Phalacrocorax Auritus Research Articles

Spatial and temporal composition of the avifauna from the barrier islands of the San Ignacio-Navachiste-Macapule lagoon complex, Sinaloa, Mexico

We analyzed the composition and abundance of the avifuana inhabiting the barrier islands of the San Ignacio-Navachiste- Macapule lagoon system from July 2006 to June 2007. Species richness and relative abundance were determined for the whole complex and for each island. The cumulative abundance was 55,849 individuals belonging to 71 species, 54 genera, and 26 families, distributed as follows: 51% resident species, 5% summer migratory species, 41% winter migratory species, and 3% transient species. Families with the highest species richness were Laridae (14 species, 20%), Scolopacidae (12 species, 17%), and Ardeidae (10 species, 14%). The Pelecaniformes group had the highest cumulative abundance (38,661 individuals, 69%), whereas the anatids had the lowest cumulative abundance (0.6%). The species with the highest relative abundance were Pelecanus occidentalis (16,355 individuals, 29%), Phalacrocorax auritus (13,209 individuals, 24%), and Fregata magnificens (5,964 individuals, 11%). The 68 remaining species represented only 36% of the cumulative abundance. Nineteen bird species used the islands as breeding sites, and the ardeids represented the most important group with 12 species (60%). Pajaros and San Ignacio islands were the main breeding sites within the insular system, particularly Pájaros due to its high species richness and abundance. This study highlights the importance of the barrier islands of northern Sinaloa as breeding areas for resident and migratory species.

Effects of aquaculture on migration and movement patterns of double-crested cormorants

We analyzed 10,620 recovery records for double-crested cormorants (Phalacrocorax auritus) banded as nestlings from 1923 to 2006 to determine the population's age structure, migration routes, dispersal patterns, and the possible infl uence of the expansion of the aquaculture industry in the southeastern United States on these population characteristics. Ninety-nine percent of the birds were banded during June to August, and 78% were banded as pre-fl edged birds. Cormorants banded in the interior region of the United States comprised 91% of all birds banded from 1955 to 2006; these birds wintered primarily in the Lower Mississippi Valley and the northern Gulf of Mexico area. From 1986 to 2006, the number of bands recovered in principal aquaculture areas in the southeastern United States increased 454%, while the number of bands recovered in other areas increased 55%. Further, pre-aquaculture expansion (1923- 1985) birds were recovered at greater distances from their banding colonies than were post- aquaculture epansion (1986-2006) birds. These data indicate that the expansion of southeastern aquaculture has infl uenced double-crested cormorant movements and migration patterns.

Lack of Angling-Sized Yellow Perch in a Canadian Boreal Lake: Potential Influences of Growth Rate, Diet, and Predation by Double-Crested Cormorants

Fisheries for yellow perch Perca flavescens are economically important in North America, but in many lakes this species does not attain sizes desirable to anglers (total length [TL] > 250 mm). We investigated factors potentially contributing to the lack of angling-sized yellow perch in Dore Lake, Saskatchewan. This large boreal lake has a long history of exploitation and is subject to current controversy regarding the impact of double-crested cormorants Phalacrocorax auritus on its fisheries. We found that yellow perch in Dore Lake attained greater maximum ages (mean ± SD = 7.4 ± 1.0 years) but smaller maximum sizes (215 ± 7 mm TL) than other yellow perch populations. Thus, the lack of angling-sized yellow perch in Dore Lake is probably the result of slow growth rates rather than short life spans. Double-crested cormorants preyed heavily on yellow perch, but predation was highly skewed toward much smaller sizes (<100 mm TL) than those preferred by anglers. Stomach contents and stable nitrogen isotopes confirmed that yellow perch in Dore Lake undergo expected ontogenetic diet shifts and become predominantly piscivorous at around age 3. Analysis with stable isotopes also revealed long-term dietary differences between age-2 and age-3 yellow perch captured in littoral versus offshore habitats, suggesting some degree of intrapopulation variability in resource and habitat use among yellow perch in Dore Lake.

Contribution of Declining Anadromous Fishes to the Reproductive Investment of a Common Piscivorous Seabird, The Double-Crested Cormorant (Phalacrocorax auritus)

— 696 — The Auk, Vol. 127, Number 3, pages 696−703. ISSN 0004-8038, electronic ISSN 1938-4254.  2010 by The American Ornithologists’ Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press’s Rights and Permissions website, http://www.ucpressjournals. com/reprintInfo.asp. DOI: 10.1525/auk.2010.09200 Andrew w. Jones,1 Christopher M. dAlton,2 edwArd s. stowe, And dAvid M. post

Line transect distance sampling in aerial surveys for double-crested cormorants in coastal regions of Lake Huron

Line transect distance sampling was employed in aerial surveys of double-crested cormorants ( Phalacrocorax auritus) along the coasts of Georgian Bay and the North Channel, Lake Huron. A double-observer method was used to estimate detection probability near the transect line ( g(0) = 0.724). Detection of cormorants was not consistent but varied based on group size, location (water, land, flying), and season. Probability of detection in the area covered by the survey was often below 0.5. Incorporating both lack of detection on the flight line along with lack of detection over the covered area inherent in distance sampling provided defensible density estimates of free-ranging double-crested cormorants. Most cormorants were detected loafing on shore (land) among the many islands defining this area of the Lake Huron coast. Land detections exceeded the combined detections of birds on the water and flying. Density in 2004 ranged from a peak of 2.30 cormorants per km 2 (95% CI = 1.72–3.03) in late July to 1.21 cormorants per km 2 (95% CI = 0.78–1.70) in late August in the sampled areas extending from shore to approximately 20 km offshore. Aerial surveys employing distance sampling can be useful tools in monitoring the distribution and abundance of free-ranging double-crested cormorants and other waterbirds in the Laurentian Great Lakes.

Seasonal and annual patterns in density of double-crested cormorants in two coastal regions of Lake Huron

Aerial line transect distance sampling surveys of coastal areas in the North Channel and Georgian Bay, Lake Huron, were conducted to estimate density of double-crested cormorants ( Phalacrocorax auritus). Surveys were approximately every two weeks through summer from 2000 to 2005. In each year, density of cormorants declined towards late summer indicating a large scale outward migration of cormorants from Lake Huron. The seasonal pattern of decline differed between the two regions based on a mixed model analysis. Seasonal patterns in apparent fledging patterns may reflect differences between the North Channel and Georgian Bay in nesting phenology, nesting synchrony or some combination of these factors. Density was generally higher in the North Channel relative to Georgian Bay seasonally and during the period 2000–2002 likely reflecting higher per unit area productivity in the North Channel. In the years 2003–2005, density was lower in both regions and similar compared to earlier years of the survey likely reflecting a regime shift that occurred in Lake Huron at that time. The effect of this change was greater in the North Channel than in Georgian Bay as indicated by a greater decline in cormorant density in the North Channel after 2002.

Does Pond Water Reflectance Influence Double-crested Cormorant Selection of Aquaculture Ponds?

Double-crested cormorants, Phalacrocorax auritus, are a frequent and major avian predator on channel catfish, Ictalurus punctatus, and other aquaculture species throughout the southeastern USA. Although cormorant movements and occurrence within the aquaculture production region are understood, no studies have focused on the mechanisms utilized by these avian predators to select foraging sites within these high-density aquaculture systems. The objective of this study was to determine if cormorant abundance is associated with specific (ultraviolet to visible) light reflectance spectra within commercial catfish ponds. Three commercial farms were used in this study; each farm had four ponds classified as and another four ponds classified as based on observing cormorant numbers for 3 mo prior to reflectance measures (>100 h observation for each pond). Reflectance and pond turbidity were measured weekly for 7 wk during the period of maximal over-wintering cormorant numbers. Water samples were collected at the surface (1 cm depth) and secchi depth (10-41 cm) at two locations (upwind and downwind sides) within each pond to determine spectral reflectance and turbidity. Average pond reflectance values were not significantly different between ponds preferred and avoided by cormorants; however, upwind reflectance significantly differed from downwind reflectance between cormorant use groups. Using cross-validation discriminant analysis, the accuracy of separating upwind ponds preferred and avoided by cormorants was over 62%. Repeated measures ANOVA identified the reflectance at 370, 380, 460, 500, 510, and 620 nm as significantly different between ponds preferred and avoided by cormorants. The lower wavelengths (380-410 nm) correspond to known UV-A sensing compounds in cormorants and the other wavelengths share characteristics associated with algal biomass. Cormorants utilize ponds that have lower algal biomass when compared with avoided ponds.

American White Pelicans and Double-Crested Cormorants in Saskatchewan: Population Trends Over Five Decades

American White Pelicans and Double-Crested Cormorants in Saskatchewan: Population Trends Over Five Decades

Increased Abundance and First Breeding Record of the Neotropic Cormorant (Phalacrocorax brasilianus) on the Alluvial Plain of Mississippi

Phalacrocorax brasilianus (Neotropic Cormorant) has been observed with increasing frequency in the alluvial plain (Delta region) of Mississippi. In the past 6 years, 22 individuals have been observed in 20 separate sightings during spring and summer. These sightings have occurred at breeding colonies of other colonial waterbirds and commercial aquaculture facilities of Ictalurus punctatus (Channel Catfi sh). Two sexually mature Neotropic Cormorants have been collected at a colonial waterbird breeding colony near the Mississippi River in the western Delta region among fl ocks of Phalacrocorax auritus (Double-crested Cormorants). Twice during the summer of 2008, confi rmed nesting of Neotropic Cormorants were documented in the Delta region of Mississippi. The increased abundance and range expansion of Neotropic Cormorants in the Delta region of Mississippi may be a result of the readily available food source of cultured Channel Catfi sh.

Double-Crested Cormorants Expand their Breeding Range Onto the Boreal Shield in Saskatchewan

Double-Crested Cormorants Expand their Breeding Range Onto the Boreal Shield in Saskatchewan

Food web bioaccumulation model for polychlorinated biphenyls in San Francisco Bay, California, USA

We document the development and application of a food web bioaccumulation model for polychlorinated biphenyls (PCBs) in San Francisco Bay, California, USA. The model calculates spatial distributions of PCB concentrations in a range of invertebrate, fish, avian, and mammalian organisms, including harbor seals, double-crested cormorants, and Forster's terns. The performance of the model is evaluated against independent empirical PCB concentrations and shows a mean deviation between observed and model-calculated concentrations of 36% for female harbor seals and 5% for benthic invertebrates and jack smelt. The model was applied to produce bay-wide PCB concentration distributions in fish and wildlife species, which were compared with threshold effect concentrations to determine ecological risks and human health risks of fish consumption. Because of their high trophic position in the food web, harbor seals exhibited the highest concentrations of summation operatorPCBs, which exceeded threshold concentrations for potential adverse effects. The model was also applied to derive bay-wide target sediment concentrations for remediation as part of an ongoing total maximum daily loading characterization. The model calculated bay-wide geometric mean concentrations of summation operatorPCB in sediments of 1.6 to 73 microg/kg dry weight to meet several ecological and human health risk objectives. The bay-wide geometric summation operatorPCB concentration in the sediments at the time of the study was 11.6 microg/kg dry weight. The model was developed for assessing the behavior and risks of bioaccumulative substances on an ecosystem level.

Corrigendum — Parasitism, mercury contamination, and stable isotopes in fish-eating double-crested cormorants: no support for the co-ingestion hypothesis

Corrigendum — Parasitism, mercury contamination, and stable isotopes in fish-eating double-crested cormorants: no support for the co-ingestion hypothesis

Diet shift of double-crested cormorants in eastern Lake Ontario associated with the expansion of the invasive round goby

The proliferation of the invasive round goby ( Apollonia melanostoma) in the Great Lakes has caused shifts in the trophic ecology in some areas. We examined the diet of double-crested cormorants ( Phalacrocorax auritas) prior to, and immediately after, round goby population expansion at two colonies, Pigeon and Snake Islands, in eastern Lake Ontario from 1999 to 2007. Cormorant diet was determined from the examination of 10,167 pellets collected over the nine-year period. By the second year round gobies were found in the diet (2002 at Snake Island and 2003 at Pigeon Island) they were the main species consumed by cormorants at each colony. The dominance of round goby in cormorant diets had a significant effect on both daily fish consumption and seasonal trends in fish consumption compared to the pre-goby years. Seasonal differences that were observed during the pre-goby years were lost once gobies became the main diet component of cormorants. The rapid switch to a benthic prey such as round goby, from a largely limnetic fish diet demonstrates the adaptive foraging ability of cormorants. Round goby may act as a buffer for yellow perch and smallmouth bass, two sport fish impacted by cormorant predation in eastern Lake Ontario.

Management effects on breeding and foraging numbers and movements of double-crested cormorants in the Les Cheneaux Islands, Lake Huron, Michigan

The yellow perch fishery of the Les Cheneaux Islands (LCI) region of Lake Huron, MI suffered a collapse in 2000, attributed in part to the increase of double-crested cormorants ( Phalacrocorax auritus) in the region. A management program involving egg-oiling and lethal culling was initiated in 2004 to reduce cormorant foraging on yellow perch in the LCI. Counts of cormorant nests, nests oiled, cormorants culled, and aerial counts and telemetry surveys were used to evaluate management. Management contributed to a 74% reduction of cormorants on breeding colonies from 2004 to 2007. Cormorants used the LCI area significantly more ( P < 0.05) than surrounding areas. Aerial counts of foraging cormorants declined significantly ( P < 0.05) over the entire survey area but not within the LCI proper. However, aerial counts of cormorants in the LCI were five-fold less than cormorant counts in the same area in 1995. Reduced cormorant numbers were attributed in part to the elimination of cormorant nesting on a large colony due to the introduction of raccoons. Although the numbers of cormorants using the LCI did not decline, flocks were significantly smaller and more dispersed after management began. The reduced number of cormorants from 1995 levels and more dispersed foraging likely reduced predation on fish stocks including yellow perch in the LCI. Our findings indicate that the relationship between reduction in cormorant breeding numbers and reduced cormorant foraging in a given area is complex and may be influenced by density dependent factors such as intraspecific competition and quality of the forage base.

Response of yellow perch in Les Cheneaux Islands, Lake Huron to declining numbers of double-crested cormorants stemming from control activities

The yellow perch ( Perca flavescens) fishery of the Les Cheneaux Islands region of Lake Huron experienced an unprecedented collapse in 2000. Immediately prior to the collapse was the proliferation of double-crested cormorants ( Phalacrocorax auritus) in the area. Subsequent investigations established that double-crested cormorant predation was chief among the forces shaping the local yellow perch population and contributing to the collapse of the fishery. A double-crested cormorant control program was implemented in 2004 with the objective of benefiting the yellow perch population and fishery. This study used creel survey and gillnet fish community assessment data to evaluate the response of the yellow perch population and fishery. In all, seven key yellow perch metrics were analyzed using regression analysis with double-crested cormorant abundance as the independent variable. As double-crested cormorant abundance declined, yellow perch abundance increased, total mortality rate decreased, the angler catch rate and harvest in the recreational fishery improved, yellow perch growth rate declined and mean age increased. Increased yellow perch recruitment was documented since 2003 but it was the longevity of these year classes, (improved survival) as much or more than their magnitude of the year class, that allowed for the progress towards recovery. Questions facing managers are the sustainable level of double-crested cormorants in the region and the long term prognosis for the yellow perch fishery to fully recover to pre-double-crested cormorant levels.

Characteristics of double-crested cormorant colonies in the U.S. Great Lakes island landscape

The Great Lakes form the largest freshwater island system in the world and provide breeding habitat for a large proportion of the continental population of double-crested cormorants ( Phalacrocorax auritus). Here, cormorants have a high profile due to conflicts with humans; by 2007, most active (64%) breeding sites in U.S. waters were managed. This study used data from the U.S. Great Lakes Colonial Waterbird Database and The Nature Conservancy's Great Lakes Island GIS database to identify important features of breeding sites in the U.S. Great Lakes and broaden understanding of cormorant presence at the island-landscape scale. Islands 0.5–10 ha were used more frequently than expected, and most sites had remoteness values of ≤ 3 km. Colony size was positively correlated with years occupied and large colonies (> 1000 pairs) developed primarily (95%) on island sites > 1.0 ha. Sites supporting large colonies were more remote than those supporting smaller colonies. Presence of other colonial waterbird species, especially Herring Gulls ( Larus argentatus), also characterized cormorant sites. Islands used by cormorants comprised a small proportion ( n = 90, 3%) of the U.S. Great Lakes island resource, and < 1% of the total island area. Certain characteristics of breeding sites (e.g., small islands, proximity to mainland) may increase negative attitudes about cormorants. To understand cormorant impacts to island resources (e.g., vegetation; other colonial waterbird species), we suggest cormorant presence in the Great Lakes be considered in the broader context of island science, conservation and known threats, and at a landscape scale.

Evaluation of harassment of migrating double-crested cormorants to limit depredation on selected sport fisheries in Michigan

Diverse management techniques have been used to mitigate conflicts between humans and double-crested cormorants ( Phalacrocorax auritus) including harassment methods supplemented by lethal take. In this study we evaluated impacts of programs to harass spring migrating cormorants on the walleye ( Sander vitreus) fishery in Brevoort Lake and the yellow perch ( Perca flavescens) and walleye fisheries at Drummond Island. Cormorant foraging declined significantly ( p < 0.05) at both locations subsequent to initiation of harassment programs. Overall harassment deterred 90% of cormorant foraging attempts while taking less than 6% lethally on average at each site. Yellow perch were a predominate prey item in number and biomass at both locations. Walleye made up a small proportion of the diet at both locations. However, both walleye and yellow perch abundance increased significantly ( p < 0.05) at Drummond Island. Walleye abundance at age 3 increased to record levels in 2008 following 3 years of cormorant management at Brevoort Lake. The estimated cormorant consumption of age-1 walleye in the absence of management at Brevoort Lake during 2005 would account for 55% of the record 2006 age-1 walleye population. These results support the hypothesis that cormorant predation on spawning aggregations of sportfish was a significant mortality factor and cormorant management reduced sportfish mortality and increased abundance at both locations. Continuation of harassment programs and fishery assessments will determine whether improvement of targeted sport fisheries through control of spring migrating cormorants is sustainable.

Phenology of Six Migratory Coastal Birds in Relation to Climate Change

The migration phenology of six species of coastal birds on Mustang Island, Texas, USA was examined for a 27-year period (1978–2005). First arrival date, last date of departure, and duration of stay were quantified for three winter and three summer residents. These three variables were analyzed for changes over time and correlation with local, regional, and global temperature indices. Mean local summer temperature increased 0.03° C/year (0.74° C overall), while mean local winter temperature increased 0.10° C/year (2.76° C overall). The three winter residents had a trend for increasingly later arrival, increasingly earlier departure, and decreased duration of stay over the 27-year period. These trends reflect a shortening of the winter season for these birds and are consistent with expected responses due to warming temperatures. The three terns representing summer residents had less homogeneity in temporal trends than the three winter residents. Correlations of local temperature with arrival and departure dates, and duration of stay yielded few significant results and no overall pattern. Only Double-crested Cormorant (Phalacrocorax auritus; a winter resident) and Least Tern (Sterna antillarum; a summer resident) had significant correlations between arrival date and arrival temperature.

Book Review: The Double-crested Cormorant: Issues and Management

Book Review: The Double-crested Cormorant: Issues and Management

Isolation and characterization of eight novel microsatellite loci in the double-crested cormorant (Phalacrocorax auritus)

We describe the isolation and characterization of eight microsatellite loci from the double-crested cormorant (Phalacrocorax auritus). Genetic variability was assessed using 60 individuals from three populations. All loci were variable with the number of alleles ranging from two to 17 per locus, and observed heterozygosity varying from 0.05 to 0.89. No loci showed signs of linkage disequilibrium and all loci conformed to Hardy–Weinberg equilibrium frequencies. Further, all loci amplified and were polymorphic in two related Phalacrocorax species. These loci should prove useful for population genetic studies of the double-crested cormorant and other pelecaniform species.