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BiologyThe ivory gull breeds from late June to August, forming colonies consisting of 5 to 60 pairs. Nests of moss, straw and debris are built, situated on bare, snow-free rock and lined with dry grass and feathers. Generally two eggs are laid and incubated for 24 to 26 days. The chicks fledge after four to five weeks (2). Following breeding, ivory gulls immediately leave their colonies and disperse to their winter habitat to forage (3). Like many other gulls, this Arctic species is an opportunistic feeder (3), consuming a wide range of foods that it encounters. Small fish, such as lantern fish and juvenile arctic cod, and large zooplankton are plucked from the sea's surface, and they may also catch small mammals (3). They scavenge on dead fish and the carcasses of mammals, and will often follow polar bears and human hunters to feed on the scraps from their kills. The excrement of polar bears and seals is consumed, as well as the placentas of seals, and in the extreme cold of winter it is even known to swallow large pieces of frozen food (2). The ivory gull is vulnerable to a number of predators; polar bears and a number of birds prey on both eggs and young ivory gulls, and the best-known predator, the artic fox, is known to be capable of destroying entire breeding colonies situated on flat ground (3).