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Jun 05

Batavia not a bad place for cormorants to perch

Posted on June 5, 2017 at 2:30 PM by Christopher Cudworth

Double-crested_Cormorant_v11-12-003_lThe City of Batavia has a healthy population of double-crested cormorants. They can be seen almost every day on the stretch of river between Fabyan Forest Preserve and the faster moving water south of Clark Island.

But most famously, Batavia's cormorants can often be seen perched on the branches of an ancient dead tree on the east bank of the Fox River next to the walking bridge. 

With recent news provided by a local tree expert that the dead tree is highly compromised at its base and likely to fall due to ant and beetle damage, the City of Batavia has been considering options such as manmade perching platforms to replace the dead tree if a plan to extend the bike path along the east side of the Fox is carried out.

It wouldn't be the first manmade structure to host birds in the city. Batavia already hosts a manmade chimney swift roost in south downtown as well as a series of purple martin houses stationed around the Riverwalk. And, bird species such as nighthawks breed on industrial rooftops where tar and gravel methods are used for sealing. So Batavia plays host to a number of urbanized species of birds and animals. 

IMG_1594But given concerns from some residents  about the future of the 'cormorant tree' and overall character of the Fox River as it passes through downtown Batavia, we are sharing information about the history and ecology of cormorants in the Fox Valley and beyond. We hope it enlightens our community about the needs and characteristics of these fascinating birds and their continued presence in Batavia. 

What is a double-crested cormorant, exactly? 

The species of cormorant most commonly seen along the Fox River is called a double-crested cormorant. It is named for the tufted feathers that when dry stick up like ears on the back of the bird's head. Another species of cormorant known as the neotropic cormorant is rarely seen in the Fox Valley, but is an anomoly species known mostly to avid birders.

Cormorants are  large (33”) birds with a wingspan of 52". They have a healthy appetite for fish from a variety of species. After fishing, they can often be seen perched on semi-submerged logs with wings raised to dry out the feather Cormorant treetheir feathers. This is because cormorants are an ancient line of birds whose evolution balanced the amount of water-shedding oil in the feathers with the advantage of absorbed water that actually helps the birds dive up to 70 feet underwater while hunting fish.

Dead tree denizens

In Batavia, cormorants can also be seen perched high in the dead trees next to the walking bridge in downtown. These high places offer cormorants a sunny or breezy place to completely dry their feathers. But given the fact that the tree is no longer stable and  might soon fall into the river, considerations are being given during the process of east-side bike trail construction. There has been discussion about replacing the cormorant trees with manmade structures. This would give cormorants a place to perch near a favored fishing ground below the dam in Batavia.

Fox River nightmare

FishSmallmouthlesionAs an ecosystem the Fox River has gone through some major changes over the last 40 years. As recently as the 1970s, water quality was disturbingly poor. Environmental pollutants ranging from solvents and soaps to pesticides such as DDT were finding their way into the tributaries and main body of the Fox River. Fish such as white bass, smallmouth and largemouth exhibited signs of environmental stress. Some bore lesions due to the poor water quality, and low oxygen levels favored species such as catfish and carp but made it hard for bass and other gamefish to thrive. 

Given these dire conditions, an activist known simply as The Fox confronted companies known for polluting the river. The Fox delivered samples of  sewage or chemical waste back to the offices of the offenders in ceremonial ways. These activities coincided with the establishment of the EPA, the Clean Water and Clean Air acts. the benefits of environmental protection took hold. The Fox River ecosystem began to rebound as a result.


Through the 1980s and 90s fish populations grew healthier.At the same time, bird species such as great blue herons, common egrets, black-crowned night herons and double-crested cormorant returned to the Fox River to feed and breed.

But cormorants have proven to be controversial in many regions across the United States. Some sport fisherman insist that fish-eating birds such as cormorants deplete stocks of perch and other desirable species. Yet comprehensive studies by organizations such as the Wisconsin Department of Natural Resources, have shown that cormorants do not focus on any specific species of fish to its detriment. Cormorants are fishing opportunists much like their human counterparts.

Yet according to the website for the Chesapeake Bay Foundation, cormorants are relatively lucky to be around at all. “Even more amazing is the comeback story of cormorants. After being nearly wiped out in many areas, cormorants started multiplying in the 1970s in the United States because the federal government banned the pesticide DDT and outlawed the shooting of cormorants in 1972.

It was true. Cormorants sat at the top of the food chain where accumulation of chemicals was thinning their eggshells and that led to breeding failure. Had the pattern continued, it is likely species such as the double-crested cormorant could have become extinct.


Lake Renwick RookeryFortunately there were holdout populations that did survive here in Illinois. In the Fox Valley region, the prime holdover for cormorant populations was at Lake Renwick in Plainfield. During the 1970s and 80s, a small population survived using breeding platforms set up in the center of the lake for those purposes.

But it was not until the early 1990s that cormorant populations began to expend and show up with regularity on the Fox River. Adult birds are identified by their orange throat patch and overall dark plumage. The young vary in color but are generally dark grayish brown above and tan or white below. Adults and young both hunt fish by swimming with much of their body below the water line. Sometimes only their necks emerge from the water. Then they dive below the surface and can swim swiftly underwater using wide, webbed feet to pursue fish.

Evolutionary roots

Flightless CormorantCormorants are a very ancient line of bird species. To make things even more interesting, recent fossil discoveries show that there were transitional species of cormorant-like dinosaurs that were likely fully-feathered while still bearing teeth in their bills.

Today’s species of double-crested cormorant still resembles a dinosaur in some respects. Most importantly, it is quite effectively evolved to catch fish with its hooked, sharp beak and serpentine neck that can gulped down and swallowed many types of fish head first.

Different types of cormorants are found around the globe. Some species are used as fishing tools by human beings who place rings around their necks to prevent the birds from swallowing the fish they catch.

But perhaps the most famous line of cormorants are the flightless species found on the Galapagos Islands off the coast of Ecuador. These were the birds that so fascinated a scientist named Charles Darwin. Flightless cormorants evidence a reversal in the typical direction of evolution. For a bird to no longer need its ability to fly, it had to have near perfect conditions where other predators were not likely to rub it out. As Science Daily documents;  “In a new study unraveling the cormorant's DNA, UCLA scientists discovered genetic changes that transpired during the past 2 million years and contributed to the bird's inability to fly. Interestingly, when these same genes go awry in humans, they cause bone-development disorders called skeletal ciliopathie.”

Successful to a fault

So the cormorant truly an interesting type of bird. In some parts of the world, cormorants are considered almost too successful. Large numbers of cormorants can actually become a threat to the health of rivers, but not simply for their habit of eating fish. They are colony breeders, form large flocks, and can come to dominate popular breeding sites such as islands covered with trees.

 In some cases, their populations crowd out other species of birds such as herons and egrets. Just as damaging to the environment as a whole is the fact that cormorant feces can become a threat to the environment due to its acidity from an all-fish diet. The feces can strip leaves from vegetation, cause water quality to decline and even kill whole trees where population density becomes too great.

Batavia cormorants

CormorantThat brings us to the cormorants of Batavia perched in the dead trees next to the Fox. The birds have captured the attention and imagination of people gazing at them from below. But if the trees come down on their own, or are taking down during a bank restoration project, where will the cormorants go?

As noted, they are highly resourceful birds. If the “cormorant tree” is ultimately removed, it won’t mean the end of cormorants along the Fox River in Batavia. There are still many trees dead and alive on which the birds can perch. But the City of Batavia recognizes the importance of providing  habitat for wildlife. Thus artificial perches may be installed if and when the dead tree come down.

Public safety has to be a consideration. The trunk of the tree is riddled with ant destruction. Deep cracks run the entire length of its trunk to the first junction of branches reaching to the sky. A strong storm could take down the tree in either direction. 

The cormorants will remain because the fishery is strong, the trees are plentiful and that section of the river, despite its location in the middle of downtown, is relatively undisturbed. Thanks in part to the wisdom of conservation efforts for years ago and the grace of human protection, species such as double-crested cormorants have been able to thrive. The City of Batavia is considering plans to keep the welcome mat out. 

With the establishment of the Environmental Protection Agency in 1970s, the practice of dumping harmful chemicals and toxins was outlawed. 


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