Dear Colleagues, We are pleased to announce the publication of the following paper in The Journal of the Acoustical Society of America Express Letters: Mariana Barbosa, Lis Bittencourt, Luciana G. Andrade, Tatiana L. Bisi, Jose Lailson-Brito, Jr., and Alexandre F. Azevedo (2019). High-frequency social communication in *Sotalia guianensis. *https://doi.org/10.1121/1.5120550 Abstract This study aimed to investigate the use of high ultrasonic frequencies (above 40 kHz) in the Sotalia guianensis whistle repertoire. The whistles were classified as high-frequency (HF) whistles and very high-frequency (VHF) whistles. Seven parameters were extracted and a general linear mixed effects model was performed between the total number of whistles and VHF ones. Frequency parameters of HF and VHF whistles were the highest reported for this species so far. However, VHF whistles were rare and occurred in situations of high acoustic activity, which may represent a strategy used by dolphins to deal with higher levels of vocalization rates. The paper is open access and can be downloaded in the link below: https://asa.scitation.org/doi/10.1121/1.5120550 Kind regards, Mariana Barbosa