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At least 55 records · Page 3Linked to original sources
USGS1984

Population trends and environmental contaminants in herons in the Tennessee Valley, 1980-81

Great Blue Heron (Ardea herodias) eggs (N = 40) collected in 1980 from four of the largest colonies in the Tennessee Valley contained organochlorine pesticide, polychlorinated biphenyl (PCB), and chromium concentrations below those associated with reduced productivity. Low concentrations of organochlorine pesticide and PCB residues also were found in eggs (N = 31) from three of the larger Black-crowned Night-Heron (Nycticorax nycticorax) colonies in the Tennessee Valley. However, DDE concentrations in two of the Black-crowned Night-Heron eggs exceeded levels associated with reduced nesting success. Mercury was found in all eggs of both species with residues ranging to a high of 2.0 ppm; residues of this magnitude have not been identified as reducing nesting success of either of these two species. Green-backed Heron (Butorides striatus) eggs collected in 1981 near a former DDT manufacturing site in the Tennessee Valley had the highest DDE concentrations ever reported for this species; the effect of these high concentrations on productivity is not known. Eggshell thickness of Great Blue Heron, Green-backed Heron, and Black- crowned Night-Heron eggs averaged 7.5%, 7.6%, and 3% thinner, respectively, than shell thickness of eggs collected before 1947. This amount of thinning is not deleterious; intraclutch variation in shell thickness is often this high. Shell thickness in all three species was correlated (P lt 0.1) with DDE concentrations. The number of nesting pairs of Great Blue Herons and Black-crowned Night-Herons at each of the colonies studied has been stable or increasing during the previous decade. These population data, combined with the residue data, suggest that organochlorine pesticides, PCBs, mercury, and chromium are not adversely affecting these populations. However, we did not assess nesting success which would be a requisite for confirming this.

Colonial Waterbirds↗
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↗
USGS1997

Nesting season food habits of 4 species of herons and egrets at Lake Okeechobee, Florida

Based on the composition of nestling regurgitations collected during 3 breeding seasons, fish were the most important prey group for Great Egrets (Ardea alba: N = 200 nest-day samples; aggregate percent biomass [APB] = 73.4%), Snowy Egrets (Egretta thula: N = 115; APB = 91.4%), and Tricolored Herons (E. tricolor: N = 68; APB = 97.3%). For Little Blue Herons (E. caerulea: N = 57), grass shrimp (Palaemonetes paludosus; APB = 39.7%) ranked higher in overall importance than all fishes combined (APB = 36.5%). Dietary overlap, as measured by Schoener's Similarity Index, was greatest between Snowy Egrets and Tricolored Herons (77%) and lowest between Tricolored Herons and Little Blue Herons (30%). Diet diversity, as measured by Shannon's Index, was highest for Great Egrets (2.04), intermediate for Snowy Egrets (1.71) and Tricolored Herons (1.68), and lowest for Little Blue Herons (1.60). Great Egrets ate a wider variety of fish species and sizes, especially larger fishes, and more crayfish than the other species. Little Blue Herons ate fewer fish and more grass shrimp and insects, and ate smaller forage fishes than Tricolored Herons but similar-sized fish as Snowy Egrets. The coarse-scale trophic composition of Snowy Egret and Tricolored Heron diets did not differ significantly, but Tricolored Herons ate larger forage fishes than Snowy Egrets. Pronounced interannual and intercolony variation in diet composition suggested that Great Egrets and Little Blue Herons switched prey types as hydrologic conditions and habitat availability changed. Conversely, lack of such variation suggested that Snowy Egrets and Tricolored Herons adjusted their foraging tactics to ensure continued encounters with preferred prey despite changing habitat conditions. These results are generally consistent with other published data, help confirm some generalizations about foraging strategies and patterns of niche differentiation among these ecologically similar species, and have implications for managing the Lake Okeechobee ecosystem.

Florida↗
USGS1981

Suspected Great Blue Heron population decline after a severe winter in the Columbia Basin

The wintering range of the Great Blue Heron ( Ardea herodias ) extends further north than does that of any other member of the Ciconiiformes in North America. The northern limits of its range extend along the Pacific coast into southeastern Alaska, into Massachusetts on the Atlantic coast, and inland into southern Montana (Palmer 1962). In the northern part of its range, severe winter weather may persist for weeks or months. Little information is available regarding either the response of individual Great Blue Herons to severe winters or the effects of these conditions on populations. In this paper, we report our observations on a small heron population in Oregon and Washington that was exposed to a severe winter.

Oregon, Washington↗
USGS1980

Pollution ecology of breeding great blue herons in the Columbia Basin, Oregon and Washington

Approximately 40 pairs of Great Blue Herons ( Ardea herodias ) formerly nested in trees on or near Blalock Island about 95 km downstream from Richland, Washington, in the Columbia River (Nehls 1972 ). In conjunction with construction of the John Day Lock and Dam and before creating Lake Umatilla in 1968, large trees along the shoreline, including those in the heronry on Blalock Island, were removed except for about six cottonwood trees ( Populus sp.) that were left standing near the south bank of the river (David Lenhart, pers. comm.). As a mitigation procedure, the Umatilla National Wildlife Refuge (Umatilla) was established in 1967. The herons subsequently established a secondary heronry in the six cottonwoods; 20 pairs were present in 1971 (Nehls 1972). The inundated trees died and deteriorated; only two trees with eight nests remained in 1976 (Henny and Kurtz 1978), and we found just two nests in one tree in 1978. With a decrease in traditional nesting sites, the birds nested on islands in big sagebrush ( Artemisia tridentata ), on channel markers in the Columbia River, and on nesting platforms constructed for Canada Geese ( Branta canadensis ). The purpose of this paper is to describe the breeding biology of Great Blue Herons at Umatilla and the McNary Recreation Area (McNary) in 1978 and the relationship of organochlorine residues in eggs to eggshell thickness and reproductive success. The primary reason for conducting this study was to determine if the heptachlor seed treatment that was severely affecting Canada Geese at Umatilla (Blus et al. 1979) was also a hazard to Great Blue Herons. At the same time we also investigated possible effects of other organochlorines on the herons.

Oregon, Washington↗
USGS2020

Evaluation of survey methods for colonial waterbirds at Chase Lake National Wildlife Refuge, North Dakota

Estimating the number of breeding pairs in a mixed-species waterbird colony is difficult because colonial waterbirds are vulnerable to human intrusion and their colonies are often in remote areas with limited access. We investigated methods to estimate the number of nests of waterbirds at a large, mixed-species colony at Chase Lake National Wildlife Refuge in south-central North Dakota. The primary goals of this study were to evaluate survey methods for shrub- and ground-nesting colonial waterbirds at Chase Lake National Wildlife Refuge and to develop protocols for estimating abundance of the different species. The specific objectives were (1) to assess visible-nest counts for ciconiiform species from the perimeter of nesting areas (hereafter, perimeter counts) and observational surveys from fixed points outside the colony to count flights of adult ciconiiforms in and out of the colony (hereafter, flightline surveys) as alternatives to within-colony counts of ciconiiform nests, and (2) to assess semiautomated, pixel-based image-analysis techniques to estimate abundance of American White Pelicans ( Pelecanus erythrorhynchos ) as an alternative to traditional manual counts from aerial photographs. For shrub-nesting ciconiiform species, observers counted 2,259 and 1,759 active ciconiiform nests in 2012 and 2013, respectively, during within-colony counts of ciconiiform nests. Results from within-colony counts of ciconiiform nests indicated a positive relation between the number of nests and the area of the shrub subcolony for the three most common ciconiiform species and all ciconiiform species combined. The perimeter nest counts of ciconiiform nests at Chase Lake represented only 18.8 percent of the total active ciconiiform nests counted in 11 subcolonies in 2012, which was well below the recommended target of 50 percent. Although we found a positive relationship between the number of nests counted during perimeter counts and the number of nests counted during within-colony counts for the three most common ciconiiform species and all ciconiiform species combined, perimeter counts at Chase Lake were hampered by disturbance to nesting birds. Thus, we discontinued the perimeter counts before they were completed. We did not develop predictive models from these perimeter counts in 2012 because these models could be misleading due to inconsistent application of the survey methods, which likely would have provided inaccurate perimeter counts. The extent of this issue is unknown. Flightline surveys at Chase Lake documented patterns of ciconiiform activity that were unknown for this region. For the common ciconiiform species, the number of flights to and from the South Island at Chase Lake were greatest in the morning (7:00−12:00 central daylight time [CDT]) and least in the afternoon (12:00−17:00), and least early in the breeding season (May 29–June 20, 2013) and greatest later in the breeding season (June 24–August 1, 2013). Flightline surveys are an index but lacked comparability with within-colony nest counts because the two methods provide measures of different things (that is, adult activity away from the colony as compared to the number of nests within the colony). The overall proportions of flights generally reflected the proportions of the within-colony nest counts for the four most common species: Black-crowned Night-Heron ( Nycticorax nycticorax ), Cattle Egret ( Bubulcus ibis ), Great Egret ( Ardea alba ), and Snowy Egret ( Egretta thula ). Flightline surveys at Chase Lake indicated apparent variation related to the time of day and season, as well as a variation in detection of inbound and outbound adult ciconiiforms. For ciconiiforms at Chase Lake, the most appropriate combination of survey approaches will depend on the need for annual estimates of nest abundance of ciconiiform species, balanced with the financial, personnel, and logistical constraints associated with the survey methods. For ground-nesting American White Pelicans, the results from this study indicated that digital-image processing using remote-sensing software provides an accurate estimate of the number of American White Pelican nests. Estimates of the number of pelican nests from digital-image processing, using two commercially available remote-sensing software packages, produced nest estimates that were comparable to those of traditional manual counts from aerial photographs.

North Dakota↗
USGS2013

Evaluation of habitat quality for selected wildlife species associated with back channels.

The islands and associated back channels on the Ohio River, USA, are believed to provide critical habitat features for several wildlife species. However, few studies have quantitatively evaluated habitat quality in these areas. Our main objective was to evaluate the habitat quality of back and main channel areas for several species using habitat suitability index (HSI) models. To test the effectiveness of these models, we attempted to relate HSI scores and the variables measured for each model with measures of relative abundance for the model species. The mean belted kingfisher (Ceryle alcyon) HSI was greater on the main than back channel. However, the model failed to predict kingfisher abundance. The mean reproduction component of the great blue heron (Ardea herodias) HSI, total common muskrat (Ondatra zibethicus) HSI, winter cover component of the snapping turtle (Chelydra serpentina) HSI, and brood-rearing component of the wood duck (Aix sponsa) HSI were all greater on the back than main channel, and were positively related with the relative abundance of each species. We found that island back channels provide characteristics not found elsewhere on the Ohio River and warrant conservation as important riparian wildlife habitat. The effectiveness of using HSI models to predict species abundance on the river was mixed. Modifications to several of the models are needed to improve their use on the Ohio River and, likely, other large rivers.

Open Journal Of Ecology↗
USGS1981

Whooping crane preyed upon by golden eagle

The Golden Eagle ( Aquila chrysaetos ) is the largest predatory bird in North America and is well known for its predatory abilities. Attacks have been reported on mammals such as whitetail jackrabbits ( Lepus townsendi ) (McGahan 1967, J. Wildl. Mgmt. 31: 496), pronghorn antelope ( Antilocapra americana ) (Bruhns 1970, Can. Field-Natur. 84: 301), Mallards ( Anas platyrhynchos ) (Kelleher and O'Malia 1971, Auk 88: 186), and Great Blue Herons ( Ardea herodias ) (Carnie 1954, Condor 56: 3). This communication describes an attack on an immature Whooping Crane ( Grus americana ) by a Golden Eagle and the subsequent necropsy findings.

Colorado↗
USGS2008

Organochlorine pesticide, polychlorinated biphenyl, trace element and metal residues in bird eggs from Salton Sea, California, 2004

The Salton Sea is a highly eutrophic, hypersaline terminal lake that receives inflows primarily from agricultural drainages in the Imperial and Coachella valleys. Impending reductions in water inflow at Salton Sea may concentrate existing contaminants which have been a concern for many years, and result in higher exposure to birds. Thus, waterbird eggs were collected and analyzed in 2004 and compared with residue concentrations from earlier years; these data provide a base for future comparisons. Eggs from four waterbird species (black-crowned night-heron [Nycticorax nycticorax], great egret [Ardea alba], black-necked stilt [Himantopus mexicanus], and American avocet [Recurvirostra Americana]) were collected. Eggs were analyzed for organochlorine pesticides, polychlorinated biphenyls (PCBs), metals, and trace elements, with current results compared to those reported for eggs collected from the same species and others during 1985a??1993. The two contaminants of primary concern were p,pa??-DDE (DDE) and selenium. DDE concentrations in night-heron and great egret eggs collected from the northwest corner of Salton Sea (Whitewater River delta) decreased 91 and 95%, respectively, by 2004, with a concomitant increase in eggshell thickness for both species. Decreases in bird egg DDE levels paralleled those in tissues of tilapia (Oreochromis mossambicus ?? O. urolepis), an important prey species for herons and egrets. Despite most nests of night-herons and great egrets failing in 2004 due to predation, predicted reproductive effects based on DDE concentrations in eggs were low or negligible for these species. The 2004 DDE findings were in dramatic contrast to those in the past decade, and included an 81% decrease in black-necked stilt eggs, although concentrations were lower historically than those reported in night-herons and egrets. Selenium concentrations in black-necked stilt eggs from the southeast corner of Salton Sea (Davis Road) were similar in 1993 and 2004, with 4.5a??7.6% of the clutches estimated to be selenium impaired during both time periods. Because of present selenium concentrations and future reduced water inflow, the stilt population is of special concern. Between 1992 and 1993 and 2004 selenium in night-heron and great egret eggs from the Whitewater River delta at the north end of the Sea decreased by 81 and 55%, respectively. None of the night-heron or egret eggs collected in 2004 contained selenium concentrations above the lowest reported effect concentration (6.0 I?g/g dw). Reasons for selenium decreases in night-heron and egret eggs are unknown. Other contaminants evaluated in 2004 were all below known effect concentrations. However, in spite of generally low contaminant levels in 2004, the nesting populations of night-herons and great egrets at Salton Sea were greatly reduced from earlier years and snowy egrets (Egretta thula) were not found nesting. Other factors that include predation, reduced water level, diminished roost and nest sites, increased salinity, eutrophication, and reduced fish populations can certainly influence avian populations. Future monitoring, to validate predicted responses by birds, other organisms, and contaminant loadings associated with reduced water inflows, together with adaptive management should be the operational framework at the Salton Sea.

Hydrobiologia↗
USGS1971

Population ecology of the great blue heron with special reference to western Oregon

Great Blue Heron (Ardea herodias) begin nesting in western Oregon about 1 month earlier than reported from the Philadelphia region and about 2 months earlier than reported from Southern Alberta. The number of young fledged per nesting pair in Oregon was 2.04 in 1970 which was nearly identical to the 1.91 believed necessary to maintain a stable population in the northern United States. The level of p,p'DDE reported from two eggs in Oregon was within the same range as that reported from 40 eggs in Alberta. Although some thin-shelled eggs were being laid in Alberta, the observed production was believed sufficient for maintaining a stable population. Production rates reported from a heronry in central California suggested that the population there was also remaining fairly stable.

Canadian Field-Naturalist↗
USGS1978

Shell thinning and pesticide residues in Texas aquatic bird eggs, 1970

Significant decreases in eggshell thickness were found in 15 of 22 species of aquatic birds in Texas in 1970. Shell thickness reductions of 9 to 15 percent were found in white pelicans (Pelecanus erythrorhynchos), brown pelicans (P .occidentalis), and great blue herons (Ardea herodias). DDT family compounds were found in all eggs, and mean residues ranged from 0.4 ppm in white ibis (Eudocimus albus) to 23.2 ppm in great egrets (Casmerodius albus). GDDT residues were negatively correlated with shell thickness in five species; PCBs were negatively correlated in two. Residues in marine birds were generally lower and more uniform than levels in birds feeding in fresh and brackish water. DDT and dieldrin residues were higher in eggs from colonies near agricultural areas where these insecticides were heavily used; higher PCB residues were consistently associated with urban and industrial areas. Populations of five species have declined and deserve continued study: brown pelican, reddish egret (Dichromanassa rufescens), white-faced ibis (Plegadis chihi), laughing gull (Larus atricilla), and Forster's tern (Sterna forsteri). Population trends of four other species were undetermined and should be followed closely in future years.

Pesticides Monitoring Journal↗
USGS1979

Organochlorine residues in young herons from the upper Mississippi River-1976

Chicks of great blue herons (Ardea herodias) from four heronaries located near South St. Paul, Royalton, and Wabasha, Minnesota, and La Crosse, Wisconsin, were analyzed for organochlorines, Highest mean wet-weight concentrations, 6.43 ppm PCBs. 1.31 ppm DDE, and 1.90 ppm sigma DDT, were found in the South St. Paul chicks. Among chicks from the other three heronries, most levels were similar, but were significantly lower than levels in South St. Paul chicks. Lowest mean organochlorine levels, 0.37 ppm DDE, 0.38 ppm sigma DDT, and 0.22 ppm PCBs, were found in chicks from Royalton. All birds from South St. Paul and La Crosse contained residues of DDT and TDE whereas only one of the 10 birds from Royalton contained DDT and one contained TDE residues. Five of the 12 birds from Wabasha contained DDT; eight contained TDE. Except for PCB residues in La Crosse heron chicks, the rate of organochlorine residue accumulation in the birds was generally less than the rate of dilution caused by growth.

Pesticides Monitoring Journal↗
USGS1981

Organochlorine residues and mortality of herons

Since 1966, 72 herons found dead or moribund in the field have been analyzed for organochlorine chemicals. In addition, 36 herons were obtained through systematic collections, and carcasses were analyzed to determine sublethal exposure to organochlorines. Brains of birds found dead or moribund were analyzed to determine whether the birds had died of organochlorine poisoning. Residues of DDE were found most frequently (96 of 105 carcasses analyzed), PCBs were second (detected in 90 carcasses), and dieldrin and TDE (detected in 37 and 35 carcasses, respectively) were about equal as third and fourth most frequent. Endrin, mirex, toxaphene, and HCB were found least often (8, 9, 9, and 9 carcasses, respectively). At least one organochlorine was found in each carcass, except for six heron chicks found dead in a Maryland heronry. DDE and PCBs were present in highest concentrations; they exceeded 100 ppm in two birds each. Organochlorine concentrations were almost always higher in adult herons than in immature birds. All birds that had hazardous or lethal concentrations in the brain were adults, and most were great blue herons (Ardea herodias). Dieldrin was the chemical most often considered responsible for death. Herons died of suspected DDT and dieldrin poisoning years after the chemicals were banned in the United States. More than 20 percent of the herons found dead or moribund had lethal or hazardous concentrations of organochlorines in the brain.

Alabama, Michigan, Vermont↗
USGS2001

Changes in the nesting populations of colonial waterbirds in Jamaica Bay Wildlife Refuge, New York, 1974-1998

The Jamaica Bay Wildlife Refuge (JBWR) represents the largest protected area for over 300 species of migratory and resident birds on Long Island (LI), New York, and occupies a key position along the Atlantic flyway. We identified changes in nesting populations for 18 species of colonial waterbirds in JBWR and on LI, during 1974 - 1998, to provide a basis for future wildlife management decisions in JBWR and also at nearby John F. Kennedy International Airport. None of the populations was stable over the past 25 years in JBWR or on LI. Some populations in JBWR increased (Laughing Gull L. atricilla Linnaeus, Great Black-backed Gull L. marinus Linnaeus, Forster's Tern Sterna forsteri Nuttall) while others decreased (Herring Gull Larus argentatus Coues, Snowy Egret Egretta thula Molina), but only Cattle Egrets (Bubulcus ibis Linnaeus) have disappeared from the refuge. Common Tern (S. hitundo Linnaeus), Least Tern (S. antillarum Lesson), Roseate Tern (S. dougallii Montagu), Black Skimmer (Rynchops niger Linnaeus), Black-crowned Night Heron (Nycticorax nycticorax Linnaeus) and Great Egret (Ardea alba Linnaeus) populations all increased on LI over the sampling period although the Common Tern colonies in JBWR have been declining since 1986. The continued protection of the colony sites, particularly saltmarsh islands, in JBWR will be important to the conservation efforts of many colonial waterbird populations on Long Island. The JBWR colonies may serve as a source of emigrants to other Long Island colonies, and in some cases, act as a 'sink' for birds immigrating from New Jersey and elsewhere.

Northeastern Naturalist↗
USGS2009

Species differences in the sensitivity of avian embryos to methylmercury

We injected doses of methylmercury into the air cells of eggs of 26 species of birds and examined the dose-response curves of embryo survival. For 23 species we had adequate data to calculate the median lethal concentration (LC50). Based on the dose-response curves and LC50s, we ranked species according to their sensitivity to injected methylmercury. Although the previously published embryotoxic threshold of mercury in game farm mallards (Anas platyrhynchos) has been used as a default value to protect wild species of birds, we found that, relative to other species, mallard embryos are not very sensitive to injected methylmercury; their LC50 was 1.79 ug/g mercury on a wet-weight basis. Other species we categorized as also exhibiting relatively low sensitivity to injected methylmercury (their LC50s were 1 ug/g mercury or higher) were the hooded merganser (Lophodytes cucullatus), lesser scaup (Aythya affinis), Canada goose (Branta canadensis), double-crested cormorant (Phalacrocorax auritus), and laughing gull (Larus atricilla). Species we categorized as having medium sensitivity (their LC50s were greater than 0.25 ug/g mercury but less than 1 ug/g mercury) were the clapper rail (Rallus longirostris), sandhill crane (Grus canadensis), ring-necked pheasant (Phasianus colchicus), chicken (Gallus gallus), common grackle (Quiscalus quiscula), tree swallow (Tachycineta bicolor), herring gull (Larus argentatus), common tern (S terna hirundo), royal tern (Sterna maxima), Caspian tern (Sterna caspia), great egret (Ardea alba), brown pelican (Pelecanus occidentalis), and anhinga (Anhinga anhinga). Species we categorized as exhibiting high sensitivity (their LC50s were less than 0.25 ug/g mercury) were the American kestrel (Falco sparverius), osprey (Pandion haliaetus), white ibis (Eudocimus albus), snowy egret (Egretta thula), and tri-colored heron (Egretta tricolor). For mallards, chickens, and ring-necked pheasants (all species for which we could compare the toxicity of our injected methylmercury with that of published reports where methylmercury was fed to breeding adults and was deposited into the egg by the mother), we found the injected mercury to be more toxic than the same amount of mercury deposited naturally by the mother. The rank order of sensitivity of these same three species to methylmercury was, however, the same whether the methylmercury was injected or maternally deposited in the egg (i.e., the ring-necked pheasant was more sensitive than the chicken, which was more sensitive than the mallard). It is important to note that the dose-response curves and LC50s derived from our egg injections are useful for ranking the sensitivities of various species but are not identical to the LC50s that would be observed if the mother bird had put the same concentrations of mercury into her eggs; the LC50s of maternally deposited methylmercury would be higher.

Archives of Environmental Contamination and Toxico↗
USGS1991

Use of Wetland Habitats by Selected Nongame Water Birds in Maine

We examined the use of 87 palustrine and lacustrine wetlands by nongame water birds in central and eastern Maine using 3,527 h of observation (1,501 visits) made during April-August, 1977-85. Wetlands used by 15 species of water birds were distinguished from those not used, according to 20 habitat features. The species were the common loon (Gavia immer) , pied-billed grebe (Podilymbus podiceps), double-crested cormorant (Phalacrocorax auritus), American bittern (Botaurus lentiginosus), great blue heron (Ardea herodias), green-backed heron (Butorides striatus), osprey (Pandion haliaetus), bald eagle (Haliaeetus leucocephalus), northern harrier (Circus cyaneus), Virgima rail (Rallus limicola), sora (Porzana carolina), spotted sandpiper (Actitis macularia), common snipe (Gallinago gallinago), herring gull (Larus argentatus), and belted kingfisher (Ceryle alcyon). Predictive models of habitat use were developed for each species. Water birds were classified by similarity of habitats used, and species use was contrasted by wetland type. Smaller, isolated wetlands were used by fewer (P < 0.05) species than larger wetlands in complexes; many species had large area-requirements (pied-billed grebe, common loon, herring gull, double-crested cormorant, bald eagle) or preferred to use wetlands near other wetlands (common loon, herring gull, great blue heron, spotted sandpiper, osprey, bald eagle). Wetland area contributed more to overall variation in species richness on wetlands than wetland isolation, although on small wetlands (<3.6 ha) isolation was a better predictor of species richness than wetland area. Wetlands with intermediate amounts (33-66%) of emergent vegetation supported more species (P< 0.05) than closed (>66%) or open (<33%) wetlands. Low pH typified wetlands used by large-bodied piscivores (common loon, cormorant, osprey). Other water birds were associated with more densely vegetated, chemically buffered wetlands. Habitat features associated with wetland use by each waterbird species are reported, as are numerical responses of waterbird populations to wetland features and estimates of annual variation in habitat occupancy. Lacustrine wetlands supported a distinct, low diversity community of water birds, including most fish-eating species. Waterbird diversity at forested palustrine wetlands was intermediate between lacustrine communities and more species-rich assemblages at palustrine emergent and scrub-shrub wetlands. Regional variation in wetland characteristics and water bird use was associated with surficial geology, soils, and management practices. Management for nongame water birds in Maine should consider providing emergent and aquatic-bed vegetation with variable cover-to-water ratios, accommodating species-specific habitat needs, focusing on species of restricted distribution and low abundance, and maintaining wetland complexes. Bird use and habitat information from 87 wetlands and models of habitat selection for each species are provided in appendixes.

Fish and Wildlife Research↗
USGS1997

Nesting season food habits of 4 species of Herons and Egrets at Lake Okeechobee, Florida

Based on the composition of nestling regurgitations collected during 3 breeding seasons, fish were the most important prey group for Great Egrets (Ardea alba: N = 200 nest-day samples; aggregate percent biomass [APB] = 73.4%), Snowy Egrets (Egretta thula: N = 115; APB = 91.4%), and Tricolored Herons (E. tricolor. N = 68; APB = 97.3%). For Little Blue Herons (E. caerulerr. N = 57), grass shrimp (Palaemoneles paludosus; APB = 39.7%) ranked higher in overall importance than all fishes combined (APB = 36.5%). Dietary overlap, as measured by Schoener's Similarity Index, was greatest between Snowy Egrets and Tricolored Herons (77%) and lowest between Tricolored Herons and Little Blue Herons (30%). Diet diversity, as measured by Shannon's Index, was highest for Great Egrets (2.04), intermediate for Snowy Egrets (1.71) and Tricolored Herons (1.68), and lowest for Little Blue Herons (1.60). Great Egrets ate a wider variety of fish species and sizes, especially larger fishes, and more crayfish than the other species. Little Blue Herons ate fewer fish and more grass shrimp and insects, and ate smaller forage fishes than Tricolored Herons but similar-sized fish as Snowy Egrets. The coarse-scale trophic composition of Snowy Egret and Tricolored Heron diets did not differ significantly, but Tricolored Herons ate larger forage fishes than Snowy Egrets. Pronounced interannual and intercolony variation in diet composition suggested that Great Egrets and Little Blue Herons switched prey types as hydrologic conditions and habitat availability changed. Conversely, lack of such variation suggested that Snowy Egrets and Tricolored Herons adjusted their foraging tactics to ensure contin-ued encounters with preferred prey despite changing habitat conditions. These results are generally consistent with other published data, help confirm some generalizations about foraging strategies and patterns of niche differentiation among these ecologically similar species, and have implications for managing the Lake Okeechobce ecosystem.

Waterbirds↗
USGS1979

Dispersal and migratory patterns of San Francisco Bay produced herons, egrets, and terns

San Francisco Bay, California, including its fringing marshes, supports a large and diverse water related avifauna (Grinnell and Wythe 19271 Sibley 1952, Gill 1973, 1977). Certain of man's alterations of the Bay's shallower wetlands have resulted in increased habitat diversity which has allowed colonization by several species of birds including some colonial nesting species. The extensive dikes associated with salt production and some areas of higher ground created by dredge spoils have provided increased tide-free substratum, some of it insular, suitable for nesting. The resulting numbers of Snowy Egrets ( Egretta thula) , Black-crowned Night Herons ( Nycticorax nycticorax ), Forster's Terns ( Sterna forsteri ), and Caspian Terns ( Sterna caspia ) using these areas now represent a significant portion of the northern California breeding populations of these species. In conjunction with a study of the breeding birds of the South San Francisco Bay Estuary (Gill 1973, 1977) from 1971 to 1973, we banded 187 Great Blue Herons ( Ardea herodias ), 1499 Snowy Egrets, 1615 Black-crowned Night Herons, 2943 Forster's Terns, and 743 Caspian Terns; often this represented a substantial portion of these species banded in the western states during these years (Table 1). Recoveries from these bandings through 1977 plus additional recoveries from a few earlier and some more recent bandings provide the data for this report on dispersal patterns and migration of San Francisco Bay produced herons, egrets, and terns.

California↗