Phalacrocorax Auritus Research Articles

Spatial and temporal patterns of avian paramyxovirus-1 outbreaks in double-crested cormorants (Phalacrocorax auritus) in the USA.

Morbidity and mortality events caused by avian paramyxovirus-1 (APMV-1) in Double-crested Cormorant (DCCO; Phalacrocorax auritus) nesting colonies in the US and Canada have been sporadically documented in the literature. We describe APMV-1 associated outbreaks in DCCO in the US from the first reported occurrence in 1992 through 2012. The frequency of APMV-1 outbreaks has increased in the US over the last decade, but the majority of events have continued to occur in DCCO colonies in the Midwestern states. Although morbidity and mortality in conesting species has been frequently reported during DCCO APMV-1 outbreaks, our results suggest that isolation of APMV-1 is uncommon in species other than DCCO during APMV-1 outbreaks and that the cause of mortality in other species is associated with other pathogens. Populations of DCCO do not appear to have been significantly affected by this disease; however, because at least 65% of the APMV-1 outbreaks in DCCO in the US have involved APMV-1 strains classified as virulent to poultry (virulent Newcastle disease virus), its persistence and increased occurrence in DCCO warrants continued research and surveillance.

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.

USDA APHIS Wildlife Services Efforts to Protect and Restore the Great Lakes Region of North America

Author(s): Beckerman, Scott F.; McConnell, John E.; Guikema, Aaron T. | Abstract: In a time when fresh water is increasingly in demand, the Great Lakes region of North America contains approximately 20% of the globe’s fresh water resources. The Great Lakes offer nearly an infinite number of recreational opportunities for residents of the region and helps support one of the largest economies in the world. Understanding this, U.S. President Barack Obama and 16 federal agencies have made restoring the Great Lakes a national priority by establishing the Great Lakes Restoration Initiative (GLRI). Congress appropriated $300 million to $475 million per year between 2010 and 2013 to implement the GLRI. An Action Plan describes how the GLRI is being executed from 2010 through 2014 and describes the most significant ecosystem level challenges for the Great Lakes. These challenges are categorized into 5 major Focus Areas for restoration including: combating invasive species; promoting nearshore health by protecting watersheds from polluted run-off; and habitat and wildlife protection and restoration, among others. To protect and restore the Great Lakes as part of the GLRI, the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services program (WS) is combating the spread of terrestrial invasive species, such as mute swans and feral swine; managing double-crested cormorants on sensitive islands; protecting native turtles from meso-predators; and enhancing native trout streams by removing beaver dams impeding stream flow to protect and enhance native fish/wildlife and their habitats. In addition, WS is managing overabundant populations of Canada geese and ring-billed gulls to promote water quality and improve nearshore health. This presentation highlights objectives, measurable ecological targets, and specific actions accomplished by WS during 2011-2013 to protect in-stream and riparian habitat and fish restoration through beaver damage management and efforts to protect aquatic habitat and native wildlife through mute swan management within the Great Lakes ecosystem.

Population dynamics of double‐crested cormorants in two interior breeding areas

ABSTRACTBecause of rapid population expansion, conflicts between double‐crested cormorants (Phalacrocorax auritus) and humans have increased, particularly at aquaculture facilities in the Lower Mississippi River Valley (LMRV), United States. Although key demographic information on the Interior population is sparse, management decisions for population reduction are already in place across their breeding range. New evidence suggests the Appalachian Mountains may act as a migration divide for Interior cormorants, causing some birds to migrate between LMRV and the western Great Lakes, whereas others migrate between Florida and the eastern Great Lakes. Most of the banded cormorants recovered near LMRV aquaculture facilities were banded as nestlings at colonies from the central Great Lakes west to the northern Great Plains. We selected 2 geographically distinct Interior cormorant breeding areas: west of the Great Lakes in Lake of the Woods (LOW) and eastern Lake Ontario (ELO), located on either side of the migration divide in the province of Ontario, Canada, to study population dynamics. We used age‐specific classes for our mark‐recapture analysis (Program MARK) on data collected from 9,498 color‐banded cormorants during the breeding seasons of 2000–2008. Adult survival was the same for both areas (LOW = 0.84 ± 0.09 SE, ELO = 0.83 ± 0.05 SE). Finite rates of population growth (λ) were also similar (LOW = 1.01, ELO = 0.97) and sensitivity analyses indicated that adult survival was the most influential vital rate contributing to λ for both breeding areas. However, young‐of‐the‐year survival estimates were distinctly less in ELO (0.19 ± 0.02 SE) than in LOW (0.45 ± 0.10 SE) and sensitivity analysis revealed that young‐of‐the‐year survival played a key role in ELO population growth. Moreover, ELO breeding area fidelity (F) was much greater (0.94 ± 0.05 SE) than the F estimates for all age classes in LOW (between 0.68 ± 0.19 SE and 0.80 ± 0.13 SE). Considering these regional demographic differences, we recommend that future management efforts be based on migratory flyways within the Interior population. © 2013 The Wildlife Society

Using Ecopath Modeling to Describe Historical Conditions for a Large, Boreal Lake Ecosystem prior to European Settlement

AbstractTo help guide restoration efforts at a large‐lake ecosystem (Lac la Biche) in Alberta, Canada, I used Ecopath modeling software to create an energetically plausible model representing the system prior to European settlement. Over the last 200 years, Lac la Biche has shifted from a system dominated by predatory fish (e.g., Walleyes Sander vitreus and Northern Pike Esox lucius) to one dominated by forage fish and double‐crested cormorants Phalacrocorax auritus. In 2005, the Fisheries Management Branch of Alberta Environment and Sustainable Resource Development initiated a fisheries restoration program focused on increasing the abundance of Walleyes and average fish size in Lac la Biche; restoration would target a nondescript “historical” ecosystem configuration based on contemporary assumptions of what the system might have looked like. I used Ecopath to organize the main assumptions and information on the historical Lac la Biche ecosystem into an energetically plausible representation for the year 1800. From the modeling process, I learned that most of the assumptions regarding the trends in species biomass between contemporary and historical systems were appropriate guides for model balancing; however, the magnitude of the expected differences between 1800 and the present day were often larger than predicted, especially for infrequently sampled species (e.g., Yellow Perch Perca flavescens, White Suckers Catostomus commersonii, Spottail Shiners Notropis hudsonius, and Burbot Lota lota). Testing the validity of single‐species assumptions in an ecosystem context is important for improving our understanding of ecosystem structure and function. In a historical context, model creation based on assumptions and available information is important for developing ecosystem baselines that can provide context to and guide future fisheries management. Historical baselines are also important for highlighting ecosystem potential and productive capacity and for counteracting the effects of the shifting baseline syndrome.Received February 13, 2012; accepted August 2, 2013Published online December 23, 2013

Abundance, distribution, and species assemblages of colonial waterbirds in the boreal region of west-central Manitoba and east-central Saskatchewan

Central and southern Manitoba contain some of the largest breeding populations of several colonial waterbird species in North America. Despite the value of this region for waterbirds, very little monitoring has been conducted on Lake Winnipeg, Lake Winnipegosis, or Lake Manitoba in the past three decades and little is known about the smaller boreal lakes in adjacent areas to the north. In June 2011, boat surveys were conducted on 11 boreal lakes in west-central Manitoba and east-central Saskatchewan to examine current abundance and distribution of colonial waterbirds in that region. Data from this survey were compared with abundance of colonial waterbirds on Lake Winnipegosis and Lake Manitoba from an aerial survey of these lakes in 2012. Waterbird colonies were located on 7 of the 11 lakes in 2011 and included Double-crested Cormorants (Phalacrocorax auritus) (2373 adults, 1134 pairs in 7 colonies), Common Terns (Sterna hirundo) (1367 adults, 772 pairs in 29 colonies), Forster’s Terns (Sterna forsteri) (20 adults, 11 pairs in 1 colony), Herring Gulls (Larus argentatus) (876 adults, 568 pairs in 23 colonies), and Ring-billed Gulls (Larus delawarensis) (3752 adults, 16 colonies). Common Terns and Herring Gulls appeared to be predominantly breeders and pair abundance for both species increased in a sigmoidal fashion; lakes <100 km2 in area had few breeding pairs. Numbers of Double-crested Cormorants and especially, Ring-billed Gulls, may have included a sizeable non-breeding component. Densities (pairs/lake area) of Common Terns and Herring Gulls were about 2 and 4 times higher, respectively, on these lakes than on Lake Winnipegosis and Lake Manitoba, while Double-crested Cormorant and Ring-billed Gull densities were higher on lakes Winnipegosis and Manitoba. Additional studies of productivity in relation to lake characteristics and connectivity among colonies throughout the region would further our understanding of the importance and sustainability of waterbird populations in this region of the boreal forest.

The cumulative effects of management on the population dynamics of the Double‐crested Cormorant Phalacrocorax auritus in the Great Lakes

Wildlife species have been subject to control efforts throughout human history due to real or alleged human–wildlife conflicts. The Double‐crested Cormorant Phalacrocorax auritus in the interior of North America is no exception, with recent population growth leading to increased conflicts and consequently the development of many control programmes. These control programmes are usually conducted at local scales, often with little or no effort to assess their cumulative effects at the population level. We attempted the first comprehensive assessment of the cumulative effects of control at various spatio‐temporal scales, focusing on 199 colonies of Double‐crested Cormorant monitored during a 29‐year period. Linear models were used to assess the relationship between colony‐specific growth rates and a set of candidate factors using an information‐theoretic approach. Colony‐level density‐dependent effects and local control efforts had the greatest influences on population growth. We detected a cumulative effect of management, whereby (i) the reduction in population growth rate was generally stronger when different control activities such as culling or egg oiling were combined, and (ii) past control operations tended to have a pervasive impact on growth rates, especially egg oiling and nest destruction, which negatively affected local recruitment. However, our results also suggest that catastrophic events and the culling of breeding adults that occurred at least 2 years previously could fuel subsequent recruitment or natural immigration from nearby colonies, for instance if the breeding success of remaining pairs was increased through a diminution of density‐dependent regulatory processes. Density‐dependence at the metapopulation level constituted a third source of regulation, as local growth rates were reduced with increasing number or proximity of active neighbouring colonies. We also found evidence that the culling of Double‐crested Cormorants wintering in the southeastern USA could negatively impact the population growth of individual breeding colonies in the Great Lakes, although further research integrating models of migratory connectivity is needed to reach more definitive conclusions. Finally, despite previous studies emphasizing its importance, the net effect of management‐induced dispersal appeared small at large spatial scales. We show that this can be explained in part by control strategies (e.g. spatially clustered operations). The continuation of Cormorant management efforts will provide an opportunity to refine the present assessment of the relative importance of density‐dependence, breeding vs. non‐breeding season management and dispersal, particularly if population models are coupled with monitoring programmes within an adaptive management framework.

Modeling Population Dynamics and Fish Consumption of a Managed Double‐Crested Cormorant Colony in Minnesota

AbstractThe recovery of the double‐crested cormorantPhalacrocorax auritusthroughout North America has led to increased human–cormorant competition over fishery resources and has forced managers to evaluate cormorant effects and consider management alternatives at local and broader scales. We present a method for modeling local double‐crested cormorant populations under varying levels of culling intensity based on a colony managed at Leech Lake, Minnesota, during 2005–2011. In this case study, the cormorant colony was evaluated under no, moderate, and intensive control rates and compared with the observed population response. Cormorant diets for fledged (adults and subadults) and nestling cormorants were described during 2004–2007 and 2010. Annual fish consumption and 95% confidence intervals were estimated from 1992 to 2011 using a bioenergetics model and Monte Carlo methods. Total feeding effort and fish consumption has been reduced by nearly 90% since cormorant control began in 2005 (consumption reduced from 20.01 kg/ha in 2004 to 1.98 kg/ha in 2011) and by 46–73% annually, depending on the number of birds arriving each spring and the applied culling intensity. Averaged across all years and periods, fledged cormorants consumed 0.75 kg·bird−1·d−1and nestlings consumed 0.45 kg·bird−1·d−1. Respectively, average fledged and nestling diets were comprised of Yellow PerchPerca flavescens(61.0% and 77.4%),Coregonusspp. (12.3% and 9.4%), minnowsNotropisspp. (9.9% and 2.2%), Trout‐perchPercopsis omiscomaycus(4.1% and 0.4%), and WalleyeSander vitreus(4.6% and 3.6%), though considerable seasonal and temporal variability was observed. The bioenergetics model used to estimate total fish consumption was sensitive to this variability, which was strongly associated with the dynamics of the population of CiscoCoregonus artedi. Some fish population and fishery statistics were described by changes in cormorant predation pressure, but these relationships were compromised by other concurrent management activities.Received April 1, 2013; accepted August 20, 2013

MORPHOLOGIC AND MOLECULAR IDENTIFICATIONS OF DIGENETIC TREMATODES IN DOUBLE-CRESTED CORMORANTS (PHALACROCORAX AURITUS) FROM THE MISSISSIPPI DELTA, USA

Increasing numbers of Double-crested Cormorants (Phalacrocorax auritus) in the Mississippi River Delta, USA, have been observed over the past few decades. This piscivorous bird is a definitive host for numerous digenetic trematodes, some of which may cause pathology in a fish host. We conducted a 2-yr survey of intestinal trematodes in 35 Double-crested Cormorants collected in the Mississippi Delta. We counted gastrointestinal trematodes, identified them to species using morphometric and molecular techniques, and sequenced the 18S and cytochrome oxidase I (COI) genes. We collected 4,909 trematodes, representing five digenetic species: Drepanocephalus spathans, Hysteromorpha triloba, Pseudopsilostoma varium, Austrodiplostomum ostrowskiae, and Ascocotyle longa. The most prevalent trematode of the Double-crested Cormorants was D. spathans (91%), followed by H. triloba (78%), P. varium (74%), A. ostrowskiae (57%), and A. longa (29%). Among these, the life cycles are only known for H. triloba and A. longa. Novel DNA sequences of the COI gene were obtained for D. spathans, A. ostrowskiae, P. varium, and A. longa adults. Using these DNA sequences, the identification and confirmation of the larval stages of these parasites in the fish and snail hosts will be possible.

Resistance of the size structure of the fish community to ecological perturbations in a large river ecosystem

Summary Frequency distributions of log‐scaled abundance and body size for aquatic biota, including fish, yield size spectra that provide gross estimates of food‐web capacity (number of individuals supported by the food web indexed by the midpoint height or y‐intercept) and ecological efficiency (rate of decreasing organismal abundance with increasing body size as indicated by the size‐spectra slope). Size spectra are known to respond in predictable fashion to exploitation by commercial (marine) fisheries, but there has been relatively little research of size spectra in freshwater systems and less evaluation of how community size‐structure responds to the wider array of ecological perturbations prevalent in freshwater systems. We used a 29‐year experimental gillnet data set to test the responses of food‐web capacity and ecological efficiency (as indexed by size spectra) of a large river fish community to variations in predatory demand (population expansion of double‐crested cormorant, Phalacrocorax auritus) and perturbations affecting primary production (reductions in total phosphorus and warming summer water temperature). Fish community capacity (size‐spectra elevation) and ecological efficiency (size‐spectra slope) showed low interannual variation (coefficients of variation 5.6 and 15.4%, respectively). Though highly stable, food‐web capacity decreased over time concurrent with declining total phosphorus concentrations and increasing cormorant abundance. Interannual variation in ecological efficiency was not related to the measured perturbations. Relative abundance of the core species that comprised 95% of the community remained relatively consistent over time. The fish community size‐structure was also stable and resistant to ecological perturbation. However, we found measurable changes in the composition of secondary species, and these were associated with an increase in cormorant abundance and decrease in total phosphorus. The lack of change in core community species representation and in overall size structure suggest community‐level compensatory mechanisms were operating.

PREVALENCE OF AVIAN PARAMYXOVIRUS 1 AND AVIAN INFLUENZA VIRUS IN DOUBLE-CRESTED CORMORANTS (PHALACROCORAX AURITUS) IN EASTERN NORTH AMERICA

Although it is well established that wild birds, such as cormorants, carry virulent avian paramyxovirus serotype 1 (APMV-1; causative agent of Newcastle disease) and avian influenza virus (AIV), the prevalence of these viruses among Double-crested Cormorants (Phalacrocorax auritus) in the Great Lakes region of North America has not been rigorously studied. We determined the prevalences of APMV-1 and AIV in Double-crested Cormorants from the interior population of eastern North America. From 2009 to 2011, oropharyngeal and cloacal swabs and serum samples were collected from 1,957 individual Double-crested Cormorants, ranging from chicks to breeding adults, on breeding colony sites in Michigan, Wisconsin, and Mississippi, USA, and Ontario, Canada, as well as on the wintering grounds of migratory populations in Mississippi, USA. Prevalence of antibodies to APMV-1 in after-hatch year birds was consistently high across all three years, ranging from 86.3% to 91.6%. Antibody prevalences in chicks were much lower: 1.7, 15.3, and 16.4% in 2009, 2010, and 2011, respectively. Virulent APMV-1 was detected in six chicks sampled in 2010 in Ontario, Canada. Only one adult was positive for AIV-specific antibodies and five individuals were positive for AIV matrix protein, but the latter were negative for H5 and H7 AIV subtypes. We provide further evidence that Double-crested Cormorants play an important role in the maintenance and circulation of APMV-1 in the wild, but are unlikely to be involved in the circulation of AIV.

Marking power lines to reduce avian collisions near the Audubon National Wildlife Refuge, North Dakota

Overhead power lines can pose collision risks to birds. Risks may be mitigated through marking lines with high-visibility devices, but the effectiveness of line marking remains unclear. Effectiveness is particularly poorly described for lines bisecting open water, where detection of carcasses can be difficult. We marked 3 of 9 spans (lines between adjacent structures) along a causeway crossing open water and 2 adjacent spans over lake shores between Lake Sakakawea and Lake Audubon near Audubon National Wildlife Refuge, North Dakota, USA. Over 3 years, we found 1,186 avian carcasses, including 276 attributed to power-line collision. American coots (Fulica americana; n = 83) and double-crested cormorants (Phalacrocorax auritus; n = 27) were the species most commonly associated with power-line collision, but we also found carcasses of 51 other species, including a piping plover (Charadrius melodus; n = 1). Multi-variable modeling indicated line marking over open water reduced predicted collisions per span per season (mid-April through mid-October, 2006–2008) from 10.3 to 5.8. Birds with high-aspect-ratio wings benefitted most from line marking (e.g., shorebirds and gulls). If the 9 open-water spans we studied were unmarked for 30 years, we predicted 2,775 collisions. We predicted only 1,560 collisions if all of these spans were marked. Our data demonstrate that a wide variety of avian species are at risk of collision with lines bisecting open water, marking lines can reduce collision risk, and because collisions persisted and some line markers fell off power lines, improvements to effectively mark lines are needed. © 2013 The Wildlife Society.

Mercury exposed: Advances in environmental analysis and ecotoxicology of a highly toxic metal

Mercury exposed: Advances in environmental analysis and ecotoxicology of a highly toxic metal

Relative Vulnerability of PIT‐Tagged Subyearling Fall Chinook Salmon to Predation by Caspian Terns and Double‐Crested Cormorants in the Columbia River Estuary

AbstractWe quantified the percentage of PIT‐tagged subyearling fall Chinook Salmon Oncorhynchus tshawytscha that were consumed by Caspian terns Hydroprogne caspia and double‐crested cormorants Phalacrocorax auritus nesting on East Sand Island in the Columbia River estuary by electronically recovering PIT tags that were deposited on the bird colonies. We released 23 groups of PIT‐tagged subyearling fall Chinook Salmon from hatcheries in the lower Columbia River downstream of Bonneville Dam from 2002 to 2010. Vulnerability to avian predation was compared between PIT‐tagged subyearlings of two Columbia River basin stocks: tule and upriver bright (URB). Recoveries of PIT tags revealed that overall predation rates were significantly different between the tule stock (22%) and URB stock (3%); for fish that were detected as entering the lower Columbia River during the same week, predation rates also differed between stocks (tule: 21%; URB: 2%). Minimum predation rates on tule subyearlings originating from hatcheries downstream of Bonneville Dam were among the highest documented for any salmonid species in the Columbia River basin to date, occasionally exceeding 35% of the available fish. The ratio of URB fish consumed by the two avian predators indicated that the percentages were nearly equal (cormorant [%]: tern [%] = 51:49), whereas the ratio for tule‐stock fish consumed by the two avian species was not uniform (cormorant: tern = 81:19). Differences in predation rates between the tule stock and the URB stock may be attributable to migration behaviors exhibited in the estuary. We estimate that more than 8 million tule fall Chinook Salmon subyearlings released from hatcheries annually are consumed by double‐crested cormorants and Caspian terns nesting on East Sand Island; ongoing management actions by multiple federal, state, and tribal governments, if successful, will decrease predation on fall Chinook Salmon stocks.

Quantification of cormorant litter and nutrient deposition to Great Lakes island ecosystems

Ornithogenic nutrients derived from waterbirds such as the double-crested cormorant (Phalacrocorax auritus, Lesson) have been linked to habitat change within nesting colonies. For the islands of Lake Erie, where increasing cormorant populations and subsequent habitat change have spurred management activity, estimates of the quantity and chemical characteristics of avian-derived contributions are lacking. To evaluate the quantity and chemical characteristics of ornithogenic litterfall beneath a double-crested cormorant colony on a western Lake Erie island we investigated the mass of material and nutrient composition (PO43−, NO3− and NH4+) reaching the forest floor under three nest densities (Low: 1–96 nestsha−1; Medium: 97–255 nestsha−1 and High: >255 nestsha−1). As expected, litterfall (total mass) input differed among nest densities with the most substantial input (225.05g/m2week−1) measured under High nest density conditions. Nutrient concentrations also showed increases with nest density to a point, where mean PO43− and NH4+ concentrations showed no differences between Medium and High nest density sites. As well, NO3− concentrations were highest under Medium density, with no differences in this nutrient observed between Low and High density. Collectively, litterfall nutrient composition was similar to those linked to habitat changes in other waterbird colonies. Similarities in the concentrations of several nutrients between Medium and High nest density categories suggest that management actions aimed at reducing allochthonous nutrient contributions should try to sustain nest density at or below 96 nestsha−1.

Phylogeography and population genetic structure of double-crested cormorants (Phalacrocorax auritus)

We examined the genetic structure of double- crested cormorants (Phalacrocorax auritus) across their range in the United States and Canada. Sequences of the mitochondrial control region were analyzed for 248 cor- morants from 23 breeding sites. Variation was also examined at eight microsatellite loci for 409 cormorants from the same sites. The mitochondrial and microsatellite data provided strong evidence that the Alaskan subspecies (P. a. cincinn- atus) is genetically divergent from other populations in North America (net sequence divergence = 5.85 %; UST for mitochondrial control region = 0.708; FST for microsatellite loci = 0.052). Historical records, contemporary population estimates, and field observations are consistent with recog- nition of the Alaskan subspecies as distinct and potentially of conservation interest. Our data also indicated the presence of another divergent lineage, associated with the southwestern portion of the species range, as evidenced by highly unique haplotypes sampled in southern California. In contrast, there was little support for recognition of subspecies within the conterminous U.S. and Canada. Rather than genetically distinct regions corresponding to the putative subspecies (P. a. albociliatus (Pacific), P. a. auritus (Interior and North Atlantic), and P. a. floridanus (Southeast)), we observed a distribution of genetic variation consistent with a pattern of isolation by distance. This pattern implies that genetic dif- ferences across the range are due to geographic distance, rather than discrete subspecific breaks. Although three of the four traditional subspecies were not genetically distinct, possible demographic separation, habitat differences, and documented declines at some colonies within the regions, suggests that the Pacific and possibly North Atlantic portions of the breeding range may warrant differential consideration from the Interior and Southeast breeding regions.

Double-crested Cormorants (Phalacrocorax auritus) of Leech Lake, Minnesota: Temporal Variation of Diets and Assessment of Differential Prey Selection in Adults

In 1998, after 160 y without documented nesting, Double-crested Cormorants (Phalacrocorax auritus) recolonized Leech Lake, Minnesota. Competition for nesting space with the state threatened Common Tern (Sterna hirundo), and concern regarding potential walleye (Sander vitreus) and yellow perch (Perca flavescens) population declines prompted culling of cormorants and research into their diet. Stomach contents of adult and subadult cormorants were collected in 2004, 2005, and 2006 (186, 356 and 348, respectively) and from cormorant chick regurgitants in 2005 and 2006 (151 and 114, respectively). Perca flavescens (>70% composition and biomass) and shiner species (Notropis sp.) (>4% composition and biomass) were the main components of subadult and adult cormorant diets in 2004 and 2005 and the diet of chicks in 2005. However in 2006, whitefish species (Coregonus sp.) was the majority of percent biomass consumed by subadults and adults (43.4%) and a large proportion of percent biomass consumed by chicks (17.8%). In 2006 percent biomass of Corengonus sp. was different from other years for adults and subadults (P < 0.001) and chicks (P < 0.01) and may have been a product of a warming event die-off in late summer. All eight of the select common prey species varied (P < 0.01) in percent biomass between at least one of the ten delineated periods within 2004, 2005, or 2006. Differential prey selection by adults for self-feeding and provisioning for chicks was detected in Coregonus sp. (P < 0.01). While the diet of Leech Lake cormorants mainly consists of small abundant fish (P. flavescens and Notropis sp.), cormorant diet can vary within and among years. This study represents the first description of the diet of cormorants from a midwestern location other than the Great Lakes and reinforces the importance of site specific diet assessment, as the particular abundant prey species differs between locations.

BREVETOXICOSIS IN SEABIRDS NATURALLY EXPOSED TO KARENIA BREVIS BLOOMS ALONG THE CENTRAL WEST COAST OF FLORIDA

Harmful algal bloom events caused by the dinoflagellate Karenia brevis occurred along the central west Florida, USA, coast from February 2005 through December 2005 and from August 2006 through December 2006. During these events, from 4 February 2005 through 28 November 2006, live, debilitated seabirds admitted for rehabilitation showed clinical signs that included disorientation, inability to stand, ataxia, and seizures. Testing of blood, biologic fluids, and tissues for brevetoxin by enzyme-linked immunosorbent assay found toxin present in 69% (n=95) of rehabilitating seabirds. Twelve of the 19 species of birds had evidence of brevetoxin exposure. Commonly affected species included Double-crested Cormorants (Phalacrocorax auritus), Brown Pelicans (Pelecanus occidentalis), Great Blue Herons (Ardea herodias), and Common Loons (Gavia immer). Serial blood and fecal samples taken from several live seabirds during rehabilitation showed that brevetoxin was cleared within 5-10 days after being admitted to the rehabilitation facility, depending on the species tested. Among seabirds that died or were euthanized, the highest brevetoxin concentrations were found in bile, stomach contents, and liver. Most dead birds had no significant pathologic findings at necropsy, thereby supporting brevetoxin-related mortality.

Assessing Efficacy of Non-Lethal Harassment of Double-Crested Cormorants to Improve Atlantic Salmon Smolt Survival

Abstract Salmo salar (Atlantic Salmon) smolts are exposed to predation pressure as they migrate from freshwater into the estuary and near-shore marine environment. In particular, Phalacrocorax auritus (Double-crested Cormorants) are a predator of Atlantic salmon smolts during their estuary and near-shore migration. National Oceanic and Atmospheric Administration's (NOAA) National Marine Fisheries Services’ (NMFS) telemetry data collected prior to this study (1997–2003), suggest that smolts are being removed from the Narraguagus River on their downstream out-migration. This removal may be the result of Cormorant predation. We investigated whether smolt survival could be improved by disrupting normal Cormorant foraging activity by integrating passive smolt tracking and active harassment techniques. Smolt movement and usage of various portions of the estuary according to light condition and tidal stage were explored along with concurrent avian harassment. Although harassment only occurred in approximately 33...

Set-Back Distances to Protect Nesting and Roosting Seabirds Off Vancouver Island from Boat Disturbance

Abstract. Recreational boat traffic is increasing worldwide and there is a need for scientifically based regulations that sustain both seabirds and wildlife viewing. The effects of boat disturbance to seabirds off Vancouver Island, Canada were quantified by testing distances that roosting or nesting birds showed an agitation response to an approaching motorboat or a kayak. The effects of species sensitivity, vessel type, habituation and season on agitation distance were examined. At 40 m from approaching boats, nesting Double-crested (Phalacrocorax auritus) and Pelagic (P. pelagicus) cormorants, Black Oystercatchers (Haematopus bachmani), Glaucous-winged Gulls (Larus glaucescens), and Pigeon Guillemots (Cepphus columba) had less than 6% probability of being agitated with either a kayak or motorboat, while at 50 m there was less than 2% probability of agitation. Roosting birds had larger response distances than nesting birds. Roosting Harlequin Ducks (Histrionicus histrionicus) were particularly sensitive ...