Divorce in Northern Flickers

Divorce is widespread among species of birds and may either be an adaptive
strategy to secure a better mate or territory or be a non-adaptive result
of a failure to maintain the pairbond. I examined the causes and
consequences for divorce in the Norther Flicker (Colaptes auratus), a
migratory woodpecker with a high annual mortality rate. In a long-term
population study of 1793 breeding pairs over 17 years, the within-season
divorce rate was 4.6% and the between-season divorce rate was 15.5%.
Retained pairs within a season initiated their renest 5 days faster than
divorced birds which had no greater fledgling production, suggesting that
within-season divorce was making the best of a bad job with severe time
constraints. Poor performance in the year prior to divorce was not
strongly associated with divorce and analysis of multiple breeding stages
revealed that divorcing individuals in the subsequent year had later
laying dates, smaller clutches and fewer fledglings than retained pairs
but no better performance than widowed individuals. Analyzing the data
separately by sex showed that neither males nor females benefitted from
divorce. Thus, there is a reproductive cost linked to finding a new
partner per se, but no reproductive advantage associated with divorce. New
mates after divorce were usually not older (not higher quality) than
previous mates, so intrasexual competition was probably not driving
partnership splits. The most plausible explanation seems to be a
"bet-hedging" hypothesis in which birds re-pair rapidly in
spring if their previous mate does not quickly arrive during spring
migration. Divorce in Northern Flickers does not appear to be adaptive and
future studies on arrival and interactions of individuals in spring will
elucidate proximate constraints on relocating the previous partner.