Mariana Swiftlets recorded per
party hr on the Honolulu Christmas Count, 1944- 2014 (see Count
Page), indicating expansion of numbers after
introduction in the 1960s. Fluctuations likely result from variation in
foraging areas on count day. Graphs of Christmas Count data developed as part
of The Birds of the Hawaiian Islands: Occurrence, History, Distribution, and
Status by Robert L. Pyle and Peter Pyle http://hbs.bishopmuseum.org/birds/rlp-monograph/