Los Farallones

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

Auklet Class of 2020

There are approximately 500 wooden boxes (shown with a rock on top in the photo) scattered around on Southeast Farallon Island that are used as nesting habitat by Cassin’s auklets, the small seabird I’m holding in the photo. These boxes have been checked every year since 1982, where pairs of auklets using each box can be identified by a uniquely numbered metal band placed on the right leg. Some of the auklets that recruit into these boxes were banded as chicks, allowing us to track age-specific patterns of behavior, reproduction, and mortality. The bird in my hand is the oldest known-age individual currently breeding in the followed nest boxes, a female based on bill depth measurements with the band # 131319997. She received this band as a fledgling back in 2001, first started breeding at age 3, and has produced 16 offspring with 3 different mates so far in her long life. We discovered her incubating a fresh new egg this year in box 212 with a new mate. At age 19, she is nearing the end of her life, and time will tell whether she manages to survive this winter to breed again next year.


This figure shows all of the known-age birds breeding in the boxed population this year. Dark grey squares at the top represent the hatch year of each bird (band #’s along the x-axis), gaps are years where they were not detected, and colors show the type of breeding attempt numbered by how many chicks were fledged each year. Cassin’s auklets lay a single egg per clutch (blue squares), will relay if the initial attempt fails (yellow), and occasionally double brood (lay another egg) after they fledge their first chick (pink). Auklets can recruit as early as age 2 and live to be up to 23 years old. Most birds don’t live into old age, but a few like 131319997 surpass all expectations.

By Mike Johns