Why Do Birds Divorce?

Natural History, Oct, 2000 by Richard Milner

In most of Europe, blue tits (Parus caeruleus), relatives of North American chikadees, form strong, persistent pair bonds that last through many breeding seasons. But blue tit females studied on the Mediterranean island of Corsica abandon a previous mate 59 percent of the time. What causes such a high rate of "divorce" among these Corsican blue tits?

According to ornithologist Jacques Blondel and colleagues at France's National Center for Scientific Research, the divorce rate is determined by large variations in the quality of breeding sites on the island.

While males cling to the old homestead, many females simply move to habitats where vegetation is denser, caterpillars (their staple food) are more abundant, and parasites are less profuse. So when a Corsican female leaves her mate, she does so to find a better home in a nicer neighborhood with better dining opportunities. ("High Divorce Rates in Corsican Blue Tits: How to Choose a Better Option in a Harsh Environment," Oikos 89, 2000)