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Living crocodilians communicate using visual, acoustic, chemical, and/or tactile signals. As adults, gharials (Gavialis gangeticus) vocalize only rarely, and reportedly do not produce infrasound. On-going ecological and behavioral studies of the largest remaining wild population of gharials, living in the Chambal River, north India, indicate that gharials breed at well-defined arenas established by dominant males, and then reproductive females assemble and nest in large colonies nearby. Detailed behavioral observations, supported by 24hr acoustic and still/video imagery, at breeding and nesting sites, at multiple locations in successive years, have documented complex social interactions, including acoustic signaling between and amongst adults, as well as young. Male gharial produce an explosive, concussive “pop” sound underwater, in 1-3 short, loud audible bursts . A “pop” is always sudden and high volume, resembling a stoppered bottle being opened rapidly, like a wine bottle being uncorked. We used hydrophones and aerial mics, to record the “pop” signals of 15+ male gharial, totaling in excess of 500 samples. Spontaneous recordings were obtained as gharials behaved normally under natural conditions. At one site frequented by a breeding male, with few females (<10 in 2017) vs. many (>30 in 2018), “recruiting” pops directed at females predominated in 2017, whereas “challenging” pops were frequent in 2018, when other males were present. In 2018, at this site, overall pop frequency more than doubled, relative to 2017. During hatching and afterwards (~4-6 wks), at each crèche site, a guardian male “pops” often to 1) alert and recruit hatchlings, and 2) announce his presence and location to females in the vicinity of the creche. Each male gharial produces a stereoptypic and characteristic series of “pops,” performed underwater, and consisting of 1, 2, or 3 pops. Temporal patterning, rather than frequency differences, appears to be the primary feature of this unique signal, not known in other crocodilians, that presumably facilitates individual recognition. The “pop” or syllable duration ranged from 0.013 to 0.023 seconds, and the time interval between syllables ranged from 0.103 to 0.555 seconds. Distinctive low and high frequencies were characteristic of each pop, ranging from >100-2400 Hz to >10,000-22,000 Hz. Immediately preceding a pop, infra-sound is produced. Signal analyses: Raven Pro & Avisoft software. This is an interim progress report for 2017-18.
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