In addition to the foraging behavior, chick growth, and food availablity projects we’ve talked about so far in the blog, we’re also monitoring the stress levels of the birds. We do this by taking blood samples to look for a stress hormone called corticosteroid, or as we like to say, cort. Cort is hormone that humans also have and we can use it to see how the foraging conditions affect the birds’ stress.
First you have to catch the birds. We do this using the noose carpets that we worked so hard to make. We spread these nets with little loops of fishing line tied on over the birds’ favorite rocks and anchor the edges with cord.
The hardest part is sitting in the cold waiting for them to catch. Sometimes a little auk will hover in the air for a second above the carpted rock and then turn away to avoid it. Despite all of the birds that manage to walk along the carpets without getting caught, eventually things get crazy. Since little auks are very social, once one bird lands on a carpet, two or three friends might come to join it. Sooner or later a bird will get a noose or two or three around its leg.
Cort levels start to rise about 3 to 5 minutes after capture. Since we want to measure their normal stress levels and not the stress of capture, the race is on to retrieve the bird as soon as possible. Derek and I take turns running up the hillside to get the bird. First we start our stop watches then we spring into action. When we arrive at the bird we hold it in one hand and free it with the other. Panting, we deliver our prized catch to Nina. (Sometimes this job makes me feel like a bird dog).
All of the cort samples have to be finished in 3 minutes from when the bird was caught. Laurel keeps track of all the capillary tubes and vials and labels. In addition to the sample for cort, we take a few drops to genetically sex the bird since the two sexes of our little black-and-white bird look identical. A third sample gets “shmeared” on a slide so our Polish collegues can count white blood cells.
We have “done cort” three times: first in late incubation, then in early chick rearing and finally in mid chick rearing. During late incubation, we checked for a brood patch, the bare spot where the parent put the egg directly against it’s skin to keep it warm.
During chick rearing we also use the opportunity to collect diet samples. Little auks return from the sea with meals of copepods to feed their chicks. They carry the copepods below their tongue in a spot called the gular pouch. One of their defenses from predators is to spit out the copepods so sometime we collect only partial samples. We can remove the diet sample by gently opening the bird’s mouth, massaging the gular pouch and scooping out the copepods with a modified Polish toothpick. Since the parents make many foraging trips per day, losing one meal doesn’t hurt the chick.
The final step is banding and measuring the bird to keep track of it in the future.
We also use magic marker on the chests of some of the birds so we can watch them during the 48 hr feeding watch. It’s so nice to see the birds feeding their chicks after we release them!
