Cormorant, Florida



Phalacrocorax auritus


A large waterbird with a stocky body, long neck, medium-sized tail, webbed feet and a medium sized hooked bill. BL: 70–90 cm (28–35 in); Wingspan 114–132 cm (45–52 in); Wt: 1200–2500 g (42.36–88.25 ounces).  Males and females do not display sexual dimorphism.  Plumage is dark-colored with bare super-loral skin and gular skin that is yellow or orange. An adult in breeding plumage will be mostly black with the back and coverts being a dark grayish towards the center. Nuptial crests, for which the species is named, are white, black or a mix of the two. These are located just above the eyes with the bare skin on the face of a breeding adult being orange. A non-breeding adult will lack the crests and have more yellowish skin around the face. The bill of the adult is dark-colored.  The plumage of juvenile Florida Cormorants is more dark grey or brownish. The underparts of a juvenile are lighter than the back with a pale throat and breast that darkens towards the belly. As a bird ages, its plumage will grow darker. The bill of a juvenile will be mostly orange or yellowish.

Family

Phalacrocoracidae

Order

Pelecaniformes Sub-order: Sulae

Class

Aves

Range

Florida cormorants breed across North America, as far north as southern Alaska. They winter in North America as far south as Sinaloa, Mexico, and are common on marine and inland waters throughout their range.

Habitat

It is found near rivers, lakes and along the coastline.

Life Expectancy

In the wild approximately 6 years (average) to 17 years (extreme)

Sexual Maturity

Approximately 2 years of age

Diet

In the wild, it eats aquatic animals like fish, crustaceans and amphibians.

Status

IUCN – Least concern; US Migratory Bird Treaty Act – Protected

Behaviors

Florida cormorants are very gregarious. They can be found in small and large groups both on the breeding grounds, and during the winter. When threatened by a predator, cormorants may threaten the predator or vomit fish at them. If the predator is large, the adults usually leave the nest, and circle overhead. Crepuscular and diurnal, it 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 1.5–7.5 m (5–25 feet) 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 flies low over the water, with its bill tilted slightly upward, sometimes leaving the colony in long, single-file lines. Its food can be found in marine, brackish and salt bodies of water. 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. Cormorants regurgitate pellets containing undigested parts of their meals such as bones. These pellets can be dissected by biologists in order to discover what they ate. Cormorants are monogamous and breed in colonies of up to three thousand pairs. The male chooses a nest site and then advertises for a female by standing in a “wing-waving display” that shows off the brightly-colored skin on his head and neck. Males also perform elaborate courtship dances, including dances in the water where they present the female with nest material. After forming a pair, double-crested cormorants lose their crests. Double-crested cormorants do not defend a large territory around the nest. They defend a small area immediately around the nest that is less than one meter in diameter. Double-crested cormorants breed between April and August, with peak activity occurring in May through July. The males arrive at the breeding colony first and chose a nest site. They then advertise for a mate. The male and female work together to repair an old nest or to build a new one of sticks, twigs, vegetation and flotsam and jetsam found nearby, including rope, fishnet, buoys and deflated balloons. The male brings most of the material to the female who builds the nest and guards it from other colony members who would otherwise steal the nest materials. The nests typically built on the ground, but are occasionally built in trees. After nest construction is complete, the female lays 1 to 7 (usually 4) pale bluish-white eggs with a chalky coating. The eggs are laid 1 to 3 days apart. Both parents incubate the eggs, which hatch asynchronously after 25 to 28 days. The newly hatched young are altricial, and are cared for by both parents. Both parents feed the chicks regurgitated food. The young begin to leave the nest when they are 3 to 4 weeks old. They can fly at about 6 weeks and dive at 6 to 7 weeks. The chicks become completely independent of their parents by 10 weeks of age. Double-crested cormorants do not breed until they are at least 2 years old.

Adaptions

Florida cormorants use calls and physical displays to communicate with one another. While cormorants use their small range of calls in certain social situations, they are largely silent. One example of the physical displays used to communicate between cormorants is the “wing wave display” used by males to attract a mate. They have a hook-like tip on the upper maxilla of their bill and specialized muscles that aid them in grasping their slippery prey.

Special Interests

The Florida Cormorant was first described by Rene Primevere Lesson in 1831. Its common name refers to the same nuptial crests. Other common names of this species include Crow-duck, Shag and Taunton Turkey (in New England). There are five subspecies recognized: P. a. albociliatus (Farallon Cormorant that breeds along the NA Pacific Coast), P. a. auritus (Double-crested Cormorant that breed from the Great Basin and Rocky Mountains east into central and eastern North America), P. a. Cincinnatus (White-crested Cormorant that is found only along southern coast of Alaska and on the Aleutian Islands, ranging west from Kodiak to Chuginidak in the Aleutians), P. a. floridanus (Florida Cormorant is found from southern and central Texas east to the Atlantic and from North Carolina south to Florida) and P. a. heuretus. These subspecies are differentiated by size and the color and shape of their crests. Double-crested cormorants account for a large portion of the bird population that winters in the Florida Bay, along with the roseate spoonbills, great white herons, and reddish egrets. Double-crested cormorants may nest with up to thirteen other species of colony-nesting birds. Within these mixed colonies, they may affect nest-site availability to other species, and provide food for the other species by means of chicks, eggs, pellets, regurgitated fish and stolen food. Cormorants also hunt in mixed flocks, benefiting others and benefiting others through their combined effort to find prey. The Double-crested Cormorant makes a bulky nest of sticks and other materials. It frequently picks up junk, such as rope, deflated balloons, fishnet, and plastic debris to incorporate into the nest. Parts of dead birds are commonly used too. Large pebbles are occasionally found in cormorant nests, and the cormorants treat them as eggs. Double-crested Cormorant nests often are exposed to direct sun. Adults shade the chicks and also bring them water, pouring it from their mouths into those of the chicks. In breeding colonies where the nests are placed on the ground, young cormorants leave their nests and congregate into groups with other youngsters (crèches). They return to their own nests to be fed. Accumulated fecal matter below nests can kill the nest trees. When this happens, the cormorants may move to a new area or they may simply shift to nesting on the ground.

Folklore

Conservation

The Florida Cormorant’s numbers decreased in the 1960s due to the effects of DDT. Colonies have also been persecuted from time to time in areas where they are thought to compete with human fishing. Recently the population of Florida Cormorants has increased. Some believe 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. In 1894, Thomas McIlwraith in his book, Birds of Ontario, concludes his section on Double-crested Cormorants by saying: “When the young are sufficiently grown, they gather into immense flocks in unfrequented sections, and remain until the ice-lid has closed over their food supply, when they go away, not to return till the cover is lifted up in the spring.” Linda Wires and Francesca J. Cuthbert state that there is solid indication that cormorants were once at least as common in North America as they are now, and most likely much more so, but were killed off physically, like so many other predatory and game species, in the 19th century, although beginning earlier than that, and continuing to the present. Double Breasted Cormorant in its natural habitat. For 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 lethal culling of populations and measures to thwart reproduction, in an effort to control their growing numbers. The U.S. Fish and Wildlife Service retains oversight, and the control measures 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 situation. The Canadian government has scheduled a mass culling of the birds on Middle Island, a small island in Lake Erie and part of Point Pelee National Park, to begin as early as April 2008. This is an attempt to keep the small island in balance and preserve its vegetation, but opponents to he plan have pointed out that it is based on faulty information, provided in part by anglers who view cormorants as competitors. A website has been set up to provide information on the birds and plan as well as to prompt visitors to provide feedback and compel the Minister of Environment to put a stop to the planned slaughter. Double-crested cormorants and other fish-eating birds are considered by some to be detrimental to commercial fisheries and fish farms. However, the extent of their impact on fish populations is difficult to quantify, and has been demonstrated by some studies to be very small. Some landowners also complain of lowering of property values as a result of the impact of double-crested cormorants on vegetation. Finally, double-crested cormorants have been implicated as vectors for fish diseases and parasites.

Jacksonville Zoo History

This is the first cormorant species known to have been exhibited at the Jacksonville Zoo. The Florida Cormorant first arrived at our Zoo in 2008.

Exhibit

Emerald Forest Aviary