Los Farallones

Dispatches from Point Blue’s field station on the Farallon Islands National Wildlife Refuge

The Birds Have Arrived!

The seabird breeding season on the Farallons has begun! We’ve been watching Common Murres, Brandt’s Cormorants, Cassin’s Auklets, and Pigeon Guillemots arrive to the islands, as they do each spring/summer season.

Common Murres at nesting sites

The first birds to start nesting were the Cassin’s Auklets. These are cute little seabirds that hang out at night on the island (safety from the cover of darkness) and spend the day at sea or at their nest. 

Their nests are burrows in the ground that usually consist of a long tunnel with a turn right before the actual nest. Cassin’s Auklets will also nest in crevices in rocky habitat. We want to be able to collect data on these birds that breed on the Farallons as a way to monitor the health of the population. Parameters such as reproductive success, timing of breeding, and chick growth and development can be used to accomplish this, and this data can easily be collected by simulating the nest environment using nest boxes. We make the nest boxes out of plywood and construct a tunnel using PVC pipe. The top of the box has a removable lid that allows us to see inside the nest and collect the data.

Cassin’s Auklet Nest Box
We are able to look at both mates of a nest because Cassin’s Auklets take turns incubating the egg each day. In most cases, if you find a bird in a box one day, the next day you should find its mate. Checking a nest box is an interesting task. First you must completely block the entrance to the tunnel using your foot or knee so that the bird can’t escape. At the same time you must be able to bend over and peer under the box lid. It’s a bit like doing yoga. If a bird is present, you need to grab it in one swift movement to avoid hurting the egg or the bird. A biologist here described this as being not unlike an alien abduction. Imagine a bright light as the roof of your home opens up, you are snatched up, measurements are taken and you’re returned with a metal band on your ankle. I try to keep this perspective in mind when I’m holding a Cassin’s and its beak is clamped down on my fingers or its claws have lodged themselves under my cuticle. I also know that the collection of this data will aid in monitoring these birds.
Nest box check

We can track specific individuals in a population by putting a metal band around their leg with a unique number for each bird. We know the ages of birds that we banded as chicks, and we always check band numbers to see if a bird we find is one of known age. We also band birds that are mates of known age birds.

Banding a Cassin’s Auklet
New bands

When known age individuals are found, both they and their mates have condition data recorded. This includes measuring the bill depth (used to sex the individual), wing cord length, weight, and egg size.

Measuring the length of an egg
Measuring the wing cord of a Cassin’s Auklet
Weighing the bird in a bag
Bird in a bag

We have over 400 boxes that get checked every 15 days as the breeding season progresses. Our first check yielded about 70 birds and our second yielded about 150 additional birds! We continue to check the boxes without birds in them through the summer to see if any new Cassin’s Auklets decide to move in. Each time I lift the lid of a nest box is like a surprise. Will there be a Cassin’s Auklet? Will there be another species of bird? Will there be an egg? Two eggs?? Fortunately, there are over 400 surprises out there waiting for us.