When birds choose a mate it often comes down to one thing -- location, location, location. Michael Ellis has this Perspective.
A friend of mine asked if there were any birds that mated for life or did they all just play around. Well, there are local birds that form long-lasting pair bonds of several different kinds. Some—including many corvids, such as ravens and scrub jays—hang out with each other during the entire year, not just at breeding time. The resident Canada geese and the chaparral-dwelling wrentits also have long relationships that can last more than 10 years.
Most songbirds have the same mate every spring, but this has more to do with site fidelity rather than long-term partnership. Males usually arrive early on the breeding site and use songs and displays to define, control, and defend the exact territory they had the previous year. If a female arrives and the same male is there from the previous year, courtship ensues, copulation follows, and both tend to the incubation and raising of young. But if last year’s male has lost his territory, then the new guy will do just fine. So prime real estate, that five-bedroom house in Atherton, is more important than the individual.
However, there is a direct correlation between fitness and the ability to secure a great spot in the forest.
Twelve species of seabirds breed in our region, and most of them mate for life. But again, it’s fidelity to territory, rather than to individuals.
Scientists are discovering through DNA analysis that pair bonding does not necessarily mean complete faithfulness. There is a lot of cheating going on. The proper term for this is “extra pair copulation,” and both males and females do it. This may increase the genetic diversity and therefore the viability of the offspring. But we are far from understanding the complexities of avian sexual relations.