It’s no picnic – divorce. Yet the fitness consequences for Seychelles warblers appear to be fairly limited, both in the short and long term.
It can happen: you exchange vows and promise eternal fidelity, only to conclude a year later that your apparently worthless partner needs to be swapped for someone else. On the idyllic Cousin Island in the Indian Ocean, it occurs with some regularity: around 14 per cent of pair bonds among monogamous Seychelles warblers (Acrocephalus sechellensis) proved to have broken down prematurely between 1997 and 2021. Young and old males in particular have little luck in love and divorce most frequently.
So writes Groningen ecologist Frigg Speelman on 31 December in Ecology Letters, analysing data from long-term field studies on the small island in the Seychelles. Because biologists have been meticulously monitoring the small green-brown birds there for 24 years, the long-term effects of marital troubles on individual fitness can be mapped out in relatively good detail.
Of the 1,063 pairs, 149 – around 14 per cent – divorced during that period. Relatively few. By comparison, in roughly 40 per cent of corn bunting partnerships, the birds throw in the towel. Most warblers therefore remain faithful to one another. Wise, since partners who know each other inside out can coordinate parental duties more easily and need to invest relatively little energy in courtship. The longer the pair bond holds and the higher the reproductive success, the lower the probability of divorce.
Young and old males in particular have little luck in love
Among individuals that do divorce, it is above all young females who lose their breeding territory in the process that appear to come off worst. They have lower survival rates than females who retain their breeding territory or never divorce at all.
Although divorce is thus relatively uncommon among Seychelles warblers, a large proportion ultimately end up alone. Of the 1,063 pairs studied, 69 per cent end in widowhood. Fortunately, remarrying is then a perfectly viable option.