Baird, R.W., S.D. Mahaffy, and J.K. Lerma. 2021. Site fidelity, spatial use, and behavior of dwarf sperm whales in Hawaiian waters: using small-boat surveys, photo-identification, and unmanned aerial systems to study a difficult-to-study species. Marine Mammal Science doi 10.1111/mms.12861. Abstract Dwarf sperm whales (Kogia sima) have been studied rarely at sea. We used photo-identification, boat- and drone-based behavioral observations, and citizen science photo contributions to examine site fidelity, spatial use, and behavior in Hawaiʻi. Sighting rates were highest in island slope (500-1,000 m) waters. Over 40% of photo-identified individuals were linked by association in the same social network. More than half of the very distinctive individuals were seen more than once, and 28.5% were seen in multiple years, with one individual seen 14 times over a 15-year span. Re-sighted individuals and those in the main cluster of the social network were found in significantly shallower water than individuals that were not re-sighted or that were in isolated clusters. Distances between re-sighting locations suggest small home ranges. This suggests an insular slope-dwelling population that overlaps with an offshore population. Evidence of unsuccessful predatory attempts by large sharks was recorded on four individuals, and linear wounds consistent with interactions with line fisheries were documented on three individuals. Surface and subsurface behavior recorded by drone revealed vigilance behavior likely to minimize predation risk. Lessons learned from this study can be applied elsewhere to increase knowledge of this poorly-known and difficult-to-study species. The paper can be viewed at https://onlinelibrary.wiley.com/share/author/SJEICJSDQH2CS5W2GNTJ?target=10.... The supporting information file can be downloaded from https://onlinelibrary.wiley.com/doi/10.1111/mms.12861 There are two drone videos provided as supporting information, available at https://youtu.be/HborwUZicXY and https://youtu.be/3U0lLjIqaO4 Please contact me for a pdf. Robin ================================================================= Robin W. Baird, Ph.D. Research Biologist, Cascadia Research Collective Affiliate Faculty, Hawaiʻi Institute of Marine Biology Mailing address: Cascadia Research Collective 218 1/2 W. 4th Avenue Olympia, WA 98501 USA Follow us on Facebook<https://www.facebook.com/CascadiaResearch/> Updates from our July/August 2021 Kaua‘i field project<https://www.cascadiaresearch.org/hawaiian-cetacean-studies/JulAug2021>