Although a breeding population of black-browed albatrosses has been known to exist at the Ildefonso Archipelago, Chile, for > 90 years the population has never been censused using scientifically defendable methods. To estimate population size, and examine the accuracy and practicality of various census methods, the population was censused in the 2002/03 breeding season using a) ground-truthed aerial photography, b) yacht-based photography, c) ground counts, d) quadrat sampling and e) point-distance sampling. Compared to ground-truthed aerial photography (judged the most accurate) yacht-based photography underestimated population size by 55%, ground counts by 13%, quadrat sampling by 11% and point-distance sampling by 9%. Ground-truthed air photography revealed that in the 2002/03 breeding season 47,000 pairs of black-browed albatrosses bred at the Ildefonso archipelago. After the Falkland Islands/Malvinas, South Georgia and Diego Ramirez, the Ildefonso Archipelago holds the fourth largest population of black-browed albatrosses in the world.
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