The following copyrighted material is intended for individual use of the researcher, and may not be copied or distributed without written permission from the copyright holder. You may use it for non-profit scholarly purposes. The reference for this article is: Rivas, J. A., Thorbjarnarson, J. B., M. C. Muñoz, and R. Y. Owens. 1999 Eunectes murinus: caiman predation. Herpetological Review. 30(2): 101
Eunectes murinus (green anaconda). Caiman predation (Click here for a pdf
version). Anacondas and caimans are two
large predators that use very similar habitats in the seasonally flooded
On 25 of May 1996 we discovered a large caiman (>90 cm svl) firmly gripping the head of a radio-implanted female anaconda (494 cm TL, 29 kg), who in turn had wrapped herself around the caiman’s head and neck. After approximately 15 min the snake relaxed her coils, apparently losing the struggle with the caiman. We interrupted the event to recover the transmitter when the snake stopped struggling. One of the teeth of the caiman had gone right through the skull and into the brain region, other tooth mark where present in the first fifth but did not look life threatening. The snake died two month later in captivity due to a generalized infection. As we had found this snake severely wounded from 2 months previous to being preyed on by the caiman, it is likely that she was not in top physical shape and this may have played some role in the attack.
Another instance took place 29 of April 1996 in a roadside channel covered partially by water hyacinth (Eichhornia ssp). The caiman (> 90 cm svl) was on the left side of the anaconda (approximately 2.5 m), gripping it by the anterior 1/5 of its body. The snake had thrown a loop of its body over the dorsal surface of the caiman and wrapped its posterior body and tail around the caiman’s left hind leg. The snake, although much smaller than the caiman, was wrapped so tightly around the hind leg that the head of the caiman was pulled towards its hindquarters. The snake was observed to periodically tighten its loop, causing the caiman to flip over to the right and under the water. The caiman repeatedly attempted to drag the snake out of the water, but each time the anaconda managed to flip the caiman and pull it back under water. The wrestling match continued for five hours, often punctuated by both animals submerging for periods of ten to fifteen min. Finally, at 1900 h as the light faded, we saw an unidentified caiman of similar size leaving the area with no snake in its mouth
Five days later (04 of May) we found a dead male anaconda (247 cm total length, 5.5 kg), with wounds from a caiman bite on the anterior 1/5 of its body. The wounds matched position of the teeth of a caiman skull 29.5 cm long, with an estimated svl of 120.8 cm (total length 226 cm) and weight of 43 k (Thorbjarnarson, unpublished). The snake showed no signs of decomposition, indicating a recent death. We surmise that the snake escaped from the caiman but subsequently died from its wounds. Judging by the relationship of masses, we surmise that it was the caiman trying to eat the snake and not vice-versa.
The last observation (03/19/1997) also involved a large caiman attacking a small female anaconda (152 cm total length, 1.7 kg). The caiman (> 90 cm) was in a small roadside pool with the snake in its mouth when we found it. Upon our approach, the caiman dropped the seriously wounded female anaconda. Although the snake survived, we consider this a predation event since it was not struggling when we arrived and thus would not have survived without our intervention.
In total we found twelve events of caimans killing anacondas (six males and six females). Based on our observations and examination of the anacondas (presence of deep circular bite marks matching the size and position of caiman teeth), we determined that all six males and two of the females had been killed by spectacled caimans. The males that were found dead was significantly larger (mean 270.67) than the average male in the population (mean 219.07; t-test; p<0.001). A possible explanation for this is that larger males are more likely to escape from the attack of the caiman and then they die afterwards from the wounds (as in the second event reported). Smaller animals are eaten as evidenced by some cases where we found only one piece of the animals. Interactions between these two sympatric reptiles seem to be quite common. To study the life history of each species is important to fully understand the dynamics of their relationship.
Acknowledgment: We are in debt to M. Quero and P Azuaje for their cooperation with the project. W. Holmstrom helped in the data collection and P. Calle was great help in the implantation for the transmitters. We also thank P. Andreadis, G. M. Burghardt for editorial comments on the early versions of the manuscript. This research was possible thanks to joins grants from The Wildlife Conservation Society, The National Geographic Society, CITES and the Venezuela Fish and Wildlife Service (Profauna). We thank COVEGAN for allowing us to work in their ranch and all the cooperation with this project.
Submitted by Jesús A. Rivas, Dept. of
Ecology & Evolutionary Biology,