Dear colleagues, My co-authors and I are excited to share our recent publication in JASA Express Letters: Szesciorka, A.R., McCullough, J.L.K., Oleson, E.M. 2023. An unknown nocturnal call type in the Mariana Archipelago. *JASA Express Letters* 3, 011201. https://doi.org/10.1121/10.0017068 Abstract: In spring/summer of 2018 and 2021, the Pacific Islands Fisheries Science Center Cetacean Research Program deployed drifting acoustic recorders in the U.S. Exclusive Economic Zones surrounding the Mariana Archipelago. Manual assessments revealed a low-frequency (median 473–554 Hz), short-duration (median 0.596 s), stereotypic tonal nocturnal call throughout the Mariana Archipelago. Based on time of year, spatiotemporal patterns, clear division among calls (i.e., no chorusing), comparisons with known vocalizations of whales, turtles, and fish, and presence of Bryde's whale calls, and because the call has not been detected elsewhere, we hypothesize this 500-Hz pulsed call is produced by Bryde's whales (*Balaenoptera brydei*). As always, feel free to reach out to me at angela@szesciorka.com if you have any questions or cannot access the article. Let's solve the mystery together! Angie -- *Angela R. Szesciorka, M.Sc., Ph.D.* NSF Office of Polar Programs Postdoctoral Fellow Marine Mammal Institute, Oregon State University Office: 541-867-0362 | Pronouns: Dr/she/her