Spot-billed pelicans breed seasonally, each nesting pair fledging one clutch per year. Pairs are monogamous by year but not for life. At the beginning of each new breeding season courtship rituals begin anew. Pairing occurs approximately one week after pelicans arrive at their breeding grounds. Spot-billed pelicans use a number of different social signals in courtship, both vocal and visual, including bowing, head swaying, bill clapping, head turning, and various moaning, grunting, and high-pitched yipping noises. The pair, once formed, will begin to build their nest. The male brings sticks to the female, who builds the nest underneath her, anywhere from 5 to 30 meters above ground in the branches of a tree. Up to 15 pairs have been documented with nests in the same tree in a season. These nests, once completed, will be defended with hissing, sighing, and bill-jabbing movements if another bird lands too close. Mates greet each other at the nest with neck stretching and a series of groans.
Mating System: monogamous
Spot-billed pelicans breed once per year during an autumn breeding season. They lay 3 eggs at intervals of 36-48 hours. The eggs are then incubated for an average of 30 days. If all the eggs in a nest are removed or destroyed at the beginning of the season, then a second clutch is laid within a week of their loss. However, if at least one egg remains there will be no replacement clutch. Breeding success is high in this species, with an average of two fledged young per nesting pair. Nestlings, though born helpless, are only fed by their parents for their first few weeks of life. Developing quickly, they are left to fend for themselves within the colony after just a few weeks, scavenging for food within the breeding grounds. Fledging occurs between 60 and 90 days, with the young able to actually hunt on their own at approximately 12 weeks. Spot-billed pelicans reach sexual maturity after 30 months or during their third year.
Breeding interval: Spot-billed pelicans breed once per year.
Breeding season: In Sri Lanka, the breading season extends from December to March or April, but in India the season starts two months earlier, in October.
Average eggs per season: 3.
Average time to hatching: 30 days.
Range fledging age: 60 to 90 days.
Average time to independence: 12 weeks.
Average age at sexual or reproductive maturity (female): 30 months.
Average age at sexual or reproductive maturity (male): 30 months.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)
The majority of parental investment is in caring for the eggs rather than nestlings. Eggs are well tended by adults against egg predators, who rarely are able to steal eggs unless there is some sort of human disturbance to the nesting area. Although both the male and female take turns incubating their clutch, the female, who seems reluctant to leave the eggs even when pushed off by her mate, does the majority of incubation. After hatching, the young are fluid-fed by both parents for the first week and protected in the nest for the first two to three weeks until they develop the skills to defend themselves. After two to three weeks there is little parental involvement; the nestlings gather at the base of their nesting trees and scavenge for food scraps until fledging. They continue to live within the colony, which offers them some safety from predators and the food scraps they need to survive. Little direct parenting is provided once the nestlings leave the nest.
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)