Los Farallones

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

A Migration North

Estimates of the migration paths and overwintering locations of Pigeon Guillemots tagged on Southeast Farallon Island in the summer of 2017. Each color represents a single individual.

The month of July often brings reflection on the events that have unfolded throughout the seabird season. Here on the Farallon Islands National Wildlife Refuge, we’ve documented the earliest eggs on record, witnessed extremely high occupancy and chick success, an now wait with anticipation as some fully-feathered chicks begin to exercise their new flight feathers for the first time. Just as we start to consider our own uncertainties once we leave the island, these fledglings will also soon depart the Farallones to begin the task of learning to make a living in a complex and dynamic world. Some species, like the Cassin’s Auklet, remain relatively close to the islands year-round, taking advantage of productive waters along the Central California Coast. Other species, like the Pigeon Guillemot, head out on a longer migration north to areas protected from the high seas and intense storms of winter.

Point Blue has been deploying small archival light recording tags, called geolocators, on Pigeon Guillemots since 2017. These light-level data, along with some spatial and movement masks, can be used to estimate latitude and longitude every 12 hours for up to 2 years, simply based on the timing and length of daylight experienced by each bird. It has long been assumed that Pigeon Guillemots from the Farallones move north following the breeding season, based on counts of individuals and a few band recoveries. Data retrieved from birds that are recaptured (visualized in the figure on the right) not only provide confirmation of this migration, but add new information on the coordination, timing, and specific overwintering areas used in British Columbia and Southeast Alaska. These new data will also allow us to examine the potential risks these birds face during the non-breeding season, particularly the threat of exposure to oil spills and climate-driven environmental change.

By Mike Johns

Pigeon Guillemot carrying a geolocator tag over a green color band on its left leg. Photo by Theresa Rizza / Point Blue
Collection of recovered geolocators ready to calibrate out in the sun. The barnacle growing on one is an indication of how much time these birds spend on the water.