The Least Expected
June 3, 2020
People often ask when they learn about our work on the Farallones, “So, how are the bird counts going?”. While counting established long-term index plots is one method we use for tracking population change of ground nesting species like Western Gulls, Brandt’s Cormorants, or Common Murres, determining the number of birds that nest underground is a bit more involved. Over half of the world’s population of Ashy Storm-petrels, a small hand-held size relative of the albatross, use crevices within the rocky talus slopes of the Farallones as prime nesting habitat. Despite a robust local breeding population of many thousands, their nocturnal behavior and discreet nest sites means we almost never see this species, let alone have an opportunity to obtain accurate estimates of their population size. The most effective way to gauge trends in the number of storm-petrels present throughout the breeding season is to set up a long fine-mesh net, play their social calls from a loudspeaker, and record the total number of newly caught and previously banded birds during a three hour netting session. A metric termed catch per unit effort. The video below is a time-lapse of one such netting session. You can hear the calls from the loudspeaker, and see the lights of San Francisco in the background as we extract birds from the net and band them under the red light of our headlamps.
On a good night we can catch over 100 Ashy Storm-petrels, and on a really good night we can catch some unexpected rarities. Curious visitors from far reaching locations that get caught up in the commotion. Fork-tailed Storm-petrels which breed along the coasts of the Pacific Northwest and Alaska are the most common non-island breeder we catch, with the first one documented in 1990. A Tristram’s Storm-petrel, typically found breeding on islands off Japan and in the central Pacific was caught in 2006, and a Wedge-rumped Storm-petrel which breeds off the west coast of South America was captured in 2015. A few weeks ago, we were excited to discover a Least Storm-petrel in the net, a species that only breeds on islands off the west coast of Mexico. This was the second record for the island, as one had previously been captured in 2016. It’s amazing to consider these miniature seabirds, in some cases traveling across entire ocean basins, making a living in seemingly harsh maritime conditions. Working on the Farallones isn’t just about counting birds. Occasionally, after long hours and little sleep, we are lucky enough to have a brief encounter with some true open-ocean wanderers.
By Mike Johns