The kittiwake is a seagull whose mating behavior is basically monogamous. Normally, the birds separate for several months after the completion of one breeding season and reunite at the beginning of the next. Whether or not the birds actually do reunite, though, may be affected by the success of their “relationship” the season before. A total of 769 kittiwake pair-bonds were studied (30) over the course of two breeding seasons; of those 769, some 609 successfully bred during the first season; the remaining 160 were unsuccessful. The following season, 175 of the previously successful pair-bonds “divorced,” as did 100 of the 160 whose prior relationship left something to be desired. Can we conclude that the difference in the two divorce rates (29% and 63%) is statistically significant?

Breeding in Previous Year Successful Unsuccessful Number divorced Number not divorced 175 434 609 29 100 60 160 63 Total Percent divorced