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Phalacrocorax brasilianusneotropic cormorant(Also: neotropical cormorant)

By Daniel Karp

Geographic Range

Neotropical cormorants breed from Cape Horn, South America to northern Texas, southwestern Louisiana, and southern Arizona. In winter, they have been recorded wandering as far outside their breeding range as California, Saskatchewan, and Pennsylvania. Generally they are restricted to the southern United States, Central America, the West Indies, and South America. They are non-migratory, but are nomadic during the non-breeding season. (Howell, 1995)

Habitat

Neotropical cormorants are found in a variety of habitats, although close proximity to deep water is preferred. Availability of perches for sunning and drying their wings is also important in habitat preferences. Neotropical cormorants can be found in fresh, brackish, or salt water, bays, lagoons, streams, salt ponds, seashores, and lakes. In the United States, they are commonly found in coastal marshes and swamps. Elevation is not a concern, as birds are found from sea level wetlands to high mountain lakes in the Andes. (Stiles, 1989; Telfair and Morrison, 1999)

  • Range elevation
    0 to 5000 m
    0.00 to 16404.20 ft

Physical Description

Neotropical cormorants are jet black, aquatic birds, weighing between 1.2 and 1.4 kilograms. They range in length from 63.5 to 68.5 cm, with an approximate wingspan of 102 cm. A pale green gular patch at the base of the bill with a white “v” outline distinguishes them from similar species, such as double-crested cormorant (Phalacrocorax auritus). They have roughly equivalent neck and tail lengths, but are easily detectable in flight. Double-crested cormorants have shorter tails. A faint greenish shine on the upper wings and back may be detectable under correct lighting conditions. Juvenile birds lack this green shine and are generally paler. Their breasts are brown instead of black, and their beaks may appear yellower. Juveniles may be especially difficult to tell apart from other cormorant species due to their dull gular patches. There is no discernible sexual dimorphism. (Howell, 1995; Sibley, 2000; Telfair and Morrison, 1999)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    1.2 to 1.4 kg
    2.64 to 3.08 lb
  • Range length
    63.5 to 68.5 cm
    25.00 to 26.97 in
  • Average wingspan
    102 cm
    40.16 in

Reproduction

Neotropical cormorants are monogamous throughout the breeding season. They engage in intricate displays to attract mates. Males choose the nest site and females assess the location, either accepting or rejecting the offered nest. Courtship displays are characterized by birds waving their wings and calling. A variety of different displays exist, including the gaping display (necks are stretched upward and calls are made), pointing (the neck slowly and silently sways), kink throated display (an arched neck posture), and both pre-takeoff and post-landing displays. Monogamy is thought to be annual, as neotropical cormorants pick new mates each year. (Morrison, 1979; Telfair and Morrison, 1999)

Neotropical cormorants have comparatively long breeding seasons, lasting from June to mid-October in Texas, April to June in Argentina, and October to November along the Patagonian coast. Males choose nest sites in small trees or other structures. Normally nests are located between 0.9 and 6.1 meters in height. While males choose nest sites and bring nest material, it is the female that actually constructs the nest. Portions of previous nests are often re-used. Nests are usually composed of a thick outer layer of twigs and sticks, lined with soft grasses and seaweed. The mean external diameter of nests is 34.4 cm, with a height of 14.2 cm. Neotropical cormorants nest communally, spacing nests at a minimum of 70 to 75 cm apart. Colonies may be massive, up to several thousand individuals. Eggs are oval, with light blue and chalky white hues. Average dimensions are 54.54 by 33.68 mm. Mean clutch size is 3 to 4 eggs, though the range is from 1 to 7. An average of 2.1 young survive past the first ten days after hatching. Eggs are laid at two day intervals. Incubation begins after two days and lasts 23 to 26 days with a mean of 24.6. Eggs hatch asynchronously. (Morrison, 1979; Quintana, 2004; Telfair and Morrison, 1999)

  • Breeding interval
    Neotropical cormorants breed once yearly.
  • Breeding season
    Neotropical cormorants have comparatively long breeding seasons lasting from June to mid-October in Texas, April to June in Argentina, and October to November along the Patagonian coast.
  • Range eggs per season
    1 to 7
  • Average eggs per season
    3-4
  • Range time to hatching
    23 to 26 days
  • Average time to hatching
    24.6 days
  • Average fledging age
    8 weeks
  • Average time to independence
    11 weeks

Neotropical cormorant hatchlings are altricial and are attended to for eleven weeks. At 8 weeks the young are capable of swimming and diving. By twelve weeks the young are completely independent. Until then, the parents brood, feed, and protect their chicks. In the heat, the chicks are shaded, and, in the cold, they are brooded. Chicks emit a distinctive call for feeding, and both parents respond by regurgitating liquid into their mouths. As the chicks develop, they are eventually fed whole fish. Studies document 3 to 8 feedings per day. Parents engage in no nest sanitation techniques and feces and rotten fish frequently build up in the nest. (Morrison, 1979; Telfair and Morrison, 1999)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female

Lifespan/Longevity

The oldest reported wild neotropical cormorant was caught after being banded for 12 years and 7 months. Generally, mortality rates are highest in the initial stages of life. Fledglings often die when parents abandon their nest following human disturbance, starvation, or storms. At this point predators such as common raccoons (Procyon lotor) and grackles (Quiscalus) exploit open, unprotected nests. (Telfair and Morrison, 1999)

Behavior

Neotropical cormorants awkwardly waddle on land but are effective perchers and agile swimmers. Flight is characterized by gliding with rounded wings. To take-off, cormorants orient towards the wind and run along the water to promote lift. In water, neotropical cormorants sit quite low. Their set back, webbed feet and their sleek bodies allow for effective underwater pursuit of prey. After swimming, much time is spent in preening and sunning in the wing-spread position to dry their feathers. Neotropical cormorants often fly in a V formation and are gregarious nesters. Besides defense of nest site, there are infrequent intraspecific antagonistic interactions. Outside of the breeding season, neotropical cormorants are usually solitary. However, it is not uncommon to see birds engaging in flock feeding. (Quintana, 2004; Telfair and Morrison, 1999)

Communication and Perception

The majority of intraspecific communication is through vocalizations. When alarmed, neotropical cormorants emit a simple guttural call. During flock feeding, calls are common. Males are generally more vocal than females, but both sexes are usually silent outside of the breeding season. Hatchlings use food-begging calls to beg for food. Neotropical cormorants also communicate through visual displays, primarily during courtship. (Telfair and Morrison, 1999)

Food Habits

Some research suggests that neotropical cormorants are aquatic generalists, eating fish, frogs, tadpoles, and dragonfly nymphs. Other research indicates that fish and shrimp comprise an overwhelming majority of their diets. To forage, neotropical cormorants generally pursuit dive. However, in large flock feeding situations, birds also engage in plunge-diving techniques. Sometimes birds may even line up to "herd" fish. Studies show adults are more adept feeders than juveniles, who take some time to learn effective foraging methods. (King, 1989; Telfair and Morrison, 1999)

  • Animal Foods
  • amphibians
  • fish
  • insects
  • aquatic crustaceans

Predation

Raccoons and grackles, both great-tailed and boat-tailed, feed on eggs and young. However, grackles seem to raid nests only after human disturbance has caused the cormorants to abandon their nests for a short period. Interestingly, neighbors tend to protect other birds’ nests when the parents leave to forage. (Morrison, 1979)

Ecosystem Roles

Interspecific competition with double-crested cormorants could contribute to limiting the extent of their northern range. An interesting mutualism between neotropical cormorants and roseate spoonbills (Ajaia ajaja) has been observed in Texas, in which individuals of both species group together for more effective predator protection. Moreover, studies have shown that neotropical cormorant guano provides vital biotic sustenance for aquatic ecosystems, and helps maintain nutrient levels. (Telfair and Morrison, 1999)

Mutualist Species

Economic Importance for Humans: Positive

Some fishermen use neotropical cormorants to locate abundant fish schools. Their guano may even help augment biomass in aquatic ecosystems.

Economic Importance for Humans: Negative

Many fishermen think that neotropical cormorants decimate fish populations, thereby depleting fish reserves. These birds are often shot near fisheries. (Telfair and Morrison, 1999)

Conservation Status

Neotropical cormorants were evaluated as species of least concern in 2001 by BirdLife International due to their large range (18 million km^2) and large population size (estimated 2 million individuals). However, the species is protected under the Migratory Bird Treaty Act. Neotropical cormorants still face human threats, as they are hunted, poisoned by pesticides, and driven from their habitats. (Telfair and Morrison, 1999)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Daniel Karp (author), Stanford University, Terry Root (editor, instructor), Stanford University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

freshwater

mainly lives in water that is not salty.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

Howell, S. 1995. Guide to the Birds of Mexico and Northern Central America. Oxford: Oxford University Press.

King, K. 1989. Food habits and organochlorine contaminants in the diet of Olivaceous Cormorants in Galveston Bay, Texas. Southwestern Naturalist, 34: 338-343.

Morrison, M. 1979. Breeding biology and specific mortality of Olivaceous Cormorants. Southwestern Naturalist, 24: 259-266.

Quintana, F. 2004. Diving behaviour and foraging areas of the neotropic cormorant at the marine colony in Patagonia, Argentina. Wilson Bulletin, 116: 83-88.

Sibley, D. 2000. The Sibley Guide to Birds. New York: Chanticleer/Knopf.

Stiles, G. 1989. The Birds of Costa Rica. Ithaca, New York: Cornell University Press.

Telfair, R., M. Morrison. 1999. "Neotropic Cormorant (Phalacrocorax brasilianus)" (On-line). The Birds of North America Online. Accessed June 12, 2007 at http://bna.birds.cornell.edu/BNA/account/Neotropic_Cormorant/.

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