Food habits of the long-nosed snake (Rhinocheilus lecontei), a 'specialist' predator?

We explored predator specialization by examining dietary variation in the w idespread North American long-nosed snake, Rhinocheilus lecontei. We examin ed the stomach contents of more than 800 museum specimens, and supplemented our findings with published dietary records. Sixty-six percent of 135 prey eaten by R. lecontei were lizards, 26% were mammals, and 7% were squamate eggs; teiid lizards of the genus Cnemidophorus comprised 72% (64 of 89) of all lizard prey. Ninety-four percent of specimens with food contained a sin gle item, and all 79 prey for which we determined direction of ingestion we re swallowed head-first. Among those specimens containing food, long-nosed snakes from Mexico were significantly larger, and ate a higher percentage o f mammals, than specimens from the United States. Larger R. lecontei someti mes fed on larger prey, and perhaps excluded smaller prey from their diet. To assess relative trophic niche breadth for R lecontei, we compared the pe rcentage of lizards and of Cnemidophorus in the diet of long-nosed snakes w ith the percentage with which other terrestrial snakes consumed lizards as their modal prey, and with which these same snakes ate members of their pre ferred lizard prey genus. Although we uncovered no statistical basis for la belling R. lecontei a specialist, its diet may often be restricted to lizar ds and even to Cnemidophorus, and therefore recognizing long-nosed snakes a s specialist predators remains a subjective decision. Our study also demons trates that quantitative natural history can place related species in a res ource use continuum, and thereby can help to elucidate the evolutionary bas is for specialization.