The Timing of Pair Formation in Harlequin Ducks.

The timing of pair formation varies within and among species of ducks. In this study we documented the chronology of pair formation in a population of wintering Harlequin Ducks (Histrionicus histrionicus) in southwestern British Columbia. Harlequin Ducks began forming pair bonds in October and over half of the females were paired by December. This timing is much earlier than other ducks of similar size. A segment of this population was individually marked, and we documented the reunion of mates in subsequent years. In all cases where both members of the pair returned to their wintering grounds they reunited in the fall. New pair bonds, involving young males and females, were formed in the spring. We suggest that pair reunion in this species reduces the costs of courtship and pair bond maintenance and allows males to pair early in the nonbreeding season, compared to other species.