Sunday, May 21, 2006

Following Nesting Brandt's Cormorants

Like many of the seabird species, Brandt's Cormorants are well into their nesting season. These large foot propelled diving birds feed on a variety of fishes and nest in dense colonies in some of the island's flat areas. Breeding populations are up this year in many areas, and most birds are currently incubating eggs. Male cormorants gather nesting material from native vegetation and then display for females, showing off their bright blue gular pouches.

Our Brandt's Cormorant studies, like much of our seabird research, involve following how individuals survive and reproduce throughout their lives. We do this by banding birds as chicks with metal and color bands like the ones shown here. The numbers and letters provide a "name tag" we can use to follow the same cormorants every year throughout their lives, which can last over 20 years. To do this we resight bands and birds at their nest sites through a telescope from an observation blind above our main study colony. This can be challenging, imagine reading the numbers on the metal band above on a bird 200 feet away through a telescope. It is a task that requires a lot of patience!

Currently, we are following over 100 nests of breeding banded birds in our main study colony. Here is a map of one of the areas. The numbers mark nest sites of followed birds. While we will obtain breeding success information on all nests, the blue numbers mark nests we are sure to check at least every 5 days, to gain valuable information on the timing of egg laying and chick hatching. This is long tedious work, that requires many hours spent watching cormorants on their nests, often waiting long periods to see into their nests and confirm their bands. However, the rewards are great, as the information gathered from individual birds allows us to assess the variation in survival and reproduction between birds of known age and experience. This additional layer of data helps to improve our ability to examine how the breeding activities of seabirds can reflect changes in the ocean environment. Its definitely something to think about as you're sitting in a cold blind on a hilltop, waiting for your cormorants to stand up....