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White Ibis
Eudocimus albus
Order
CICONIIFORMES
– Family
THRESKIORNITHIDAE
Authors: Kushlan, James A., and Keith L. Bildstein
Revisors: Heath, Julie A., and Peter Frederick

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Behavior

Figure 3. Courtship greeting display

Locomotion

Walking, Hopping, Climbing, Etc

Walk slowly while foraging. In Spartina marshes while searching for fiddler crabs, individuals walk at rates averaging 25 to 40 steps/min, with birds on the peripheries of large flocks stepping more frequently than other birds (Bildstein 1983, 1984; Petit and Bildstein 1987). Birds feeding in aquatic habitats often walk much more rapidly, especially when groping in standing water for fish. Individuals leap over one another as flocks move across feeding grounds. Adults rarely climb except when perched in day roosts. Young are capable of climbing small shrubs and bushes by the end of their second week (De Santo et al. 1990).

Flight

Fly with rapid wingbeats (3.3 flaps/s [0.3, 9; Urban 1974]) alternating with gliding at between 60 to 100 m, sometimes in excess of 45 km/h (Pennycuick and De Santo 1989). Infrequently soar to between 500 and 1,000 m (Bateman 1970), especially when traveling long distances (>20 km) between colony and foraging sites. Cost of powered flight estimated at approximately 0.1 g fat/km (Pennycuick and De Santo 1989). Ibises arriving to foraging areas or colonies may ‘stoop’ from high altitudes – folding wings and losing altitude rapidly. Fly in cohesive flocks, typically in a variable “V” formation or in long skeins. Entire flock may perform intricate maneuvers, especially during prebreeding flights in early spring. Individual birds engage in spectacular aerobatics, including free-fall into roost. Young and adults tend to flock separately during first few months, with young in looser flocks (Petit and Bildstein 1986).

Swimming

Chicks reported to swim if they fall in water (Audubon 1844).

Self-Maintenance

Preening, Headscratching, Stretching, Bathing, Anting, Etc

Spend much of the day preening (Rudegeair 1975b), usually at day roosts. Often interrupt feeding bouts to preen. Ventral surface (belly) preened by extending neck out, bill down, and biting feathers with bill tip. Run bill along surface of the wing and bite feathers, working along it or bringing the bill over shoulder to preen under-wing. Back preened directly by turning head, lower belly by placing head between legs. Pay particular attention to head and neck. Use cupped nail of middle toe to scratch overwing. Oil gland is frequently used by rubbing side of head and bill, then rubbing these on back, rolling head side to side. Frequently shakes head or body with loosely held wings. Allo-preening noted only during courtship and nest-building.

Bathe in water 5–20 cm deep. Crouch into water, submerging and shaking first one wing and then the other, or both simultaneously, as though in flapping flight. Usually followed by prolonged preening. Group bathing common during courtship at edges of colonies.

Sunbathing, Thermoregulation, Temperature Metabolism

Interrupt feeding to stand or lie in vegetation in sun with wings drooped. Also shade nest by facing away from sun and spreading wings over contents. As a result, in extreme circumstances entire colonies of incubating and brooding birds may face the same direction. Nestlings have poor thermoregulatory ability and are quickly killed by exposure to sun. When heat stressed, adults and young pant and gular flutter. Bill is gaped and throat oscillated four times/s (Rudegeair 1975b). Rate increases with increasing temperature.

Sleeping And Roosting

Typically sleep with head tucked under wing over back. Roost close together at traditional sites, usually in the tops of live or dead trees, often with other wading birds. When not on the nest, parents often roost at colony site, especially early in the season.

Daily Time Budget

In s. Florida, 13 hr roosting and nest attentiveness, 0.75 hr flying, 10.25 hr foraging (Kushlan 1977c). In coastal S. Carolina nonbreeding adults need spend only 2.5 (females) to 3.5 (males) hr feeding on fiddler crabs to meet daily energy needs (Bildstein 1987).

Agonistic Behavior

Physical Interactions

Defend territories, position, and mates with forward bill thrusts, by jabbing and biting, and by supplanting flights. Fight with rivals by biting and holding the opponent’s head or wing (Frederick 1986a, Babbitt and Frederick 2007). Propensity to fight and fighting ability vary considerably among males. Males fight with males of similar bill length, and longer bills are important in determining outcome of fights over mates and nests, and in captivity, determining whether males breed (Babbitt and Frederick 2007). Mated males, encountering attempted cuckoldry upon returning to nest sites, sometimes pull feathers from intruding males and inflict facial lesions; facial scars, eye injuries, and crippled legs are more common among males than among females. Females are sometimes pecked around the head and back by males before and after extra-pair copulations (Frederick 1987a). Some of these attacks result in bleeding. Unattended eggs at colony sites are sometimes destroyed by adults prospecting for nest sites (Frederick 1987b).

Communicative Interactions

Threat displays include the “forward threat” in which the bird assumes horizontal posture, moves toward or lunges at opponent, may or may not make contact. “Ritualized sparring” at nest site involves two birds standing erect and bill gaping; exchange snaps. In “supplanting flights,” a bird flies at its opponent with neck extended and bill gaping, attempts to alight on other bird.

Appeasement displays occur mostly among females. At nesting, head-rubbing display with top of head and nape rubbed on back, bill turned from horizontal to vertical and back to horizontal. Female appeasement display at nest involves a slow approach with head and body low, feathers slicked back, head turned to show side of face to male.

Spacing

Will defend against other species in aggregations. Individual distance varies with likelihood of piracy, distances increasing when individuals are foraging for large or difficult-to-handle prey.

Territoriality

At colony site, display territory in immediate area of nest (see Sexual Behavior) established, advertised, and defended by male. Display sites tightly defended by males with forward threats and short jabs. Supplanting used to attract female. Nest built in display territory and defended by both sexes. No territories on feeding sites except individual distances.

Nature And Extent Of Territory

Nest territory usually extends only as far as incubating or brooding parent is able to stretch its neck. In Louisiana, distance between nests averaged 0.65 m (SE = 0.03, n = 170, range = 0–2.0; Hammatt 1981); in S. Carolina in needle rush (Juncus roemerianus), 0.69 m (n = 54; Frederick 1987a), in mulberry (Morus sp.), 1.04 m (n = 104; Post et al. 1985); in mangroves in Florida 0.54 m (Girard and Taylor 1979).

Dominance Hierarchy

Stable and somewhat linear hierarchies in captive groups are apparently based on relative size, both within and between sexes (Bildstein 1993). In a captive flock, male Scarlet Ibises with longer bills were more likely to win male-male interaction than males with shorter bills (Babbitt and Frederick 2007). No information on dominance hierarchies in the wild.

Sexual Behavior

Mating System

Monogamous, with frequent extra-pair copulation. Care by both parents is apparently necessary for successful rearing of young.

Pair Bond

Courtship behavior well documented (Palmer 1962, Rudegeair 1975b, Hancock, Kushlan and Kahl 1992). Display sleeping, display shaking, display preening, and supplanting flights, are common in “bachelor parties,” groups of displaying males. Display flights, in which portions of a flock of sometimes more than several thousand individuals spiral up and down, occur at and around colony sites, especially following rains. Group bathing by hundreds of birds at a time may also be a form of display, usually performed on the edges of breeding colonies during courtship. Display preening, head rubbing, and bill popping are the primary mating displays of males. Head rubbing is quickly initiated, and may include a complete roll of the bill from left to right or only a quick touch of the top of the head in a pumping motion, reminiscent of the scratch display of herons. Full bill popping includes twig grasping and nibbling, or may not be accompanied by complete extension of the neck.

Females approach displaying males cautiously in the appeasement posture, especially showing the side of their face to the male. Male gives forward threats and will attack, grabbing and shaking the female’s head. Before pair bonding is complete, female sometimes becomes bloodied. During courtship, the pair uses greeting displays and mutual stick shaking, typically with necks crossed (Fig. 3); display preening, auto- and allopreening, and standing touching each other. Greeting displays may include twig grasping and honking vocalizations by males, and squealing vocalizations by females, the latter disappearing later in courtship.

Copulation takes place at the nest site, or on the nest platform. To begin, male places his neck over that of female as they engage in mutual twig grasping. Male mounts, achieving and maintaining his position by treading feet and flapping wings. Female cradles male by partially lifting wings while standing, raises tail during final moments. Both birds remain at nest for several days, before female begins to spend time foraging. Pair remains together for one nesting episode.

Extra-Pair Copulations

Common in the latter stages of pair formation and even into incubation (Frederick 1987a). Males initiate such copulations; females, although capable of resisting, seldom do so. Over 6% of the fertilized eggs laid may result from copulations outside the mated pair.

Social And Interspecific Behavior

Degree Of Sociality

Highly gregarious at all times; highly colonial nester, in large and densely populated colonies, crèches when leaving the nest, feed in flocks almost exclusively, roost communally, and fly to and from foraging, roosting, and breeding sites in flocks (Smith 1995b).

Play

Young at colony sites manipulate twigs and grassy vegetation in their mandibles. Well-fed captive individuals pick up and work over prey in their bills without eating them.

Interactions Other Than Predation With Members Of Other Species

Commensal feeding widely reported--generally other birds following the ibis as it walks slowly through the water (Kushlan 1978b). Also subject to piracy from other species feeding within its aggregation (Kushlan 1978a). Usually, relatively large prey are stolen.

Predation

Predation on adults probably not important. Alligators (Alligator mississipiensis) and perhaps large birds of prey take adults. Unguarded eggs and hatchlings are at great risk to Fish Crows (Corvus ossifragus) (Shields and Parnell 1986). Boat-tailed Grackles (Quiscalus major), both adult and ambulatory young Black-crowned Night-Herons (Nycticorax nycticorax), gulls, and perhaps vultures, as well as to Northern Opossums (Didelphis marsupialis), Raccoons (Procyon lotor), and rat snakes (genus Elaphe). At some locations as many as 44% of the eggs are lost to Fish Crow predation (Shields and Parnell 1986) and at others little or no nest predation (Frederick and Collopy 1989b). Nestlings are vulnerable to night-herons until they are at least two weeks old. The impact of predation on eggs and nestlings is exacerbated when food for ibises is scarce and parents must spend more time away from their nests (Dusi and Dusi 1968, Bildstein et al. 1990). Eggs and young are also at risk when other ibis steal nest material and knock out nest contents.

Crows usually take all the eggs in a clutch, such predation being highest nearest crow nests. Predation by crows is reduced with greater nest attentiveness by parental ibises (Shields and Parnell 1986) and increased where elevated perch sites for crows are available within a colony. Percent nest exposure affects vulnerability to avian predation (Rudegeair 1975b, Allen-Grimes 1982). Percent of eggs lost to avian predators varies from 7% to 75% among colony sites (Post et al. 1985, Shields and Parnell 1986, Frederick 1987c). Disturbance increases rates of predation significantly (see Conservation and Management).

Males tend to remain at the nest, as any departures put nest and its contents at risk and females at risk of extra-pair copulations (Kushlan 1973a, Frederick 1987a). Defense is by use of standard threat repertoire, including attacks, most directed at conspecifics. Ibises are extremely wary, both when nesting and foraging, more so than other wading birds nesting or foraging with them. In coastal S. Carolina, feeding individuals flush during fly-overs of large birds, including Great Blue Herons (Ardea herodias), Ospreys (Pandion haliaetus), and Red-tailed Hawks (Buteo jamaicensis), as well as helicopters and fixed-wing aircraft. When feeding in areas with tall and short vegetation, ibises avoid tall vegetation, possibly to aid detection of predators. In S. Carolina Spartina marshes, flocking behavior is not linked to increased hunting success, suggesting that flocking during feeding is a response to predation risk (Petit and Bildstein 1987).