White Terns (Gygis alba) are common in the northwestern Hawaiian Islands, but in the main Hawaiian Islands they are found only on Oahu, where they are listed as threatened by the State of Hawaii. I censused the White Tern population on Oahu from October 2001 to January 2003, and I investigated breeding success and seasonality during monthly visits to four sites. I observed a total of 694 adult White Terns on Oahu, of which approximately 500 (72%) were breeding birds. Active nests were present during all months, but most eggs were laid from January to April (65%), with a peak in egg laying during March (22%). Nest success was 74%, and pairs produced a mean of 0.98 fledglings/year. One pair fledged successive young less than three months apart. The incubation period at one nest was 35 days, and the fledging periods at two nests were 43 and 47 days. The White Tern population on Oahu has increased from a single breeding pair in 1961 to approximately 250 pairs in 2002, a growth rate of 14% per year. White Terns on Oahu exist entirely in urban and suburban areas, and their reproduction is not inhibited by the numerous predators and sources of disturbance.
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