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Why do incubating procellariiform birds lose weight?
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Procellariiform
Black-browed albatross (Diomedea melanophris).
Incubating procellariiform birds lose weight because they undergo a period of fasting while attending to their nesting duties.1
Unlike many other bird species, mated procellariiforms do not feed each other during the incubation period. Instead, they share the responsibility of incubation by taking turns for periods of several days each. While one partner remains at the nest to incubate the egg and guard the site, it is unable to forage for food. Consequently, the bird at the nest fasts and loses weight, while the partner currently at sea is able to feed and gain weight.1