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R.M. Erwin

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

At least 73 records · Page 4Linked to original sources
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↗
USGS1986

Waterfowl and wetlands management in the coastal zone of the Atlantic Flyway: Meeting and summary comments

A conference on waterfowl and wetlands along the Atlantic coast of North America was held in Wilmington, Delaware in September 1986. Discussions centered around coastal impoundments and Open Marsh Water Management as methods of mosquito control and waterfowl enhancement. Single purpose management of coastal marshes, whether for mosquito control or waterfowl, may not be the most beneficial approach. Where management options are available, the management for habitat heterogeneity may be indicated.

Colonial Waterbirds↗
USGS1985

Habitat comparisons and productivity in nesting common terns on the mid-Atlantic coast

Nesting Common Terns (Sterna hirundo) were studied at a number of barrier beaches and small islands of tidal salt marsh in New Jersey and the Eastern Shore of Maryland-Virginina from 1980 through 1982. Data were collected on clutch sizes, nest spacing, and nesting success. The principal null hypothesis tested was that no difference in reproductive success exists between beach and marsh habitats. Nests were monitored from egg-laying in mid-May until mid-July when young fledged. Clutch sizes varied among colonies and across years but no systematic effect of year, habitat, or colony size on mean clutch size per colony was detected. Analyses of nest productivity (estimated using both the Mayfield method and using a colony average) failed to reveal significant effects of habitat or colony size but showed a stronger year effect. Storm tide flooding and egg chick disappearance (presumably predation by Herring Gulls Larus argentatus and Laughing Gulls L. atricilla nesting nearby) accounted for most nest failures. Losses due to both these mortality factors were unpredictable from year to year. Nest spacing in salt marsh colonies was much closer than it was on barrier beaches. In mixed-species colonies with Black Skimmers (Rynchops niger), distances between tern and skimmer nests were also much smaller in marsh colonies than they were on beaches. The limited amount of wrack (windrows of dead, matted vegetation) preferred by marsh-nesting terns probably explains these spacing differences. Several lines of evidence suggest that terns prefer beaches to marshes for nesting, however, the uncertainty of predation and flooding may often obscure any intrinsic differences in habitat quality. Long-term field studies are essential for testing hypotheses related to differential fitness of individuals among habitats.

Colonial Waterbirds↗
USGS1984

Feeding flights of nesting wading birds at a Virginia colony

Feeding flights of Snowy Egrets (Egretta thula), Tricolored Herons (E. tricolor), Little Blue Herons (E. caerulea), and Cattle Egrets (Bubulcus ibis) were monitored at a small nesting colony near Chincoteague, Virginia during late May and June 1979. All four species varied their flight directions over a series of days. Cattle Egrets oriented in a different direction (toward uplands) from the other three wetland-feeding species, which oriented toward Spartina marsh areas. None of the species showed a tendency to form groups while departing from or arriving at the colony. Tide level had little influence on flight directions used. Comparisons are made between these results and those from a similar study in coastal North Carolina.

Virginia↗