Geology Reports⌕ Search

Geology topics

R.M. Erwin

Publications and source records attributed to R.M. Erwin.

At least 73 records · Page 4Linked to original sources
USGS1991

Approaches to the conservation of coastal wetlands in the Western Hemisphere

Coastal wetlands rank among the most productive and ecologically valuable natural ecosystems on Earth. Unfortunately, they are also some of the most disturbed. Because they are productive and can serve as transportation arteries, coastal wetlands have long attracted human settlement. More than half of the U.S. population currently lives within 80 km of its coasts, and one estimate places 70% of all humanity in the coastal zone. Human impacts to coastal wetlands include physical alteration of hydrological processes; the introduction of toxic materials, nutrients, heat, and exotic species; and the unsustainable harvest of native species. Between 1950 and 1970, coastal wetland losses in the U.S. averaged 8 100 ha/year. In Central and South America, development pressures along the coastal zone rank among the most serious natural resource problems in the region..... Here, we (1) briefly describe coastal wetland avifauna, (2) discuss the threat of global warming on coastal wetlands, (3) use several Western Hemisphere wetlands as site-specific examples of development pressures facing these habitats, and (4) provide synopses of nongovernmental and governmental approaches to wetland conservation. Overall, we provide a socio-economic context for conservation of coastal wetlands in the Western Hemisphere. We suggest that efforts aimed at conserving sites of particular importance for their biological diversity should be pursued within a framework of wise use that addresses the broader issues of human population growth and economic development.

The Wilson Bulletin↗
USGS1990

Feeding activities of black skimmers in Guyana

Discrepancies appear in the literature concerning the influence of time of day and tide on feeding activities of Black Skimmers (Rhynchops niger). Observations from Guyana, South America, suggest that skimmers do feed during the day, but are strongly cued to receding tides.

Colonial Waterbirds↗
USGS1990

Industrial strength herons: The Black-crowns of Baltimore

The largest night-heron colony in Maryland is located at the foot of the Key Bridge in Dundalk, Maryland, in an industrial area. Foraging herons were followed from the colony during May-July, . Most birds followed landed near industrial/urban sites. Availability of perches and lights (at night) may serve to enhance the heron's prey capture success.

Maryland Magazine↗
USGS1989

Predator-prey interactions, resource depression and patch revisitation

Generalist predators may be confronted by different types of prey in different patches: sedentary and conspicuous, cryptic (with or without refugia), conspicuous and nonsocial, or conspicuous and social. I argue that, where encounter rates with prey are of most importance, patch revisitation should be a profitable tactic where prey have short 'recovery' times (conspicuous, nonsocial prey), or where anti-predator response (e.g. shoaling) may increase conspicuousness. Predictions are made for how temporal changes in prey encounter rates should affect revisit schedules and feeding rates for the 4 different prey types.

Behavioural Processes↗
USGS1989

Patterns of species co-occurrence of nesting colonial Ciconiiformes in Atlantic coast estuarine areas

Patterns of co-occurrence of 11 species of nesting colonial Ciconiiformes in estuarine areas of the Atlantic coast from Maine to Florida were examined using Reciprocal Averaging and Detrended Correspondence Analyses. The first RA ordination axis categorized the species into two groups: species of large birds that often nest in the tops of large trees, and species of smaller birds that usually nest lower down in trees, bushes, or on the ground. The Great Blue Heron (Ardea herodias) showed the largest positive ordination score on this axis, followed by the Wood Stork (Mycteria americana) and the Great Egret (Casmerodius albus). The other 8 species were clumped on the first ordination axis and showed little separation. The second RA axis showed an ordering of relative species abundances along an apparent north-south gradientThere were no consistent similarities of ordination scores of any species pairs or groups on all the major axes, suggesting that no consistent similarities in relative abundances of 2- or 3-species 'assemblages' were found throughout the entire Atlantic Coastal Plain.

Colonial Waterbirds↗
USGS1989

Responses to human intruders by birds nesting in colonies: Experimental results and management guidelines

Colonies of nesting wading birds and seabirds were studied at coastal sites in Virginia and North Carolina to determine distances at which birds flushed in response to human intrusion. There were few statistically significant relationships between flushing distances and colony size. Similarly, there were few differences between responses during incubation compared to post-hatching periods.

Colonial Waterbirds↗
USGS1988

Correlates of nest-defense behavior of common terns

Nest-defense behavior was studied at seven Common Tern (Sterna hirundo) colonies in southern coastal New Jersey during June and July 1981. Data were collected weekly on numbers of adults, nests, eggs, and young in relation to the frequency and intensity of dive attacks on a human intruder by nesting terns. I explored the relationships between attack behavior and colony size/density, seasonality, and brood survival. The results provide little support for social facilitation since neither colony size (range 30-250 nests) nor density was related to mean attack frequency; however, in larger colonies, fewer birds participated in dive attacks. Although the intensity of attacks was strongly seasonal, patterns were very different among colonies and peak attack rates did not always coincide with peak hatching periods. Defense levels declined late in the season in most colonies regardless of whether brood survival was high or low. Colonies with individuals that attacked early in the season had higher overall nesting success than in colonies where individuals showed little early season aggression.

Journal of Field Ornithology↗
USGS1987

Relationships between nesting populations of wading birds and habitat features along the Atlantic Coast

Using previously published atlas data for 122 mixed-species wading bird colonies on islands along the Atlantic coast (Maine to Florida, 1976-77), we examined relationships between population sizes of 11 species of egrets, herons, ibises, and wood storks (Mycteria americana) and nine habitat variables. On nautical charts, we measured four island characteristics (area, length, width, shape), three isolation factors (distances to nearest island, mainland, and a water barrier),, and two variables related to potential feeding habitat within 5 km of the center of the colony (wetland area and land-water interface, i.e., the linear distance between the marsh/upland and all water bodies within the same 5-km radius). One univariable and five multivariable .procedures were used to determine which habitat features were best related to population size .(all species combined). Multicollinearity problems among the variables limited interpretation for most procedures. Both univariable and the multivariable procedures indicated that land-water interface was the most important of the nine variables, but for all models, less than 10% of the total variance was explained (rz is less than 0.10). The size of the colony was not related to the amount of wetland area (within 5-km).per se. Colony data showed better 'structure' when examined on the basis of geographic and disturbance gradients. Population sizes of colonies near man-altered habitats were compared with those surrounded by relatively natural habitats in three geographic zones: north, middle, and south. Significant differences were found in colony size among the three zones (south largest) and between disturbance types. Surprisingly, in all three zones, colonies near man-altered areas were larger on average than those near more natural habitats in this region. A possible reason for this difference is suggested.

Book chapter↗
USGS1986

Winter distribution and oiling of common terns in Trinidad: A further look

Common Terns were studied during January and March 1985 in Trinidad as part of wintering terns in Latin America. Eighty-nine birds were captured, 33 in January, 56 in March. Terns averaged 102 .+-. 0.9 g, with March birds weighing more than those caught in January. This weight is similar to that reported earlier by Blokpoel et al. (1982, 1984) and is considerably less than weights of either premigratory immature or adult Common Terns. Terns in Trinidad appear to be opportunistic, using human fishing for their food source and roosting on boats, oil platforms and other man-made structures. One-half of the captured sample of birds had at least detectable amounts of oil on the plumage. This represents the highest frequency of oiling reported yet for any seabird living under 'baseline' (non-spill) conditions in North or Central America. Oiling had no apparent major effect on the condition of birds since oiled birds had similar weights and blood parameters when compared to unoiled birds.

Journal of Field Ornithology↗