American White Pelicans: The Latest Avian Problem for Catfish Producers

Animal Damage Control offices in Arkansas, Louisiana, and Mississippi began receiving complaints concerning American white pelicans (Pelecanus erythrorhynchos) foraging in commercial channel catfish (Ictalurus punctatus) ponds in 1990. Because of the relatively shallow pond depth and high fish stocking rates used by most producers, commercial catfish ponds provide a near perfect foraging environment for American white pelicans. Since 1993, pelicans seem to have become more persistent in their foraging efforts and therefore, more difficult to disperse from catfish farms. Damage abatement recommendations have consisted of harassment measures similar to those used for other piscivorous birds, issuance of depredation permits, and draining water from fields used as loafing sites. In order to learn more about pelican numbers and movements Animal Damage Control, Denver Wildlife Research Center (ADC/DWRC) biologists began aerial censuses in the Delta Region of Mississippi and a radio-telemetry study during the winter of 1993-1994. Information provided by these studies will be used to develop American white pelican damage management strategies in the southeastern United States and elsewhere

Foraging Behaviors of Snowy Egrets (\u3ci\u3eEgretta thula\u3c/i\u3e) and Yellow-crowned Night-Herons (\u3ci\u3eNyctanassa violacea\u3c/i\u3e) in South Louisiana

We report two previously undescribed foraging techniques used by Snowy Egrets (Egretta thula) and Yellow-crowned Night-Herons (Nyctanassa violacea) to catch crawfish (Procambarus spp.). Snowy Egrets were selecting crawfish that had recently molted their shells and Yellow-crowned Sight-Herons were targeting crawfish that were emerging from their burrows. These observations were conducted on commercial crawfish ponds near Catahoula, LA, USA

Plumage Changes in Double-crested Cormorants (\u3ci\u3ePhalacrocorax auritus\u3c/i\u3e) Within the Breeding Season: the Risks of Aging by Plumage

Scant attention has been given to the molting patterns of known-age Double-crested Cormorants (Phalacrocorax auritus). In general, subadult individuals are identified with a tan, buffy or mottled chest, and adults are identified with a black chest. While studying Double-crested Cormorant population dynamics in Ontario, Canada, with known-age birds, it was noted that the plumage of many (\u3e 75%) breeding adults changed from black to heavily mottled during the course of the breeding season. No pattern with age was observed; plumage changed in equal proportions for all ages from 2-year-olds to 7-year-olds. A similar but reverse pattern has been observed with Double-crested Cormorants roosting at sites in the southeastern USA during fall migration. Whereas the majority of the roost had juvenile/subadult plumage in September, by mid-January the roost had shifted to 75% adult black plumage. The mechanism behind the plumage change is unknown, but extreme caution is advised when using plumage to age cormorants, especially during the winter months. By describing our observations with Doublecrested Cormorants, we hope to encourage future formal research on within-season plumage changes

Overview of American White Pelican Impacts to Southeastern Aquaculture

In 1990, USDA Wildlife Services offices in Arkansas, Louisiana, and Mississippi began receiving complaints concerning American white pelicans (Pelecanus erythrorhynchos) foraging in commercial channel catfish (Jctalurus punctatus) ponds. Because of the relatively shallow pond depth and high fish stocking rates used by most producers, commercial aquaculture provides a near perfect foraging environment for an increasing American white pelican population. Although pelicans are not currently as numerous as double-crested cormorants (Phalacrocorax auritus), individual farmer losses to pelican predation can be devastating. American white pelicans are capable of eating about 2 kg per day and as many as 2000 pelicans have been observed foraging in one catfish pond in the delta region of Mississippi. Not only do American white pelicans forage at aquaculture facilities, they also carry various diseases that can infect many aquaculture species. Since 1993, Wildlife Services, National Wildlife Research Center biologists have conducted research to learn more about pelican ecology. Here, I provide an overview of American white pelican research and their impacts to southeastern aquaculture

Seasonal climatic niche and migration movements of Double-crested Cormorants

Avian migrants are challenged by seasonal adverse climatic conditions and energetic costs of long-distance flying. Migratory birds may track or switch seasonal climatic niche between the breeding and non-breeding grounds. Satellite tracking enables avian ecologists to investigate seasonal climatic niche and circannual movement patterns of migratory birds. The Double-crested Cormorant (Nannopterum auritum, hereafter cormorant) wintering in the Gulf of Mexico (GOM) migrates to the Northern Great Plains and Great Lakes and is of economic importance because of its impacts on aquaculture. We tested the climatic niche switching hypothesis that cormorants would switch climatic niche between summer and winter because of substantial differences in climate between the non-breeding grounds in the subtropical region and breeding grounds in the northern temperate region. The ordination analysis of climatic niche overlap indicated that cormorants had separate seasonal climatic niche consisting of seasonal mean monthly minimum and maximum temperature, seasonal mean monthly precipitation, and seasonal mean wind speed. Despite non-overlapping summer and winter climatic niches, cormorants appeared to be subjected to similar wind speed between winter and summer habitats and were consistent with similar hourly flying speed between winter and summer. Therefore, substantial differences in temperature and precipitation may lead to the climatic niche switching of fish-eating cormorants, a dietary specialist, between the breeding and non-breeding grounds

Migration Patterns of Double-crested Cormorants Wintering in the Southeastern United States

Migration patterns of Double-crested Cormorants (Phalacrocorax auritus) wintering in the southeastern U.S. are poorly understood. Movement data were analyzed from 28 cormorants captured in Alabama, Arkansas, Louisiana and Mississippi and equipped with satellite transmitters. Four (three immature, one adult) cormorants did not migrate and stayed in the southeastern U.S. throughout the year. During spring, cormorants captured in Alabama migrated east of the Mississippi River and primarily west of the Appalachian Mountains. Cormorants from Arkansas, Louisiana and Mississippi migrated north along the Mississippi River Valley, the Missouri River Valley and/or the Ohio River Valley. The earliest departure for spring migration was 26 March, whereas the latest departure was 12 May. Adult cormorants departed for spring migration earlier than immature cormorants. The average departure date for fall migration was 1 October. Mean duration of spring migration was twelve days, and cormorants traveled an average of 70 km per day

Seasonal Habitat Selection by American White Pelicans

Resource utilization strategies of avian migrants are a major concern for conservation and management. Understanding seasonal habitat selection by migratory birds helps us explain the ongoing continental declines of migratory bird populations. Our objective was to compare the secondorder and third-order habitat selection by the American White Pelican (Pelecanus erythrorhynchos; hereafter pelican) between the breeding and non-breeding grounds. We tested the Lack hypothesis that habitat selection by migratory birds is stronger on the breeding grounds than on the nonbreeding grounds. We used random-effect Dirichlet-multinomial models to estimate the second-order habitat selection between the seasons with the GPS locations of 32 tracked pelicans. We used Gaussian Markov random field models to estimate the third-order habitat selection by pelicans at the breeding and non-breeding grounds, accounting for spatial autocorrelation. Pelicans strongly selected waterbodies and wetlands at both non-breeding and breeding grounds, tracking their foraging habitats between the seasons at the home range level. However, pelicans exhibited seasonal differences in the strength of the third-order selection of wetlands and waterbodies with foraging habitat selection being stronger at the breeding grounds than at the non-breeding grounds, supporting the Lack hypothesis

Large- and Small-Scale Climate Influences Spring Migration Departure Probability of American White Pelicans

Endogenous (e.g., age and sex) and exogenous (e.g., climate and resource availability) factors influence avian migration phenology. However, little is known regarding the migration ecology of birds at the non-breeding grounds, including the American white pelican (Pelecanus erythrorhynchos). We used Global Positioning System transmitters to track the movements and migration of 51 pelicans from 2002 to 2012. We used the Kaplan–Meier model to estimate pelican spring migration probabilities to quantify partial migration with 94 spring migration events and used the Cox proportional hazards model to evaluate the effects of the North Atlantic Oscillation index (NAOI), Southern Oscillation Index (SOI), and spring daily precipitation on the propensity of pelican spring migration departures. Increases in the NAOI and SOI enhanced the propensity of pelican spring departure. The propensity of spring departure was also positively related to daily precipitation. Male pelicans have greater spring migration probabilities than female pelicans. Spring migration departure probabilities of adult pelicans are greater than those of immature pelicans. Therefore, both large-scale and local climatic conditions affect pelican spring departure probabilities. Advanced migratory phenology of pelicans caused by climate changes with warming temperature and increased precipitation may result in the mismatch of pelican spring arrival with food resource availability of breeding grounds and subsequent pelican population declines

Morphometric Variation during Chick Development in Interior Double-crested Cormorants (\u3ci\u3ePhalacrocorax auritus\u3c/i\u3e)

In numerous avian species, egg size is correlated to female body condition, hatchling size and nestling growth. Recent demography studies of Interior Double-crested Cormorants (Phalacrocorax auritus) suggest a migratory divide across the Great Lakes; western populations winter in the Gulf of Mexico region of the southeastern United States (Alabama, Arkansas, Louisiana, and Mississippi) with extensive catfish (Ictalurus punctatus) aquaculture, and eastern populations winter in Florida, where catfish aquaculture is not pervasive. If Double-crested Cormorants have improved their overall body condition through catfish exploitation, then egg and chick sizes should also be affected. Three breeding areas in Ontario (east, central, and west) were selected for empirical measures of size variation. During the breeding seasons of 2006 and 2007, egg, naked young, fledgling, and adult morphometric data were collected. Eggs in eastern areas (volume = 465.8 ± 3.9 cm³) were on average larger than eggs in central (volume = 458.1 ± 3.5 cm³) and western (volume = 451.7 ± 3.5 cm³) areas. However, chicks in eastern areas (culmen = 54.9 ± 0.6 mm) were smaller than chicks in central (culmen = 57.6 ± 0.4 mm) and western (culmen = 59.3 ± 0.3 mm) areas, not only at hatching, but throughout development and fledging. A comprehensive Double-crested Cormorant morphometric gradient that may suggest a potential reproductive advantage for birds exploiting aquaculture facilities is presented

Experimental\u3ci\u3e Bolbophorus damnificus \u3c/i\u3e(Digenea: Bolbophoridae) Infections in Piscivorous Birds

In order to determine potential definitive hosts of the digenetic trematode, Bolbophorus damnificus, two American White Pelicans (Pelecanus erythrorhynchos), two Double-crested Cormorants (Phalacrocorax auritus), two Great Blue Herons (Ardea herodias), and two Great Egrets (Ardea alba) were captured, treated with praziquantel, and fed channel catfish (Ictalurus punctatus) infected with B. damnificus metacercariae. Patent infections of B. damnificus, which developed in both American White Pelicans at 3 days post-infection, were confirmed by the presence of trematode ova in the feces. Mature B. damnificus trematodes were recovered from the intestines of both pelicans at 21 days post-infection, further confirming the establishment of infection. No evidence of B. damnificus infections was observed in the other bird species studied. This study provides further evidence that Double-crested Cormorants, Great Blue Herons, and Great Egrets do not serve as definitive hosts for B. damnificus