I know you count on the SEANET blog to keep a finger on the pulse of all things seabird. Because I bear this mantle of responsibility so solemnly, I spend a lot of time perusing twitter, Facebook, blogs, and all sorts of other sources to keep you informed. Today, I couldn’t choose between two fascinating seabird stories, so you get a bonus, two-for-one deal!
The first story: Male Gannets are from Mars, Female Gannets are from…somewhat farther away?
A new study out this month in Marine Ecology Progress Series investigated sex-specific differences in foraging in Northern Gannets. The researchers utilized both satellite tags (to track a small number of birds) and analysis of blood and feather samples which can reveal what sort of prey the birds have eating, and where they caught it. During the chick-rearing season, they found that hard working gannet moms were traveling substantially farther afield than gannet dads in order to provision the chicks. Once the babies had fledged, the differences disappeared and males and females traveled similar distances to forage. No differences were seen in males and females of less than breeding age, suggesting that providing food to the young is the driver for longer trips, rather than inherent sex differences. Whether females not rearing chicks make longer trips as well is generally difficult to assess since it’s nearly impossible to catch a gannet when it’s not on a nest.
This study is not the first to detect sex differences in foraging distances or strategies; such findings are rather common in the bird literature. But these findings are important. In any scientific study, one of the first questions in study design is “what constitutes a representative population?” What subset of animals will best reflect the reality of the larger group? In this case, it’s clear that males and females must be considered separately, for instance, when governments are debating how to define the boundaries of a marine reserve. A reserve drawn up to meet the foraging needs of male gannets will clearly be inadequate to protect the foraging waters of females with young. And that would be a critical population to target for protection, after all.
The second story: The scent of romance…or incest avoidance?
Storm Petrels are the bloodhounds of the seabird world. While many birds have a rather underdeveloped sense of olfaction, the diminutive storm petrels track their preferred food source largely by smell, and can even be lured alongside birdwatching cruises from great distances by tossing an oily fish slurry onto the surface of the water. So it probably shouldn’t come as much of a surprise that the birds also use smell to choose a mate. The study, just out in Animal Behaviour, used swabs taken from European storm petrels and presented birds with the scent of a close relative, and an unrelated individual, each smelly swab being placed at one end of a Y shaped maze. Reliably, the birds steered clear of the scent of a relative, and chose the route to the exotic smell of an unrelated bird. This kind of inbreeding avoidance is particularly critical in a population where birds come back to nest in the same colony where they hatched, and where mating is generally for life; chances are, your sister or brother is at the colony looking to breed at the same time, and the wrong choice will lead to a lifetime of inbred offspring.
Studies have shown the same smell preference for unrelated individuals in mammals, including humans. Turns out, our sweat reflects the composition of MHC molecules on our cells. These markers are the tiny flags that allow the body to recognize its own cells and attack foreign ones. The more distantly related the individuals, the more likely their MHC molecules are to differ. MHC is one of the markers used to match organ donors with recipients, in fact. Not a surprise to this readership, I’m sure, that we share much in common with a musky-smelling, diminutive seabird.