This file contains the flight trackline Global Positioning System (GPS) point data from the aerial surveys. Surveys were flown at 60 meters (200 feet) above sea level at 160 kilometers per hour (90 knots) ground speed. The surveys were flown in a high-winged, twin engine Partenavia PN 68 Observer aircraft following methods developed for seabirds by Briggs et al. (1987). GPS points were recorded every five seconds to allow adequate spatial coverage of the trackline (222 meters is traversed every five seconds at the survey speed of 160 kilometers per hour) and to limit the size of the resulting data files. Data was collected using a laptop computer running the program dLOG (R.G. Ford Consulting, Inc.) that allowed us to simultaneously collect coordinates (NAD27 map datum) and sea surface temperature (SST, degrees Celsius [°C]) determined via a belly-mounted, digital infrared radiation pyrometer (Heitronics™ KT19.85; measurement interval = 1 s, response time = 3 ms, emissivity = 0.99). SST values were appended to GPS flight data based on date and time. Observers sat on both sides of the aircraft and scanned the sea surface through bubble windows. Each of two observers counted and identified seabirds and marine mammals occurring within a 50-meter strip on their side of the aircraft for a total maximum strip-width of 100 meters when both observers were surveying simultaneously. At least one observer surveyed at all times, but individual effort was discontinued when glare obscured greater than 25% of an observer's field of view. To ensure that we maintained a strip width of 50 m, we estimated sighting angles from the aircraft to the water using clinometers. Observers rechecked sighting angles with a clinometer several times during each survey. These data are associated with the following publication: Mason, J.W., McChesney, G.J., McIver, W.R., Carter, H.R., Takekawa, J.Y., Golightly, R.T., Ackerman, J.T., Orthmeyer, D.L., Perry, W.M., Yee, J.L. and Pierson, M.O. 2007. At-sea distribution and abundance of seabirds off southern California: a 20-Year comparison. Cooper Ornithological Society, Studies in Avian Biology Vol. 33. References- Briggs, K.T., W.B. Tyler, D.B. Lewis, and D.R. Carlson. 1987. Bird communities at sea off California: 1975–1983. Studies in Avian Biology 11.