Young and inexperienced Arctic seabird couples are the most likely in their colonies to 鈥渄ivorce鈥�, despite seeming to get no immediate benefits from doing so.
Like many other seabirds, (Uria lomvia) are socially monogamous: they pair up for life and reunite at the same nesting site each year to mate and work together to raise their chicks. This makes it important to find the right partner. Being out of sync when swapping places on the cliff edge can quickly end with the egg plummeting into the freezing water below. Some couples don鈥檛 work well together, with 9 per cent of thick-billed murre couples divorcing every year.
To investigate the drivers and outcomes of these separations, at McGill University, Canada, and her colleagues studied 24 years of data covering 145 unique breeding pairs from Nunavut, Canada鈥檚 northernmost territory.
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The researchers found that, like in other monogamous birds, unsuccessful breeding is the main grounds for divorce in thick-billed murres. Young, inexperienced couples are using dangerous ledges to nest on, increasing the chances of their chicks dying before fledging. 鈥淏reeding experience and nesting site are probably key factors in divorcing in long-lived seabirds,鈥� says Gousy-Leblanc.
But she was surprised to find that recoupled birds have fewer fledglings in the year following divorce than pairs that stayed together, and they don鈥檛 find a better nesting site. 鈥淣ormally, if you decide to change partners it is for better, not for worse,鈥� says Gousy-Leblanc. Instead, birds who stay with their partner succeed in fledging approximately 50 per cent of their chicks, but divorcees only succeed about 10 per cent of the time.
at Woods Hole Oceanographic Institution in Massachusetts says that this finding will force a rethink on the real benefits of divorce in seabirds. Improved fledging success may not be the immediate perk of divorcing.
Sun says the birds may be hedging their bets by divorcing. 鈥淚ndividuals may change partners simply because they want more genetic diversity in their offspring,鈥� she says.
Gousy-Leblanc and her colleagues also found that the new partners of divorcees are no more experienced than their exes, supporting the idea that separation isn鈥檛 always down to better options. It may be that some divorces are forced, or that younger birds are worse at selecting a compatible mate.
The low fledging success rates following divorce may be a case of 鈥渇irst-year syndrome鈥�, says Sun, where the newly recoupled birds 鈥渘eed time to fine-tune their behaviour鈥� with one another.
Looking at the outcomes of divorce over a longer period would allow this to be tested, says Gousy-Leblanc. It may be that new couples just need to stick it out for a bit longer.
Animal Behaviour
