July 18, 2024
The weather on San Miguel Island can be unpredictable. Censuses conducted for population abundance estimates for California sea lions have traditionally been done by taking photo images from an airplane or by walking through the rookery and counting pups using a tally counter. Unfortunately, the latter method can disturb the seals and affect our counts. Due to the foggy conditions we experienced last week, we did not think the plane would be an option to conduct the pup census this year. So, we started the census using drones, which can be flown at a lower altitude than a plane and is less disruptive than hiking around the colony. This is the way science is done at remote locations; there is a need to be flexible in your plans!
We flew drone missions last weekend, after which the weather changed to clear blue skies during the day. Our colleagues, Sarah Chinn and Millie Brower, were able to finish the census in an airplane in a few hours on July 15.
That date is special to me because it is my birth date. Chris’s birthday was on July 16. We had different but equally delicious desserts – brownies and cake – on our respective birth dates, prepared by our dear friend, Heather.
While we were having a nice weather window, Heather was able to leave the island to return to work in Seattle. A friend and colleague, Jim Tietz of Point Blue Conservation Science, has joined us for the remainder of our time on the island this summer. He is an excellent birder.
Jim, Chris, and I have been doing a mortality survey of dead California sea lion and northern fur seal pups. These counts along with the live pup counts obtained from the aerial censuses allow us to get an idea of total pup production, which in turn allows us to estimate the population abundance of California sea lions and northern fur seals this year. Did I mention that the wind and fog returned after our nice travel day? Alas.
One thing that I noticed almost immediately after arriving on the island this summer was that something was going on with the Western Gulls. San Miguel Island is a rookery for them as well. I am used to them trying to hit or poop on us. We also usually see a lot more of them. Western Gull reproduction has been nearly zero this year on San Miguel. From a high sand dune, we counted ~500 individuals at Point Bennett, but only encountered four chicks while passing through their colonies. After talking with Point Blue Conservation Science colleagues on the Farallon Islands National Wildlife Refuge, we learned that the Western Gulls there are also experiencing poor reproduction and low colony attendance. Farallon Island biologists are uncertain why the gulls are failing to reproduce, but they suspect there is a lack of accessible pelagic foods such as anchovies and squid.
Brandt’s Cormorants and Brown Pelicans are also in low attendance at San Miguel Island with only about 50 cormorants and 5 pelicans seen on or near their colonies at Point Bennett. Again, Point Blue biologists on the Farallon Islands reported low colony attendance and poor reproduction for the Brandt’s Cormorants.
Thank you for tuning in! Watch for our next blog coming soon.
Field work at San Miguel Island is permissible under Channel Islands National Park Service Permit # CHIS-2022-SCI-0021.
