or suitable nest sites less common. They adopt a defence posture, which consists of raising the humeri up and bringing the wrists together, drawing the neck into the body and shaking the head sideways, fluffing up the head feathers and squawking. Bill-jabbing and fights can break out, the two combatants locking bills and wrestling for up to 90 minutes. Mate choice is likely to be based partially on the length of the tail streamers, a bird having longer tail streamers being more attractive as a mate. This tropicbird also probably mates assortatively for tail streamer length, meaning mates likely have streamers of about equal length. In the leadup to breeding, males initiate an aerial courtship display of flying in large circles, alternating between gliding, short periods of rapid wing-beating, and low flight within a few metres of the water, while making sharp cackling calls. Initially flying in small groups, birds then pair off to repeat the display in pairs before bonding. Once pairs have established a nest, they do not perform the display. The timing of breeding depends on location; in some places, birds breed in a defined breeding season, whereas in others, there is none. South of the equator, the latter is likely to be true. On islands near the equator, laying usually occurs from June to November, the majority of chicks fledging around January to February. On Christmas Island, breeding takes place at different times on different parts of the island due to prevailing weather conditions. Some birds may remain at the breeding site year-round. On sub-tropical Lady Elliott Island off Queensland, they nest in winter, which scientists think may be timed to avoid the common breeding times of most migratory species of seabird, such as the noisy Wedge-tailed Shearwater (mutton bird). Not much is yet known about their habits though. The female red-tailed tropicbird lays one egg, which both parents incubate for 42 to 46 days. The male generally takes the first turn on the egg after it is laid. Ranging from long (averaging between , depending on location) and wide, the oval eggs are pale tan with brown and red-black markings that are more prominent on the larger end. Born helpless and unable to move around (nidicolous and semi-altricial), the chicks are initially blind, opening their eyes after 2–3 days. Until they are a week old, they open their beak only upon touch, so the parents