Seasonal species richness of birds on the world’s islands and its geographical correlates Frank A. La Sorte1, Marius Somveille2, Adriaan M. Dokter1 and Eliot T. Miller1 1Cornell Lab of Ornithology, Cornell University, Ithaca, NY 14850 USA 2Centre for Biodiversity and Environment Research, Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, UK The 3,410 islands that contained sufficient occurrence information to estimate survey completeness for at least one season. The island ID number (OBJECTID) and name from Sayre et al. (2019). The number of records and the observed species richness for each island and season (1 = winter, 2 = spring, 3 = summer, 4 = autumn). The richness estimate with the slope, completeness, and ratio values from the survey completeness analysis for each island and season. Island area, distance to the mainland, proximity metric, longitude, latitude, and if the island was selected for analysis.