Chilly rattlesnakes strike slower, but not as slow as expected

Abstract

You know that feeling when it's simply too hot to move; the heat is so oppressive that all you can do is sit indoors with a cool drink? Surprisingly, rattle snakes also struggle with heat in the summer, only they can't resort to the cool drink. ‘The habitats of many rattlesnake species become too hot during the day’, says Malachi Whitford from San Diego State University and the University of California, Davis, USA, so the reptiles’ solution for the problem is to become nocturnal and hunt at night, but that results in an alternative drawback. ‘Night time temperatures can get quite cold’, says Whitford, explaining that lower body temperatures could slow the snakes’ lightning fast reactions. Which made Grace Freymiller, Timothy Higham, Rulon Clark and Whitford wonder how much of an effect chilly conditions might have on the snakes’ abilities to catch dinner.‘Safety for the snake and for us is very important…we never put ourselves within the strike range of the snake’, says Whitford, describing how he and his colleagues corralled the vipers with snake hooks and tongs when collecting Mohave rattlesnakes (Crotalus scutulatus) in New Mexico and western rattlesnakes (Crotalus oreganus helleri) in southern California. Back at San Diego State University, Whitford waved an inflated balloon in front of the animals in an attempt to get them to land a bite. ‘We wanted something that would not injure their fangs, which are fairly delicate’, he says, adding that the snakes seem unperturbed when the balloon exploded. ‘Snakes do not have the best hearing…so the pop of the balloon did not startle them – although it made me jump on more than a few occasions’, he laughs. Filming the snakes striking the balloon at temperatures ranging from 15 to 35°C, the team could see that the warmer snakes were definitely the liveliest. ‘One Mojave rattlesnake, nicknamed Hulk, was renowned for being quite intimidating. At 35°C, he would strike very quickly at anything that moved and constantly try to escape the enclosure’, Whitford recalls.Sure enough, when the team the measured the speed of the snakes’ movements, the chilliest snakes were more sluggish than the hottest, with the coldest snakes striking at speeds of up to 3.73 m s−1, while the hottest snakes launched themselves at the balloon as fast as 5.26 m s−1. The coolest reptiles also opened their mouths more slowly and were less likely to have a go at a balloon victim. However, when the team compared the impact of temperature on the snakes’ attack speeds, the coldest snakes were moving faster than the team would anticipate if their speed was set by body temperature alone, suggesting that the chilly animals also rely on springy tendons to help catapult themselves at a potential snack. In addition, the hottest snakes landed fewer successful strikes than the colder animals, although Whitford suspects that the hot animals might have been pulling back a little, in order to scare off potential threats, instead of trying to plunge their fangs in.Even though cold rattlesnakes are more vulnerable, Whitford cautions that the feisty animals are still lethal. ‘A cold rattlesnake is still a very dangerous animal, so don't try to pick it up!’ he warns.