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At least 19 recordsLinked to original sources
USGS1999

Exposure of great egret ( Ardea albus ) nestlings to mercury through diet in the Everglades ecosystem

We estimated exposure of great egret ( Ardea albus ) nestlings to mercury in food in the Florida Everglades, USA, by collecting regurgitated food samples during the 1993 to 1996 breeding seasons and during 1995 measured concentrations of mercury in individual prey items from those samples. Great egret nestlings had a diet composed predominantly of fish (>95% of biomass), though the species composition of fish in the diet fluctuated considerably among years. Great egrets concentrated on the larger fish available in the marsh, especially members of the Centrarchidae. The importance of all nonnative fish fluctuated from 0 to 32% of the diet by biomass and was dominated by pike killifish ( Belonesox belizanus ) and cichlids (Cichlidae). Total mercury concentrations in prey fish ranged from 0.04 to 1.40 mg/kg wet weight, and we found a significant relationship between mass of individual fish and mercury concentration. We estimated the concentration of total mercury in the diet as a whole by weighting the mercury concentration in a given fish species by the proportion of that species in the diet. We estimate that total mercury concentrations in the diets ranged among years from 0.37 to 0.47 mg/kg fish (4-year mean = 0.41 mg/kg). We estimated total mercury exposure in great egret nestlings by combining these mercury concentrations with measurements of food intake rate, as measured over the course of the nestling period in both lab and field situations. We estimate that, at the 0.41 mg/kg level, nestlings would ingest 4.32 mg total mercury during an 80-day nestling period. Captive feeding studies reported elsewhere suggest that this level of exposure in the wild could be associated with reduced fledging mass, increased lethargy, decreased appetite, and, possibly, poor health and juvenile survival.

Environmental Toxicology and Chemistry↗
USGS2008

Assessing habitat use by breeding Great Blue Herons (Ardea herodias) on the Upper Mississippi River, USA

Approximately 7,610 to 3,175 pairs of Great Blue Herons ( Ardea herodias ) nested along 420 river km of the Upper Mississippi River (UMR) from 1993 to 2003. Numbers declined precipitously in the mid-1990s stabilizing somewhat in the early 2000s. The average number of nests in colonies was 349 (SD = 283). Annual colony turn over rate for the eleven year period was 0.15 and ranged from 0.06 to 0.29 each year. The number of years that a colony was active was positively correlated with the average number of nests present while the colony was active. Of the eight colonies active in 1993 that averaged more than 349 nests, four were abandoned by 2003. Only one colony grew to greater than 349 nests during the study period. Custer et al. (2004) suggested that herons on the UMR may be limited by forage resources or foraging habitat and social factors, as evidenced by the even spacing of colonies that reflects the maximum feeding range of herons on the river. To rule out nesting and foraging habitat limitation, landscape habitat features of terrestrial and aquatic areas were examined for colony areas and areas without colonies. Available fish monitoring data were used to examine potential interactions between herons and forage resources. Colony areas did not differ from areas without colonies in any habitat feature. Indices of potential heron forage fish increased from 1993 to 2002, although low indices of fish abundance in 1993 were likely influenced by flood conditions that year. Although fish availability to herons is related to flows and water levels, available data suggested that herons did not negatively impact their potential forage base. Numbers of herons were not correlated with indices of fish abundance from the preceding year on a pool-wide scale. Indices of fish abundance were higher within 5 km of colonies than farther than 5 km from colonies, and indices of fish abundance increased from June through August both near and far from colonies. Numbers of herons and locations and sizes of colonies varied annually, whereas landscape features typically vary little if at all from year to year. Indices of fish abundance also varied greatly by sample location and year. Disturbance, particularly by humans in this highly used river, should be examined in relation to limiting foraging opportunities and influencing behavior (colony and individual) and productivity in colonies.

Illinois, Iowa, Minnesota, Missouri, Wisconsin↗
USGS2001

Investigation of eggshell thickness and biochemical indicators of contaminant exposure in Great Blue Herons(Ardea herodias) from Mason Neck National Wildlife Refuge

Mason Neck National Wildlife Refuge supports the largest great blue heron (Ardea herodias) rookery in the State of Virginia. The presence of bioaccumulative compounds such as polychlorinated biphenyls and DDT in fish collected from the Potomac River and tidal tributaries along the Refuge led to this study. The objective was to determine if there were any indications of pollutant-induced eggshell thinning or evidence of biochemical exposure to contaminants. We examined eggshell thickness and biomarkers of contaminant exposure in livers of embryos collected from the refuge and Coaches Island, a reference location in Chesapeake Bay. There was no evidence of eggshell thinning. Cytochrome P450 activity, measured as ethoxyresomfin-O-dealkylase (EROD) and benzyloxy-resorufin-O-dealkylase (BROD), was not significantly different in embryos from the two colonies. Biochemical indicators of oxidative stress can be reflected as changes in levels of reduced thiols, oxidized glutathione, and thiobarbituric reactive substances (TBARS). Although there were significant differences in the levels of reduced glutathione (GSH) and total thiol (TSH) activities in the embryo livers, there were no statistically significant differences in TBARS, protein-bound sulfhydryls (PBSH), oxidized glutathione (GSSG) and the ratio of GSSG to GSH. In fact, the concentrations of GSH and TSH were higher in the Mason Neck birds relative to Coaches Island. Under conditions of increased oxidative stress at least one or more of the following would be expected: decreased concentrations of reduced thiols (GSH and TSH), increased GSSG, and increased TBARS. In conclusion, we did not detect eggshell thinning or find evidence of a biochemical response to contaminant exposure in the Mason Neck great blue herons.

Report↗
USGS1995

Evaluation of an extendable pole-net to collect heron eggs in the canopy of tall trees

A pole, extendable from 2 to 8 m, with a nylon-mesh collecting net, was used to retrieve eggs from nests of Great Blue Herons (Ardea herodias) in the canopy of floodplain forests. A total of 200 eggs was collected for contaminant analysis from ten colonies along the upper Mississippi River during the spring of 1993. Low egg breakage (1%) and acceptable survival of embryos in an incubator to pipping (55%) indicated that the device was useful.

Colonial Waterbirds↗
USGS1997

Mercury concentrations in feathers of wading birds from Florida

Primary or tail feathers were collected from 92 wading birds in Florida from Lake Okeechobee and wetlands farther south, from 1987 to 1990. Mean concentrations detected in feathers of nestlings were 2.0 ppm Hg in roseate spoonbills (Ajaia ajaja), 3.5 ppm Hg in great blue herons (Ardea herodias), 4.7 ppm Hg in great white herons (Ardea herodias occidentalis), and 7.1 ppm Hg in great egrets (Casmerodius albus). Concentrations in feathers of great white herons increased with the age of the bird, from 4.7 ppm Hg in nestlings, to 6.7 ppm Hg in juveniles, and 8.2 ppm Hg in adults. Mercury concentrations were greatest in species consuming large fish. Feathers collected from wood storks (Mycteria americana) contained an average of 3.3 ppm Hg. Mercury concentrations in feathers of wading birds from southern Florida were greater than those reported in feathers of wading birds from Asia. Both liver and feather Hg concentrations were known for 25 wading birds. The regression of liver (wet weight) Hg concentrations (Y) on feather Hg concentrations (X) was: log(Y) = 1.52 log(X) - 0.722. The correlation coefficient was 0.84. If reproductive disorders are expected when concentrations in feathers of adult birds average 9 ppm Hg, as might be inferred from a published laboratory study on mallards (Anas platyrhynchos), then Hg in southern Florida may be high enough to reduce productivity of wading bird populations. However, additional controlled studies are needed before a minimum toxic concentration in feathers can be designated with confidence.

Ambio↗
USGS2015

Determining habitat quality for species that demonstrate dynamic habitat selection

Determining habitat quality for wildlife populations requires relating a species' habitat to its survival and reproduction. Within a season, species occurrence and density can be disconnected from measures of habitat quality when resources are highly seasonal, unpredictable over time, and patchy. Here we establish an explicit link among dynamic selection of changing resources, spatio-temporal species distributions, and fitness for predictive abundance and occurrence models that are used for short-term water management and long-term restoration planning. We used the wading bird distribution and evaluation models (WADEM) that estimate (1) daily changes in selection across resource gradients, (2) landscape abundance of flocks and individuals, (3) conspecific foraging aggregation, and (4) resource unit occurrence (at fixed 400 m cells) to quantify habitat quality and its consequences on reproduction for wetland indicator species. We linked maximum annual numbers of nests detected across the study area and nesting success of Great Egrets (Ardea alba), White Ibises (Eudocimus albus), and Wood Storks (Mycteria americana) over a 20-year period to estimated daily dynamics of food resources produced by WADEM over a 7490 km2 area. For all species, increases in predicted species abundance in March and high abundance in April were strongly linked to breeding responses. Great Egret nesting effort and success were higher when birds also showed greater conspecific foraging aggregation. Synthesis and applications: This study provides the first empirical evidence that dynamic habitat selection processes and distributions of wading birds over environmental gradients are linked with reproductive measures over periods of decades. Further, predictor variables at a variety of temporal (daily-multiannual) resolutions and spatial (400 m to regional) scales effectively explained variation in ecological processes that change habitat quality. The process used here allows managers to develop short- and long-term conservation strategies that (1) consider flexible behavioral patterns and (2) are robust to environmental variation over time.

Florida↗
USGS2013

Perfluorinated compound concentrations in great blue heron eggs near St. Paul, Minnesota, USA, in 1993 and 2010-2011

A great blue heron (Ardea herodias) colony on Pig's Eye Island on the Mississippi River near St. Paul, Minnesota, USA, is located near several potential perfluorinated compound (PFC) sources. The PFC concentrations in great blue heron eggs reported from a 1993 collection from the Pig's Eye colony were among the highest measured in bird eggs worldwide. The objective of this investigation was to determine whether PFC concentrations in great blue heron eggs at the Pig's Eye colony have changed since 1993. Total PFC concentrations in great blue heron eggs collected at the Pig's Eye colony in 2010 and 2011 (geometric mean = 340 and 492 ng/g wet wt) were 60% lower than the 1993 collection (1,015 ng/g wet wt). Among PFCs, perfluoroalkyl sulfonate concentrations were lower and perfluoroalkyl carboxylate concentrations were higher in the 2010 and 2011 collections. Two of 20 (10%) of the eggs analyzed from Pig's Eye in 2010 and 2011 were >1,000 ng PFCs/g wet weight and the maximum PFC value (2,506 ng PFCs/g wet wt) measured in 2010 and 2011 was among the highest PFC concentration reported in bird eggs. These high concentrations are at levels associated with physiological and neurological effects in birds.

Minnesota↗
USGS1997

Contaminant concentrations and biomarker response in great blue heron eggs from 10 colonies on the upper Mississippi River, USA

In 1993, great blue heron ( Ardea herodias ; GBH) eggs were collected from 10 colonies on the upper Mississippi River (UMR). They were then artificially incubated until pipping and analyzed for mercury, selenium, and organochlorines. Livers of embryos were analyzed for hepatic microsomal ethoxyresorufin- O -dealkylase (EROD) activity and four measures of oxidative stress. Brains were measured for asymmetry and blood was measured for the coefficient of variation of DNA (DNA CV). Organochlorine concentrations were generally low (geometric mean DDE = 1.3 μg/g wet weight; polychlorinated biphenyl [PCB] = 3.0 μg/g; 2,3,7,8-tetrachlorodibenzo- p -dioxin [TCDD] = 11.5 pg/g). Eggshell thickness was negatively correlated with DDE concentrations. Mercury (geometric mean = 0.8 μg/g dry weight) and selenium (3.1 μg/g dry weight) concentrations in GBH eggs were within background levels. EROD activity was not correlated with total PCBs, TCDD, or toxic equivalents (TEQs), based on the relative contribution of individual PCB congeners, dibenzodioxins (PCDDs), and dibenzofurans (PCDFs) to total calculated TEQs. Three of the four measures of oxidative stress were correlated with mercury concentrations. Twenty of 43 (47%) embryo brains were asymmetrical and the embryos with asymmetrical brains had higher EROD concentrations in the liver and higher DNA CV in the blood than embryos with symmetrical brains.

Environmental Toxicology and Chemistry↗
USGS2001

Persistent organochlorine pollutants in eggs of colonial waterbirds from Galveston Bay and East Texas, USA

Eggs of neotropic cormorants ( Phalacrocorax brasilianus ), black-crowned night herons ( Nycticorax nycticorax ), and great egrets ( Ardea alba ) nesting on several locations in Galveston Bay (TX, USA) and at two control sites outside the bay were collected during April–May 1996 and analyzed for chlorinated pesticides, PCBs, polychlorinated dibenzo- p -dioxins, and polychlor-inated dibenzofurans. Additionally, concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TCDD-EQs) were determined by use of relative potency factors (TEQs) or the H4IIE-luc bioassay TCDD-EQs. Concentrations of 1,1,-dichloro-2,2-bis( p -chlo-rophenyl)ethylene (DDE) were greater in eggs of neotropic cormorants from Alexander Island (mean = 1,040 ng/g wet wt) in the Houston Ship Channel (Houston, TX, USA) and in those from Telfair Island (mean = 1,460 ng/g wet wt), a reference location outside the bay, than in most locations inside the bay (mean range = 119–453 ng/g wet wt). Mean PCB concentrations were greater in eggs of neotropic cormorants from Alexander Island (mean = 5,720 ng/g wet wt) than in eggs of cormorants from areas farther away from the ship channel, including two reference sites outside the bay (mean range = 404–3,140 ng/g wet wt). The TCDD was the main dioxin congener detected in eggs from all locations within Galveston Bay. Instrumental TEQs in eggs ranged from 67 pg/g wet weight at control sites to 452 pg/g wet weight at Alexander Island. Concentrations of TCDD-EQs determined in the H4IIE assay were correlated with instrumental TEQs and were greater in eggs of cormorants from islands within the bay, although these were farther away from the ship channel. Overall, concentrations of DDE, PCBs, TCDD, and TCDD-EQs were less than the threshold levels known to affect reproduction. However, some eggs contained concentrations of total PCBs or DDE greater than what would elicit adverse effects on birds. No identifiable deformities or abnormalities were detected in embryos collected from all sites.

Environmental Toxicology and Chemistry↗
USGS2002

Wading birds as bioindicators of mercury contamination in Florida, USA: Annual and geographic variation

Mercury contamination in wetland biota is often dynamic, difficult to predict, and costly to track. In this paper, we present results from a six-year study of growing feathers of piscivorous birds as monitors of wetland Hg exposure in Florida, USA, wetlands. Between 1994 and 2000, we collected feathers of growing great egret ( Ardea alba ) nestlings from colonies in the freshwater Everglades of southern Florida, and during 1998, feathers were collected from chicks of both great egrets and white ibises ( Eudocimus albus ) at a variety of colonies throughout peninsular Florida. Coastal colonies showed significantly lower feather Hg concentrations than did inland sites. Within the Everglades, we found significant effects of both geographic location and year on age-adjusted mean total Hg concentrations in feathers. Over the course of our study, Everglades colonies maintained their Hg concentration rankings relative to one another, but all showed strongly declining Hg concentrations (mean of 73% averaged across colonies, between 1994 and 2000). Using a previously established predictive relationship between Hg consumption in food and feather Hg for great egrets, we estimated that Hg concentrations in the aggregate diet of egrets have been reduced by an average of 67%. We conclude that the Everglades has undergone a biologically significant decline in Hg availability in the wetland food web, possibly because of decreased local inputs.

Florida↗
USGS2011

A comparison of avian communities and habitat characteristics in floodplain forests associated with valley plugs and unchannelized streams

Channelization of streams associated with floodplain forested wetlands has occurred extensively throughout the world and specifically in the southeastern United States. Channelization of fluvial systems alters the hydrologic and sedimentation processes that sustain these systems. In western Tennessee, channelization and past land-use practices have caused drastic geomorphic and hydrologic changes, resulting in altered habitat conditions that may affect avian communities. The objective of this study was to determine if there were differences in avian communities utilizing floodplain forests along unchannelized streams compared to channelized streams with valley plugs, areas where sediment has completely filled the channel. During point count surveys, 58 bird species were observed at unchannelized sites and 60 species were observed at valley plug sites. Species associated with baldcypress-tupelo ( Taxodium-Nyssa ) swamps (e.g. Great Egret ( Ardea albus ) and Black-crowned Night Heron ( Nycticorax nycticorax )) and mature hardwood forests with open midstories (e.g. Eastern Wood-Pewee ( Contopus virens ), Yellow-throated Vireo ( Vireo flavifrons ), Cerulean Warbler ( Dendroica cerulea ) and Scarlet Tanager ( Piranga olivacea )) were either only found at unchannelized sites or were more abundant at unchannelized sites. Conversely, species associated with open and early successional habitats (e.g. Tree Swallow ( Tachycineta bicolor ), Northern Mockingbird ( Mimus polyglottos ) and Blue Grosbeak ( Passerina caerulea )) were either only found at valley plug sites or were more abundant at valley plug sites. Results of habitat modelling suggest that the habitat characteristics of floodplain forests at unchannelized sites are more suitable for Neotropical migrant bird species of conservation concern in the region than at valley plug sites. This study, in combination with previous research, demonstrates the ecological impacts of valley plugs span across abiotic and biotic processes and tropic levels.

River Research and Applications↗
USGS1993

Resource protection for waterbirds in Chesapeake Bay

Many living resources in the Chesapeake Bay estuary have deteriorated over the past 50 years. As a result, many governmental committees, task forces, and management plans have been established. Most of the recommendations for implementing a bay cleanup focus on reducing sediments and nutrient flow into the watershed. We emphasize that habitat requirements other than water quality are necessary for the recovery of much of the bay's avian wildlife, and we use a waterbird example as illustration. Some of these needs are: (1) protection of fast-eroding islands, or creation of new ones by dredge deposition to improve nesting habitat for American black ducks(Anas rubripes), great blue herons(Ardea herodias), and other associated wading birds; (2) conservation of remaining brackish marshes, especially near riparian areas, for feeding black ducks, wading birds, and wood ducks(Aix sponsa); (3) establishment of sanctuaries in open-water, littoral zones to protect feeding and/or roosting areas for diving ducks such as canvasbacks(Aythya valisineria) and redheads(Aythya americana), and for bald eagles(Haliaeetus leucocephalus); and (4) limitation of disturbance by boaters around nesting islands and open-water feeding areas. Land (or water) protection measures for waterbirds need to include units at several different spatial scales, ranging from ?points? (e.g., a colony site) to large-area resources (e.g., a marsh or tributary for feeding). Planning to conserve large areas of both land and water can be achieved following a biosphere reserve model. Existing interagency committees in the Chesapeake Bay Program could be more effective in developing such a model for wildlife and fisheries resources.

Chesapeake Bay↗
USGS2020

Ultraviolet-assisted oiling assessment improves detection of oiled birds experiencing clinical signs of hemolytic anemia after exposure to the Deepwater Horizon oil spill

While large-scale oil spills can cause acute mortality events in birds, there is increasing evidence that sublethal oil exposure can trigger physiological changes that have implications for individual performance and survival. Therefore, improved methods for identifying small amounts of oil on birds are needed. Because ultraviolet (UV) light can be used to identify thin crude oil films in water and on substrate that are not visually apparent under normal lighting conditions, we hypothesized that UV light could be useful for detecting small amounts of oil present on the plumage of birds. We evaluated black skimmers ( Rynchops niger ), brown pelicans ( Pelecanus occidentalis ), clapper rails ( Rallus crepitans ), great egrets ( Ardea alba ), and seaside sparrows ( Ammodramus maritimus ) exposed to areas affected by the Deepwater Horizon oil spill in the Gulf of Mexico as well as from reference areas from 20 June, 2010 to 23 February, 2011. When visually assessed without UV light, 19.6% of birds evaluated from areas affected by the spill were determined to be oiled (previously published data), whereas when examined under UV light, 56.3% of the same birds were determined to have oil exposure. Of 705 individuals examined in areas potentially impacted by the spill, we found that fluorescence under UV light assessment identified 259 oiled birds that appeared to be oil-free on visual exam, supporting its utility as a simple tool for improving detection of modestly oiled birds in the field. Further, UV assessment revealed an increase in qualitative severity of oiling (approximate % of body surface oiled) in 40% of birds compared to what was determined on visual exam. Additionally, black skimmers, brown pelicans, and great egrets exposed to oil as determined using UV light experienced oxidative injury to erythrocytes, had decreased numbers of circulating erythrocytes, and showed evidence of a regenerative hematological response in the form of increased reticulocytes. This evidence of adverse effects was similar to changes identified in birds with oil exposure as determined by visual examination without UV light, and is consistent with hemolytic anemia likely caused by oil exposure. Thus, UV assessment proved useful for enhancing detection of birds exposed to oil, but did not increase detection of birds experiencing clinical signs of anemia compared to standard visual oiling assessment. We conclude that UV light evaluation can help identify oil exposure in many birds that would otherwise be identified visually as unexposed during oil spill events.

Ecotoxicology↗
USGS1995

The value and vulnerability of small estuarine islands for conserving metapopulations of breeding waterbirds

Compelling arguments for preserving large habitat ‘islands’ have been made for a number of animal groups, but most commonly for terrestrial birds. We argue that, for many species of waterbirds nesting in coastal estuaries, maintaining numerous small islands may be a more effective management strategy than maintaining larger islands or reserves. In this study, the number of great white heron Ardea herodias nests over a 5-year period (1986–91) was negatively correlated with island area in the Florida Keys, USA. Nest densities were highest in the 2–10 ha island size range and lowest for islands larger than 100 ha. These small islands also attract nesting black skimmers Rynchops niger , brown pelicans Pelecanus occidentalis , and several species of terns and gulls. Small estuarine islands are vulnerable to sea level rise, erosion from watercraft, and, for dredge material islands, lack of sufficient maintenance because of competing needs for beach nourishment. Managers need to enforce more buffering and protection of these islands and argue for more dredged material allocations in some areas.

Florida↗
USGS2014

Physiological condition of juvenile wading birds in relation to multiple landscape stressors in the Florida Everglades: effects of hydrology, prey availability, and mercury bioaccumulation

The physiological condition of juvenile birds can be influenced by multiple ecological stressors, and few studies have concurrently considered the effects of environmental contaminants in combination with ecological attributes that can influence foraging conditions and prey availability. Using three temporally distinct indices of physiological condition, we compared the physiological response of nestling great egrets ( Ardea alba ) and white ibises ( Eudocimus albus ) to changing prey availability, hydrology (water depth, recession rate), and mercury exposure in the Florida Everglades. We found that the physiological response of chicks varied between species and among environmental variables. Chick body condition (short-term index) and fecal corticosterone levels (medium-term) were influenced by wetland water depth, prey availability, region, and age, but not by mercury contamination. However, mercury exposure did influence heat shock protein 70 (HSP70) in egret chicks, indicating a longer-term physiological response to contamination. Our results indicate that the physiological condition of egret and ibis chicks were influenced by several environmental stressors, and the time frame of the effect may depend on the specialized foraging behavior of the adults provisioning the chicks.

Florida↗
USGS2015

Linking dynamic habitat selection with wading bird foraging distributions across resource gradients

Species distribution models (SDM) link species occurrence with a suite of environmental predictors and provide an estimate of habitat quality when the variable set captures the biological requirements of the species. SDMs are inherently more complex when they include components of a species' ecology such as conspecific attraction and behavioral flexibility to exploit resources that vary across time and space. Wading birds are highly mobile, demonstrate flexible habitat selection, and respond quickly to changes in habitat quality; thus serving as important indicator species for wetland systems. We developed a spatio-temporal, multi-SDM framework using Great Egret ( Ardea alba ), White Ibis ( Eudocimus albus ), and Wood Stork ( Mycteria Americana ) distributions over a decadal gradient of environmental conditions to predict species-specific abundance across space and locations used on the landscape over time. In models of temporal dynamics, species demonstrated conditional preferences for resources based on resource levels linked to differing temporal scales. Wading bird abundance was highest when prey production from optimal periods of inundation was concentrated in shallow depths. Similar responses were observed in models predicting locations used over time, accounting for spatial autocorrelation. Species clustered in response to differing habitat conditions, indicating that social attraction can co-vary with foraging strategy, water-level changes, and habitat quality. This modeling framework can be applied to evaluate the multi-annual resource pulses occurring in real-time, climate change scenarios, or restorative hydrological regimes by tracking changing seasonal and annual distribution and abundance of high quality foraging patches.

PLoS ONE↗