Winter Movements / by Michael Johns

After several years of geolocator tagging work (see image below), we finally have enough information to begin to paint a better picture of the non-breeding winter distribution of Cassin's auklets from Southeast Farallon Island. At the start of any research project, the most important first step in the analysis process is to visualize the data. The idea behind this visualization was to depict three key environmental characteristics of the auklet's winter habitat in a single plot; sea surface temperature (SST), depth, and distance from island. SST will be used as a proxy for productivity, as colder water in this region is generally associated with nutrient rich upwelling processes, depth to characterize the preferred ocean zone (shallow shelf, steep slope, or deep abyssal plain), and distance from island to explore the possible limits of their dispersal. 

Glancing at this plot, you can see by October birds are fairly spread out between 45°N (dark purple colors - Northern California area) and roughly 33°N (orange colors - Southern California). They are also exposed to quite a range of SST, from 14°C up to nearly 22°C. By late January, all of the birds are relatively close to the island (small bubble size) and experiencing roughly the same SST, before spreading out again in late February, with most birds staying at around 35°N. The 2015-16 season was a particularly warm year for SST, which my explain why only birds in the northern reaches were finding water colder than 14°C. The next step in this exploratory process is to look at auklet movements during the 2016-17 and 2017-18 seasons, which were moderate to average years for SST in the eastern north Pacific. Ultimately, these and possibly additional environmental covariates will be used to model the winter habitat use of Cassin's auklets off the California Coast. 

Note the geolocator tag on the left leg of this Cassin's auklet. Geolocators are devices which record ambient light levels that are later used to estimate latitude and longitude. 

Tagging data courtesy of a partnership between Point Blue Conservation Science and the USFWS. Remotely sensed environmental data were downloaded from the NOAA repository https://coastwatch.pfeg.noaa.gov/erddap. This plot was created in R with the ggplot2 package.