BRANTA — Matthew A. Hayes
Divorce and extra-pair paternity as alternative mating strategies in monogamous Sandhill Cranes
Institution: University of South Dakota, USA
Supervisors: H Britten, JA Barzen (International Crane Foundation)
Details: MSc 2005 (Completed)
Address: 400 S. Sneve Ave., #4, Sioux Falls, SD 57103, USA (Nov 2005) Email
Subject Keywords: Divorce, extra-pair paternity, monogamy, reproductive success, territory retention
Species Keywords: Sandhill Crane Grus canadensis
Thesis Online online here
The objective of this study was to investigate monogamy in a dense breeding population of banded greater sandhill cranes (Grus canadensis tabida). Over a 13-year period, permanent divorce (17.4%; 12 of 69 pairs) and annual divorce rate (4.8%) were low. Females were less capable of retaining a territory than males following divorce, but no significantly (c2 = 0.818, p<0.4). All females that left a territory acquired a new territory and mate (n=7), whereas males that left a territory were less capable (25%, n=4). Retaining the territory did not increase in reproductive fitness for either sex (Fisher's exact = 0.736, p<0.35). For divorced pairs, reproductive success prior to divorce was not significantly different than pairs that did not divorce (t=0.84, p<0.3). Although nine of 24 cranes increased reproductive success with a new mate, divorcing, in general, did not increase individual reproductive success (paired t=0.92, p<0.25). Following divorce, females had higher reproductive success than males, but not significantly (Fisher's exact = 1.521, p<0.2). Although no one divorce hypothesis best explained all divorces, the 'better option! hypothesis best explained half of the divorces. Most individuals that divorced chose a higher quality territory compared to a higher quality mate. Many females that divorced re-paired with banded individuals that had recently lost a mate. In general, females appeared to be the sex that chose to divorce in sandhill crane pairs.
The presence of extra-pair paternity (EPP) in this population of sandhill cranes was tested using microsatellite markers. The frequency of EPP was measured at 11.1% (5 of 45 chicks). In four chicks, the social male was rejected as the genetic father; in one chick, the social female was rejected as the genetic mother. Two extra-pair chicks were from one pair that has been socially bonded for a minimum 12-year period. The male was rejected as genetic father of both chicks. The other cases of EPP may be authentic infidelity; however it is possible that mate replacement, due to divorce or mate loss, occurred prior to capture. Although the frequency of EPP in this dense population of sandhill cranes is slightly higher than other long-lived perennially monogamous species, it seems to provide a rarely used alternative to monogamy.