Diet Of Double-crested Cormorants Research Articles

Microplastics in the diet of nestling double-crested cormorants (Phalacrocorax auritus), an obligate piscivore in a freshwater ecosystem

Anthropogenic debris, namely plastic, is a concern across aquatic ecosystems worldwide, with freshwater systems being understudied relative to marine systems. In this study, we quantified and characterized debris in the diet of double-crested cormorant chicks (Phalacrocorax auritus) from three sites in two of the Laurentian Great Lakes to (i) determine whether or not the diet of double-crested cormorants in the Laurentian Great Lakes includes anthropogenic debris, (ii) characterize the size, shape, and type of debris incorporated, and (iii) examine relationships between the amount of debris ingested and their proximity to industrial–urban centres. Overall, >86% of cormorants in our study had anthropogenic debris (mostly fibers) in their digestive tracts with no correlation between site and the amount of debris ingested. The ingested debris includes microplastics, natural fibres from textiles, and other anthropogenic materials (e.g., glass). To the best of our knowledge, this is one of the first studies to examine anthropogenic debris in a diving bird in the Laurentian Great Lakes and one of few studies investigating this in freshwater birds.

Eating the Invaders: The Prevalence of Round Goby (Apollonia melanostomus) in the Diet of Double-Crested Cormorants on the Niagara River

Abstract. The Round Goby (Apollonia melanostomus) is a small benthic fish, native to the Eurasian Ponto-Caspian region, that has rapidly spread through the entire Laurentian Great Lakes system since its 1990 discovery in Lake St. Clair. Tolerant of high population densities, the exotic Round Goby competes aggressively with native fish for food and habitat, and has increasingly been exploited by endemic Great Lakes predators. A management program for the Upper Niagara River, initiated in 2004, has provided an opportunity to study the interactions between these invaders and the Double-crested Cormorant (Phalacrocoiax auritus), a native top predator. The gut contents of 1,119 cormorants nesting at two sites in the Upper Niagara River from 2004 to 2007 were examined, and the species composition of ingested prey (by number and weight) was quantified for the 600 stomachs that contained identifiable prey. Results of these analyses indicate that Round Goby can constitute up to 85% of the biomass in cormorant diet...

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.

Influence of Diet of Double-Crested Cormorants on Thiamine, Lead, and Mineral Contents of Their Eggs

ABSTRACT Throughout much of the Great Lakes basin, reproduction of several fish species is impaired by deficiency of thiamine in their eggs, an effect attributed to consumption of thiaminase-containing forage species, primarily alewife (Alosa pseudoharengus.) Because the double-crested cormorant (Phalacrocorax auritus) nesting on islands in Lake Ontario is known to consume considerable amounts of alewife, we examined cormorant food habits and measured thiamine content in eggs collected in 1999 from six separate nests of cormorants from colonies near Lake Ontario and contrasted them with food habits and eggs of cormorants from Oneida Lake where the alewife is rare. Thiamine concentrations in eggs varied between 4.31 and 11.24 nmoleslg with no significant (P>0.18) difference between mean concentrations for Lake Ontario and Oneida Lake (8.08 vs 8.36 nmoles/g) even though alewife comprised approximately 65 vs 0 % of their diets, respectively. Consumption of other thiaminase-containing species was minor in both lakes. Therefore, consumption of alewife and other thiaminase containing fishes by cormorants on Lake Ontario did not appear to significantly impair the levels of thiamine in their eggs. However, we found that the concentration of thiamine in eggs (T; nmoles/g) was inversely related (P<0.02) to lead (Pb) concentration (μg/g) according to the equation: T = −3.142 Pb + 16.25. This relationship may reflect the known ability of thiamine to chelate lead and increase its excretion.

Little Galloo Island, Lake Ontario: A Review of Nine Years of Double-crested Cormorant Diet and Fish Consumption Information

The diet of double-crested cormorants ( Phalacrocorax auritus) on Little Galloo Island (LGI) in the eastern basin of Lake Ontario has been quantified since 1992. Over the past nine years considerable information has been generated on cormorant feeding ecology through the examination of approximately 12,000 pellets collected on LGI, where three distinct cormorant feeding periods, pre-chick, chick, and post-chick, are delineated by differences in diet composition and daily fish consumption. Yellow perch ( Perca flavescens) were the major prey during pre-chick and post-chick feeding periods. Alewife ( Alosa pseudoharengus), which move inshore to spawn in mid-June, dominated (>60%) cormorant diets during the chick feeding period. Mean daily fish consumption (14.6) during the pre-chick feeding period was significantly greater than during the chick feeding (9.3) or post-chick feeding (8.0) periods. The proportion of smallmouth bass ( Micropterus dolomieu) in the diet increased over the season (0.8% to 7.2%), while the size of bass consumed declined (214 mm to 143 mm). Forage fish (mainly alewife, three-spine sticklebacks [ Gasterosteus aculeatus] and minnows) comprised 58% of the diet of LGI cormorants, followed by panfish (37%) (yellow perch, pumpkinseed [ Lepomis gibbosus], rock bass [ Ambloplites rupestris]) and gamefish (5%) (mostly smallmouth bass). On the average LGI cormorants consumed about 32.8 million fish annually, weighing about 1.4 million kilograms. Cormorants from LGI consumed more biomass of smallmouth bass and yellow perch annually than is taken by sport (bass and yellow perch) and commercial (perch) fishermen.

Spatial and temporal variation in the diet of double-crested cormorants (Phalacrocorax auritus) breeding on the lower Great Lakes in the early 1990s

We sampled 1573 pellets and 560 boli regurgitated at double-crested cormorant (Phalacrocorax auritus) colonies on the three lower Laurentian Great Lakes (Lake Ontario, Lake Huron, and Lake Erie) during the breeding season in 1992 and 1994. This constitutes the first extensive study of cormorant diet in this region. We found significant spatial and temporal heterogeneity in diet among colonies within a lake. Differences in diet among colonies were usually consistent with knowledge of changes in fish behaviour during the cormorant breeding season, differences in the surrounding bathymetry among breeding colonies, and the proximity of colonies to the preferred habitat of prey species. Our results indicate that temporal and spatial variation, as well as the technique for diet determination, are very important factors that must be considered when assessing the effects of double-crested cormorant predation on fisheries.

Spatial and temporal variation in the diet of double-crested cormorants (&lt;I&gt;Phalacrocorax auritus&lt;/I&gt;) breeding on the lower Great Lakes in the early 1990s

Spatial and temporal variation in the diet of double-crested cormorants (&lt;I&gt;Phalacrocorax auritus&lt;/I&gt;) breeding on the lower Great Lakes in the early 1990s