Why Are We Protecting The Double Crested Cormorant

Cormorants are protected under the Migratory Bird Treaty Act of 1918 and the U.S. Fish and Wildlife Service retains oversight and control measures that are not extended to the general public (no hunting season).  Many government agencies at different levels in both the U.S. and Canada continue to wrestle with how best to respond to the Cormorant situation.  Cormorants are included under this federal protection and this has become problematic for USFWS.

There are six types of cormorants native to North America. The most abundant and widespread is the Double-crested Cormorant, which can be found throughout the continent in freshwater and in seawater along the coasts into Northern Quebec and up into the reaches of Alaska, and the Neotropic cormorant which are commonly found in or around southwestern waterways.

Cormorants are excellent at catching fish which is their main diet. These birds have long serrated bills with the shape of a hook at the end, for catching and holding their prey. These birds are also excellent swimmers with strong stubby legs. The cormorant has the ability to submerge its body into the water where all that is seen is its head.

What Is A Double Crested Cormorant

Double Crested Cormorant Eating FishThe double-crested Cormorant (Phalacrocorax auritus) is a member of the Cormorant family of Seabirds. It occurs along inland waterways as well as in coastal areas, and is widely distributed across North America, from the Aleutian Islands in Alaska down to Florida and Mexico. Measuring 70–90 cm (28–35 in) in length, it is an all-black bird which gains a small double crest of black and white feathers in breeding season. It has a bare patch of orange-yellow facial skin. Five subspecies are recognized.  It is a large water bird with a stocky body, long neck, medium-sized tail, webbed feet, and a medium-sized hooked bill.

The double-crested cormorant is found near rivers and lakes and along the coastline. It mainly eats fish and hunts by swimming and diving. Its feathers, like those of all cormorants, are not waterproof and it must spend time drying them out after spending time in the water. Once threatened by the use of DDT, the numbers of this bird have increased markedly in recent years. The double-crested cormorant swims low in the water, often with just its neck and head visible, and dives from the surface. It uses its feet for propulsion and is able to dive to a depth of 4 ft to 24 ft for 30–70 seconds. After diving, it spends long periods standing with its wings outstretched to allow them to dry, since they are not fully waterproofed. This species fly’s low over the water, with its bill tilted slightly upward, sometimes leaving the colony in long, single-file lines.

The Migration and Diet Of A Double Crested Cormorant

Double Crested CormorantThe Double Crested Cormorant is a common and widespread species, it winters anywhere that is ice-free along both coasts, as far north as southern Alaska (on the west coast) and southern New England (on the east coast). It can be found as far south as Mexico and the Bahamas. It migrates from the coldest parts of its breeding range, such as eastern Canada, and has occurred in Europe as a very rare vagrant, for example in Great Britain, Ireland, and the Azores.

Food can be found in the sea, freshwater lakes, and rivers. Like all cormorants, the double-crested dives to find its prey. It mainly eats fish, but will sometimes also eat amphibians and crustaceans. Fish are caught by diving under water. Smaller fish may be eaten while the bird is still beneath the surface but bigger prey is often brought to the surface before it is eaten. Double-crested cormorants are also considered pests to aquaculturists because of their intense predation on fish ponds which can cause thousands of dollars in losses to farmers.  The adult Cormorant will consume fish up 1-2 lbs.

The Double Crested Cormorant has caused extensive damage to vegetation where they nest due to excessive guano and physical destruction.  Accumulation of cormorant droppings, which contribute excessive ammonium nitrogen, phosphorous, metals and reduce pH and stripping leaves for nest material may kill trees within 3–10 years.   Changes in soil have been shown to affect plant species composition resulting in reduced number of species and opportunity for exotic, invasive plants to take root.

Distribution of the Double Crested Cormorant

Distribution of Double Crested CormorantWhat the distribution and range map doesn’t show is the Cormorants that have taken permanent residency in the southwest, Arizona and New Mexico.

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What Is The Neotropic Cormorant

The Neotropic CormorantThe Neotropic Cormorant is a medium-sized Cormorant found throughout the American tropics and subtropics, from the middle Rio Grande and the Gulf and Californian coasts of the United States south through Mexico and Central America to southern South America, where he is called by the Indian name of "biguá". It also breeds on the Bahamas, Cuba and Trinidad. It can be found both at coasts (including some mangrove areas) and on inland waters.

The Neotropic Cormorant in the southern populations tend to be bigger than the more northerly birds. It is small and slender, especially compared to the larger, heavier-looking Double-Crested cormorant. It has a long tail and frequently holds its neck in an S-shape. Adult plumage is mainly black, with a yellow-brown throat patch. During breeding, white tufts appear on the sides of the head, there are scattered white plumes on the side of the head and the neck, and the throat patch develops a white edge. The upper wings are somewhat grayer than the rest of the body. Juveniles are brownish in color.

Neotropic Cormorants work in groupsIts diet consists mainly of small fish, but will also eat tadpoles, frogs, and aquatic insects. Information about its prey is sparse, but inland birds seem to feed on small, abundant fish in ponds and sheltered inlets, less than 10 cm (3.9 in) in length, with an individual weight of a gram or two. This cormorant forages for food by diving underwater, propelling itself by its feet. Its dives are brief, between 5 and 15 seconds. It is also known to forage in groups, with several birds beating the water with their wings to drive fish forward into shallows.

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Distribution of the Neotropic Cormorants

Distribution of the Neotropic CormorantAgain, what the distribution and range map doesn’t show is the Cormorants that have taken permanent residency in the southwest, Arizona and New Mexico.

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The Resurgence Of The Neotropic And Double Crested Cormorant

Recently the population of double-crested and Neotropic Cormorants have increased since the 1960’s. Some studies have concluded that the recovery was allowed by the decrease of contaminants, particularly the discontinued use of DDT.  The population may have also increased because of aquaculture ponds in its southern wintering grounds. The ponds favor good over-winter survival and growth.

AlewifeFor populations nesting in the Great Lakes region, it is believed that the colonization of the lakes by the non-native alewife (a small prey fish) has provided optimal feeding conditions and hence good breeding success. Double-crested cormorants eat other species of fish besides alewives and have been implicated in the decline of some sport-fish populations in the Great Lakes and other areas. Scientists are not in agreement about the exact extent of the role of cormorants in these declines, but some believe that double-crested cormorants may be a factor for some populations and in some locations.

In light of this belief, and because of calls for action by the public, the United States Fish and Wildlife Service (the U.S. federal government agency charged with their protection) has recently extended control options to some other government entities. This includes culling of populations and measures to thwart reproduction, in an effort to control their growing numbers.

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