Feathered friends opt for same-sex nests

The Laysan albatross ‘Wisdom’ is the world’s oldest known wild bird. Picture: John Klavitter

Wisdom, a Laysan albatross, has reached the age of 68. According to the US Fish and Wildlife Service, the world’s oldest known bird arrived back at her breeding colony on Midway Atoll in November. She had laid an egg by December 3rd. This season’s chick may be her 37th.

Midway, a 6km2 coral island near Hawaii, is named for its location, half way longitudinally around the world from Greenwich. A crucial sea-battle was fought there during the 2nd World War; one American and four Japanese aircraft carriers were sunk. The albatross colony on the atoll, with over a million pairs, is the largest in the world.

Biologist Chandler Robbins ringed Wisdom in 1956 when she was at least five years old. Returning to Midway in 2002, she has nested almost every year since. The notorious tsunami of March 2011 killed over 100,000 seabirds there, but Wisdom survived. She has outlived Robbins; he died in 2017, aged 98.

The Laysan is one of 18 albatross species. Devoted monogamists, pairs stay together until death does them part. Only if its partner dies will an albatross remarry, or so it was assumed. Then Lindsay Young and Eric VanderWerf, studying birds at Hawaii’s Oahu Island, made a surprising discovery. Albatross domestic arrangements, they found, are more flexible than was previously thought.

Male albatrosses target hooked baits, trailed on long lines behind fishing boats. Females are less inclined to do so. Trapped underwater, more males than females drown, which may explain why fewer turn up at breeding colonies each year. In 2008, the sex ratio at Oahu was 41 males to 59 females.

The shortage of potential male partners doesn’t prevent Oahu albatross spinsters from breeding, however; they form same-sex partnerships and begin nesting together. A female gets herself pregnant through casual encounters with, mostly-paired, males. When both same-sex birds lay eggs, there’s a problem. Albatrosses can raise only one chick at a time, so the extra egg is discarded.

Female-only nests, the researchers found, are less successful than those of heterosexual pairs. The hatching rate for female-female unions was just 41%, compared to 87% for ‘straight’ ones. Fledging rates, however, were similar; 75% compared to 77%. The overall success rate of same-sex pairs, at 31%, was less than half the heterosexual norm of 67%. This may be a poor return on the effort the birds put in, but it is preferable to not nesting at all. There’s also an element of Russian roulette. Discarding the second egg means that each female has only a fifty-fifty chance of passing on her genes. However, DNA analysis showed that, when partners nested for several years, each parent produced at least one chick.

But female-only marriages are less stable. A spouse may switch to a male partner at the beginning of a subsequent season. Successful ones are prone to doing so; birds failing to produce chicks are more likely to remain in female-female relationships. One lasted 19 years.

Wisdom has had several partners during her long life. Her current one, a male, has been with her since 2006. It’s not known if any of her past liaisons were same-sex ones.

This year’s egg should hatch after 65 days incubation. All going well, the chick will fledge about 160 days later and breed for the first time when seven or eight years old.

- Lindsay Young et al. Successful same-sex pairing in Laysan albatross. The Royal Society Biology Letters. 2008.

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