Ardea Herodias Research Articles

Sociality Among Foraging Ardeidae: Does Plumage Coloration Influence Nearest-Neighbor Spacing?

Increased sociality in herons, family Ardeidae, is often considered to be associated with the occurrence of white plumage. If white plumage increases sociality, we hypothesized that white-plumaged birds should forage closer to one another and dark birds should remain more solitary. We tested this hypothesis by investigating the inter-individual spacing (nearest neighbor distance) in two pairs of closely related species that differ in plumage coloration: (1) Great Blue Heron (Ardea herodias)/Great Egret (A. alba) and (2) Little Blue Heron (Egretta caerulea)/Snowy Egret (E. thula). All birds observed were in adult plumage. We recorded distances to nearest conspecific, nearest congeneric, nearest white (regardless of species) and nearest dark bird to each focal bird within a given (focal) pond. Because species occurred in varying numbers, we compared the observed mean distances with randomly generated distances based on the total number of birds in the pond. All observations were conducted under steady water levels, avoiding drying ponds as this might concentrate prey. We found that Snowy Egrets were significantly farther from conspecifics and dark congenerics (Little Blue Herons) than expected under a null model of random spacing within the focal pond. Little Blue Herons also were spaced farther apart from white congenerics (Snowy Egrets) than expected. Great Blue Herons and Great Egrets exhibited no distinct social tendencies and neither avoided nor preferred foraging near other herons. Our results do not support the hypothesis that white-plumaged birds exhibit increased social tendencies relative to dark-plumaged birds within a given pond.

Great Blue Heron Productivity at Mason Neck National Wildlife Refuge in Northern Virginia, and the Potential Impacts of Weather During a 13-Year Interval

Abstract The reproductive performance of a large Great Blue Heron (Ardea herodias) colony was documented and the potential effects of weather on reproductive performance was investigated. Annual surveys were conducted during the last week of May or the first week of June between 1992 and 2004 and were designed to count all fledglings and nests in and around the heronry. Mean number of fledglings per nesting attempt during the 13-year interval was 1.57 ± 0.22 fledglings (range: 1.14 to 1.87). Mean number of fledglings per successful nest during the study was 1.80 ± 0.18 fledglings (range: 1.44 to 2.06). The number of fledglings per nesting attempt was similar to other long-term studies for the species, but the productivity based on fledglings per successful nest was typically lower. Stepwise regression analysis indicated that both fledglings per nesting attempt (active nest) and fledglings per successful nest were significantly influenced by weather patterns (number of days with greater than 0.30 inches of...

Use of Vanishing Bearings to Locate New Wading Bird Colonies

Abstract Estimating the size of breeding populations of colonial nesting wading birds is a priority for waterbird management but locating colonies can be difficult. Existing methodologies to locate wading bird colonies require use of airplanes and/or a systematic search of likely colony locations on the landscape. This study describes the use of vanishing bearings of Great Blue Herons (Ardea herodias) as they depart coastal foraging sites to determine the number and location of associated breeding colonies. In 2002, frequency analysis of the vanishing bearings identified 23 modes at ten sites while in 2003, 29 modes at 15 sites were identified. Of these modes, about one-half (twelve in 2002 and 15 in 2003) were associated with a known colony. Groupings of vanishing bearings unassociated with known colonies prompted searches for unknown colonies. Searches in 2002 and 2003 found three colonies missed during routine colony inventories using information from the public. Intensive searches in 2004 and 2005 at ...

Predation of Eared Grebe by Great Blue Heron

Great Blue Herons (Ardea herodias) typically prey upon fish and other aquatic organisms, and they occasionally take small mammals and birds. We observed a Great Blue Heron attack, kill, and attempt to consume an Eared Grebe (Podiceps nigricollis). The heron was unable to swallow the grebe, and it abandoned the carcass after approximately 30 min. An examination of the carcass showed that the grebe lacked obvious physical deformities. Our observation, coupled with a similar one nearby, indicates that Great Blue Herons attack and kill birds larger than reported previously.

Contamination and Biomarkers in the Great Blue Heron, an Indicator of the State of the St. Lawrence River

In 1996-1997, nine breeding colonies of the great blue heron on the St. Lawrence River and its estuary (Québec, Canada) were investigated in the framework of a biomonitoring program. Fledglings from colonies in freshwater were more contaminated with mercury, PCBs and many organic contaminants than those from estuarine colonies. The level of contamination in the St. Lawrence River is generally below the levels of toxicological effects for the great blue heron. The molar ratio of retinol: retinyl palmitate in heron eggs was correlated with total PCBs (r=0.79) and Mirex (r=0.90). In plasma, all biochemical parameters were significantly different between freshwater and marine colonies. Plasma retinol concentrations at the Dickerson and Hérons colonies were significantly lower compared with those at Grande Ile (p<0.05) and Steamboat (p<0.001). Based on retinoid and beta-carotene concentrations in eggs, low plasma retinol was not associated with possible dietary deficiency. Plasma retinol was negatively correlated with many PCB congeners, total PCBs (r=-0.78), p,p'-DDE, trans-nonachlor and alpha-HCH. Similarly, the hormone T3 was correlated with many PCB congeners, total PCBs (r=-0.69) and the same organochlorine chemicals. Plasma LDH concentrations were different among freshwater colonies, Grande Ile and Hérons colonies having LDH values significantly greater than those of Steamboat (respectively, p<0.05 and p<0.01). Globally, the health status of the St. Lawrence great blue heron population was judged to be acceptable, however, several biomarkers indicated positive responses to contaminants.

Effects of Lake Characteristics and Human Disturbance on the Presence of Piscivorous Birds in Northern Wisconsin, USA

Despite current anthropogenic alterations to riparian areas and littoral zones of lakes, little information is available on how human-induced alterations affect lacustrine habitat use by many piscivorous birds in northern Wisconsin, USA. The influence of lake characteristics and human disturbance on species richness and the presence of seven species of piscivorous birds was determined on 98 lakes located primarily in Vilas and Oneida counties, Wisconsin. Lakes were surveyed for species presence using shoreline perimeter surveys with total searching time standardized to two, one-hour surveys per lake. Piscivorous bird species richness was highest on large lakes with high pH levels. Using logistic regression, many species were found to be present on lakes possessing characteristics associated with high abundances of fish, including lake surface area, pH, and water clarity. At least one of these variables was included in the final models for species richness and presence of the Common Merganser (Mergus merganser), Bald Eagle (Haliaeetus leucocephalus), Great Blue Heron (Ardea herodias), and Ring-billed Gull (Larus delawarensis). Three species avoided lakes possessing characteristics associated with high levels of human disturbance; the Osprey (Pandion haliaetus) was not found on lakes with low percentages of macrophytes, the Common Merganser was absent on lakes with low water clarity, and the Common Loon (Gavia immer) was not present on lakes with many cottages. Many species of piscivorous birds were widespread regardless of the degree of human development, indicating that habituation to humans may have occurred. In addition, density-dependent factors may have precluded identification of optimal lake characteristics for some species due to habitat saturation.

Phylogenetic Analysis of Avian Poxviruses Among Free-Ranging Birds of Virginia

Polymerase chain reaction was used to amplify a portion of the avian poxvirus core 4b gene of infected free-ranging birds that presented at the Wildlife Center of Virginia during the 2003 and early 2004 years. The species of bird infected were a great blue heron (Ardea herodias), two American crows (Corvus brachyrhyncos), two American robins (Turdus migratorius), two mourning doves (Zenaida macroura), a red-tailed hawk (Buteo jamaicensis), a blue-gray gnatcatcher (Polioptila caerulea), a northern mockingbird (Mimus polyglottos), a house finch (Carpodacus mexicanus), and a northern cardinal (Cardinalis cardinalis). Phylogenetic analysis was performed using the consensus sequences determined for each avian case in Virginia in combination with avian poxvirus core 4b gene sequence from isolates previously described in Europe and that of vaccinia virus. Alignment of DNA sequences identified areas of point mutations and, in the case of a single mourning dove, the incorporation of a triplet of nucleotides. Maximum-likelihood analysis grouped the 2003-2004 Virginia avian poxviruses into a clade distinct from those reported in European free-ranging birds, with the exception of a single case in a mourning dove that clustered within one European clade. The cladogram that resulted from our analysis of the European isolates is in agreement with those previously published. This study identified a distinct clade of avian poxvirus unique from four clades previously described and associated with epornitics in free-ranging birds, where the core 4b gene DNA sequence has been the basis of comparison.

Comparative use of longline oysterbeds and adjacent tidal flats by waterbirds

Commercial oyster Crassostrea spp. cultivation in intertidal habitats may degrade foraging habitat of waterbirds. Consequently, we compared species abundances, community similarity and diversity of waterbirds using longline oyster culture beds and adjacent control plots on tidal flats of Humboldt Bay, California. Abundances of most species differed significantly between treatments, with seven of 13 shorebirds Charadriiformes and three of four wading birds Ciconiiformes more abundant on longline plots. By contrast, Black-bellied Plover Pluvialis squatarola were more abundant on control plots. Marbled Godwit Limosa fedoa, Long-billed Curlew Numenius americanus and Dunlin Calidris alpina showed mixed results depending on location and Great Blue Heron Ardea herodias were more abundant only on one control plot. Community composition was similar on longline and control plots, although diversity (H′) was greater on longline plots. Varying species' responses to longline techniques may have been associated with interspecific differences in diet and foraging behaviour, and the impacts of longlines and oyster-harvesting on prey distribution. Overall, longlines did not negatively affect the foraging behaviour of most species, but the underlying causes for increased bird use may lead to impacts on other trophic levels and over a longer temporal scale.

Polybrominated Diphenyl Ether Trends in Eggs of Marine and Freshwater Birds from British Columbia, Canada, 1979−2002

Temporal, spatial, and interspecific trends in polybrominated diphenyl ether (PBDE) flame retardants were determined in eggs of marine and freshwater bird species from the province of British Columbia, Canada. Temporal trends in the Fraser River estuary, 1983-2002, were examined by analysis of eggs of great blue herons (Ardea herodias) and from the Strait of Georgia marine ecosystem, 1979-2002, in eggs of double-crested cormorants (Phalacrocorax auritus). Results were compared to those from eggs of the osprey (Pandion haliaetus) taken along the lower Fraser River and along the Columbia River near Castlegar, British Columbia, and of a pelagic seabird, the Leach's storm-petrel (Oceanodroma leucorhoa), collected at a colony on the Queen Charlotte Islands. Mean concentration of sigmaPBDE, 455 microg/kg w.w., were highest in heron eggs collected in 2002 from the Fraser estuary. Concentrations in eggs of cormorants and ospreys taken from sites of varying urban influence tended to be about half that value. Leach's storm petrel eggs had only trace amounts of sigmaPBDE (3.38 microg/kg), despite having similar concentrations of PCBs and organochlorine pesticides to the other species. PBDEs increased exponentially with a doubling time of 5.7 years in eggs of both herons and cormorants. Over this period of increasing PBDEs, major chlorinated hydrocarbons, such as PCBs and DDE, were stable or decreased. The PBDE pattern was relatively consistent in most years and sites, with BDEs 47 > 100 > 99 > 153 > 154 > 28 > 183. This was interpreted as evidence of technical pentaBDE formulations as primary sources of the contamination, with the octaBDE formulations as secondary. Higher resolution analysis of a subsample of the eggs revealed the presence of up to nine other congeners, including BDE209 (range: 0.9-1.8 microg/kg), indicating exposure and uptake of decaBDE sourced congeners in North American foodchains. At some locations, concentrations of pentabrominated congeners and mixtures in fish are approaching levels potentially toxic to fish-eating birds, based on rodent studies and calculations of dietary intake from fish data.

Metal Concentrations, Foraging Distances, and Fledging Success of Great Blue Herons Nesting along the Hanford Reach of the Columbia River

An ecological risk assessment of the spatial distribution of metal concentrations along the Hanford Reach of the free-flowing Columbia River in southcentral Washington, identified great blue herons, Ardea herodias, at potential risk through the ingestion of contaminated riverine biota, especially fish. We measured metal concentrations in livers of pre-flight herons from the Hanford Reach and excrement samples taken from the same nests. Nests were distributed among three colonies situated upstream and downstream from nine retired plutonium production reactors along the river where metals in reactor coolant waters had been released directly into the river or disposed to shoreline retention basins and ditches. Distances traveled by parent herons to foraging areas along the river shore were determined by visually tracking parent birds as they flew from nests to upriver and downriver foraging sites. Foraging flight distances varied between colonies with mean distances ranging between 0.7 and 3.1 km. Cadmium, Cr, and Pb concentrations were higher in excrement than in the livers of pre-flight herons but the opposite was noted for Cu, Hg, and Zn. Highest metal concentrations of Cr, Cu, Zn, Cd, and Pb, were measured in excrement taken from heron nests at the colony located upstream from all reactors. These results were consistent with metal concentrations reported in river sediment from the same regions, indicating excrement from the heron nests may be a useful indicator of dietary uptake of metals by herons. Fledging success and eggshell thickness measurements were used as an index of health of the local heron population. The results indicate that the reproductive health of great blue herons nesting along the Hanford Reach is among the highest reported in the continental United States.

Evidence from nature: interspecies spread of heron hepatitis B viruses

Heron hepatitis B viruses (HHBVs) in three subspecies of free-living great blue herons (Ardea herodias) from Florida, USA, were identified and characterized. Eight of 13 samples were positive in all assays used, whereas sera from egrets, which are also members of the family Ardeidae, were negative in the same assays. Comparative phylogenetic analysis of viral DNA sequences from the preS/S region of previously reported and novel HHBV strains isolated from captive grey herons (Germany) and free-ranging great blue herons (USA), respectively, revealed a strong conservation (95 % sequence similarity) with two separate clusters, implying a common ancestor of all strains. Our data demonstrate for the first time that different subspecies of herons are infected by HHBV and that these infections exist in non-captive birds. Phylogenetic analysis and the fact that the different heron species are geographically isolated populations suggest that lateral transmission, virus adaptation and environmental factors all play a role in HHBV spreading and evolution.

The Training and Transfer of Real-World Perceptual Expertise

A hallmark of perceptual expertise is that experts classify objects at a more specific, subordinate level of abstraction than novices. To what extent does subordinate-level learning contribute to the transfer of perceptual expertise to novel exemplars and novel categories? In this study, participants learned to classify 10 varieties of wading birds and 10 varieties of owls at either the subordinate, species (e.g., "great blue crown heron,""eastern screech owl") or the family ("wading bird,""owl") level of abstraction. During training, the amount of visual exposure was equated such that participants received an equal number of learning trials for wading birds and owls. Pre- and posttraining performance was measured in a same/different discrimination task in which participants judged whether pairs of bird stimuli belonged to the same or different species. Participants trained in species-level discrimination demonstrated greater transfer to novel exemplars and novel species categories than participants trained in family-level discrimination. These findings suggest that perceptual categorization, not perceptual exposure per se, is important for the development and generalization of visual expertise.

ORNAMENTAL PLUME DEVELOPMENT AND THE “PREALTERNATE MOLTS” OF HERONS AND EGRETS

Abstract To investigate molts and ornamental-plume development in herons and egrets, we examined 448 specimens of 10 North American species. We found no evidence for a prealternate molt, despite widespread opinion that such a molt occurs and includes the ornamental plumes. Our data indicate that these plumes emerge during the later stages of the definitive prebasic molt in August–November, grow slowly through January– February, and are retained until replacement during the following prebasic molt. The preformative (traditionally termed “first-prebasic”) molt shows substantial variation in extent. In 91.9% of 86 first-year individuals collected between November and May, this molt included the development of ornamental plumes that were similar in form, but shorter in length, than those of adults. Male Great Blue (Ardea herodias) and Little Blue (Egretta caerulea) herons developed longer ornamental plumes than females, presumably a result of sexual-selection strategies.

Minghella's Mountain

FILM REVIEW Minghella's Mountain David Heddendorf IN CHARLES FRAZIER'S 1997 NOVEL COLD MOUNTAIN, the transplanted Charleston belle Ada Monroe ponders the wording of a letter she is writing to Inman, the Confederate soldier she awaits. At last she writes a single sentence, "Come back to me is my request," taking the line from "a ragged love song." The borrowed lyric signals her growth from "pose and irony" to "just saying what your heart felt, straight and simple and unguarded" (272). In the recent film version of Cold Mountain, written and directed by Anthony Minghella, Ada also writes "Come back to me" in a letter, but she is not recalling a song, or thinking about how best to express herself. The line occurs as part of an emphatic voiceover appeal: "If you are fighting, stop fighting. If you are marching, stop marching....Come back to me is my request." We hear the letter read aloud to the wounded Inman, who shortly afterward climbs from his hospital window and begins his long walk home. The revised handling of the letter is typical. Where Frazier the novelist slowly initiates characters into new outlooks on life, Minghella tightens his cinematic focus on a love story. By Frazier's own account in an article for Salon, Cold Mountain owed its original impulse not to the Civil War, and still less to the Ada-Inman romance, but to his fascination with "a very old way of life" in the Appalachian Mountains. Needing a "point of access" into this dimly recalled world, Frazier chose the war and the love story that Minghella recognized as the makings of an epic movie. Under Minghella's direction the readyfor -Hollywood themes become the heart of the picture, while the old way of life fades into the background. At first a reader might notice few differences in the film, aside from the usual screenplay tweaking: scenes shuffled, episodes conflated, lines of dialogue redistributed. The "goatwoman" Inman stumbles across in the woods is made into his rescuer in the film, after he and the preacher Veasey are shot by the Home Guard. Where Inman hunts down three Federal raiders who have terrorized a widowed mother, Minghella streamlines and softens the brutal episode. Such revisions have little effect on the overall story, while helping to squeeze Frazier's sprawling tale into a two-and-a-half-hour movie. 58 Other changes, however, say more about Minghella's artistic design. For instance, Inman carries a copy of William Bartram's Travels through both novel and film. While Frazier has Inman discover the book in a box of charitable donations, Minghella's Ada gives the Travels to Inman as a going-away present, thus staging their passionate farewell. Instead of consoling Inman with beloved landscape descriptions, the battered volume becomes his Ada-talisman and a hiding-place for his sweetheart's portrait. Frazier fans who see the film might miss a scene in which Ada and her friend Ruby encounter a great blue heron that approaches them, staring, before spreading its wings and taking flight. In lieu of this bird passage Minghella invents another. As Inman lies gurgling with his horrible throat wound, a dove fills the screen with translucent wings, heralding a dreamlike flashback in which Ada and Inman stand in an empty church. The dove, we discover, is trapped in the building. Nearly wordless, the couple exchange soulful looks as Inman tenderly captures the dove and releases it at the door. The haunting scene is almost impossible to imagine in Frazier's novel. For one thing, Frazier's Inman would more likely draw his fearsome LeMat's pistol and blast the bird out of the air. This reluctant soldier, as portrayed in the novel, canbe ruthless and cold-blooded. He doesn't just talk about how the war has ravaged his spirit—he routinely shoots and clubs men to death. Killing in self-defense or on behalf of others, he is nonetheless hard and remorseless, and speaks in harsh, sardonic accents. Genteel Ada, plenty prickly herself, meets her match in his proud, detached silences. Minghella sands the edges off these difficult characters, and converts them into warm, attractive people. As in...

Winter–spring food habits of an island population of Coyote Canis Latrans in Baja California, México

Food habits of the coyote (Canis latrans) on San Luis Gonzaga Island of Baja California, Mexico were investigated. We collected 239 scat samples for analysis on 14 May 1997. Samples ranged from fresh to approximately 2 months old. Frequency of diet components was 48.9% birds, 21.9% fish, 14.8% plants, 3.6% mammals, 4.0% insects, 0.7% reptiles, 0.5% arachnids, and 5% crustaceans. The last group had not previously been recorded in this region. Great blue herons (Ardea herodias) composed 11% of the diet. Other members of the Ardeidae family accounted for an additional 23.4%. From March through May, the large coyote population on the island depends mainly on scavenging bird carcasses, and has minimal impact on endemic rodent species on the island, some of them listed as threatened by the Mexican government.

Factors Influencing Great Blue Heron Nesting Productivity on the Pacific Coast of Canada from 1998 to 1999

Surveys were conducted at 35 Great Blue Heron (Ardea herodias) colonies in urban and rural landscapes of south-coastal British Columbia, Canada, to investigate low nesting productivity during 1998 and 1999 compared to a decade ago. Nesting failure was common (59% of 1,247 nests) and widespread (in 90% of 31 colonies) and accounted for 96% of the variation in nesting productivity among colonies in 1999. Nesting failure was more frequent in small colonies (<50 nests) than in large colonies (≥50 nests). Human disturbance has probably increased due to growth in the human population in the region, and direct disturbance from the Bald Eagle (Haliaeetus leucocephalus) was more frequent in 1999 than a decade earlier. Eagles predated eggs, nestlings, and fledglings and were probably responsible for most of the observed nesting failure. Direct disturbance by humans was infrequent, but heron nesting productivity was negatively correlated with the frequency of human pedestrians near colonies. We suggest that Great Blue Heron breeding failure was more frequent in 1998 and 1999 compared to a decade ago because of the combined effects of human disturbance from land development and an increased frequency of eagle predation.

A historical record of mercury contamination in Southern Florida (USA) as inferred from avian feather tissue.

During the late 1980s, the upper trophic-level biota of the Everglades (FL, USA) was recognized as being highly contaminated with mercury (Hg). However, the timing and pattern of that increase is poorly known, and no information is available about mercury contamination in Everglades wildlife prior to 1974. We measured methylmercury concentrations in feathers of white ibises (n = 33), great egrets (n = 7), anhingas (n = 21), and great blue herons (n = 12) from museum specimens collected from 1910 through 1980 and combined them with more recent feather samples collected from live birds (1985-2000, n = 98, 37, 49, and 7, respectively). We found no evidence of contamination of museum samples with inorganic mercuric preservatives (0.01-0.28% of total Hg in feathers). All species showed relatively low concentrations of mercury through the 1970s (<5 microl/L dry wt for anhingas, ibises, and egrets, <10 microl/L for herons). Samples from all species taken during the 1990s showed a large and significant increase (4-5X) in MeHg concentration. This evidence suggests that most of the increase in Hg deposition during the 20th century in south Florida occurred during the last two to three decades, which is consistent with information about local source deposition. Contamination levels prior to the 1970s appear to have been associated with normal reproduction in these birds, suggesting partial evidence for a threshold of reproductive impairment.

Mosquito and arbovirus activity during 1997-2002 in a wetland in northeastern Mississippi.

The species composition and population dynamics of adult mosquitoes in a wetland near Iuka, MS, were analyzed over a 6-yr period (1997-2002) and reverse transcription-polymerase chain reaction (PCR) detection rates of arboviruses determined during five of those years. Blood meals of three likely vector species were identified using a PCR-based method that allows identification of the host to species. Culex erraticus (Dyar & Knab) composed 51.9% of the population during the 6-yr period with 295 females collected per trap night. Eastern equine encephalomyelitis (EEE) virus was detected in six genera of mosquitoes [Coquillettidia perturbans (Walker), Culex restuans Theobald, Culex salinarius Coquillett, Culex erraticus (Dyar & Knab), Anopheles crucians Wiedemann, Anopheles quadrimaculatus Say, Aedes vexans (Meigen), Ochlerotatus triseriatus Say, and Psorophora ferox Humboldt) with positive pools occurring in 1998, 1999, and 2002. Culiseta melanura Coquillett occurred at a low level (< 1%) and was not infected. Saint Louis encephalitis virus was detected once in a single pool of Cx. erraticus in 1998. Neither West Nile virus nor LaCrosse virus was found. Minimum infection rates per 1000 females tested of competent vectors of EEE virus were variable and ranged from 0.14 for Cx. erraticus to 40.0 for Oc. triseriatus. Thirty-nine species of birds were identified in the focus with blood-engorged mosquitoes found to contain meals (n = 29) from eight avian species. The majority of meals was from the great blue heron, Ardea herodias L. (n = 55%), but when bird abundance data were adjusted for avian mass, the brown-headed cowbird, Molothrus ater (Boddaert); blue jay, Cyanocitta cristata (L.); and northern mockingbird, Mimus polyglottos (L.), were overrepresented as hosts.

Clinostomum complanatum and Clinostomum marginatum (Rudolphi, 1819) (Digenea: Clinostomidae) are separate species based on differences in ribosomal DNA.

Infections by metacercariae of Clinostomum (Leidy, 1856) species adversely affect aquacultured fish and are potentially transmissible to humans. Molecular methodologies are efficient tools, which enable diagnosis of all life-history stages of trematodes in their diverse hosts. The small subunit of ribosomal DNA genes of adults of the Old World Clinostomum complanatum (Rudolphi, 1819) and the New World Clinostomum marginatum (Rudolphi, 1819), obtained from a little egret Egretta garzetta (Linnaeus, 1766) and the great blue heron Ardea herodias (Linnaeus, 1758), respectively, were amplified, sequenced, and aligned. The resulting alignment was used to develop a genetic assay to differentiate between these species.

Great Blue Heron Predation on Stocked Rainbow Trout in an Arkansas Tailwater Fishery

Abstract Fisheries managers seldom have adequate information to assess their stock losses to avian piscivores, which function as apex predators in many aquatic food webs. Our primary objective was to estimate the number of stocked rainbow trout Oncorhynchus mykiss consumed by great blue herons Ardea herodias on the Bull Shoals and Norfork tailwaters of north-central Arkansas. Between November 2000 and December 2001, we periodically surveyed great blue herons along 150.7 river km on the tailwaters of the Bull Shoals and Norfork dams. Heron density (number/km) in or along the river ranged from 0 to 4/km per survey, with the highest mean number located near the Bull Shoals Dam (2.31 herons/km). We recorded 467 prey captures by herons during 202 observation hours. Sculpin Cottus spp. were the most common prey (N = 120). Most prey (87%) measured 14 cm or less in length, and most captured live trout (85.4%) fell between 10.5 and 28.0 cm in length. While live trout represented only 48 of 359 identifiable prey it...