DIVORCE IN GREAT TITS - CHANCE OR CHOICE - AN EXPERIMENTAL APPROACH

I measure divorce rates in great tit (Parus major) pairs in the year following an experimental alteration of their clutch or brood size. I show that pairs with experimentally reduced clutches or broods produce fewer fledglings and have higher divorce rates, while pairs with enlarged clutches or broods raise more fledglings and have lower divorce rates, as compared with control pairs. The manipulation probably influences divorce rates through its effects on reproductive success, and individuals use fledgling production to assess the quality of their breeding situation. Divorce thus results from an active choice and ultimately is a means for individuals to increase future reproductive success. Whether divorce is proximately a result of an avoidance of the previous partner or the previous territory is not clear, although the former seems a more likely alternative.