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Living crocodilians are known to 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 in 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 data and still and 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 by young. Adult male gharials produce explosive, concussive “pop” sounds underwater, in 1-3 short, loud, audible bursts. A “pop” is always sudden and high in volume. Using hydrophones and aerial mics, we recorded over 500 samples of “pop” signals of 14 male gharials, behaving normally under natural conditions. Each male gharial produced a stereo-typed series of 1-3 “pops” underwater. Temporal patterning, rather than frequency differences, appears to be the primary feature of this unique crocodilian signal which presumably facilitates individual recognition. Immediately preceding a pop, infrasound is produced. Duration ranges from 0.013 to 0.036 seconds, and the time interval between syllables ranges from 0.045 to 0.745 secs. Distinctive low and high frequencies were characteristic, ranging from 100-2400 Hz to 10,000-22,000 Hz. During breeding (late Feb-early Mar), popping occurs in four distinct contexts, namely 1) external disturbances, 2) patrolling, 3) male-male interactions, and 4) courtship between potential mates. At one site frequented by a breeding male, with relatively few (<10 in 2017) vs. many (>30 in 2018) females, “recruiting” pops directed at females dominated in 2017, whereas “challenging” pops dominated in 2018, when challengers visited. During hatching until ~4-6 weeks afterwards (late May-early July), at each communal nesting site, a guardian male will “pop” often to 1) alert and recruit hatchlings, and 2) announce his presence and location to females in the vicinity of the crèche. Each guardian male can be identified by his distinctive “popping” at a specific crèche, year after year.
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