• Gape size;
  • Nerodia sipedon;
  • sexual dimorphism;
  • Storeria dekayi;
  • Thamnophis sirtalis


  • 1
    For gape-limited predators such as snakes, it should be possible to predict the relationship between maximum prey size and body size from the relationship between maximum prey size and gape size and between gape size and body size. Such predictions were generated for Water Snakes, Nerodia sipedon L., using a data subset and then tested with a larger data set.
  • 2
    Gape size was computed based on jaw length and width and cyclical regression was used to identify prey of maximum size for snakes of a given gape or mass.
  • 3
    Predicted and observed maximum prey cross-section–snake mass allometry were in good agreement. Predicted maximum prey mass–snake mass allometry somewhat exceeded observed allometry which did not differ from 1.
  • 4
    Observed minimum prey size–snake size allometry was significantly greater than 0, indicating that larger snakes drop small prey from their diets.
  • 5
    Gape size–body size allometry in two other natricine snakes (Thamnophis sirtalis, Storeria dekayi) suggest that patterns of ontogenetic change in prey size should differ among species in predictable ways.
  • 6
    Sex differences in gape size–snake size allometry suggest that sex differences in maximum prey size should increase with increasing snake size, even when linear measures of head dimensions do not.