) untilled tracts of upland habitat (hereafter called Odd area). Among 8 habitat classes that composed all suitable nesting habitat of each study area, nest success estimates averaged 25% in Woodland, 19% in Brush, 18% in Hayland, 16% in Wetland, 15% in Grass, 11% in Odd area, 8% in Right-of-way, and 2% in Cropland. We detected no significant difference in nest success among species: mallard (11%), gadwall (14%), blue-winged teal (15%), northern shoveler (12%), and northern pintail (7%). Annual nest success (pooled by study area and averaged [unweighted] over all study areas) was 17% in 1982, 15% in 1983, 7% in 1984, and 14% in 1985. We estimated that predators destroyed 72% of mallard, gadwall, blue-winged teal, and northern shoveler nests and 65% of northern pintail nests. In prairie, average nest success decreased about 4 percentage points for every 10 percentage points increase in Cropland, suggesting that under conditions of 1982-85, local populations of these species probably were not stable when Cropland exceeded about 56% of available habitat. We found recent remains of 573 dead ducks during 1983-85; most were females (Anas spp.) apparently killed by predators. In some years, mallards and northern pintails were more numerous among dead ducks than we expected. More females than males were found dead among mallards and northern shovelers, suggesting higher vulnerability of females. Of factors we examined, nest-success rate appeared to be the most influential factor in determining mallard production. Nest success varied both geographically and annually.

Prairie pothole region↗
USGS1995

Contributions of the Conservation Reserve Program to populations of breeding birds in North Dakota

Previous studies have shown that habitat provided by the Conservation Reserve Program (CRP), a feature of the 1985 farm bill, is used by many birds. The present study quantitatively assesses the importance of the CRP by estimating changes in breeding-bird populations of North Dakota projected if CRP land would revert to cultivation. Of 18 species that were common in CRP or crop fields or both, 12 were more abundant in CRP habitats. Six of these species had suffered significant population declines during 1967-1990, according to the North American Breeding Bird Survey. In contrast, none of the six species that were more common in cropland than in CRP fields had declined significantly. Termination of the Conservation Reserve Program and a return of enrolled land to cultivation is projected to cause population declines in North Dakota exceeding 17% for Sedge wren (Cistothorus platensis), Grasshopper sparrow (Ammodramus savannarum), Savannah Sparrow (Passerculus sandwichensis), Dickcissel (Spiza americana), and Lark Bunting (Calamospiza melanocorys).

The Wilson Bulletin↗
USGS1995

Point counts of birds: what are we estimating?

Point counts of birds are made for many reasons, including estimating local densities, determining population trends, assessing habitat preferences, and exploiting the activities of recreational birdwatchers. Problems arise unless there is a clear understanding of what point counts mean in terms of actual populations of birds. Criteria for conducting point counts depend strongly on the purposes to which they will be put. This paper provides a simple mathematical conceptualization of point counts and illustrates graphically some of the influences on them.

General Technical Report↗
USGS1995

Conservation Reserve Program and migratory birds in the northern Great Plains

U.S. Department of Agriculture programs have mediated supply and demand of commodities and maintained the agricultural industry, but several programs have also offered various kinds of conservation benefits. The 1985 Food Security Act (Farm Bill) featured the Conservation Reserve Program (CRP), which paid farmers to plant perennial cover on highly erodible lands and to leave this land intact for a 10-year contract period. During that period we conducted two studies to determine the value of CRP fields to breeding birds in the northern Great Plains.

Great Plains↗
USGS1995

Migratory bird population changes in North Dakota

The status of migratory bird populations in North America has received increased attention in recent years. Much of this consideration has been on Neotropical migrants, especially those associated with eastern forests. The status of migratory bird populations in the Great Plains has received far less attention. During the past quarter-century, populations of many species of birds that breed in the northern Great Plains have increased or declined, as indicated by trends from the North American Breeding Bird Survey. In 1967 Stewart and Kantrud (1972) conducted a survey of breeding bird populations throughout North Dakota. This study offered a rare glimpse of bird populations breeding in the northern Great Plains as well as important baseline data on breeding bird populations. These data help us evaluate relationships between birds and habitat conditions. We repeated the survey to compare bird populations in North Dakota during 1967 with those in 1992 and 1993.

North Dakota↗
USGS1994

Wildlife habitat management on the northern prairie landscape

The northern prairie landscape has changed dramatically within the past century as a result of settlement by Europeans. Natural ecosystems have been disrupted and wildlife populations greatly altered. Natural resource agencies control only limited areas within the landscape, which they cannot manage independently of privately owned lands. Wildlife managers need first to set quantifiable objectives, based on the survival, reproduction, and distribution of wildlife. Second, they need to build public support and partnerships for meeting those objectives. Finally, they need to evaluate progress not only with respect to attitudes of the public and partners but, more importantly, of the wildlife response. This paper describes some useful tools for managing information at all phases of this process. We follow by discussing management options at a landscape level. Examples are given that involve agency lands as well as private lands, managed for biological resources and diversity as well as economic sustainability.

Landscape and Urban Planning↗