Geology topics
Robert E. Stewart
Publications and source records attributed to Robert E. Stewart.
Global climate change: USFWS coastal research
Scenarios of global climate change are still ambiguous; however, increasing sea level and atmospheric carbon dioxide (CO 2 ) concentrations seem certain, although rates of change are still being debated. Predictions for other aspects of climate change, such as temperature, tropical storm frequency and intensity, and precipitation, are still in debate, and all predictions for local (e.g., watershed) or regional effects are far from being useful for site-specific planning. While recognizing the weakness of current climate models, especially at regional and local scales, the U.S. Fish and Wildlife Service, in fulfilling its mandate for wildlife habitat protection and maintenance, advocates understanding the processes involved and forecasting potential changes. Because coastal wetlands constitute critical habitat for a significant portion of fish and wildlife under the Service's conservation charge, the Service's National Wetlands Research Center will study some of the most vulnerable coastal habitats of the Southern United States, namely coastal emergent marshes, submerged aquatic vegetation, forested wetlands, and communities of benthic invertebrates. Studies will include developing landscape-level data bases on National Wildlife Refuge wetland complexes along the coasts of the south Atlantic and Gulf of Mexico. Comparisons will be made between accreting and subsiding coastal marshes. Greenhouse and mesocosm experiments will be conducted on key species from each habitat type to determine their responses to elevated inorganic carbon, salinity, temperature, and ultraviolet radiation.
Ecological distribution and crude density of breeding birds on prairie wetlands
Breeding populations of 28 species of wetland-dwelling birds other than waterfowl (Anatidae) were censused on 1,321 wetlands lying within the prairie pothole region of North Dakota. Ecological distribution and two crude measures of relative density were calculated for the 22 commonest species using eight wetland classes. Semipermanent wetlands supported nearly two-thirds of the population and were used by all 22 species, whereas seasonal wetlands contained about one-third of the population and were used by 20 species Semipermanent, fen, and temporary wetlands contained highest bird densities on the basis of wetland area; on the basis of wetland unit, densities were highest on semipermanent, permanent, alkali, and fen wetlands. The highest ranking of semipermanent wetlands by all three measures of use was probably because these wetlands, as well as being relatively numerous and large, were vegetatively diverse. The fairly large proportion of the bird population supported by seasonal wetlands was a result of wetland abundance and moderate vegetative diversity. Increased vegetative diversity results from the development of characteristic zones of hydrophytes at sites where water persists longer during the growing season. Frequent cultivation of prairie wetlands results in the replacement of tall, robust perennials by bare soil or stands of short, weak-stemmed annuals that likely are unattractive to nesting birds.
Ferruginous hawk populations and habitat use in North Dakota
Ferruginous hawks ( Buteo regalis ) were studied in central North Dakota on a 1,259-km 2 intensive study block and on a surrounding study area (16,519 km 2 ) from 1977 to 1979. A total of 629 occupied nests was examined. Highest nest densities (0.08 nest/km 2 ) were in the Missouri Coteau in 1979. Few nests were found on the more intensively cultivated Drift Plain. We estimated the breeding population in the study area each year using 148 sample plots ( x̄ = 440 nesting pairs). Pairs that nested on the ground selected only sites on rugged landforms in isolated areas, mostly end and dead-ice moraines. Land use within 1.0 km of nests was mostly (76.5%) pasture and haylands. About 95% of the area around ground nests was grassland. Tree and tower nesting birds appeared less sensitive to surrounding land use. Pairs on the intensive study block used a wide variety of nest sites including trees (63.6%), ground (20.9%), power line towers (8.0%), haystacks (5.4%), and rock piles, utility poles, and shrubs (2.1%). Reoccupancy rates were higher (63.7%) for tower nests than for other sites. Nest success was related to the type of nest site and was highest (86.7%) in certain power line towers. Mean number of young fledged per occupied nest was highest (2.8) for ground nests. Summer storms were a major cause of loss; tree nests were particularly vulnerable. Richardson's ground squirrels ( Spermophilus richardsonii ) were taken as prey most often. Ferruginous hawks are closely associated with grasslands, particularly native prairie.
Breeding bird populations in the spruce region of the central Appalachians
No abstract available.