Fitness consequences of long-term pair bonds in barnacle geese: monogamy in the extreme

In barnacle geese Branta leucopsis, pair-bond members generally remain toge ther every day, each year, often for life. Geese that maintain long-lasting pair bonds during their lifetime produce more offspring than those with sh orter pair durations. This result was shown while statistically controlling for the birds' life span and the proportion of life spent without a partne r, two variables that also influence lifetime reproductive success. I argue that continuous partnerships are maintained in highly competitive goose so cieties because of the constant need for female-male cooperation, without w hich acquiring adequate resources for reproduction would be prohibitive for both sexes.