Fidelity at the frontier: divorce and dispersal in a newly colonized raptor population

• Published in: Animal behaviour 2014-07, Vol.93, p.59-68
• Main Authors: Martin, R.O., Koeslag, A., Curtis, O., Amar, A.
• Format: Article
• Language: English
• Subjects: Accipiter melanoleucus; Animal behavior; better option hypothesis; Birds; black sparrowhawk; breeding dispersal; colonization; Dispersal; Hypotheses; Hypothesis testing; incompatibility hypothesis; partner fidelity; population growth; range expansion; range margin
• ISSN: 0003-3472; 1095-8282
• DOI: 10.1016/j.anbehav.2014.04.018

Divorce and breeding dispersal are key life history parameters that can be influenced by, and in turn have an influence on, the structure of populations. Variation in these parameters in small populations can potentially play an important role in the colonization of new areas, yet to date there has been little empirical investigation of this process. We studied the circumstances surrounding divorce in a newly established population of black sparrowhawks, Accipiter melanoleucus, on the Cape Peninsula, South Africa over an 11-year period between 2001 and 2012. Divorce was more likely following breeding failure and individuals that divorced and dispersed improved their subsequent breeding success. Territory quality had no influence on the frequency of divorce, and dispersing individuals did not move to territories of higher quality. During the study period the population size increased approximately three-fold, but because the range expanded, nest density did not increase significantly. In the first half of the study (2001–2006), divorce rates were low (4%) compared with rates previously reported for raptors and other birds. In the latter half (2007–2012) divorce rates were 14%. Although there was weak support for a difference in divorce rates between these two periods there was no evidence that divorce rates varied with population size or nesting density. Our results suggest that adaptive hypotheses (‘better option’ or ‘incompatibility’) best explain patterns of divorce in this expanding population and that potential feedbacks between divorce and population processes were unlikely to have played an important role during the growth of this recently established population. •We investigated divorce and dispersal decisions in an expanding raptor population.•We collected data on decisions following 125 breeding attempts made over 12 years.•Improvements in breeding success following dispersal not linked to territory quality.•Low rates of divorce during earlier stages of colonization.•No evidence that colonization assisted by density-dependent mating decisions.