Birds are monogamous because their young are tiny, helpless and immature (or altricial) and require loads of parental care. For an indication of just how altricial most nestlings are, look to a typical pied flycatcher nest.

Are birds mostly monogamous?

About 90 percent of bird species are monogamous, which means a male and a female form a pair bond. ... A pair bond may last for just one nesting, such as with house wrens; one breeding season, common with most songbird species; several seasons, or life. Social monogamy seems to be more common than sexual monogamy.

Are birds or mammals more monogamous?

The amount of social monogamy in animals varies across taxa, with over 90% of birds engaging in social monogamy while only 3–9% of mammals are known to do the same. This list is not complete. Other factors may also contribute to the evolution of social monogamy.