to the Oregon border. Three 1979 surveys were 

 flown from a high-wing Cessna 182 or 210 and 

 the remaining six were flown in U.S. Coast Guard 

 helicopters. In 1980 we conducted five aerial 

 surveys. Four of these were made in a high-wing 

 Cessna 172, and one was flown from a U.S. 

 Coast Guard helicopter. Photographs of seabird 

 colonies were taken either through the open 

 window of a plane or open door of a helicopter. 

 Both color slides (ASA 64, 200, and 400) and 

 black-and-white film (ASA 132 and 400) were 

 exposed in a 35-millimeter camera equipped with 

 either a 70- to 2 10- millimeter zoom lens or a 

 300-millimeter lens. Flight altitudes varied, but 

 most photographs were taken from an altitude 

 between 150 and 250 meters. We were careful 

 not to flush nesting seabirds or marine mammals 

 by flying too low, and we are satisfied that we 

 caused no disturbances during our aerial surveys. 



Seabirds flush readily from their nests 

 when "buzzed" by low-flying aircraft, therefore it 

 is imperative to fly high enough to avoid disturbing 

 them. For the study area from Point Conception 

 to the Oregon border, we recommend a flight 

 altitude of 200 meters or higher. Common Murres 

 in coastal California nest primarily on the flat 

 tops of islands and, possibly, excluding murres 

 nesting on the Farallon Islands, appear somewhat 

 accustomed to low-flying aircraft. Murres in 

 other regions also frequently nest on cliff faces 

 where more care is needed to avoid flushing birds. 

 Helicopters are more disturbing to birds than 

 fixed-wing aircraft, and should maintain a higher 

 altitude. Telephoto lenses, especially zoom lenses 

 in the 70- to 300-millimeter range, are needed to 

 photograph seabird colonies well enough to make 

 accurate counts later from the photos. Rapid 

 shutter speeds of 1/1,000 second or 1/500 second 

 are important to dampen vibrations. We usually 

 used high speed color slide film because it enabled 

 us to shoot at rapid shutter speeds even on cloudy 

 days. 



Most counts of Brandt's Cormorants and 

 Common Murres were made from projected 

 slides. In the case of Brandt's Cormorants, we 

 counted individual nests and determined the 

 number of breeding birds by multiplying the 

 number of nests by two. Brandt's Cormorant 

 nests are conspicuous and easy to count from 

 aerial photographs. Our estimates for this species 

 are probably as accurate as any estimates included 

 in this catalog. Numbers of Common Murres 

 were estimated either by counting individual birds 

 on slides or by blocking off groups of 10's, 50's, 

 or 100's, depending on the sizes of colonies and 



the quality of our photographs. 



Time of day and of year influence the 

 number of Common Murres at a colony. The 

 greatest numbers of murres are seen in early 

 morning, before the egg-laying season. Both 

 members of each breeding pair, as well as non- 

 breeding birds, are presumably present on the 

 colony at this time. Later in the season, during 

 the incubation and nestling stages of nesting, the 

 number of murres on a colony at any one time 

 decreases because one member of each pair is 

 frequently at sea. Most of our surveys were flown 

 during the incubation and nestling stages, near 

 mid-day. A correction factor must be added to 

 the murre count to account for this variability in 

 colony attendance. Addition of a correction 

 factor to our counts of murres from photographs 

 should result in an adjusted estimate of the 

 breeding population which is more representative 

 than the straight count from the photographs. 

 We used a factor of two-thirds, as proposed by 

 Ainley (1976). A factor of two-thirds implies 

 that fewer than half of the birds are away from 

 the colony at the time of a survey, an assumption 

 which we feel is reasonable. To obtain the 

 adjusted total, we multiplied the count obtained 

 from the photographs by 1.67. Our estimates of 

 murre numbers included in this catalog are only 

 the adjusted totals. The actual numbers of 

 murres counted from slides, which may be the 

 most useful numbers for later historical compari- 

 sons, can be obtained by dividing the number 

 listed in this catalog by 1 .67. 



Brandt's Cormorants and Common Murres were 

 censused primarily by counts made from aerial 

 photographs. Here, Brandt's Cormorant nests 

 are shown at Piedras Blancas (477 00 7). Photo 

 by Jay Nelson 



10 



