More than 90 percent of bird species form pair bonds during the breeding season, but how often do these birds get divorced? While bird emotions are still debatable for many ornithologists, the strength of pair bonds varies and bird divorces can occur for a wide range of reasons. Understanding why birds bond and why those bonds can dissolve can help birders better understand the breeding behavior of their favorite species.

Bird Pair Bonds

While some birds do mate for life, not all pair bonds are a lifelong commitment. Even a faithful commitment is one that may last just a short while, depending on the bird species. The typical bird mating bonds can have a wide range of lengths, including…

• A Few Minutes: For some birds, such as the ruby-throated hummingbird, the pair bond lasts only as long as necessary for the male to catch the female's attention and for the birds to mate. After copulation, the male leaves and the female is solely responsible for building a nest, incubating the eggs and caring for the chicks, with no help from the male.
• Single Nest: Some bird pairs last only as long as necessary to raise a single brood of chicks. In species that only produce one brood per year, this bond may last for several weeks or months, but in species where multiple broods are common, the individual birds may seek out different partners for each mating.
• All Season: Many bird mating bonds last an entire season, from the first spring courtship until the last chick has left the nest and no longer requires parental care, even if several broods are raised during the season. This saves adult birds the time and energy of finding different mates in a short period of time, but they still enjoy the benefits of multiple nests and more offspring.

• Several Years: Birds that mate for life stay together for many breeding seasons if they successfully produce healthy chicks. This is common in large birds that have long incubation periods or post-hatching care periods, because then they do not need to waste time and energy each year finding a suitable mate. Even these long term bonds may not last, however, and birds can divorce for several reasons.

Why Birds Divorce

The ultimate goal of bird pair bonds is to successfully mate and raise healthy chicks; there are no childfree bird pairs. If producing chicks is difficult, a bonded pair may separate and seek different mates, but there are several other reasons that can also lead to an avian divorce.

• Natural End of Season: Depending on the typical length of a species' mating bond, birds often separate after the end of the breeding season and go their separate ways. While this is a natural termination of the bond, it could be considered a divorce, and the birds will seek out new mates for the next nesting season.
• Inability to Procreate: If a mated pair is unable to produce eggs, if those eggs do not hatch or if the chicks are unhealthy and do not live, it is likely that the adults will split and search for new mates in order to have better chances of producing surviving offspring. The divorce could happen in the same nesting season or may happen in the non-breeding season and the birds will court new partners at their next opportunity.
• Death of a Mate: When one partner dies, the remaining bird often seeks out a new mate in the next breeding season in order to continue producing offspring. Depending on the time of death, the surviving adult may miss a breeding season before they are able to secure a bond with a new mate. The same type of divorce may occur if one bird in a pair is gravely injured and unable to breed.
• Upgrading Mates: Birds are always interested in mates that give them the best chance for the strongest, healthiest offspring, and they may divorce an existing mate if a new and better partner comes along. A competitive adult may approach a mated pair and attempt to lure one of the partners into a new bond, either through courtship or fighting. It is in the birds' best interest to mate with the strongest partners, and pair bonds can be broken when a bond with a better mate can be created.
• Climate Change: A change in environmental conditions can turn a once undesirable mate into a more appealing prospect, therefore changing pair bonds through bird divorces. For example, a bird with slightly different plumage that provides better camouflage during a drought period may be seen as more desirable than in years when local vegetation is lush, and could upgrade mates during that period.

While birds have many reasons for changing mates, it is important to realize that the idea of "divorce" is not negative to birds as it can be to humans. For birds, the greater loyalty lies toward their future offspring and choosing a mate that can help create stronger chicks, even if that means switching mates in order to have a better chance of breeding success.

Remarriage

After a divorce, birds will "remarry" to try and continue procreating with each new breeding season. While less desirable birds – those that are unhealthy, show unusual coloration such as leucistic plumage or those that are smaller or less robust than their competition – may find it difficult to secure a strong, lasting pair bond, the instinctive urge to pass on one's genome to the next generation never ends, and birds will always seek to mate with the best possible partner to ensure their species continues.

Photo – Swan Family © monkeywing