Anhinga

Gliding just beneath the surface of the water, at first glance, it appears to be a snake. But upon closer inspection, you might notice the narrow spike of a beak at the head. It’s a snakebird, a colloquial name for the anhinga, slithering through the water with just its head and neck poking out. When anhingas aren't slyly swimming through the shallows, they are easy to spot hanging themselves out to dry. Unlike most waterbirds, anhingas don't have waterproof feathers. While that may seem like a disadvantage for their watery lifestyle, their wet feathers and dense bones allow them to stalk prey completely submerged. They’ve also acquired the nickname “water turkey” for their long, fan-shaped tail. The name anhinga comes from the Tupi Indians in Brazil and means “devil bird" or "evil spirit of the woods” – which makes their scientific name, Anhinga anhinga, doubly devilish. This bird is a little smaller than a great blue heron, reaching up to 36 inches in height, weighing up to 4 pounds, and with an impressive wingspan of up to 4 feet. Being members of the darter family (Anhingidae), they are related to cormorants and pelicans, and do resemble the neotropic cormorant. Males and females are easily distinguished, as males have an iridescent green-black head and neck, while females have a golden-brown head, neck, and breast. They sport a cluster of silvery white feathers on the forewings and upper back. Anhingas have very long, thin, necks, small snakelike heads with long pointed bills, yellow-brown legs, and scarlet eyes (females sometimes have dark brown, yellowish, or pink eyes; males' are surrounded by a bright blue patch of skin during breeding season). They have broad, pointed wings and are graceful fliers that can travel long distances without needing to flap their wings, similar to the flight of a turkey vulture. Kettles of anhingas often migrate with other birds and have been described as resembling black paper gliders. In flight, they have a distinctive cross-shaped silhouette.

Anhingas live in North, Central, and South America. Within that range, their population is split into two separate subspecies. Their range extends along the coasts from North Carolina’s southern coast into the Gulf of Mexico, all the way through much of South America, from Colombia to Ecuador, and in the east of the Andes to Argentina. In South America, they inhabit much of the watery Amazon River Basin. They live in tropical and subtropical areas, preferring shallow, slow-moving, sheltered waters of the brackish or fresh variety, with nearby perches and banks for drying and sunning. They live near lakes, marshes, and mangrove swamps with tall trees and thick vegetation, and in shallow lagoons and bays. Generally not found in extensive areas of open water. Mostly non-migratory, though the northernmost individuals move south for winter.

The anhinga does not have oil glands for waterproofing its feathers like most water birds. When it swims, it gets completely soaked through, which allows it to move more efficiently under water. The fact that their feathers are less water resistant than other birds helps them to swim underwater, where they spear fish with their long neck and sharp beak, surfacing in order to flip their catch into their mouth for consumption. They lose heat quickly in water as they have no layer of feathers to provide insulation; thus, the sun's heat helps them to maintain their body temperature. Often seen perched on a snag above the water, with wings half-spread. As adept at swimming as the anhinga is, it is equally talented at soaring (once its waterlogged feathers dry out), taking advantage of rising thermals and achieving altitudes of several thousand feet. While soaring, it holds its wings out flat and straight, its neck outstretched or slightly kinked. Anhingas are usually quiet birds, but they can make vocalizations, usually consisting of clicks, rattles, grunts, and croaks.

An anhinga’s diet consists of many small- to medium-sized fishes, with a sprinkling of crustaceans and invertebrates. It swims slowly underwater – or hangs motionless just below the surface, its neck crooked like a cobra – stalking fish around submerged vegetation, and spearing them through their sides with a rapid thrust of its partially opened bill. Backward slanted serrations keep the fish from slipping off. They usually stab with both mandibles, but may use the upper mandible only on small fish. The side-spearing habit of the anhinga suggests that the usual hunting method is by stalking rather than pursuit. They have specialized muscles and vertebral structure in their neck to facilitate the stabs. Sometimes an anhinga’s thrust is so powerful that it has to swim to shore and pry the fish off its beak by rubbing it against a rock or limb. Though generally they just toss it off the bill and position it for swallowing headfirst.

Anhingas are monogamous, forming strong pair bonds, which last for life. Courtship displays include waving their wings, raising the tail up over the back, pointing the bill skyward, bowing deeply, and aerial performances. Breeding is seasonal in North America. In latitudes that are subtropical or tropical, breeding can be throughout the year. Anhingas are colonial and typically nest in small aggregations along with much larger numbers of herons, egrets, ibises, and cormorants. Nests are relatively bulky, made up of sticks and other vegetation, and situated in a fork within the canopy of live trees. The nesting colony is almost always located over water. They are highly territorial, using exaggerated displays when defending their nest site: spreading their wings and snapping their beak to threaten an intruder, pecking each other on the neck and head, sometimes leading to a fight.

The male begins nest construction before he has a mate, by placing large sticks and green material in the forks of trees 15 to 20 feet high. The male collects nearly all the nesting material, and once he secures his mate, the female then finishes building. The nest – a bulky platform of sticks, somewhat more compact than heron nests – is then used from year to year. It is often lined with fresh leaves, green twigs, willow leaves, and catkins. Over time, excrement can build up on the outer rim of the nest giving it a white appearance. Incubation of 2 to 5 whitish or pale blue eggs takes around 25 to 30 days and is shared between parents. Chicks are naked and helpless when they hatch. They are brooded for 12 days by both parents and remain in their nest for three weeks. Around the age of 2 weeks, if the chicks are disturbed, they can drop into the water to swim away. Then, at least sometimes, they are able to climb back up to nest using their feet and bill. Anhinga parents first feed chicks by dripping regurgitated fish and fluid directly into their open bills. When the chicks are older, they put their heads directly into their parents’ bills to get the food. Chicks climb out of their nest onto nearby branches around 3 weeks to work on building up their flight muscles, and they fledge at about 6 weeks old. The young stay for several more weeks with their parents before becoming independent and reach maturity when they are about 2 years old. The oldest recorded anhinga was at least 12 years old.

According to the IUCN Red List, despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable. The IUCN Red List rates the species as Least Concern. Potential threats to anhingas include habitat degradation and discarded fishing lines, which pose a threat because the birds can easily get tangled up in them. DDT (poison) had an effect on their reproductive success, and banning this pesticide in the United States has benefited those populations that breed in the south of the country. Humans don’t interact much with these birds. Though we inhabit the same regions as they do, we don’t typically fish for the species that these birds often feed on, so conflicts are minimal.

Where I learned about anhingas, and you can too!

All About Birds
www.allaboutbirds.org/guide/Anhinga/overview

Audubon
www.audubon.org/field-guide/bird/anhinga
www.audubon.org/news/get-know-anhinga-or-snakebird

Texas Breeding Bird Atlas
txtbba.tamu.edu/species-accounts/anhinga/

US Fish & Wildlife Service
fws.gov/story/2022-03/anhinga

Florida Fish & Wildlife Conservation Commission
myfwc.com/wildlifehabitats/profiles/birds/waterbirds/anhinga/

IUCN Red List
www.iucnredlist.org/species/22696702/93581588

WhatBird
identify.whatbird.com/obj/621/_/anhinga.aspx

Animalia
animalia.bio/anhinga

Wilderness Classroom
wildernessclassroom.org/wilderness-library/anhinga/

Animals Network
animals.net/anhinga/

Bird Watching Academy
www.birdwatchingacademy.com/anhinga/