Experimental Manipulation of Tail Color Does Not Affect Foraging Success in a Caudal Luring Rattlesnake

Snakes that exhibit caudal luring typically have a conspicuously colored tail tip. We conducted a field experiment to test the adaptive significance of tail color. A sample of 169 neonate Pigmy Rattlesnakes (Sistrurus miliarius) was treated by coloring their yellow tails with either black pigment similar to their cryptic body color or yellow ink as a procedural control. Snakes were released and recaptured over the next three months. Tail color manipulation did not significantly influence the proportion of snakes with palpable food. Also, the treatments did not affect growth in SVL or mass. These findings suggest that snakes with cryptic tails did not experience reduced prey capture. The presence of conspicuous tail coloration in this species may be explained by phylogenic inertia, selective benefits of small magnitude, or by habitat-related differences in prey composition or abundance. Ambush foragers often employ mimicry to enhance foraging success. In some species, the ambusher presents a structure that resembles the food of the ambusher's prey to draw potential victims within striking distance (Reiserer, 2002). Examples of these lures include the highly modified dorsal fin of anglerfishes (Pietsch and Grobecker, 1978), the tongue of Alligator Snapping Turtles (Macroclemys temminckii; Drum- mond and Gordon, 1979), and the toes/feet of certain anurans (Radcliffe et al., 1986; Hagman and Shine, 2008). These systems, wherein the mimic benefits and the dupe are consumed, have been termed aggressive mimicry by Vane-Wright (1976) or feeding mimicry (Schuett et al., 1984). The use of lures appears to be of particular importance in ambush foraging species. Some ambush foraging snakes employ the tip of the tail as a lure (reviews in Neill, 1960; Heatwole and Davison, 1976; Strimple, 1992). Caudal luring has been suggested or documented for snakes in seven families (Boidae, Tropidophiidae, Pythonidae, Elapidae, Dipsadidae, Colubridae, Viperidae), but the greatest number of caudal luring species appear to be viperids (Rabatsky, 2008). In most of the well- described examples, two qualities characterize the caudal lure: (1) the tail tip is moved in a manner that resembles an invertebrate (e.g., worm, caterpillar) that would be suitable prey for anurans or lizards; and (2) the tail tip is colored to contrast with the otherwise cryptic body pigmentation (Neill, 1960; Heatwole and Davison, 1976; Rabatsky, 2008; for exceptions see Leal and Thomas, 1994; Tiebout, 1997). Many pitvipers have a yellow tail tip when young, and it has been suggested that this condition is ancestral for the clade (Neill, 1960). The Pigmy Rattlesnake, Sistrurus miliarius, exhibits a yellow tail as a neonate and is documented to use the tail as a lure (Jackson and Martin, 1980; Rabatsky and Farrell, 1996; Rabatsky and Waterman, 2005). Pale tail coloration that contrasts with cryptic body coloration may increase the effectiveness of caudal luring by making the lure more visible while diminishing the likelihood that the prey detects the lure's attachment to a predator (Rabatsky, 2008). In the course of a long- term study of S. miliarius in east-central Florida (Farrell et al., 2008), we addressed the adaptive significance of the contrasting color of their caudal lure in a manipulative field experiment. We artificially colored the tails of newborn rattlesnakes, released them, and later recaptured the neonates to determine whether noncontrasting tail color decreased foraging success and growth rate.