Saturday, October 18, 2008

Cassin's Auklets

Tonight a bunch of Cassin's Auklets invaded the island. These small, softball sized seabirds spend most of their time out in the ocean, but do come to land occasionally. Usually it's during the breeding season when they come to the island, for obvious reasons. Their breeding season runs from about April to August. They bring food to their chicks at night because of all the Western Gulls on the island at this time. The Western Gulls are pretty vicious and will peck at and kill anything that goes near it's nest. So under the cover of darkness the auklet's fly in and do their best to avoid any gulls. Since it's not the breeding season you wouldn't expect the auklets to come to the island, but every so often, usually on cloudy or moonless nights they land and start "singing." Tonight was one of those nights. Their song is a kind of screeching, squeaky door sound. Really quite bizarre (see video below for sound). When out to sea they feed on fish and krill (a shrimp-like animal) by diving. Since they are evolved to swim and dive, their feet are set way back on their bodies, just like loons. This fact makes them pretty awkward on land. Add to that the fact that they're flight is a bit out of control, seeing as usually they just need to go straight and fast over the open ocean. This results in some fun for us biologists. You can go out with a headlamp, spot these guys and catch them if you are quick enough. It does have it's dangers though. While walking up the lighthouse path, birds scared by our presence take off, sometimes straight at you and occasionally run into you. Keeps you on your toes.

PRBO has been studying Cassin's Auklet populations on the island for many years. Unfortunately, their breeding population has been on the decline. A couple years ago they had complete nesting failure, meaning not one chick successfully fledged. They believe it was related to the fact that their main food source, krill, were not very abundant that year. The krill weren't abundant because the usual ocean upwelling (cold water brought to the surface by winds) wasn't as strong. The reason for that is up for debate, but could be related to climate change. Since these birds are fairly long lived (~20 years), one bad year won't threaten the entire population, but it is still cause for concern. Hopefully, we'll start seeing more success.

1 comment:

Andrew said...

Sweet!! I would love to have witnessed that sight. I hope you caught some.