Geographic variation in the foraging behavior of the garter snake, Thamnophis elegans

Summary

Behavioral comparisons were made of two populations of the garter snake Thamnophis elegans: a typical population with semi-aquatic habits and diet (inland population), and a coastal population that has entered a terrestrial feeding niche. Laboratory-born snakes of both populations were compared for their tendency to eat fish and their aquatic foraging behavior.

A significantly higher proportion of inland snakes than coastal snakes ate the first fish offered, and during 16 weeks on a fish diet inland snakes ate live and dead fish significantly more frequently. In both populations individual differences were extreme: some snakes never refused fish, while others refused consistently to the point of starvation.

In foraging trials, inland snakes spent a significantly greater proportion of time on aquatic foraging behaviors (craning and cruising, and diving), made significantly more aerial and underwater attacks, and captured more fish than coastal snakes. Coastal snakes that engaged in aquatic foraging used the same behavioral repertoire as inland snakes. Coastal snakes that declined to perform aquatic foraging were subsequently induced to exhibit the full aquatic foraging repertoire by extreme food deprivation and a potent prey stimulus situation. Apparently, the coastal population has retained all the elements of its aquatic foraging repertoire, but its tendencies to perform them have diminished.