Things are rarely as they appear. For birds in which there is little differentiation in outward appearances, it is easy to assume that two birds sitting on a nest are a male-female pair. But when biologists start testing blood for sex identification, it reveals an altogether different story for the Laysan albatross. Some of these findings have made their way into the news lately.
This morning at the World Seabird Conference, biologist Dr. Lindsay Young presented her research from eight years of studying female-female pairings of the Laysan albatross in Hawaii. Her driving interest was to figure out if these birds are genetically wired to prefer their own sex or were they simply expressing what scientists call a “behavioral flexibility” because of a skewed male-female ratio. There are way more female birds than male ones. It is the old question – nature or nurture? The answer, in part, depended on finding out how the females fared in their parenting and survival, and if the females were willing to switch their mates to male should the opportunity present itself. She did her best to steer clear of the “dicey territory” that this type of investigation inherently drifts into, given human inclination to anthropomorphize, at least when it comes in handy for their own preconceived notions of “normality.”
First she turned to the genetic fathers of the offspring, for the females were sitting on viable eggs. These males often had other established mates of their own (albatross often stay in supposedly monogamous pairs) and took the extra females in both consensual and forced – often when the female’s other protective female partner was absent – copulations. Both females would take turns incubating the egg, an adjustment for the birds, who usually have the male incubate for the first three weeks before the female takes over. The juggling throws the females off a bit. Some get a bit antsy and leave their brooding duties, to the detriment of the egg. Something about this switch also causes energy stress to the females that results in failed nests early on (and the need for females to take a breeding sabbatical the next year).
But if the egg survived past that initial stage, the chick had just as much likelihood of making it to its first flight as the offspring of male-female pairs. Two moms, ultimately, did just fine.
As for making a switch back to hetero pairing, it did happen, but interestingly, seemed more likely to happen if the female-female pairing had successfully produced an offspring.
Yes, Young concluded, it is behavioral, a plasticity of pairing that allows for reproduction even when there are not enough males to go around in the conventional arrangement. Yet if the albatrosses weren’t adopting this strategy, the population would not be growing but staying steady or even declining. It’s physically hard on the females, but it’s good for colony health, and what’s good for the colony is good for the Laysan albatross. Overall, these all-female pairs are responsible for raising a fifth of the colony’s chicks.