If conditions are favorable, the mating process begins shortly after white-faced ibises return from their wintering locations. If conditions are not favorable, mating can be delayed temporarily or not undertaken at all in that year. Nesting occurs in dense, large colonies. It is unknown when the male and female bond. Some appear to return from wintering locations already as mated pairs, some seem to form pairs in the one or two weeks proceeding mating. It is also unknown how long this pairing lasts. Males display at multiple possible nesting sites, including previously used nests. Males use “ritualized bill probing” and also give a call that interested females answer with another call. Females choose the actual nesting site.
Mating System: monogamous
White-faced ibises breed once per year. The breeding season in North America is from April to May. In the event of unfavorable breeding conditions, this season can sometimes last until mid-June or the season can be skipped altogether. In South America the breeding season occurs in November and December. Eggs are laid at a one to two day interval with the average number of eggs laid each season being three to four and a range of two to seven. The eggs hatch after 20 days (range: 17 to 26). Before the young can fly on their own they are fed by their parents. During the first week after hatching there is a 60% mortality rate for third and fourth eggs produced, compared with a 5% mortality rate for first and second eggs. Young fledge after five weeks and are independent after eight weeks.
Breeding interval: White-faced ibises breed once yearly.
Breeding season: Nesting generally occurs April to June in North America and November to December in South America.
Range eggs per season: 2 to 7.
Average eggs per season: 3.5.
Range time to hatching: 17 to 26 days.
Average time to hatching: 20 days.
Average fledging age: 5 weeks.
Average time to independence: 8 weeks.
Average age at sexual or reproductive maturity (female): 2 years.
Average age at sexual or reproductive maturity (male): 2 years.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)
Average eggs per season: 3.
White-faced ibis parents take turns in making the nest and guarding it. The male starts guarding the nest while the female gathers materials and then the role reverses while the female builds the nest the male gathers materials. Once the eggs have been laid, the parents take turns in caring for the eggs, normally the males during the day and the females at night. Both sexes will fiercely guard the nest and the area around the nest within a meter against intruders. They shade or incubate the eggs to keep them at the correct temperature. This treatment continues for the first week following hatching and occurs to a lesser extent (left alone for up to three hours) during the second week and is absent in the third week. Both male and female adults will feed the young. This is done by regurgitating partially digested food. The parents will also take the young on both a short walk and a short flight around the colony. There is no evidence to believe there is an association between the parents and young after they have reached independence.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Male, Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)