2024-10-072024-10-072024-10-07P. Marcos Gorresen, Richard J. Camp, and Eben H. Paxton. 2024. Distribution and trends of endemic Hawaiian waterbirds, 1986–2023. Hawai‘i Cooperative Studies Unit Technical Report HCSU-113. University of Hawai‘i at Hilo. 40 pages. http://hdl.handle.net/10790/5396https://hdl.handle.net/10790/5396This study updates the status assessment of four endemic endangered Hawaiian waterbird species—ae‘o (Hawaiian stilt, Himantopus mexicanus knudseni), ‘alae ke‘oke‘o (Hawaiian coot, Fulica alai), ‘alae ‘ula (Hawaiian gallinule, Gallinula galeata sandvicensis), and koloa maoli (Hawaiian duck, Anas wyvilliana)—from 1986 to 2016 by incorporating new data from 2017–2023. State-space models, which account for biological and sampling variation, were fitted to estimate population sizes and trends from both core and non-core wetland survey sites. Long-term trends (1986–2023) largely show increasing populations for all four species, but recent short-term trajectories (2013–2023) are to a greater degree than previous analyses, predominantly negative, indicating accentuated declines in some island populations. Summer counts have declined relative to winter counts over the 38-year period, indicating potential changes in habitat availability and breeding patterns due to shifting rainfall patterns. Although negative trends were apparent in some non-core wetlands, our study underscores the importance of both core and non-core wetlands for waterbird populations.Technical Report41 pageshttp://rightsstatements.org/vocab/NoC-NC/1.0/ae‘o‘alae ke‘oke‘o‘alae ‘ulaAnas wyvillianaendemic Hawaiian waterbirdFulica alaiGallinula galeata sandvicensisHawaiian cootHawaiian duckHawaiian gallinuleHawaiian stiltHimantopus mexicanus knudsenikoloa maolipopulation trendswetlands