Dear colleagues, The following article was recently published online: Lammers, M.O. and Castellote, M. (2009). "The beluga whale produces two pulses to form its sonar signal" Biology Letters, doi:10.1098/rsbl.2008.0782 Odontocete cetaceans use biosonar clicks to acoustically probe their aquatic environment with an aptitude unmatched by man-made sonar. A cornerstone of this ability is their use of short, broadband pulses produced in the region of the upper nasal passages. Here we provide empirical evidence that a beluga whale (Delphinapterus leucas) uses two signal generators simultaneously when echolocating. We show that the pulses of the two generators are combined as they are transmitted through the melon to produce a single echolocation click emitted from the front of the animal. Generating two pulses probably offers the beluga the ability to control the energy and frequency distribution of the emitted click and may allow it to acoustically steer its echolocation beam. A PDF copy of the article is available at http://rsbl.royalsocietypublishing.org/content/early/2009/02/27/rsbl.2008.07... or by request from lammers@hawaii.edu. Best wishes, ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Marc O. Lammers, Ph.D. Hawaii Institute of Marine Biology P.O. Box 1106 Kailua, HI 96734 Tel: +1(808) 375-0010 Fax: +1(808) 247-5831 lammers@hawaii.edu