Size The greater flamingo is the tallest flamingo, standing 20 to 150 cm (47-59 in.) and weighing up to kg lbs.). Males reach full size between one-and-a-half and two years. Male flamingos are slightly larger than females

Population

The lesser flamingo is the most numerous of all flamingo species, with an estimated population of 1.5 to 2.5 million individuals.

The second most numerous flamingo species is the greater flamingo. Exact numbers of these birds are difficult to assess because of their extensive range and migration patterns.

The Chilean flamingo is the most numerous of the south American flamingos. Estimated total population is not more than 200,000 individuals, and the population is in a decline.

The James' flamingo has an estimated population of 64,000 individuals.

Estimated population of the Andean flamingo is 33,927 birds with a decreasing trend.

In 1956, the Caribbean flamingo numbers were estimated at only 21,500. Since then, the population has increased to a current estimate of 850,000 to 880,000 birds and a stable trend.

Lifecycle
Flamingos are very social birds; they live in colonies whose population can number in the thousands. These large colonies are believed to serve three purposes for the flamingos: avoiding predators, maximizing food intake, and using scarcely suitable nesting sites more efficiently.^[29] Before breeding, flamingo colonies split into breeding groups of about 15 to 50 birds. Both males and females in these groups perform synchronized ritual displays.^[30] The members of a group stand together and display to each other by stretching their necks upwards, then uttering calls while head-flagging, and then flapping their wings.^[31] The displays do not seem directed towards an individual, but occur randomly.^[31] These displays stimulate "synchronous nesting" (see below) and help pair up those birds that do not already have mates.^[30]

Flamingos form strong pair bonds, although in larger colonies, flamingos sometimes change mates, presumably because more mates are available to choose.^[32] Flamingo pairs establish and defend nesting territories. They locate a suitable spot on the mudflat to build a nest (the female usually selects the place).^[31] Copulation usually occurs during nest building, which is sometimes interrupted by another flamingo pair trying to commandeer the nesting site for their use. Flamingos aggressively defend their nesting sites. Both the male and the female contribute to building the nest, and to protecting the nest and egg.^[33] Same-sex pairs have been reported.^[34]

After the chicks hatch, the only parental expense is feeding.^[35] Both the male and the female feed their chicks with a kind of crop milk, produced in glands lining the whole of the upper digestive tract (not just the crop). The hormone prolactin stimulates production. The milk contains fat, protein, and red and white blood cells. (Pigeons and doves—Columbidae—also produce crop milk (just in the glands lining the crop), which contains less fat and more protein than flamingo crop milk.)^[36]

For the first six days after the chicks hatch, the adults and chicks stay in the nesting sites. At around 7–12 days old, the chicks begin to move out of their nests and explore their surroundings. When they are two weeks old, the chicks congregate in groups, called "microcrèches", and their parents leave them alone. After a while, the microcrèches merge into "crèches" containing thousands of chicks. Chicks that do not stay in their crèches are vulnerable to predators.^[37]