Phalacrocorax Auritus Research Articles

Dispatches

Dispatches

‘State of Lake Superior’: A review

‘State of Lake Superior’: A review

Distribution, relative abundance, and prey demand by double-crested cormorants on Manitoulin Island lakes vs. Lake Huron Coast

An aerial distance sampling survey of double-crested cormorants ( Phalacrocorax auritus) was conducted in the northern region of Lake Huron (North Channel; four largest lakes of Manitoulin Island; South Shore of Manitoulin Is. facing the main body of the lake) to assess the relative distribution, abundance and prey demand by cormorants on inland lake vs. coastal habitat. On a per area basis, the density (approx. 1–2 cormorants ∙ km − 2 ) and prey demand (approx. 1.2 kg ha − 1 ) of cormorants in the four inland lakes matched that of the North Channel. The South Shore had approximately half the density and prey demand as the other two areas. Cormorants on the inland lakes of Manitoulin Island represented 13% early in the season and a high of 33% of the total population for this region of Lake Huron later in the summer. Estimating regional distributions of cormorants within the Great Lakes basin is important because mapped nest colonies and nest counts are not representative of the actual distribution of foraging cormorants during and after the nesting season. There are two general conclusions to emerge from this survey. First, aquatic productivity from both Great Lakes coast and inland lakes contributes to trends in population and distribution of cormorants in the northern region of Lake Huron and perhaps elsewhere. Second, inland aquatic ecosystems are important throughout a season for foraging cormorants from the Great Lakes and may become more important as Great Lake productivity trends downward.

Evaluation of Offshore Stocking of Lake Trout in Lake Ontario

AbstractRestoration stocking of hatchery‐reared lake trout Salvelinus namaycush has occurred in Lake Ontario since 1973. In U.S. waters, fish stocked through 1990 survived well and built a large adult population. Survival of yearlings stocked from shore declined during 1990–1995, and adult numbers fell during 1998–2005. Offshore stocking of lake trout was initiated in the late 1990s in response to its successful mitigation of predation losses to double‐crested cormorants Phalacrocorax auritus and the results of earlier studies that suggested it would enhance survival in some cases. The current study was designed to test the relative effectiveness of three stocking methods at a time when poststocking survival for lake trout was quite low and losses due to fish predators was a suspected factor. The stocking methods tested during 2000–2002 included May offshore, May onshore, and June onshore. Visual observations during nearshore stockings and hydroacoustic observations of offshore stockings indicated that release methods were not a direct cause of fish mortality. Experimental stockings were replicated for 3 years at one site in the southwest and for 2 years at one site in the southeast. Offshore releases used a landing craft to transport hatchery trucks from 3 to 6 km offshore out to 55–60‐m‐deep water. For the southwest site, offshore stocking significantly enhanced poststocking survival. Among the three methods, survival ratios were 1.74 : 1.00 : 1.02 (May offshore : May onshore : June onshore). Although not statistically significant owing to the small samples, the trends were similar for the southeast site, with survival ratios of 1.67 : 1.00 : 0.72. Consistent trends across years and sites indicated that offshore stocking of yearling lake trout during 2000–2002 provided nearly a twofold enhancement in survival; however, this increase does not appear to be great enough to achieve the 12‐fold enhancement necessary to return population abundance to restoration targets.Received November 29, 2010; accepted May 18, 2011

Controls on Abundance and Distribution of Yellow Perch: Predator, Water Quality, and Density‐Dependent Effects

AbstractUnraveling the diverse forces controlling the abundance and distribution of fish across a landscape has been challenging, in part because few techniques exist to address multiple factors simultaneously in a single analysis. We used spatially explicit, varying‐coefficient generalized additive models to relate the summertime abundance and distribution of yellow perch Perca flavescens to a variety of predatory, water quality, landscape, and density‐dependent factors. The model used 25 years of fishery‐independent trawling data from southern Green Bay, Lake Michigan, an area that supported major fisheries for yellow perch until their decline in the 1990s. Local catch per unit effort (CPUE) of both age‐0 and age‐1 and older yellow perch was affected by the abundance of double‐crested cormorants Phalacrocorax auritus, dissolved oxygen, water clarity, and bottom depth, but not water temperature. In addition, the local response of age‐0 yellow perch CPUE to most predictor variables, including their own global density, had a unique spatial structure. For instance, increased cormorant abundance was related to declines in local yellow perch CPUE, especially near cormorant nesting islands, while increased dissolved oxygen levels were correlated with increased local yellow perch CPUE in shallow nearshore areas of southern Green Bay. In addition, local yellow perch CPUE increased near the mouth of the Fox River during years with higher water clarity, suggesting that water quality may be limiting to yellow perch in this region. Our results suggest that it is important to explicitly account for the different ways in which predictor variables influence fish abundance across the aquatic landscape.

Determinants of local and migratory movements of Great Lakes double-crested cormorants

AbstractWe investigated how individual strategies combine with demographic and ecological factors to determine local and migratory movements in the double-crested cormorants (Phalacrocorax auritus). One hundred and forty-five cormorants were captured from 14 nesting colonies across the Great Lakes area and fitted with satellite transmitters. We first tested the hypotheses that sexual segregation, density-dependent effects, and the intensity of management operations influenced home range size during the breeding season. The influence of these factors appeared to be limited in part due to random variability in foraging and dispersal decisions at individual and colony levels. We also designed a statistical framework to investigate the degree and determinants of migratory connectivity. Our analyses revealed a significant migratory connectivity in cormorants, although we also observed a nonnegligible amount of individual variability and flexibility. Our data were most consistent with the existence of a migratory divide across the Great Lakes, with western populations using mainly the Mississippi Flyway and eastern populations the Atlantic Flyway. Previous and current studies suggest that the divide cannot be explained by past divergence in isolation, a way to diminish travel cost, or the Appalachians constituting an ecological barrier per se but is rather the consequence of the distribution of suitable stopover and nonbreeding areas. However, a parallel migration system and no migratory divide could not be entirely ruled out with present data.

Spatial and temporal comparisons of double-crested cormorant diets following the establishment of alewife in Lake Champlain, USA

Increasing numbers of double-crested cormorants (Phalacrocorax auritus) on Lake Champlain have caused concerns related to potential impacts on the yellow perch (Perca flavescens) population. However, with the establishment of alewife (Alosa pseudoharengus) in 2003, cormorant foraging may have changed. We examined cormorant diets from four areas of Lake Champlain to assess past, current, and potential future impacts of cormorants on the changing fish community. During the breeding seasons of 2001–2002 and 2008–2009, we observed spatial and temporal differences in cormorant diets. Yellow perch dominated diet composition during 2001–2002 at Young Island (73% and 90% yearly weight totals) during all reproductive periods. Four Brothers Islands diet composition in 2002 varied according to reproductive period. In 2008 and 2009, alewife were predominant in diets at Four Brothers Islands (56% and 71%) and the South site (65% and 62%), with yellow perch comprising a high proportion of diets at Young Island (44% and 56%). Results from a MANOVA confirmed differences among sites, reproductive period, and the interaction of these factors (P<0.0001) when describing diet compositions for the post-alewife years. PCA results denoted a general shift in cormorant diets from 2001–2002 to 2008–2009. Our study demonstrated that the diet of piscivorous birds may shift with a new forage species and may vary significantly within a single large water body. Accordingly, efforts to manage piscivorous birds with the intent to decrease mortality of specific fish species should be site specific when possible.

Interactions Between Double-crested Cormorants and Other Ground-Nesting Species

Increasing populations of Double-crested Cormorants (Phalacrocorax auritus; hereafter cormorants) are of concern regarding the displacement of other species from breeding colonies, but little is known about such interactions. Agonistic interactions between ground-nesting cormorants and American White Pelicans (Pelecanus erythrorhynchos; hereafter pelicans) were investigated and compared to those involving cormorants and Herring Gulls (Larus argentatus). Also, a survey of cormorant eggs in nests of other ground-nesting species was conducted. Of 158 agonistic interactions between cormorants and pelicans, 83% were threat displays, 9% attempts to steal nest material and 8% involved some form of physical contact. Pelicans defended their nests less frequently and engaged in fewer physical contacts (8%) in colonies mixed with cormorants compared to areas with only pelicans (33%). Herring Gulls engaged in more physical contact (26%) with cormorants in a mixed colony than when nesting only with other gulls (4%). Cormorant eggs were found in 1–26% of Herring and Ring-billed Gull (L. delawarensis) nests searched in the Great Lakes, and 0.3% of Caspian Tern (Hydroprogne caspia) nests at one location. The results indicate cormorants routinely engage in agonistic interactions with other ground-nesting birds; however, the type and importance of interactions varies. Site- and species-specific evaluation of interactions involving cormorants and other birds is recommended before taking management steps to reduce nest site competition.

Effects of management on double-crested cormorant nesting colony fidelity

The increase of double-crested cormorant (Phalacrocorax auritus; hereafter, cormorant) populations during the last 2 decades has impacted many stakeholder groups. The negative effects of nesting cormorants on trees and other vegetation have motivated private organizations and government agencies to manage nesting colonies and reduce their impacts to private property and public resources. Management-induced reproductive failure has been shown to influence cormorant inter-annual nesting colony fidelity, but not complete abandonment from a nesting colony site. We attached very high frequency (VHF) transmitters and Global Positioning System (GPS) transmitters to nesting cormorants to monitor their movement response on a managed site (Young Island, VT [YI]) and an unmanaged site (Four Brothers Islands, NY [FB]). Additionally, we monitored these sites to determine the influence of management activities on subsequent-year colonization. On YI, management consisted of egg-oiling all cormorant nests (some nests had been oiled in previous years) and culling approximately 20% of adults. Annual dispersal rates did not differ between managed and unmanaged sites, but a nesting period interaction occurred with greater dispersal on the managed site following the incubation period. After 4 years of both egg oiling and culling, cormorant nesting on YI declined to zero. Simultaneously, cormorant numbers increased on the nearby unmanaged FB. We propose either the cumulative effect of partial or complete reproductive failure (8 yr) or simply the inclusion of adult culling (4 yr) caused the abandonment. From a colony-specific management perspective, the rapid decline was beneficial to the goal of restoring the vegetative community on YI. The effects of adult culling at nesting colonies, prior-year reproductive failure caused by egg oiling, or the combination of these factors may be required for complete and rapid nesting site abandonment. The use of culling adult breeders reduced nesting and likely limits the cost and logistics of control and allows more rapid initiation of mitigation measures and island habitat restoration. © 2011 The Wildlife Society.

Influence of increasing populations of Double-crested Cormorants on soil nutrient characteristics of nesting islands in western Lake Erie

Animals can influence the structure of an ecosystem by changing the levels of nutrient input. This is of particular importance for the islands of western Lake Erie, which are relatively nutrient poor, but have experienced increases in nutrient input from growing double-crested cormorant ( Phalacrocorax auritus) populations. The objectives of this study were to evaluate changes in soil characteristics (nutrients [nitrate (NO 3), total P], pH, and δ 13C [as a tracer of cormorant-associated nutrients]) across a gradient of cormorant nest density on two islands (Middle and East Sister) in western Lake Erie. For both islands, soil pH decreased and P concentrations increased with nest density. On Middle Island, soil nitrate concentrations increased with cormorant nest density, and varied with breeding phenology, with highest concentrations during the early and mid nesting season (272 ± 19 μg g − 1 ) and lowest concentrations late in the season (165 ± 11 μg g − 1 ). Following a 3-year absence of nesting activity at sites on Middle Island, soil nitrate concentrations were similar to those at low density sites. In contrast, nitrate concentrations measured on East Sister Island did not correlate with temporal or spatial patterns of cormorant nesting and remained elevated 10 years post-cormorant use. While the results of this study confirm that chronic input of allochthonous materials alters soil properties of these islands, the unique conditions of each island must be considered when predicting ecological effects and setting long-term management objectives.

Archaeological Evidence for a Double-Crested Cormorant (Phalacrocorax auritus) Colony in the Pacific Northwest, USA

Double-crested Cormorants (Phalacrocorax auritus) were not observed breeding in the inner coast of Washington and British Columbia until the 1920s and 1930s, whether the breeding was either a re-colonizing event or a new expansion was unknown. Archaeological evidence from Watmough Bay, a shell midden site on Lopez Island, San Juan Islands (Washington State), was analyzed to place the recent changes in breeding distribution in deeper historical context. The Watmough Bay faunal assemblage contains large numbers (n = 2,397) of cormorant bones. Of those specimens that could be identified to species (n = 358), 99.7% were identified as Double-crested Cormorants. The majority (97%, n = 2,336) of the cormorant remains are from juveniles or chicks, which were collected while still at the colony. Radiocarbon dating indicates the majority of the site accumulated between AD 300– 600. Evidence for a ca. 1,500-year-old Double-crested Cormorant colony near Lopez Island confirms that the species did breed in the region prior to the early 20th century. The study further documents the value of archaeological data for current wildlife management.

Assessing the Validity of the Accelerometry Technique for Estimating the Energy Expenditure of Diving Double-Crested CormorantsPhalacrocorax auritus

Over the past few years, acceleration-data loggers have been used to provide calibrated proxies of energy expenditure: the accelerometry technique. Relationships between rate of oxygen consumption and a derivation of acceleration data termed "overall dynamic body acceleration" (ODBA) have now been generated for a range of species, including birds, mammals, and amphibians. In this study, we examine the utility of the accelerometry technique for estimating the energy expended by double-crested cormorants Phalacrocorax auritus to undertake a dive cycle (i.e., a dive and the subsequent pause at the surface before another dive). The results show that ODBA does not calibrate with energy expenditure in diving cormorants, where energy expenditure is calculated from measures of oxygen uptake during surface periods between dives. The possible explanations include reasons why energy expenditure may not relate to ODBA but also reasons why oxygen uptake between dives may not accurately represent energy expenditure during a dive cycle.

Double-crested cormorants and urban wilderness: conflicts and management

In this paper we examine the management of human-double-crested cormorant conflicts in urban nature areas using the Leslie Street Spit in Toronto, Ontario as our focal study area. We examine the management perspectives of various stakeholders and how they shift over time in response to site ecology and stakeholder input. We categorize management perspectives on a spectrum from complete human domination to near absence of human intention. Two broad management categories emerge from this framework: interventionist and laissez-faire. Interventionists recognized need for management of cormorants, laissez-faire argued for no management of a cormorant colony that has deforested 24% of the site through their nesting activities. We conclude that for urban nature areas, particularly those with a unique, rare, or contentious ecology, a hands-off, laissez-faire management approach is not conducive to improving human-nature relations. Rather, for urban nature sites nature management must promote a respectable balance between human and non-human life, for the long-term benefit of both.

Effects of Double‐Crested Cormorants (Phalacrocorax auritus Less.) on Island Vegetation, Seedbank, and Soil Chemistry: Evaluating Island Restoration Potential

The unique plant community on Middle Island, Lake Erie, Canada, has been greatly modified by double‐crested cormorants (Phalacrocorax auritus Less.) whose population has increased enormously in the last two decades. The aims of this study were to assess the impact of cormorants on island tree canopy, understorey vegetation, soil seedbank, and soil chemistry. The ultimate objective was to assess the resilience of the vegetation community for recovery should cormorant nest densities decrease significantly. Forty‐three point stations were established in a grid system covering the entire island. The herbaceous and woody vegetation was surveyed over 2 years and tree crown damage was assessed at each point station. In 2008, soil samples were collected for both chemical analysis and a seedbank inventory. Vegetation and seedbank species richness were impoverished compared to the vegetation surveyed prior to cormorant colonization. Cormorants affected not only the tree canopy where they nested but also the understorey vegetation. Exotic plant species were very common in the standing vegetation and constituted the bulk of the abundance in the seedbank. However, there was little relationship between aboveground vegetation and seedbank composition. Cormorants appeared to have little influence on seedbank richness, abundance, and composition. Notably, several species of conservation interest were found in the aboveground vegetation and in the seedbank providing a positive sign for future efforts to restore island plant communities.

Evidence for Sex Differences in Mercury Dynamics in Double-Crested Cormorants

Aquatic fish-eating birds can demethylate methylmercury in their livers. In this study, we determined whether a previously documented male bias in mercury concentration in double-crested cormorants ( Phalacrocorax auritus ) was due entirely to the depuration of mercury into eggs or might also in part be related to sex differences in methylmercury demethylation or biliary excretion capability in the liver. We found egg depuration accounted for less than a fifth of the mercury concentration difference between males and females, hence not entirely explaining the sex difference. Females had a significantly steeper slope for the negative relationship between percent methylmercury (i.e., percentage of total mercury that is methylmercury) and total mercury concentration than did males. This suggests that females have a greater capacity to demethylate methylmercury, which might be reducing the amount of methylmercury available for depuration to eggs. We also found a significant negative relationship between methylmercury concentration and liver mass for females only; thus females might also have a greater capability to excrete methylmercury compared to males. Therefore, we conclude that the male bias in mercury concentration might also result from females having a greater capability to excrete mercury compared to males.

Migration and Winter Movements of Double-Crested Cormorants Breeding in Georgian Bay, Ontario

Abstract. Double-crested Cormorants (Phalacrocorax auritus) breeding in the Great Lakes and wintering in the southeastern United States were implanted with satellite transmitters to assess their movements. During 2007 and 2008, 26 cormorants from Georgian Bay, Ontario, Canada, were tracked in order to, variously, identify staging areas, characterize migration routes, winter habitat use, and home range size, assess philopatry of returning breeders, and test for a relationship between winter habitat use and arrival at the breeding ground. Females left summer areas earlier and spent more time in staging areas than did males. However, both sexes left the staging areas and arrived in the wintering grounds at approximately the same time. There was no difference in latitude between wintering males and females, or in winter residency time (n = 136 days for both sexes). The predominant winter habitat types were lakes and coasts with only seven of 26 (26.9%) birds wintering on aquaculture sites. Contrary to expecta...

Refinement of Biomarker Pentosidine Methodology for use on Aging Birds

There is no reliable method for determining age for most species of long-lived birds. Recent success using the skin chemical pentosidine as a biomarker has shown promise as an aging tool for birds. Pentosidine levels have been determined only from the breast tissue of carcasses, and we sought to refine the procedure with respect to biopsy size and location for safe and effective use on living birds. We compared pentosidine concentrations in 4 skin-size samples (4, 6, 8, and 20-mm diameter biopsies) from the breast of black vulture (Coragyps atratus) carcasses. We also compared pentosidine levels from breast and patagial tissue to document potential differences among collection sites of deceased vultures (with unknown ages) and monk parakeets (Myiopsitta monachus; with actual, minimal, and unknown ages). Pentosidine concentrations (pmol pentosidine/mg collagen) were similar among the 4 sizes of vulture breast skin (P = 0.82). Pentosidine concentrations for the breast (0 = 8.9, SE = 0.55, n = 28) and patagium (0 = 8.9, SE = 0.51, n = 28) of vultures were similar, but in parakeets, pentosidine was higher in the breast (0 = 15.9, SE = 1.30, n = 105) than the patagium (0 = 11.5, SE = 1.10, n = 105). We made pentosidine-based age estimates for vultures and parakeets using a general age curve for wild birds. We also made vulture age estimates using plumage characteristics and a cormorant (Phalacrocorax auritus) age curve. Vulture pentosidine-based age estimates appear to correspond to plumage-based age estimates. Pentosidine-based age estimates for 88% of the known-aged parakeets (n = 17) were within 6 months of actual ages. Even though known ages were not available for all birds, we found a positive trend in pentosidine versus age for both species. We suggest that 6-mm diameter skin samples from the patagium of living vultures and other similar-sized birds will provide sufficient tissue for reliable age estimation and will not impair flight ability.

Effects of Lipid Extraction and Lipid Normalization on Stable Carbon and Nitrogen Isotope Ratios in Double-Crested Cormorants: Implications for Food Web Studies

Abstract. Cormorants are desirable subjects for food web studies using stable isotopes (C and N) because of global fisheries conflicts, but no validated lipid-normalization procedures are currently available for any cormorant species. Accordingly, the effects of chloroform-methanol and petroleum-ether lipid extractions and three published lipid-normalization models on stable C and N isotope signatures in Double-crested Cormorant (Phalacrocorax auritus) muscle and liver tissues were investigated. The presence of lipids in cormorant muscle and liver decreased δ13C values by approximately 1–2‰, more so than has been reported in other birds. Cormorants showed large variation in the relationship between the C:N ratio of bulk tissue and the change in δ13C values after lipid extraction, violating a major assumption of published lipid-normalization models. Despite this violation, two of the three tested models performed reasonably well for correcting δ13C values. The circumstances under which these models might f...

Male Biased Parasitism in Cormorants and Relationships with Foraging Ecology on Lake Erie, Canada

Existing hypotheses only partially explain male biased parasitism in mammals and birds. The present study examined whether male biased parasitism by a common trematode and nematode exists in breeding Doublecrested Cormorants (Phalacrocorax auritus) from Lake Erie and if any sex bias in parasitism could be explained by sex differences in body size and foraging ecology, evaluated using stable isotope profiles (based on δ13C, δ15N). Male cormorants had three times the abundance of Drepanocephalus spathans (a trematode) than females; however, there were no significant sex differences in abundance or intensity of Contracaecum spp. Relationships between body size and parasitism were either non-existent or inconsistent. Stable carbon isotope profiles indicated that male and female cormorants that foraged in more pelagic habitats had more Contracaecum spp. In summary, male biased parasitism was present in a sample of Lake Erie cormorants and differences in foraging ecology might affect the levels of parasitism in cormorants.

Mercury in parasitic nematodes and trematodes and their double-crested cormorant hosts: Bioaccumulation in the face of sequestration by nematodes

Endoparasites can alter their host's heavy metal concentrations by sequestering metals in their own tissues. Contracaecum spp. (a nematode), but not Drepanocephalus spathans (a trematode), were bioaccumulating mercury to concentrations 1.5 times above cormorant hosts. Nematodes did not have significantly greater stable nitrogen isotope values (δ 15N) than their hosts, which is contradictory to prey–predator trophic enrichment studies, but is in agreement with other endoparasite–host relationships. However, Contracaecum spp. δ 13C values were significantly greater than their hosts, which suggest that nematodes were consuming host tissues. Nematodes were accumulating and thus sequestering some of their cormorant hosts' body burden of methyl mercury; however, they were not dramatically reducing their hosts' accumulation of methyl mercury.