What Is a Group of Cormorants Called?

A group of cormorants is most commonly called a “colony,” particularly when the birds are nesting or roosting together, but English also offers several more colorful collective nouns: a “flight” of cormorants, a “gulp,” a “swim,” and even a “sunning.” The word you reach for depends partly on what the birds are doing at the moment, and partly on whether you prefer everyday birdwatching language or the quirkier tradition of medieval English venery terms. Beyond the vocabulary, what makes cormorant groups genuinely interesting is the sophisticated social behavior behind them, from hierarchical roosting arrangements to coordinated underwater hunting.

Where These Collective Nouns Come From

Most collective nouns for animals trace back to the fifteenth-century English tradition of “terms of venery,” elaborate group names that were partly practical hunting vocabulary and partly a word game among the literate upper class. Books of courtesy and hunting manuals popularized terms for hundreds of species, and many of those names stuck around long after anyone needed them for falconry or fowling. “Colony” is the term that scientists and birders actually use today for a breeding or roosting aggregation of cormorants, and it appears in ornithological literature far more than any alternative. “Flight” tends to come up when describing cormorants in the air, traveling between feeding grounds and roost sites. “Gulp” is the charming outlier; its origin is murky, but it probably alludes to the bird’s habit of swallowing fish whole, sometimes visibly struggling to get a large catch down its throat. “Swim” is self-explanatory and shows up occasionally for cormorants floating together on the water. And “sunning” refers to the species’ iconic posture of standing with wings spread wide to dry after a dive.

In practice, birders and biologists overwhelmingly say “colony” for any sizeable gathering. If you are filling out a birdwatching checklist, writing a report, or just describing what you saw at the lake, “colony” is the safe, universally understood choice. The fancier terms are fun at trivia night but rare in the field.

How Big These Groups Get

Cormorant colonies range from a few dozen pairs to staggering concentrations of thousands. Research on Great Cormorants in the Netherlands recorded roosting flocks that regularly numbered between a thousand and over eight thousand birds on a single archipelago.¹ Double-crested Cormorants in North America show a similar pattern, with colony growth on the Great Lakes at one point filling nearly all available coastal nesting habitat as populations expanded.² These are not loose, accidental aggregations. Cormorants actively seek out large groups for roosting and nesting, which suggests the colony structure provides real survival advantages, from predator dilution to shared information about food sources.

Social Hierarchy Inside the Colony

A cormorant colony looks chaotic from a distance, but there is a clear pecking order at work. When birds return from foraging, the first arrivals claim positions at the center of the roost, typically on the highest and largest available perch or island. Latecomers are pushed to the edges and the rear. Research on Great Cormorants found that this spatial arrangement reflects foraging success: birds that secured central positions produced larger pellets, meaning they had eaten bigger or more fish, while birds stuck on the periphery were more likely to have little or no food in their pellets.³ The pattern suggests a dominance hierarchy where the better foragers consistently outcompete weaker ones for the safest, most desirable spots.

Age plays into this too. In studies of roosting Great Cormorants, adults tended to dominate first- and second-winter birds and occupied higher positions in the roost, where they were presumably safer from ground-level disturbances and predators.⁴ Young birds, still learning to fish efficiently, ended up at the margins. Once a bird settled into its spot, though, confrontations were rare. The hierarchy was enforced mostly through arrival order and the social weight of being an experienced adult, not through constant fighting.

Cooperative Hunting on the Water

Some cormorant species take group living beyond the roost and into the water itself, hunting fish cooperatively. Socotra Cormorants, a species that breeds on islands in the Persian Gulf and Arabian Sea, form large foraging flocks that work together to herd and concentrate schooling fish. Once a shoal is located, the sheer number of diving birds disrupts the fish school’s cohesion, making individual prey easier to catch.⁵ This is a genuinely cooperative strategy, not just many birds independently diving in the same spot. The confusion caused by dozens or hundreds of simultaneous dives breaks apart the defensive schooling behavior that fish rely on, and each individual cormorant benefits from the chaos the group creates.

Not every cormorant species hunts this way. Double-crested Cormorants, the most widespread species in North America, often forage alone or in small, loosely organized groups. But even solitary foragers return to a communal roost afterward, which is where the colony structure reasserts itself. The roost may serve as an “information center,” where birds that failed to find food can follow successful foragers out the next morning. This hypothesis is debated among ornithologists, but the consistency with which cormorants return to shared roosts, even when feeding sites are spread over a wide area, hints that social information transfer is part of the payoff of group living.

How Cormorants Communicate Within the Group

Cormorants are not songbirds. Their vocalizations are guttural, croaking, and to human ears not especially musical. But within a colony, those calls carry real information. A study of Great Cormorants during the breeding season found that males were more vocally active than females and had a larger repertoire of calls. The calls also differed between individual males, which means cormorants can potentially recognize specific neighbors by voice alone.⁶ In a densely packed nesting colony where your neighbor’s nest might be less than a meter away, being able to distinguish your mate’s call from a stranger’s is a practical necessity.

Visual displays matter too, especially the wing-spreading posture that cormorants are famous for. You have almost certainly seen a cormorant standing on a rock or piling with its wings held open. The leading explanation for this behavior is feather drying: cormorant plumage is less waterproof than that of most waterbirds, which helps them dive more efficiently but means they need to dry out afterward. Research on Double-crested Cormorants concluded that the spread-wing posture functions primarily for wing drying rather than thermoregulation, though the underlying goal of drying may be to conserve metabolic energy that would otherwise be spent staying warm with wet feathers.⁷ When a row of cormorants are all standing with wings outstretched at a roost, it creates the striking visual that gave rise to “sunning” as a collective noun.

What Happens When Cormorants Move into a Shared Colony

Many cormorant colonies are not exclusively cormorant colonies. Herons, egrets, and other waterbirds frequently nest in the same trees or on the same islands, and the arrival of cormorants can reshape the social dynamics of the entire site. In a mixed colony in northwest Italy that was tracked over seventeen years, the settlement of Great Cormorants (and later Cattle Egrets) significantly affected the nesting trends of the species that had been there first, including Grey Herons, Black-crowned Night Herons, and Little Egrets. The cormorant and egret populations increased year after year, while the pre-existing species declined.⁸

Part of the issue is that cormorants are confrontational neighbors. A study of Double-crested Cormorants nesting alongside Great Blue Herons found that cormorants engaged in more aggressive interactions than herons in the same location, and ground-nesting birds fought more than tree-nesting birds. Interestingly, cormorants surrounded by their own species had more total aggressive encounters than cormorants nesting among herons, which suggests that intraspecific competition for space and resources is fierce.⁹ If you are a heron, the takeaway is clear: nesting near cormorants is tolerable, but it is not peaceful.

The Footprint a Colony Leaves on the Landscape

Large cormorant colonies leave a visible mark on their surroundings. The most obvious impact is on trees. Cormorant guano is highly acidic and rich in nitrogen and phosphorus. In concentrated amounts, it kills vegetation, starting with the canopy above the nests and working down. Research in Europe found that cormorant nesting colonies strongly increase nitrogen and phosphorus concentrations in the soil, with the effect growing stronger close to the nests.¹⁰ A study of Double-crested Cormorant colonies on islands in the Great Lakes found that tree diversity was roughly halved on colony islands compared to reference islands with no cormorant presence, and canopy cover dropped below twenty percent in the most heavily used areas.¹¹

The result, at a long-established colony, is a landscape of bare branches, whitewashed trunks, and dense understory growth where sunlight now reaches the ground. It looks devastated, and it is genuinely transformed. But the ecological story is more nuanced than “cormorants destroy everything.” The nutrient loading can fertilize surrounding waters and create different habitat structures that benefit some species even as others are displaced. Abandoned colony sites often undergo rapid regrowth. The damage is real but not permanent in the way that, say, paving over an island would be. It is more like a disturbance event, dramatic in the short term but part of a longer cycle.

Why Double-Crested Cormorants Became Controversial

In North America, the Double-crested Cormorant has been at the center of wildlife management debates for decades. Their populations crashed in the mid-twentieth century due to pesticide contamination, particularly DDT, which thinned eggshells and devastated breeding success. After DDT was banned and other environmental protections took hold, the species rebounded dramatically. By the early 2000s, cormorant numbers in the interior and along the Atlantic coast had grown to the point where fisheries managers, aquaculture operators, and landowners were raising alarms about the birds’ impact on fish stocks and vegetation.

The U.S. Fish and Wildlife Service responded by issuing depredation orders that allowed lethal control of cormorants in certain states, including at aquaculture facilities and at winter roost sites. But the evidence that cormorant culling meaningfully helps wild fish populations is thin. As one review of the species’ population history noted, while managing fish-eating birds might increase some fish populations locally, the approach does not address the underlying causes of fish population declines across the continent and conflicts with broader conservation goals.¹² Habitat loss, water quality degradation, invasive species, and overfishing all play larger roles in fishery declines than cormorant predation, and killing cormorants can feel like blaming the symptom instead of the disease.

The legal landscape has shifted repeatedly. Depredation orders have been issued, challenged in court, struck down, and reissued in various forms. As of recent years, the regulatory framework for managing cormorants in the United States remains in flux, reflecting genuine tension between the interests of people who share waterways with these birds and the ecological reality that cormorants are native species performing a natural role in aquatic food webs.

Cormorant Species You Might Encounter

There are roughly forty species of cormorants worldwide, spread across every continent except Antarctica. A few stand out for the sheer scale or distinctiveness of their colonies:

Double-crested Cormorant: The most common North American species, found on lakes, rivers, and coastlines from Alaska to Mexico. Colonies are often conspicuous because the birds nest on exposed islands, bridge supports, and navigational markers.
Great Cormorant: The largest and most widespread cormorant globally, breeding across Europe, Asia, Africa, and eastern North America. European colonies can number in the thousands and have been studied extensively.
Socotra Cormorant: A near-endemic of the Arabian Peninsula that forms enormous breeding colonies on offshore islands, sometimes exceeding tens of thousands of pairs in a single location. Their cooperative foraging behavior is among the most studied of any cormorant.
Galápagos (Flightless) Cormorant: The only cormorant that has lost the ability to fly, found exclusively on two islands in the Galápagos. Its colonies are small, rarely exceeding a few hundred individuals, a consequence of its restricted range.
Guanay Cormorant: A South American species whose vast breeding colonies along the coast of Peru produce enormous quantities of guano, which has been harvested commercially as fertilizer for centuries.

Each of these species forms colonies, but the character of those colonies varies enormously. A Galápagos Flightless Cormorant colony of eighty birds on a lava shore and a Socotra Cormorant colony of thirty thousand pairs on a Persian Gulf island are both technically “colonies,” but the experience of standing near one versus the other would be worlds apart. The vocabulary stays the same; the reality scales by orders of magnitude.

How Cormorant Feathers Work Differently

One detail that shapes cormorant group behavior in ways most people do not expect is their plumage. Most waterbirds have feathers that are essentially waterproof, trapping a layer of air against the skin that provides insulation and buoyancy. Cormorant feathers are only partially waterproof. The outer feathers become saturated during dives, which reduces buoyancy and makes it easier for the birds to swim underwater, but it also means they get cold and heavy quickly. This is why cormorants spend so much time standing with their wings spread open after fishing: they genuinely need to dry out before they can fly efficiently again.

This plumage quirk has downstream effects on colony behavior. Cormorants cannot stay in the water indefinitely the way ducks or grebes can. They need reliable perching sites near their feeding areas, and those sites need to accommodate the wing-spreading posture, which takes up considerably more horizontal space than a bird simply standing with wings folded. When good perching and roosting habitat is limited, competition for space intensifies, which partly explains the aggressive territorial behavior observed in dense colonies. A cormorant that cannot dry its wings is a cormorant that cannot hunt again soon, so access to a good perch is not a luxury. It is a bottleneck in the bird’s daily energy budget.