Intra-Island Variation in the 'Elepaio on the Island of Hawai'i

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Abstract
The Elepaio (C. sandwichensis) exhibits great variation in plumage color on the Island of Hawaii. Analysis of specimens from localities throughout the island reveals that the variation is geographically based, and that 3 sspp. can be distinguished: C. s. bryani, a pale form found at high elevation on the southwestern slopes of Mauna Kea; C. s. ridgwayi, a dark form found in wet windward forests; and C. s. sandwichensis, an intermediate form found in forests of the Kona region. Several zones of primary intergradation and one of possibly secondary intergradation occur, but appear to be narrow. C. s. sclateri of Kauai and C. s. gayi of Oahu exhibit no similar intra-island variation. Variation among the Hawaii subspecies probably evolved in response to local variation in rainfall, and follows the predictions of Gloger''s Rule, but the selective forces involved are obscure.

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