Pelecanus Erythrorhynchos Research Articles

Predation by American White Pelicans and Double‐Crested Cormorants on Catchable‐Sized Hatchery Rainbow Trout in Select Idaho Lentic Waters

AbstractIn southern Idaho, population growth of American white pelicans Pelecanus erythorhynchos at the Blackfoot Reservoir and Lake Walcott colonies since the early 1990s has generated concerns about whether pelican predation is impacting angler catch of hatchery trout stocked in Idaho waters. To evaluate this concern, we estimated rates of pelican predation (i.e., the proportion of fish consumed by pelicans) and angler catch (i.e., the proportion of fish caught by anglers) for 19 unique springtime fish stocking events over 3 years across 12 study waters; where feasible we also estimated double‐crested cormorant Phalacrocorax auritus predation. Stocked Rainbow Trout Oncorhynchus mykiss averaged 247 mm in length and were internally PIT‐tagged (to monitor bird predation) and externally anchor‐tagged (to monitor angler catch) before stocking. Additional hatchery trout were PIT‐tagged, euthanized, and fed directly to pelicans to estimate PIT tag deposition rates at the colonies; feeding was unsuccessful for cormorants. After the juvenile pelicans and cormorants fledged in the fall, we recovered PIT tags from stocked and fed fish that were deposited at the two colonies. Deposition rates for pelican‐consumed tags averaged 21% and declined exponentially as distance increased from the colonies. Pelican predation on hatchery trout averaged 18% and ranged from 0 to 48%, whereas angler catch averaged 21% and ranged from 0 to 82%. Mean angler catch was nearly four times higher when pelican predation was low (i.e., <25%) than when pelican predation was high (≥25%). Cormorant predation estimates (available for seven stocking events) were minimum estimates only (i.e., they assumed 100% of tags consumed by cormorants were recovered) and averaged 14% (range, 2–38%). Our results suggest that predation by American white pelicans and double‐crested cormorants on catchable‐sized hatchery Rainbow Trout stocked in southern Idaho waters often exceeds the total catch of those fish by anglers who compete directly with avian predators for use of stocked trout.Received June 23, 2015; accepted November 8, 2015 Published online March 30, 2016

Linking Isotopes and Panmixia: High Within-Colony Variation in Feather δ2H, δ13C, and δ15N across the Range of the American White Pelican.

Complete panmixia across the entire range of a species is a relatively rare phenomenon; however, this pattern may be found in species that have limited philopatry and frequent dispersal. American white pelicans (Pelecanus erythrorhyncos) provide a unique opportunity to examine the role of long-distance dispersal in facilitating gene flow in a species recently reported as panmictic across its broad breeding range. This species is also undergoing a range expansion, with new colonies arising hundreds of kilometers outside previous range boundaries. In this study, we use a multiple stable isotope (δ2H, δ13C, δ15N) approach to examine feather isotopic structuring at 19 pelican colonies across North America, with the goal of establishing an isotopic basemap that could be used for assigning individuals at newly established breeding sites to source colonies. Within-colony isotopic variation was extremely high, exceeding 100‰ in δ2H within some colonies (with relatively high variation also observed for δ13C and δ15N). The high degree of within-site variation greatly limited the utility of assignment-based approaches (42% cross-validation success rate; range: 0–90% success). Furthermore, clustering algorithms identified four likely isotopic clusters; however, those clusters were generally unrelated to geographic location. Taken together, the high degree of within-site isotopic variation and lack of geographically-defined isotopic clusters preclude the establishment of an isotopic basemap for American white pelicans, but may indicate that a high incidence of long-distance dispersal is facilitating gene flow, leading to genetic panmixia.

Fritz L. Knopf, 1945–2015

He was tall and slim, and many of us remember him in his iconic cowboy hat and boots, leaning against a pickup truck out in the grasslands. Dr. Fritz L. Knopf, senior research wildlife biologist (retired) with the U.S. Geological Survey (USGS) at the Fort Collins Science Center, contributed as much as anyone to our knowledge of the natural history and ecology of the Great Plains, its endemic birds, and the conservation of this threatened landscape. Fritz passed away on October 22, 2015, after battling a brain tumor. Fritz’s long research career was focused largely on understanding how biophysical changes in landscapes influence migratory bird systems, and on ways to translate that research into conservation management and policy. He accomplished this by actively engaging with academics, resource managers, and landowners. His collaborations were distinguished by a mutual trust and respect for people, native bird populations, and the landscapes they share. He attributed his ability to work with and gain the trust of landowners (primarily ranchers on the Great Plains) to his childhood on a dairy farm in northeastern Ohio, where he ‘‘actually liked cows.’’ He understood the utility of coming to the conversations without a preconceived negative opinion about the effects of cattle and grazing. Having come to his career during the era when natural history was still an important component of resource management and conservation science, Fritz was fascinated by western history and the history of natural resource conservation. He was quick to relate stories of how the histories of George Bird Grinnell, Teddy Roosevelt, Gifford Pinchot, John Kirk Townsend, and Kit Carson shaped current western landscapes relevant to his research. In high school Fritz’s passion was baseball, and he was the starting varsity pitcher in his freshman year. In 1967 he received his undergraduate degree in biology from Hiram College in Ohio, where his mentor, James Barrow, aroused his interest in behavioral ecology. He ‘‘took every biology course they had,’’ but his favorite college course was on the Romantic poets, whose expressions of the spirit of the landscape spoke to him. Although his initial plan was to become a veterinary student, he decided that he ‘‘didn’t like the idea of the inside of an animal as much as the outside of an animal.’’ After college he moved west to Utah State University to work with David Balph, a former student of Dr. Barrow, on the behavioral ecology of Uinta ground squirrels. It was during this time that he came to love the Rocky Mountain region, where he was to spend the rest of his life and most of his research focus. In 1969, in the midst of his master’s program, he was drafted into the military. He spent time at Fort Ord, California, and at the U.S. Army Research Institute of Environmental Medicine in Natick, Massachusetts, before being discharged in 1970. He returned to Utah State, where he finished his M.S. in wildlife science in 1973. His research on colonial-nesting American White Pelicans on the Great Salt Lake earned him his Ph.D. in wildlife ecology from Utah State in 1975. Fritz began his career as an instructor in the departments of Wildlife Science and Instructional Development at Utah State (1975–1976) while continuing work on

Implications of spring water levels on the production of American white pelicans nesting at marsh lake, Minnesota

ABSTRACTWe investigated the relationship between spring water levels and production of American white pelicans (Pelecanus erythrorhynchos) nesting colonially at Marsh Lake in southwest Minnesota during 2003–2012. We obtained estimates of pelican nest and chick numbers from aerial photographs to determine population levels. We used historical streamflow data to characterize April water conditions, a period when nest‐site selection typically occurs. Pelicans used 4 islands and 1 peninsula for nesting, ranging from relatively high‐elevation sites connected to or near the mainland to more distant low‐elevation sites in the middle of the lake. The number and proportion of nests on high‐elevation sites are positively related to discharge in the Upper Minnesota River during April. In years when high water inundates low‐elevation sites during pelican nest‐site selection, pelican nests were located on the high‐elevation locations near or connected to the mainland. Over 90% of the variation in the number of nests on high‐elevation sites is related to the mean daily discharge in the Upper Minnesota River during April. In addition, the proportion of nests on high‐elevation sites also increases as mean daily discharge during April increases. However, chick production was negatively related to discharge during April. More than 84% of the variation in the number of near‐fledged chicks produced per nest was related to mean daily discharge during April. Although high‐elevation sites in close proximity to the mainland offered nesting pelicans refuge from high water levels, they also expose American white pelican nests to greater predator risk. Nest camera monitoring indicated that high‐elevation sites exhibited significantly higher predator activity than low‐elevation sites, and experienced lower nest success (i.e., probability that at least 1 egg from the nest hatched). Proposed changes in the management of Marsh Lake call for the installation of a water control structure at the Marsh Lake dam that will allow for active management of lake levels. Our study provides managers with models for predicting impacts of water levels on American white pelican production. © 2015 The Wildlife Society.

Nephromonorcha varitestisn. sp. (Digenea: Renicolidae) from the American White Pelican,Pelecanus erythrorhynchosin North Dakota, U.S.A.

ABSTRACT: Nephromonorcha varitestis n. sp. (Digenea: Renicolidae) is described based on numerous specimens found in the kidneys of an American white pelican, Pelecanus erythrorhynchos Gmelin, 1789, collected in the Turtle Mountains, North Dakota, U.S.A. Nephromonorcha varitestis n. sp. differs from morphologically similar species in the body shape and proportions, sucker and sucker:body ratios, position and extent of vitellarium, and the shape of its ovary and testis. The morphological description of the new species based on light and scanning electron microscopy is provided. Nephromonorcha varitestis n. sp. is differentiated from all other members of Nephromonorcha and morphologically similar species of Renicola. Partial sequences of nuclear ribosomal rRNA gene are provided for future phylogenetic analyses. This is the first Nephromonorcha species reported from pelicans and only the second named renicolid species from pelicans in North America.

Predation by American White Pelicans on Yellowstone Cutthroat Trout in the Blackfoot River Drainage, Idaho

AbstractExpansion of the American white pelican Pelicanus erythrorhynchos colony on Blackfoot Reservoir, Idaho, and the associated declines in adfluvial Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in the upper Blackfoot River drainage has generated concern about the impact of pelican predation on this native trout stock. During a 4‐year study, 4,653 wild Yellowstone Cutthroat Trout were tagged using a combination of radiotelemetry and PIT tags. Annual predation rate estimates were made by recovering Yellowstone Cutthroat Trout tags from the nesting islands of American white pelicans. On‐island tag recovery rates were corrected for ingested tags that went undetected during island searches and for tags that were deposited away from the nesting islands. American white pelicans consumed tagged Yellowstone Cutthroat Trout ranging from 150 mm to 580 mm TL and showed no size selection within that range for their prey. Predation rates on adult and juvenile Yellowstone Cutthroat Trout generally exceeded 20%, and the highest values were above 60%. Our independent methods (telemetry and PIT tagging) for estimating pelican predation on adult Yellowstone Cutthroat Trout produced similar results. Annual river flow conditions varied markedly and may have contributed to some of the observed range in predation rate estimates. Predation by the pelican colony appears to be a likely contributor to the recent collapse of Yellowstone Cutthroat Trout in the upper Blackfoot River drainage. In the past, overexploitation by anglers severely reduced the trout population and was remedied by implementing catch‐and‐release regulations. The current predation impact poses a greater management challenge, namely, finding a balanced approach for conserving both the native trout stock and the pelican colony.Received April 29, 2014; accepted February 5, 2015

Lake Use by Three Avian Piscivores and Humans: Implications for Angler Perception and Conservation

Humans and colonial piscivorous birds are often perceived to be in conflict over shared aquatic habitats and fisheries resources in inland lakes. We examined angler perception of birds and the relative abundance of American white pelicans (Pelecanus erythrorhynchos), double-crested cormorants (Phalacrocorax auritus), western grebes (Aechmophorus occidentalis), and boats on two lakes in Saskatchewan, Canada. Anglers perceived cormorants to be the biggest threat to fisheries (60%), compared to pelicans (47%), and western grebes (34%). The density of these birds and boats varied significantly between sections of the two study lakes. Boat density was higher in developed sections with shoreline communities (range 0-7/km2) compared to those surrounded by agricultural land or native prairie (0-1/km2). In contrast, cormorant and pelican densities were highest in areas with an undeveloped shoreline (0-22/km2), and were reduced to near zero in developed sections. Western grebes did not follow the same pattern as the other two species; grebe density was generally more uniform within lakes (0-23/km2 in all sections). Boat density was a negative predictor of pelican and cormorant density on one lake, but was a positive predictor for grebes on both lakes. Our results indicate that pelicans and cormorants avoid sections of lakes that have higher levels of human development, potentially altering the location of their foraging sites on the scale of kilometres. In contrast, western grebes were abundant in all areas of the two lakes and did not appear to avoid human development or activity. We conclude that angler perceptions are not congruent with levels of habitat use overlap with birds. In addition, western grebe responses to human activities appear counterintuitive, making interpretations difficult in a conservation context; further study is required.

Abundance and Trends of Colonial Waterbirds on the Large Lakes of Southern Manitoba

Abstract. Regular surveys of waterbird colonies are needed to identify changes in abundance and distribution. Consistent surveys have been maintained in some regions, but one area where updated surveys were needed was southern Manitoba, where Lakes Winnipeg, Winnipegosis and Manitoba had not been jointly surveyed since 1979. In mid-June, 2012, an aerial survey of the region was conducted using digital photography to estimate abundance of six colonial waterbird species that are regular breeders on these lakes. Breeding by at least one of the six species was confirmed at 131 locations. Double-crested Cormorant (Phalacrocorax auritus) was the most abundant breeder (43,388 pairs, 47 colonies), followed by Ring-billed Gull (Larus delawarensis, 41,819 pairs, 67 colonies), American White Pelican (Pelecanus erythrorhynchos, 12,680 pairs, 20 colonies), Common Tern (Sterna hirundo, 7,950 pairs, 31 colonies), Herring Gull (L. argentatus, 4,013 pairs, 90 colonies) and Caspian Tern (Hydroprogne caspia, 3,207 pairs, 14...

Comparative susceptibility of Channel Catfish, Blue Catfish, and their hybrid cross to experimental challenge with Bolbophorus damnificus (Digenea: Bolbophoridae) cercariae.

The digenetic trematode Bolbophorus damnificus has been implicated in significant losses in catfish aquaculture since the late 1990s. The complex life cycle sequentially involves the American white pelican Pelecanus erythrorhynchos, the marsh rams horn snail Planorbella trivolvis, and Channel Catfish Ictalurus punctatus. Research supports anecdotal reports from the industry, suggesting that the hybrid of Channel Catfish×Blue Catfish I. furcatus is less susceptible to disease agents that have been historically prohibitive to Channel Catfish production, namely the gram-negative bacteria Edwardsiella ictaluri and Flavobacterium columnare, as well as the myxozoan parasite Henneguya ictaluri. This current research compared the susceptibility of Channel Catfish, Blue Catfish, and their hybrid cross to an experimental challenge by B. damnificus. Fish were exposed to 0, 100, 200, and 400 B. damnificus cercariae per fish, and the numbers of metacercariae per fish were determined 14 d postchallenge. Metacercariae were recovered from all challenged fish. There were no significant differences among fish groups challenged with the same dose, suggesting Channel and Blue Catfish and their hybrid are comparably susceptible to B. damnificus infection. As such, it is recommended that producers raising hybrid catfish remain diligent in controlling populations of the snail intermediate host to prevent production losses attributed to B. damnificus, especially when loafing pelicans have been observed at the aquaculture operation.

Accumulation and hazard assessment of mercury to waterbirds at Lake Chapala, Mexico.

Lake Chapala is the largest tropical lake in Mexico. The objectives of this study were to determine bioaccumulation of Hg in fish and to evaluate the potential impacts of Hg in the diet of aquatic birds, particularly the American white pelican (AWPE), in Lake Chapala. Hg concentrations in three fish species ranged from 0.021 to 0.568 μg/g wet weight. Mercury in fish was positively and significantly correlated with total fish length (R2=0.44, P<0.05). The δ15N values in fish were significantly correlated with Hg concentrations in Chapala and the San Antonio Reservoir (R2=0.69, P<0.001 and R2=0.40, P<0.001, respectively). However, Hg concentrations in bird feathers were not significantly different between years, among locations, or among species. Hg concentrations in fish from Lake Chapala were within values reported in many parts of the world. The Hg (mean range of 2.75 to 4.54 μg/g dw) and δD (mean range of -62‰ to -11‰) values in bird feathers suggested a wide pattern of exposure for highly migratory AWPE and egrets, although birds with lower δD values in feathers appeared to have greater concentrations of Hg than those with higher δD values. Contaminant exposure in aquatic birds in Chapala during the breeding season should be monitored next to better determine the potential effects of Hg on resident aquatic birds.

American White Pelicans and Recreational Boaters on Lakes of the North American Great Plains: Habitat Use Overlap

Shoreline development and boating on lakes of the northern Great Plains of North America have increased due to recent economic prosperity. Few studies have examined the general characteristics of habitats used by foraging waterbirds and boats to determine levels of overlap. To address this issue, we conducted point count surveys of American White Pelicans (Pelecanus erythrorhynchos) and boats on two important recreational lakes in southern Saskatchewan, Canada. The majority of pelicans and boats detected used near-shore areas of the lakes, identifying the importance of shallow water habitats and providing evidence of significant overlap. The location of pelicans relative to the shore did not change in the presence of boats, and there was no significant relationship between boat numbers and pelican numbers. These analyses suggest that pelicans did not make major changes to their habitat use on the lakes as a result of boating activity. When pelicans and boats were present simultaneously at point count locations, pelicans appeared to avoid boats on one lake, but showed no detectable avoidance behavior on the other lake. The importance of interactions between recreational boating and foraging pelicans is currently unclear. Set-back distances to protect foraging pelicans from boating activity do not appear necessary based on our analyses.

American White Pelican Predation on Cui‐ui in Pyramid Lake, Nevada

AbstractAnthropogenic changes to the Pyramid Lake–Truckee River ecosystem in Nevada are suspected to have altered the predator–prey balance between American white pelican Pelecanus erythrorhynchos and Cui‐ui Chasmistes cujus. We estimated the loss of the adult Cui‐ui population to pelican predation over a 13‐year period by netting and tagging Cui‐uis as they aggregated at the mouth of the Truckee River prior to their spawning migration into the Truckee River. Cui‐ui access to the Truckee River typically required traversing a shallow delta (a foraging advantage for these American white pelicans). Dams and greater frequency of low stream flows also contributed to American white pelican foraging success. We used tag recoveries from Pyramid Lake's nesting colony of American white pelicans along with an experiment to estimate the chance of tag recovery within the colony to calculate the number of tagged fish taken by American white pelicans. We also used numbered tags to test whether there was a size preference for Cui‐uis taken. Our results showed that the primary source of adult Cui‐ui mortality was from American white pelican predation in the Truckee River. Within a 13‐year period American white pelicans had taken 90% of the tags deployed during the first 7 years of the interval. There was no preference for the size of Cui‐uis taken. A better understanding of the effects of heavy cropping by American white pelicans on Cui‐ui population dynamics is still needed.Received March 26, 2013; accepted October 8, 2013Published online January 24, 2014

Influence of Climate Change on Productivity of American White Pelicans, Pelecanus erythrorhynchos

In the past decade, severe weather and West Nile virus were major causes of chick mortality at American white pelican (Pelecanus erythrorhynchos) colonies in the northern plains of North America. At one of these colonies, Chase Lake National Wildlife Refuge in North Dakota, spring arrival by pelicans has advanced approximately 16 days over a period of 44 years (1965–2008). We examined phenology patterns of pelicans and timing of inclement weather through the 44-year period, and evaluated the consequence of earlier breeding relative to weather-related chick mortality. We found severe weather patterns to be random through time, rather than concurrently shifting with the advanced arrival of pelicans. In recent years, if nest initiations had followed the phenology patterns of 1965 (i.e., nesting initiated 16 days later), fewer chicks likely would have died from weather-related causes. That is, there would be fewer chicks exposed to severe weather during a vulnerable transition period that occurs between the stage when chicks are being brooded by adults and the stage when chicks from multiple nests become part of a thermally protective crèche.

Demographics of Piscivorous Colonial Waterbirds and Management Implications for ESA-listed Salmonids on the Columbia Plateau

We investigated colony size, productivity, and limiting factors for five piscivorous waterbird species nesting at 18 locations on the Columbia Plateau (Washington) during 2004–2010 with emphasis on species with a history of salmonid (Oncorhynchus spp.) depredation. Numbers of nesting Caspian terns (Hydroprogne caspia) and double-crested cormorants (Phalacrocorax auritus) were stable at about 700–1,000 breeding pairs at five colonies and about 1,200–1,500 breeding pairs at four colonies, respectively. Numbers of American white pelicans (Pelecanus erythrorhynchos) increased at Badger Island, the sole breeding colony for the species on the Columbia Plateau, from about 900 individuals in 2007 to over 2,000 individuals in 2010. Overall numbers of breeding California gulls (Larus californicus) and ring-billed gulls (L. delawarensis) declined during the study, mostly because of the abandonment of a large colony in the mid-Columbia River. Three gull colonies below the confluence of the Snake and Columbia rivers increased substantially, however. Factors that may limit colony size and productivity for piscivorous waterbirds nesting on the Columbia Plateau included availability of suitable nesting habitat, interspecific competition for nest sites, predation, gull kleptoparasitism, food availability, and human disturbance. Based on observed population trends alone, there is little reason to project increased impacts to juvenile salmonid survival from tern and cormorant populations. Additional monitoring and evaluation may be warranted to assess future impacts of the growing Badger Island American white pelican colony and those gull colonies located near mainstem dams or associated with Caspian tern colonies where kleptoparasitism is common.

West Nile Virus Transmission in Winter: The 2013 Great Salt Lake Bald Eagle and Eared Grebes Mortality Event

West Nile Virus (WNV) infection has been reported in over 300 species of birds and mammals. Raptors such as eagles, hawks and falcons are remarkably susceptible, but reports of WNV infection in Bald Eagles (Haliaeetus leucocephalus) are rare and reports of WNV infection in grebes (Podicipediformes) even rarer. We report an unusually large wild bird mortality event involving between 15,000-20,000 Eared Grebes (Podiceps nigricollis) and over 40 Bald Eagles around the Great Salt Lake, Utah, in November-December 2013. Mortality in grebes was first reported in early November during a period when the area was unseasonably warm and the grebes were beginning to gather and stage prior to migration. Ten out of ten Eared Grebes collected during this period were WNV RT-PCR and/or isolation positive. This is the first report of WNV infection in Eared Grebes and the associated mortality event is matched in scale only by the combined outbreaks in American White Pelican (Pelecanus erythrorhynchos) colonies in the north central states in 2002-2003. We cannot be sure that all of the grebes were infected by mosquito transmission; some may have become infected through contact with WNV shed orally or cloacally from other infected grebes. Beginning in early December, Bald Eagles in the Great Salt Lake area were observed to display neurological signs such as body tremors, limb paralysis and lethargy. At least 43 Bald Eagles had died by the end of the month. Nine of nine Bald Eagles examined were infected with WNV. To the best of our knowledge, this is the largest single raptor mortality event since WNV became endemic in the USA. Because the majority of the eagles affected were found after onset of below-freezing temperatures, we suggest at least some of the Bald Eagles were infected with WNV via consumption of infected Eared Grebes or horizontal transmission at roost sites.

Indirect Cannibalism by Crèche-aged American White Pelican (&lt;em&gt;Pelecanus erythrorhynchos&lt;/em&gt;) Chicks

At nesting colonies of American White Pelicans (Pelecanus erythrorhynchos), many chicks die from siblicide, severe weather, and disease; this results in carcasses available for scavenging by conspecifics (i.e., indirect cannibalism). Indirect cannibalism has not been reported previously for this species. We describe five cases of crèche-aged American White Pelican chicks consuming or attempting to consume dead younger chicks at two nesting colonies in the northern plains of North America. Cannibalism in the American White Pelican appears to be rare and likely plays no role in the species’ population ecology or dynamics; however, it might be an important survival strategy of individual chicks when food resources are limited.

Evaluation of Methods for Collecting Blood-Engorged Mosquitoes from Habitats Within a Wildlife Refuge

Mortality of American white pelican (Pelecanus erythrorhynchos) chicks attributed to West Nile virus (WNV) prompted field studies on the bionomics of mosquitoes on a wildlife refuge in northern Montana. One component of these studies was to identify blood meal sources for Culex tarsalis, the primary vector of WNV in the region, and the potential bridge vectors Aedes vexans and Culiseta inornata. To accomplish this, 3 methods were evaluated to collect bloodfed mosquitoes: a gasoline powered aspirator, CO2-baited light traps, and fiber pots in shelterbelts consisting of stands of deciduous trees and shrubs and marshes along the lake edge. Fiber pots were also deployed in open fields of prairie grasses. Overall, fiber pots were the most efficient method for collecting engorged Cx. tarsalis and Cs. inornata, largely due to shorter sampling and processing times. Aedes vexans was not collected in fiber pots but was more abundant in aspiration samples than the other 2 species. The optimal location for collecting Cx. tarsalis was dependent on trapping method. Aspirations and fiber pot placements collected more Cx. tarsalis in shelterbelts, while CO2-baited light traps collected more Cx. tarsalis in the marsh habitat. Sixteen avian and 4 mammalian hosts were identified from bloodfed Cx. tarsalis with 46 blood meals derived from birds and 49 from mammals. Aedes vexans and Cs. inornata fed predominantly on white-tailed deer (Odocoileus virginianus) and cattle (Bos taurus), respectively. Humans were identified as hosts in 33% of engorged Cx. tarsalis, 4% of engorged Ae. vexans, and 18% of engorged Cs. inornata.

Hepatitis and splenitis due to systemic tetratrichomoniasis in an American white pelican (Pelecanus erythrorhynchos)

A free-ranging, young adult, female American white pelican (Pelecanus erythrorhynchos), found dead on the grounds of the San Diego Zoo Safari Park in Southern California, had severe multifocal to coalescing necrotizing hepatitis and splenitis on postmortem examination. Histologically, within the large areas of necrosis were myriad pleomorphic, 5-20 µm in diameter, protozoal organisms with 1 to multiple nuclei. Ultrastructurally, the organisms were consistent with a trichomonad flagellate. Polymerase chain reaction and sequencing of the small subunit ribosomal RNA gene identified nucleotide sequences with 99% identity to Tetratrichomonas gallinarum, which is a common inhabitant of the intestinal tract of galliform and anseriform birds that has occasionally been associated with disease, including typhlitis and hepatitis. Damage to the cecal mucosa in the pelican from trematodes and secondary bacterial infection could have allowed invasion and systemic dissemination of the organism. Exposure of the pelican to a variety of native and exotic anseriform and galliform birds at the zoological institution could have led to cross-species infection and severe manifestation of disease in a novel host.

Mosquito and West Nile virus surveillance in northeast Montana, U.S.A., 2005 and 2006

Mosquito and West Nile virus (WNV) surveillance was conducted on a national wildlife refuge in northeast Montana in 2005 and 2006, during which outbreaks of WNV in a colony of American white pelicans (Pelecanus erythrorhynchos Gmelin) (Pelecaniformes: Pelecanidae) resulted in juvenile mortality rates of ∼ 31%. Both years, floodwater species Ochlerotatus dorsalis (Meigen) (Diptera: Culicidae), Aedes vexans (Meigen) (Diptera: Culicidae) and Ochlerotatus flavescens (Muller) (Diptera: Culicidae) comprised 78% of the total collection and heightened host-seeking activity was observed from mid-June to mid-July. Culex tarsalis Coquillett (Diptera: Culicidae) was most active from mid-July to mid-August and comprised 18% of the collection in 2005 and 20% in 2006. However, fewer than 10% of the Cx. tarsalis females collected in 2006 were obtained adjacent to the pelicans' nesting grounds. Minimum infection rates per 1000 Cx. tarsalis tested for WNV were 1.36 in 2005 and 1.41 in 2006. All pools in which WNV was detected in 2006 were composed of females collected 10 km from the nesting grounds. Substantial juvenile pelican mortality in 2006 despite reductions in the population of the primary vector and in mosquito infection rates near the colony suggests that the methods used to detect the introduction of WNV were too coarse and that amplification of the virus within the colony may reflect causes other than mosquito infection.

West Nile Virus in American White Pelican Chicks: Transmission, Immunity, and Survival

West Nile virus (WNV) causes significant mortality of American White Pelican chicks at northern plains colonies. We tested oropharyngeal/cloacal swabs from moribund chicks for shed WNV. Such shedding could enable chick-to-chick transmission and help explain why WNV spreads rapidly in colonies. WNV was detected on swabs from 11% of chicks in 2006 and 52% of chicks in 2007; however, viral titers were low. Before onset of WNV mortality, we tested blood from < 3-week-old chicks for antibodies to WNV; 5% of chicks were seropositive, suggesting passive transfer of maternal antibodies. Among near-fledged chicks, 41% tested positive for anti-WNV antibodies, indicating that they survived infection. Among years and colonies, cumulative incidence of WNV in chicks varied from 28% to 81%, whereas the proportion of chicks surviving WNV (i.e., seropositive) was 64-75%. Our data revealed that WNV kills chicks that likely would fledge in the absence of WNV, that infection of chicks is pervasive, and that significant numbers of chicks survive infection.