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Home , Caiman (genus), Yacare caiman

Herpetology Notes, volume 8: 385-387 (2015) (published online on 12 August 2015)

Infrasound production by a yacare Caiman yacare in the ,

Christopher P. Kofron1,* and Patricia A. Farris2

The social interactions of crocodilians comprise The water dance of crocodilians has been known visual, auditory, olfactory and tactile components, since the 18th century, yet it is still the least understood including posturing, vocalizing, producing infrasounds, aspect of crocodilian communication. Specifically, headslapping, jawslapping, narial geysering, blowing it is unknown whether the water dance is a visual bubbles, and multiple other activities (e.g., Garrick component of the roaring display or a non-adaptive and Lang 1977, Kofron 1991, Thorbjarnarson and physical consequence of the infrasound production Hernandez 1993, Dinets 2013a). For long distance (Dinets 2013b). The purpose of the present paper is communication, crocodilians use a combination of to augment the knowledge of display behavior by the vocalizations, headslaps or jawslaps, and infrasound . (Dinets 2011a). Regarding the yacare caiman Caiman We observed infrasound production by a yacare yacare (Daudin 1802), Dinets (2011b) reported the caiman on 17 July 2014 (dry season) in the central roaring display consisted of one to three roars, and with Pantanal in western Brazil, which is a mosaic of each roar preceded by infrasound. Infrasound comprises seasonally flooded savannahs and tropical forests. We non-vocal vibrations at frequencies below the range recorded the display behavior as a series of 16 high- of human hearing and that can carry a great distance resolution photographs (300 dpi) with a 12-megapixel through the water (Dinets 2011a, 2013b). Infrasound camera and subsequently used image enhancement tools production can be visually detected by observing water to identify and differentiate the projected water drops projecting upward into the air above the back of the from the background in each photograph. We visually crocodilian, which Vliet (1989) termed a “water dance.” estimated the total length of the yacare caiman, which The water dance is likely created by Faraday waves we then used as a reference to calculate the maximum produced when the male crocodilian vibrates its lungs height of projected water. The primary weakness of this at very low frequency (Moriarty and Holt 2011) and report is that we can only estimate the total length of the with its back submerged just below the surface of the yacare caiman and the height of the water dance rather water. The back of the crocodilian is covered by rough than present precise measurements. The findings and dermal scutes of varying shapes and sizes, some which conclusions in this article are those of the authors and may project several centimeters outward, and these may do not necessarily represent the views of the U.S. Fish direct or focus the Faraday waves. The production of and Wildlife Service. infrasound expends a great amount of energy (Dinets We made our observations from a small motorboat 2013b). of the Jaguar Research Center. The location was in the Black Channel (-17.276150, -56.697050; 105 m elevation), which is a tributary of the Cuiabá River (Rio Cuiabá) in seasonally flooded savannah at its junction with the Three Brothers River (Rio Três Irmãos). There was no wind, and the surface of the water was 1 U.S. Fish and Wildlife Service, 2493 Portola Road, Suite B, flat. At 06:35 hr we heard a yacare caiman roaring in Ventura, California 93003, USA 2 Life Science Department, Pierce College, 6201 Winnetka the distance, and at the same time we observed another Avenue, Woodland Hills, California 91371 yacare caiman floating on the surface of still open water * Corresponding author e-mail: [email protected] (depth unknown) nearby. The aquatic habitat at this 386 Christopher P. Kofron & Patricia A. Farris

Figure 1. Infrasound production by a yacare caiman Caiman yacare in a seasonally flooded savanna in the central Pantanal, western Brazil, on 17 July 2014. The male yacare caiman (approximately 2.8 m total length) is in a roaring display and with a water dance above its back. The yacare caiman was producing infrasound, which projected the water approximately 75 cm upward into the air. We recorded the display behavior as a series of 16 high-resolution photographs (300 dpi) with a 12-megapixel camera and subsequently used image enhancement tools to identify and differentiate the projected water drops from the background in each photograph. We visually estimated the total length of the yacare caiman, which we then used as a reference to calculate the maximum height of projected water. The two white arrows indicate the height of the highest projected water drop in the photograph.

particular location and point in time was continuous caiman was producing infrasound, which projected the (not fragmented). water approximately 75 cm upward into the air (Fig. Our boat slowly approached the nearby yacare caiman 1) on each occasion. According to the clock on the for a closer view and stopped at approximately 12 camera, three seconds separated the maximum heights meters distance. The back of the yacare caiman was of projected water of the two water dances. initially exposed above the water. At 06:40 hr this Infrasound production has been reported for all yacare caiman (approximately 2.8 m total length) extant of crocodilians with exception of assumed a head oblique—tail arched posture (Garrick the gangeticus (Dinets 2013c), and Lang 1977): that is, the head was elevated at an however, the estimated height of the water dance angle of approximately 25 degrees above the water, has rarely been reported. For the American the back was submerged just below the water, and the Alligator mississippiensis, the reported heights were central part of the tail (15 vertical scutes) was arched out approximately 5 cm (McIlhenny 1935) and 30 cm (Vliet of the water. The yacare caiman then roared twice in 1989, Dinets 2013b). In their diagrams of the water quick succession, with a total duration of approximately dances for the and the Nile 5 seconds and with two crescendos. Each roar was niloticus, Garrick and Lang (1977) showed preceded by a water dance above the back. The yacare a substantially greater height for the Infrasound production by a yacare caiman in the Pantanal, Brazil 387 but without estimation. For the Garrick, L.D., Lang, J.W. (1977): Social signals and behaviors of Crocodylus intermedius, although Thorbjarnarson and adult and . American Zoologist 17: 225- Hernandez (1993) did not state the estimated height 239. Godshalk, R.E. (2006): Phylogeography and conservation genetics of the water dance, their diagram showed only several of the yacare caiman (Caiman yacare) of . Ph.D. centimeters. Male alligators attain total lengths up thesis, University of Florida, Gainesville. to 4.5 m (Woodward et al. 1995), and male Orinoco Higgs, D.M., Brittan-Powell, E.F., Soares, D., Souza, M.J., Carr, crocodiles attain total lengths up to approximately 7 m C.E., Dooling, R.J., Popper, A.N. (2002): Amphibious auditory (Castro 2012). In contrast, male yacare attain responses of the American alligator (Alligator mississippiensis). total lengths up to 3.0 m (Godshalk 2006). Thus, the Journal of Comparative Physiology A 188: 217-223. Kofron, C.P. (1991): Courtship and mating of the Nile Crocodile yacare caiman is a substantially smaller species. (Crocodylus niloticus). Amphibia-Reptilia 12: 39-48. The greater height of the water dance that we observed McIlhenny, E.A. (1935): The alligator’s life history. Christopher for the yacare caiman made it more visible and from a Publishing House, Boston. greater distance to other individuals of the species. In Moriarty, P., Holt, R.G. (2011): Faraday waves produced by effect, the long-distance auditory communication was periodic substrates: mimicking the alligator water dance. accompanied also by what appeared to be a long-distance Journal of the Acoustical Society of America 129: 2411. visual communication. Thus, the water dance that we Thorbjarnarson, J.B., Hernandez, G. (1993): Reproductive ecology of the Orinoco crocodile (Crocodylus intermedius) in observed was likely an evolved functional component . II. Reproductive and social behavior. Journal of of the roaring display rather than a physical artifact of Herpetology 27: 371-379. sound production in water. Notably, all crocodilians Vliet, K.A. (1989): Social displays of the American alligator when producing infrasound usually position their backs (Alligator mississippiensis). American Zoologist 29: 1019- just below the surface of the water (Garrick and Lang 1031. 1977, Dinets 2013b). Crocodilians underwater feel Woodward, A.R., White, J.H., Linda, S.B. (1995): Maximum infrasound through the soft body tissues rather than hear size of the alligator (Alligator mississippiensis). Journal of Herpetology 29: 507-513. it (Higgs et al. 2002, Dinets 2013b), and locating the direction and source of infrasound underwater is reported to be difficult (Dinets 2011b). The accompanying water dance with its visual characteristics can obviously facilitate locating the direction and source of infrasound by crocodilians at the air-water interface.

Acknowledgements. We thank Vladimir Dinets for valuable discussion, and we thank Angela Chapman and Rick Farris for reading and commenting on the manuscript.

References

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