Unlearned appetite controls: Watersnakes (Nerodia) take smaller meals when they have the choice

Satiety and eating patterns in two species of constricting snakes

Satiety has been studied extensively in mammals, birds and fish but very little information exists on reptiles. Here we investigate time-dependent satiation in two species of constricting snakes, ball pythons (Python regius) and yellow anacondas (Eunectes notaeus). Satiation was shown to depend on both fasting time and prey size. In the ball pythons fed with mice of a relative prey mass RPM (mass of the prey/mass of the snake×100) of 15%, we observed a satiety response that developed between 6 and 12h after feeding, but after 24h pythons regained their appetite. With an RPM of 10% the pythons kept eating throughout the experiment. The anacondas showed a non-significant tendency for satiety to develop between 6 and 12h after ingesting a prey of 20% RPM. Unlike pythons, anacondas remained satiated after 24h. Handling time (from strike until prey swallowed) increased with RPM. We also found a significant decrease in handling time between the first and the second prey and a positive correlation between handling time and the mass of the snake.

Ontogenetic and sexual differences in diet in an actively foraging snake,Thamnophis proximus

Actively foraging species of snakes often consume large numbers of small prey, which creates a high meal to snake mass ratio. Because they may also rely on speed to avoid predation, this might negatively influence survival. We examined the diet of 313 western ribbon snakes ( Thamnophis proximus Say in James, 1823), a very attenuated species, in a floodplain in northeastern Texas. Of the 142 individuals with food, adult males ate 9 prey types, followed by females with 8, and juveniles only 6. The ontogenetic increase in prey diversity was predicted. However, female ribbon snakes are larger than males and their fewer prey types may reflect a strategy where smaller prey are dropped from the diet. Seasonal activity of prey and snake class was generally correlated. Overall individual prey sizes were comparably small. However, over 50% of the snakes contained multiple prey and total meal masses were similar to the maximum prey sizes of ambush foragers. Adults stopped feeding at proportionally lower meal mass to predator mass ratios than juveniles. The benefits of rapid growth for juveniles may outweigh predation risks associated with high prey consumption, but for adults of this species, consuming lighter meals may be the most stable strategy.