PREDATION BY FREE-RANGING BIRDS ON PARTIAL CORAL SNAKE MIMICS: THE IMPORTANCE OF RING WIDTH AND COLOR.

Abstract

Many of the venomous New World coral snakes (Micrurus and Micruroides) have a distinctive pattern of red, black, and yellow rings (Campbell and Lamar 1989; Savage and Slowinski 1992), which typically appear in the sequence red-yellow-black-yellow (the tricolor monad of Savage and Slowinski 1992) repeated multiple times on each snake. Relatively harmless coexisting snakes in several different genera have a similar appearance, and most recent investigations have concluded that these are cases of Batesian mimicry (Greene and McDiarmid 1981; Pough 1988a; Campbell and Lamar 1989; Savage and Slowinski 1992). Though it is clear that a precise mimic of a dangerous or unpalatable model often gains protection from predation (see Waldbauer 1988 for a review), the gradual evolution of mimicry requires that partial mimics gain some fitness benefit from even a poor resemblance to model species (Fisher 1958; Sheppard 1959). There is evidence that partial mimics gain limited protection from predation in some insect systems (e.g., Morrell and Turner 1970; Pilecki and O'Donald 1971; Shideler 1973). A large number of Neotropical snakes have some elements of the coral snake pattern (Pough 1988b), but there is very little information on the protective effects of partial mimics, largely due to the extreme difficulty of observing predation events in the field. Brodie (1993, following Madsen 1987) pioneered the use of plasticine replicas of coral snakes to gather data on rates of predation by free-ranging birds in the natural habitat of coral snakes. The soft plasticine retains the imprint of any attempted predation, which can be used to identify the predator as bird, mammal, etc. (Brodie 1993). Using this method, Brodie (1993) showed for the first time that the coral snake pattern reduces the rate of avian predation for replicas of both true coral snakes and coral snake mimics. Here we extend Brodie's (1993) method to determine bird attack rates on partial coral snake mimics that have color and pattern combinations not found in any living snake. The coloration of coral snakes includes a number of elements that can vary independently: ring color, ring width, and order of the arrangement of the rings. There is no historical infor-