Phalacrocorax brasilianus

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.

• Biogeographic Regions
• nearctic nearctic
  • native native
• neotropical neotropical
  • native native

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.

• Habitat Regions
• temperate temperate
• tropical tropical
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• coastal coastal
• brackish water brackish water

• Wetlands
• marsh marsh
• swamp swamp
• bog bog

• Other Habitat Features
• riparian riparian
• estuarine estuarine

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.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

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.

• Mating System
• monogamous monogamous

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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

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.

• Parental Investment
• altricial 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.

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.

• Key Behaviors
• flies
• glides
• natatorial natatorial
• diurnal diurnal
• motile motile
• nomadic nomadic
• solitary solitary
• colonial colonial

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.

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

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.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats non-insect arthropods

• 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.

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.

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.

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.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

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

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/ .