Are Cormorants Native to Michigan?

Double-crested cormorants are native to Michigan and have been part of the Great Lakes ecosystem for centuries. Historical records, including an 1854 government survey map that labeled two lakes in Forsyth Township, Michigan, as “Shag Lake” and “Little Shag Lake” (shag being a common vernacular name for cormorant), confirm the birds were present in the region long before modern population debates began. The confusion about whether cormorants belong in Michigan stems from a dramatic population crash in the mid-twentieth century followed by an equally dramatic recovery, which made it look to many residents as though the birds had suddenly appeared from nowhere.

How We Know Cormorants Were Here First

The evidence for cormorants being native to the Great Lakes region rests on multiple lines of documentation. That 1854 plat map from Michigan’s General Surveyors Office is one of the earliest references, and researchers who reviewed the full historical record concluded that characterizing the double-crested cormorant as “exotic” or “invasive” in the Great Lakes is inappropriate.¹ Breeding records add further weight. The first formally documented nesting colony on the Great Lakes was a group of ten nests found at Agawa Rocks on Lake Superior in 1926, though local residents told the researchers the birds had nested there “for years.” An earlier unverified report from Georgian Bay on Lake Huron places cormorant nesting in that area as early as 1919.¹

These records suggest that cormorants were breeding across the Great Lakes well before the early twentieth century, even though specific nest sites from earlier periods are harder to pin down. The broader picture from ornithological records indicates the interior population of double-crested cormorants ranged across much of central and eastern North America, with the Great Lakes sitting comfortably within that historical range.

Why Cormorants Seemed to Disappear

If cormorants are native, why do so many people in Michigan remember a time when there were none? The answer involves one of the most well-known environmental disasters of the twentieth century. Starting in the 1950s and accelerating through the 1960s, organochlorine pesticides like DDT and industrial chemicals like polychlorinated biphenyls (PCBs) accumulated in Great Lakes fish. Cormorants, as dedicated fish-eaters near the top of the aquatic food chain, absorbed enormous concentrations of these toxins. The chemicals caused eggshell thinning and reproductive failure, and cormorant populations collapsed across the region.

Studies of cormorant eggs from Wisconsin colonies in Green Bay and Lake Michigan found organochlorine concentrations roughly ten times higher than those in eggs from reference colonies in South Dakota and Minnesota.² Research on Great Lakes cormorant populations specifically linked the reproductive problems to the dioxin-like activity of PCBs rather than to pesticides alone or some unidentified industrial compound.³ By the 1970s, cormorants had been largely wiped out as a breeding species throughout the Great Lakes. An entire generation of Michigan residents grew up never seeing one.

The ban on DDT in 1972 and subsequent regulations on PCB production allowed contaminant levels in fish to slowly decline. As the food supply became less toxic, cormorant reproduction improved and numbers rebounded. By the 1990s, breeding colonies had returned to many Great Lakes islands, and populations eventually surpassed historical levels. This dramatic rebound is what created the widespread misconception that cormorants were newcomers or invaders. People who had spent decades on Michigan’s lakes without seeing a single cormorant understandably assumed the bird had never been there.

What Cormorants Eat and How That Changed

Double-crested cormorants are opportunistic fish-eaters. They dive beneath the surface, sometimes to depths of several meters, and chase down whatever prey is most abundant and energetically profitable. This flexibility means their diet shifts as the fish community around them changes.⁴

One of the most significant dietary shifts in recent decades involves the round goby, an invasive fish from the Black and Caspian Seas that entered the Great Lakes through ballast water in the 1990s. As gobies spread, cormorants took full advantage. A study of Lake Michigan waterbirds found round gobies in the guts of 94% of cormorants examined.⁵ The irony is hard to miss: a native bird that many people call invasive has become one of the most effective consumers of an actually invasive fish.

The goby connection comes with a downside, though. Round gobies are a vector for avian botulism type E, a toxin produced by bacteria that accumulate in the invasive mussels gobies feed on. That same Lake Michigan study was conducted specifically because cormorants and other waterbirds were dying in botulism outbreaks during 2010 through 2012. Round gobies were found in the vast majority of birds that tested positive for the toxin, illustrating how cormorant health has become entangled with the ecological disruptions caused by invasive species they did not bring.

The Conflict with Fisheries

The tension between cormorants and Michigan’s fishing communities is real and well-documented. Sport and commercial fishers have long complained that cormorant colonies decimate populations of desirable fish like yellow perch and walleye. The intensity of feeling on this issue is hard to overstate; it has driven regulatory action, legal battles, and a persistent belief that cormorants do not belong in the ecosystem at all.

The science, though, paints a more complicated picture. A study of Saginaw Bay in Lake Huron examined cormorant consumption of yellow perch alongside the consumption by walleye, which is the perch’s other major predator. Cormorants consumed only about 8 to 17% as many age-one yellow perch as walleye did in a given year. The researchers concluded that the combined predation pressure from both walleye and spring-nesting cormorants likely creates a recruitment bottleneck for yellow perch, but cormorants were the smaller contributor to that pressure.⁶

This does not mean the complaints are baseless. In localized situations, particularly around small islands where colonies concentrate, cormorant predation can be heavy enough to noticeably reduce the fish available to anglers. The issue is one of scale: cormorants are often blamed for fishery declines driven by a combination of factors including habitat loss, invasive species, changing water temperatures, and predation by other fish. Singling out cormorants oversimplifies the problem, but their visibility (you can watch them diving and surfacing with fish in their bills) makes them an easy target for frustration.

What Cormorant Colonies Do to Islands

If cormorant predation on fish gets the loudest complaints, their impact on island vegetation might be the most visually dramatic. Large nesting colonies can strip an island of its tree canopy within a few years. The mechanism is straightforward: cormorant droppings, called guano, are extremely high in nitrogen and phosphorus. In concentrated amounts, the nutrients acidify the soil and essentially burn the vegetation. Studies of nesting islands found that soil from colony sites was significantly more acidic and nutrient-loaded than soil from reference islands without colonies.⁷

At multiple islands across the U.S. Great Lakes, cormorants have caused total or partial loss of forest cover. The resulting change in soil chemistry makes it difficult for trees to regrow even after the birds leave or are removed.⁸ The damage can cascade. Dead trees mean lost nesting habitat for species that share those islands, particularly great blue herons and black-crowned night-herons, which prefer to nest in tree canopies rather than on the ground.

Research on mixed colonies of cormorants and great blue herons reveals an interesting dynamic. Great blue herons that ended up nesting among cormorants rather than among other herons experienced more aggressive interactions, while cormorants nesting among herons actually had fewer conflicts than those nesting in dense cormorant-only groups.⁹ As cormorant numbers grow and they shift from tree nesting to ground nesting on deforested islands, herons tend to abandon those sites entirely. For wildlife managers, this sets up a difficult balancing act between protecting a native species (the cormorant) and protecting the habitat and welfare of other native species.

Management Efforts in Michigan

Michigan has been one of the most active states in managing cormorant populations, particularly in the Les Cheneaux Islands archipelago in northern Lake Huron. Management there has combined two main techniques: oiling eggs to prevent them from hatching (a method that avoids the birds simply re-laying) and culling adult birds. Over a four-year period, oiling 42 to 78% of nests and removing between 10% and 47% of breeding adults reduced the local cormorant population by about 74%.¹⁰

The legal authority to carry out this kind of management has shifted over the years. Cormorants are protected under the Migratory Bird Treaty Act, which means federal permits are required for lethal control. A 2003 federal depredation order allowed states and tribes to manage cormorants without individual permits, but that order was struck down by a federal court in 2016 on the grounds that the U.S. Fish and Wildlife Service had not adequately assessed the environmental impact. Since then, management has continued under individual permits with more limited scope. Michigan’s Department of Natural Resources has consistently advocated for broader authority to manage cormorant numbers, reflecting the strength of local sentiment about the issue.

Whether population management “works” depends on what you are measuring. In the Les Cheneaux Islands, local cormorant numbers dropped substantially and remained lower during the management period. But cormorants are highly mobile, and birds displaced from one colony often simply relocate to another. Regional population effects are harder to demonstrate. This creates a pattern where intensive local management can reduce problems at a specific site while doing little to change the overall trajectory of the Great Lakes cormorant population.

The Wing-Spreading Behavior

If you spend any time near Michigan’s waterways, you will eventually see a cormorant standing with its wings fully outstretched, looking like a dark heraldic symbol. This posture is one of the most recognizable things about the bird, and it reflects an unusual adaptation to their diving lifestyle. Unlike most waterbirds, cormorants have feathers that are partially wettable. Each body feather has a loose outer section that absorbs water immediately and a highly waterproof central portion that stays dry.¹¹

This split design is a compromise between competing physical demands. A bird that dives for fish needs to reduce buoyancy so it can get underwater efficiently, and waterlogged outer feathers help with that. But the bird also needs insulation to survive cold water, and the dry inner portion of each feather maintains a thin layer of trapped air against the skin. Research has quantified how cormorant feathers trap this air layer, called a plastron film, within their microstructures during dives.¹² When they emerge from the water, they spread their wings to dry the outer feather layer and restore their ability to fly efficiently. It is not a sign of poor adaptation; it is a sign of extremely specialized adaptation that happens to require a conspicuous post-dive routine.

Parasites and Foraging Differences Between the Sexes

Cormorant biology includes some details that rarely make it into the popular debate about whether the birds should be managed. One of these is the finding that male and female cormorants carry different parasite loads, which appears tied to differences in where and how they forage. A study of Lake Erie cormorants found that males carried roughly three times the abundance of one trematode species compared to females. Meanwhile, both sexes that foraged in more open-water (pelagic) habitats tended to carry higher numbers of a different parasite.¹³

This kind of research matters because parasites can influence host behavior, reproduction, and survival in ways that ripple through the population. It also underscores how much cormorant ecology varies by sex, by season, and by local conditions. Two colonies fifty miles apart can have very different diets, different parasite profiles, and different impacts on local fish communities. Blanket statements about “what cormorants do” often miss this variability, whether those statements come from advocates wanting to protect the birds or from fishers wanting to eliminate them.

Cormorants as Environmental Sentinels

Because cormorants eat large quantities of fish from a specific area and accumulate whatever contaminants those fish carry, they have become valuable indicators of environmental health in the Great Lakes. The same biological trait that made them vulnerable to DDT and PCBs makes them useful monitors now. By sampling cormorant eggs or chick tissue, researchers can track changes in contaminant levels over time without having to catch and test thousands of individual fish. The Wisconsin studies that found organochlorine concentrations an order of magnitude higher than reference sites were part of this broader monitoring effort.²

Cormorant eggs have been used to track declines in legacy contaminants like PCBs and emerging contaminants like PFAS compounds. When contaminant levels in cormorant tissue drop, it typically reflects genuine improvement in water quality. When they spike, it can serve as an early warning that something new is entering the food web. For a region that depends on the Great Lakes for drinking water, recreation, and fisheries worth billions of dollars annually, having a reliable biological indicator perched on a rock with its wings spread is more useful than many people realize.