Thirteen Years of Shorebird Monitoring in the Rocky Intertidal Zone
Contributed by Cabrillo National Monument Chief of Natural Resource Science Andrea Compton and Marine Biologist Bonnie Becker
As you explore Cabrillo National Monument’s rocky intertidal area, you might notice National Park Service (NPS) staff or volunteers steadily working their way north to south, from Zones I to II (open to the public) and through Zone III (closed for research and protection purposes), and peering through binoculars with clipboard in hand. The Natural Resource Science (NRS) Division is tracking the wading birds, shorebirds, and gulls that are potentially feeding within the rocky intertidal area. In addition, the number of people using each zone is also counted. Each winter and spring when the tides fall at zero or below during the day, the staff and volunteers conduct this research to detect changes in species over time and to evaluate the relationships between human use and foraging bird species. An hour of survey effort is centered around the low tide.
This research was first initiated in 1990 by Dr. Gary Davis (NPS) and Dr. Jack Engle (UC Santa Barbara) and is associated with the broader tidepool monitoring efforts that occur each fall and spring. In 1996, the responsibilities for this research were transferred to the NRS Division who continues with this now. Shorebird sampling for this winter and spring began in November 2002 and continued through May 2003.
After 13 years of reporting, the data are showing some interesting results. There are 21 species or groups (e.g., terns) that regularly use the rocky intertidal areas. These species are listed below. A total of 43 bird species (27,309 total individuals) total have been recorded. The most common species is the western gull (Larus occidentalis). When considering the possible influence of people, 29,629people have been recorded in Zone I, 8,570 people have been recorded in Zone II, and 2487 (361 after the closure in 1996) people have been recorded in Zone III on a total of 706 days of survey efforts. The relationship between the number of people and the number of birds can be seen in the associated graph that shows a trend of fewer birds using the rocky intertidal area when more people are present.
Some Common Winter Shorebirds at CabrilloNational Monument
Great Blue Heron