Take a walk, ride your bike, drive your car, and you’re almost certain to happen across the American White Ibis (Eudocimus albus), and more likely, dozens of them, standing, feeding, flying overhead.
They are so ubiquitous as to be taken for granted; so banal as to not be worth our time to pause and consider who they are and what they do in our natural environment.
I have found them to be an endearing creature: gentle, social, curious—sometimes trusting of humans—and beautiful in flight, their body curvatures quite exotic. Edging close to them and looking into their eyes, you get the sense that they appreciate your interest and respect, wondering what we’re thinking every bit as much as we’re wondering about their thoughts.
I thought we’d benefit from learning about this important species.
Appearance
Entirely white except for bright reddish-pink legs, bill, patch around blue eyes, also black wing tips only visible in flight. Medium-sized football-shaped body, long legs, long neck, long down-curved bill. Males are significantly larger, with longer wings and bills, than females. In south Florida, males weigh nearly three pounds, approaching 28 inches in length with a 41 inch wingspan. Juveniles are medium-brown above and white below. Immatures are splotchy brown and white above as they molt into adult plumage.
Behavior
White ibises gather in groups to wade and forage in shallow wetlands and other areas of standing water. They walk slowly and deliberately with heads down, beaks probing the ground for food. Unlike larger herons who stalk prey, white Ibises are random gathers.
In flight, their necks are extended, feet trailing behind. V formations are typical, also long lines; circular patterns are also observed. Typically, birds fly between 200-300 feet above the ground, gliding and flapping intermittently.
Caution: male white ibises are very territorial of their female and nests. If threatened, they will lung forward with bill, also stand up and snap, sometimes lunge and bite.
Song
Main call is a honking sound, roughly characterized as “urnk-urnk” or “hunk-hunk.” The call is made in flight, courtship, or when disturbed. Nestlings make a high-pitched “zziu” as a begging call.
Distribution and Habitat
Breeding range runs along Atlantic coast south of the Carolinas and Gulf of Mexico, throughout the Caribbean, also both coasts of Mexico and Central America. Most common in southern Florida, where over 30,000 have been counted in a single breeding colony. The non-breeding range extends north to Virginia and east to Texas.
Habitat includes tidal flats, shallow coastal marshes, wetlands, mangroves. Also commonly found in muddy pools, ponds, flooded fields, wet lawns. As water levels rise and fall with the seasons, the bird will shift sites to forage effectively (i.e., avoiding deep water).
Feeding
A non-visible, tactile, probing feeder, with long bill penetrating ground, sweeping back and forth across bottom of submerged terrain to pick out preferred food items, such as crayfish, other crustaceans, aquatic insects, small fish. Outside the nesting season, the diet is highly variable depending on type and abundance of prey across chosen habitats. White ibises feeding in mangrove swamps focus on crabs; those in the Everglades target crayfish. When other predators are present (e.g., herons, egrets), the bird will seek small prey, since time needed to break up larger food items will likely result in its theft.
Nesting
American white ibises breed in large colonies, located on or near water. Birds pair up in the spring, the female selecting the site and building the nest, usually in branches of a tree or shrub, often over water. Males assist by bringing nest material. The bird is not faithful to breeding sites, which can be disbanded by thousands of individuals, depending upon water and food conditions, in one or two seasons. Males guard the nest and female to prevent other ibises from stealing sticks and advances of other males during nest building and egg laying.
Breeding
Pairs are predominantly monogamous and both parents care for the young. That said, males tend to engage in extra-pair copulation with other females to increase their reproductive success. One to five eggs are laid, pale blue-green in color with brown splotches, hatching after three weeks. Males attend the nest in the day, females at night. Throughout incubation, males go through a period of starvation to aggressively defend his nest and mate. Newborns have straight bills; the curve downward starts at 14 days.
Bird predators may seize anywhere from 7 percent to 75 percent of the progeny in a breeding colony. The fish crow is a prolific raider, accounting for nearly half of egg loss. Other predators include the grackle, night heron, common opossum, raccoon, rat snakes. The primary cause of nest failure is nest abandonment due to high tides.
Juvenile birds take around two years to reach adult size and weight; breeding begins in the third summer. The oldest member of the species recorded in captivity was over 20 years of age.
Conservation Status
The American white ibis is listed as “least concern” by the IUCN. The population consists of approximately 150,000 mature adults and is stable. A partial survey in 2007 found an almost six-fold increase in the population in the last 40 years. The estimated breeding range is huge—roughly 460,000 square miles. Human pollution of methylmercury, altering hormone levels, has effected mating and nesting behavior, resulting in lower reproduction rates.
Special Note
The American White Ibis is the University of Miami’s mascot, called Sebastian the Ibis. Native Americans observed that the bird was the last to seek shelter before a hurricane, and the first to emerge afterwards. As such, the bird pairs well with the university’s football team--named the Hurricanes!
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