Many bird species do mate for life (or at least until one bird in the pair dies), such as bald eagles, swans, albatrosses and puffins. However, the majority of bird species will only be monogamous for a single breeding season and will then each go their own way.
About 90% of known bird species will form monogamous pair-bonds in order to breed and to raise chicks. However, birds of many of these species are known to “cheat” on their partner.
Scientists have discovered that as many as a third of chicks born to nesting pairs might not be related to both parents. One advantage to having a wide variety of genes in a single clutch of chicks is that they will be less vulnerable to disease.
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