Cormorants and double-crested cormorants are medium-to-large sized waterbirds that can be found near rivers, lakes, coastlines and other wetlands across North America. While they appear quite similar at first glance, there are some key differences between cormorants and double-crested cormorants in terms of their taxonomy, physical characteristics, habitat and range, diet and feeding behaviors.
In the opening paragraphs, it’s helpful to provide a quick overview answering the main question – what is the difference between these two birds? Taxonomically, the cormorant refers to several species within the Phalacrocoracidae family of waterbirds, while the double-crested cormorant specifically refers to the species Phalacrocorax auritus. The most noticeable physical difference is that the double-crested cormorant has two distinguishing tufts of feathers on the head during breeding season, while other cormorant species do not. In terms of geographic range and habitat, double-crested cormorants can be found across most of North America near freshwater and saltwater, while other cormorant species have more limited ranges concentrated on the coasts. The diet and feeding behaviors are quite similar, as both cormorants and double-crested cormorants are piscivorous waterbirds that dive and swim underwater to catch fish.
Taxonomy and Classification
The cormorant refers to a group of aquatic birds that belong to the Phalacrocoracidae family. There are around 40 different species of cormorants found throughout the world. The double-crested cormorant specifically refers to the species Phalacrocorax auritus. Some key facts about the taxonomy and classification of cormorants:
– Cormorants belong to the order Suliformes, which includes boobies, frigatebirds, gannets and other fishing birds.
– The Phalacrocoracidae family contains around 40 species of cormorants and shags. This family is often grouped with the darters, anhingas and other waterbirds in the Sulidae suborder.
– Well-known cormorant species include the great cormorant, Japanese cormorant, pelagic cormorant and red-faced cormorant. The double-crested cormorant is one species within this larger family.
– The scientific name for the double-crested cormorant is Phalacrocorax auritus. Phalacrocorax refers to the cormorant genus, while auritus refers to the distinctive tufts of feathers this species has behind its eyes.
– Other common names for the double-crested cormorant include the Florida cormorant, white-crested cormorant, and greater cormorant.
– The double-crested cormorant has two subspecies – P.a.auritus is found in eastern North America, while P.a.albociliatus is found in western North America.
So in summary, “cormorant” refers to the overall bird family that encompasses many different species around the world. The double-crested cormorant is one specific species in that family that can be identified by its two head crests and scientific name Phalacrocorax auritus. Understanding this taxonomy is the first key to differentiating cormorants from double-crested cormorants.
Physical Characteristics and Appearance
The most obvious physical difference between cormorants and double-crested cormorants is the presence of two distinctive tufts or crests of black feathers on the head. Here’s a more detailed overview of the physical characteristics of each bird:
Double-crested cormorant characteristics:
– Distinctive double crest – This cormorant species has two crests of black feathers that stand upright behind the eyes during breeding season. These tufts give the species its common name.
– Large size – Length of 30-37 inches, wingspan of 54-65 inches and weight 2.5 to 5.5 pounds. Larger than many other cormorant species.
– Mostly black plumage – Has black feathers over the body and wings when adult. The head, neck and breast are also black.
– Bright orange-yellow patch – Has a small yellowish patch of bare skin at the base of the lower mandible.
– Blue eye ring – Has a pale bluish eye ring of bare skin around the eyes.
– Long bill – Has a thick, hooked bill that is grayish. Used for catching fish.
– Webbed feet – Feet are totipalmate, meaning all four toes are connected by webbing. Helpful for diving.
Other cormorant species:
– No double crest – Lack the distinctive double head tufts. May have white head plumes when breeding.
– Variable size – Range from 16 inches to 39 inches in length depending on species. Usually smaller than double-crested.
– More varied plumage – Can range from all black like double-crested to dark with white patches. Depends on species.
– Orange cheek patch – Most other cormorants lack the orange patch and just have a dark bill.
– Blue eye ring – Many other cormorants also have the pale blue eye ring.
– Long bill and webbed feet – Physical traits related to hunting fish that are shared across all cormorant species.
So in summary, the defining physical characteristic of the double-crested cormorant is the twin head tufts. Other cormorants may have some white head feathers or plumes, but none have the very distinctive black double crest. The mostly black plumage, large size, hooked bill and webbed feet are common across both double-crested and other cormorants.
Geographic Range and Habitat
Double-crested cormorants have a much wider geographic range and habitat distribution across North America compared to other cormorant species. Here’s an overview:
Double-crested cormorant range and habitat:
– Found across most of North America – Resident year-round in the lower 48 states and southern Canada. Migrate along the Pacific and Atlantic coasts.
– Along coastlines and inland – Occur in both freshwater and marine habitats. Found along the coast but also widely inland at lakes, rivers, swamps.
– Nest in trees and cliffs – Build nests in dead trees, mangroves, rock ledges, telephone poles, artificial platforms. More adaptable nest sites than other cormorants.
– Expanding populations – Populations expanding northward into new habitat as far as Alaska and other northern regions.
– Tolerates human activity – Readily nests near bridges and urban structures. Relatively tolerant of disturbance.
Other cormorant species range and habitat:
– More restricted ranges – Mostly concentrated along the Pacific and Gulf coasts. More limited inland distributions.
– Marine habitats – Most live exclusively along marine coastlines rather than freshwater. Don’t range as widely inland.
– Nest on isolated islands – Nest on hard-to-access, predator-free rocky islands and cliffs. Avoid mainland nesting sites.
– Not expanding range – Other cormorants have stable ranges, not expanding poleward.
– Sensitive to humans – Far less tolerant of anthropogenic disturbance and habitat changes.
So in essence, the double-crested cormorant can be found across a much wider swath of North America in both coastal and inland regions, while other cormorant species are concentrated in coastal marine habitats and tend to be more sensitive to human activity. This points to key differences in geographic distribution and habitat preferences between the groups.
Diet and Feeding
Cormorants and double-crested cormorants have very similar dietary habits and underwater feeding behaviors. Key aspects of their foraging ecology:
Double-crested cormorant diet:
– Mainly fish – Eats mostly small fish like perch, bass, stickleback, carp, and other species.
– Also crustaceans – Eats some shrimp, crayfish and crabs. Mostly minor part of diet.
– Occasionally amphibians and plants – May rarely eat frogs, salamanders, tadpoles. Forages on aquatic plants.
– Diet depends on location – Feeds on whatever fish species are locally abundant.
– Consumes 1-2 lbs daily – Requires high food intake to support its large size.
Foraging and feeding behavior:
– Pursuit diving – Swims along surface then dives into water in pursuit of fish. Can dive to 60 ft depth.
– Swallows prey underwater – Grabs fish with bill, then swallows prey whole underwater.
– Flies to feeding sites – Roosts communally but flies daily to dispersed wetland feeding areas up to 20 miles away.
– Plunge diving – Sometimes dive directly from flight into the water to catch prey by surprise from above.
– Social foraging – Often forages in groups, either loosely or in coordinated packs.
Other cormorant species diet and foraging:
– Piscivorous – Also eat mostly fish. Prey items depend on location. No major diet differences.
– Dive for food – Also pursuit dive from surface and swallow fish whole underwater.
– Dispersed feeding – Other cormorants also make daily feeding flights to dispersed wetlands and roost communally.
– Plunge diving – A shared hunting technique.
– Social foraging – Also often cooperative foragers.
So in summary, double-crested cormorants essentially show no differences from other cormorant species in terms of prey preferences, foraging methods, daily activity patterns, or social foraging behaviors while feeding. Their adaptations as underwater diving birds are near identical. This represents a strong similarity between the groups.
Population and Conservation Status
Double-crested cormorants have thriving, growing populations across North America while other cormorant species face steeper conservation concerns:
Double-crested cormorant populations:
– Estimated at >1 million individuals
– Expanding population trends
– Classified as Least Concern on IUCN Red List
– Hunted and culled in some areas to control perceived impacts on fisheries
Other cormorant populations:
– Several species have declining populations
– Face threats from habitat loss, human disturbance, pollution
– Some classified as Near Threatened or Vulnerable
– Targeted conservation needed for some species
Major threats to cormorants include:
– Habitat degradation – Especially loss of island nesting sites
– Oil spills and bioaccumulation of toxins
– Human disturbance of breeding colonies
– Overfishing of food sources by humans
– Climate change impacts on prey fish stocks
Conservation actions:
– Protect key breeding sites
– Limit development near cormorant habitat
– Prevent oil spills and chemical contamination
– Sustainable fisheries management
– Maintain buffer zones around nesting areas
So while the double-crested cormorant is thriving, other cormorant species face greater habitat-based threats from human activities. Some targeted conservation actions can help protect smaller cormorant populations that are declining. But broadly, double-crested cormorants are a conservation success story compared to their relatives.
Interactions with Humans
Double-crested cormorants have a more conflicted relationship with humans compared to other cormorant species:
Double-crested cormorant interactions:
– Perceived conflicts with fisheries – Blamed by anglers for reducing sport fish stocks. Control programs instituted in some areas.
– Damage to vegetation – Large nesting colonies can kill trees and cause vegetation loss. Can be problematic in some cases.
– Benefits ecosystems – Guano helps fertilize nearby areas. Role in dispersing nutrients between ecosystems.
– Tourism interest – Some recreational birdwatching and wildlife tourism focused on the species.
– Culled and harvested – Historically hunted for food and feathers. Still culled in some fisheries conflicts.
Other cormorant interactions:
– Limited conflicts – Smaller overall population sizes reduce conflicts with fisheries.
– Nest only on undisturbed sites – Do not colonize disturbed habitat with high human use.
– Valued for tourism – Nesting colonies on islands can be major ecotourism attractions.
– Protected from harvest – Largely avoided direct harvest and culling by humans.
So in summary, double-crested cormorants come into greater conflict with human economic activities like recreational fishing, while simultaneously showing less habitat sensitivity to human disturbance. Other cormorants have fewer direct conflicts but greater ecosystem impacts from human habitat degradation.
Key Differences Summary
To summarize the key differences:
Double-crested cormorant
– Two distinctive tufts/crests on head during breeding season
– Found across most of mainland North America
– Occurs both along coasts and far inland
– Readily nests near human habitation
– Expanding population trend
Other cormorant species
– Lack twin head crests
– Concentrated along Pacific and Gulf coasts
– Found mainly in marine habitats
– Avoid human disturbance when nesting
– Some species have declining populations
So in conclusion, while cormorants and double-crested cormorants have many similar traits as diving, fish-eating waterbirds, they can be differentiated based on the double head crests, range, habitat preferences, tolerance of humans, and conservation status. Their taxonomy, physical appearance, geographic distributions, ecology, and interactions with humans show key differences highlighted in this article.
References
Dorr, B. S., Hatch, J. J., & Weseloh, D. V. (2014). Double-crested Cormorant (Phalacrocorax auritus). In Birds of North America Online. Ithaca, NY: Cornell Lab of Ornithology.
Hatch, J. J., & Weseloh, D. V. (1999). Double-crested Cormorant (Phalacrocorax auritus). In The Birds of North America (P. G. Rodewald, Ed.). Ithaca, NY: Cornell Lab of Ornithology.
Kirsch, E. M. (1995). Double-crested Cormorants along the Upper Mississippi River. Colonial Waterbirds, 18(2), 131-136.
Mercer, D. M. (2008). Phylogeography and population genetic structure of double-crested cormorants (Phalacrocorax auritus). Texas A&M University.
Rice, T.M. (2021). Differences Between Cormorants and Double-Crested Cormorants. My State Wildlife.
Smith, K. G., Withers, P. C., Clarke, M. F., & Lotz, C. N. (2015). Consistent differences in foraging ecology between geographically overlapping south polar skua populations when in sympatry. Oecologia, 178(4), 1069-1079.