Double-crested cormorants are medium-sized waterbirds that are found across North America. They get their name from the two tufts of feathers that adorn their heads during mating season. Cormorants have long necks, sharp hooked bills, and webbed feet which make them excellent at catching fish. Their diet consists primarily of small fish and provides important insights into food webs and fish populations where cormorants reside.
Quick Answers
Double-crested cormorants are piscivorous, meaning they eat mostly fish. Their main prey items include:
- Small fish like minnows, perch, sticklebacks, and sculpins
- Bottom-dwelling fish like eels, gunnels, and blennies
- Schooling fish like herring, anchovies, and silversides
Cormorants are opportunistic feeders and will eat whatever small fish are most abundant in their habitat. They often forage together in large feeding flocks and can impact local fish populations.
What Types of Fish do Cormorants Eat?
Double-crested cormorants consume a wide variety of small fish species. Their Diet can vary based on location, time of year, and fish availability. Here are some of the most common fish found in cormorant diets across their range:
Minnows
Minnows refer to a large group of small, schooling fish in the Cyprinidae family. There are hundreds of different minnow species across North America that cormorants may prey on, including fathead minnows, golden shiners, emerald shiners, and spottail shiners. Minnows are a frequent prey item for cormorants where they are abundant.
Perch
Perch are spiny-rayed fish in the Percidae family. Yellow perch and walleye are two of the most common perch species eaten by cormorants. They are found in many lakes, ponds, and river systems across the cormorant’s range. Perch often swim in schools which make them easier for cormorants to prey on.
Sticklebacks
Sticklebacks are small fish in the Gasterosteidae family. The threespine stickleback is the most widespread species and is frequently eaten by cormorants. Sticklebacks are abundant in freshwater lakes, streams, and coastal marine habitats. Their small size makes them a perfect cormorant prey item.
Sculpins
Sculpins are bottom-dwelling fish in the Cottidae family. There are over 50 species of sculpins native to North America. Sculpins are less likely to form large schools, but cormorants can prey on them as they rest along rocky or sandy bottoms. Common sculpin species eaten include slimy sculpins, mottled sculpins, and torrent sculpins.
Eels
Eels in the Anguillidae family, like the American eel, are a frequent prey item where they co-occur with double-crested cormorants. Eels inhabit estuaries and watersheds along the Atlantic coast. Cormorants swallow eels whole, head first to avoid their sharp teeth.
Gunnels
Gunnels or butterfish are elongate, eel-like fish in the Pholidae family. Rock gunnels and crescent gunnels are two gunnel species cormorants feed on, especially in Pacific coastal habitats. Gunnels are bottom-dwellers and easy for cormorants to snap up.
Blennies
Blennies are small, often elongated fish that live along rocky shorelines and tidepools. Species like the crested blenny and redlip blenny are found on Pacific coasts where cormorants hunt in intertidal zones. Their camouflage makes them harder to spot, but cormorants can nab them with their quick reflexes.
Herring
Herring are schooling fish in the Clupeidae family. Pacific herring, Atlantic herring, and alewives are preyed on by coastal cormorants. Young herring and damaged individuals are most vulnerable to cormorant predation.
Anchovies
Anchovies are small schooling fish in the Engraulidae family. Northern anchovies and deepbody anchovies are abundant along the Pacific coast where cormorants hunt. Anchovies form dense balls which cormorants can feed on efficiently.
Silversides
Silversides or surf smelt are schooling fish in the Atherinopsidae family. Species like the jacksmelt and topsmelt are common prey for cormorants hunting in Pacific coast estuaries. Silversides’ small size and schooling behavior make them easy pickings.
How do Cormorants Catch and Eat Fish?
Double-crested cormorants have a number of anatomical and behavioral adaptations that help them effectively catch fish prey:
- Hooked bill – The long, sharp bill allows them to grasp slippery prey.
- Sinuous neck – Their flexible neck allows them to snatch fish from different angles.
- Webbed feet – Their partially webbed toes help them propel through the water and steer.
- Wettable feathers – Their feathers are not waterproof, allowing the birds to dive and swim underwater.
- School hunting – Cormorants often work together to herd fish into bait balls for easier feeding.
- Swift pursuit – They can swim up to 6 mph underwater to chase speedy fish.
- Vertical pursuit – Cormorants can dive up to 75 feet deep in pursuit of fish.
Cormorants most often catch fish by swimming underwater and grabbing them with their bills. They surface and swallow most fish headfirst while tilting their head back. Cormorants have expandable throat pouches that allow them to consume multiple fish in one feeding. They often carry fish back to roosts or nests to feed young. Cormorants regurgitate indigestible fish parts like bones and scales in the form of food pellets.
How Much Fish do Cormorants Eat?
An individual double-crested cormorant eats around 1 pound of fish per day on average. This amount can vary based on the size and energy content of prey fish as well as time of year. During peak feeding in the summer, cormorants may eat over 2 pounds per day. In the winter they eat closer to 0.5 pounds per day.
Over the course of a year, one cormorant is estimated to consume about 400 pounds of fish. However, this estimate increases significantly for breeding birds that must also catch enough fish to feed their chicks. Breeding cormorants may eat 500-600 pounds of fish annually.
Cormorants often feed in large flocks which can put intense pressure on local fish populations. It’s estimated that a flock of 500 cormorants could potentially eat over 4,000 pounds of fish per day. Wildlife managers frequently monitor cormorant populations and food intake to prevent impacts to recreational fisheries and aquaculture operations.
Impacts on Fisheries
The high fish consumption of double-crested cormorants allows them to exert top-down pressure on fish populations and compete with recreational and commercial fishermen in some areas. Cormorants can negatively impact fisheries in a few key ways:
- Reduce abundance of popular sportfish like perch, bass, trout, and salmon
- Compete with anglers for stocked/hatchery fish
- Decrease sizes of captured fish through predation on juveniles
- Damage gear and equipment at aquaculture facilities
Several strategies are used to mitigate conflicts between cormorants and fisheries including population control, relocation, harassment, and limiting nesting habitats. However, cormorants are native waterbirds and play important roles in freshwater and coastal ecosystems. Management practices aim to strike a balance between ecological and economic considerations.
Diet Studies
Cormorant diets have been extensively studied across North America to understand their food habits and ecological roles. The following tables summarize findings from some published cormorant diet studies in different regions and habitats.
Lake Erie Cormorant Diet
Prey Species | Percent Composition |
---|---|
Emerald Shiner | 34% |
Gizzard Shad | 18% |
Yellow Perch | 15% |
Spottail Shiner | 11% |
Other | 22% |
Data from a 2006 study on the diet of cormorants nesting on West Sister Island in Lake Erie. Shiners and perch were the dominant prey items.
San Francisco Bay Cormorant Diet
Prey Species | Percent Composition |
---|---|
Northern Anchovy | 68% |
Topsmelt | 15% |
Yellowfin Goby | 5% |
Shiner Perch | 4% |
Other | 8% |
Data from a 2000 study on the diet of cormorants nesting in San Francisco Bay. Anchovies were the most common prey.
Columbia River Estuary Cormorant Diet
Prey Species | Percent Composition |
---|---|
Northern Anchovy | 40% |
Smelt | 35% |
Shiner Perch | 15% |
Sand Lance | 5% |
Other | 5% |
Data from a 2005 study on the diet of cormorants nesting along the Columbia River estuary. Anchovies and smelt were the top prey.
Conclusion
Double-crested cormorants are consummate fish eaters that have adapted to exploit a wide variety of small fish across diverse aquatic habitats. While they occasionally take crustaceans, amphibians, and other prey, nearly all of their diet consists of fish. Cormorants can opportunistically take advantage of whatever fish are most abundant, but commonly prey on schooling fish like herring, anchovies, and shiners. Their hunting skills and appetite for fish can bring cormorants into conflict with recreational and commercial fishermen. However, cormorants play important ecological roles in food webs and their diversity of prey species provides useful data for monitoring fish populations.