Hunting strategies employed by predators include a continuum between sit-and-wait ambushing and active hunting. When the prey moves faster than the predator, ambush is preferred.
Sexual dimorphism of conspicuous tail coloration in viperid snakes is rare. Adult C. vipera demonstrate sexual dimorphic chromatisation; the tip of the tail in females is black and conspicuous over the light-colored background of the sandy dune habitat, whereas that of males is not. Both male and female C. vipera employ mainly sit-and-wait ambush and their diets are composed of nocturnally-active (Sphenops sepsoides and Stenodactylus spp.) and diurnally-active (Acanthodactylus spp) lizard species. Diurnally active lizards can be hunted actively at night by entering their burrows and by ambush during the day. Nocturnally-active lizards can be captured only by ambush, as C. vipera is too slow to chase prey.
We hypothesized that sexual dichromatisation in C. vipera is related to feeding mimicry via caudal luring and predicted that females would be more successful in sit-and-wait hunting than males and, consequently, capture a higher proportion of nocturnally-active lizards than males. To test this prediction, we determined dietary intake in free-ranging C. vipera from fecal samples and monitored their hunting behavior.
Results/Conclusions
Fecal samples of 83 male and 78 female adult C. vipera were collected. Overall, 47 Acanthodactylus spp., 15 S. sepsoides, 4 Stenodactylus spp. and 1 S. scincus were identified. Females consumed a higher proportion of nocturnally-active lizards (37.5 % vs 14.8%) than males (Chi2(1)=4.08, p=0.043) and, hence, our prediction was supported.
Sand impressions near the tail of all 78 females indicated tail wiggling. In six females, we observed nocturnal tail wiggling, in front of Stenodactylus spp, which fits in with caudal luring. Neither tail wiggling nor sand impressions near the tail were observed in males. Sexual dimorphism could have evolved from natural selection. Difference feeding habits between males and females could be a mechanism to decrease intraspecific competition. However, sexual size dimorphism in C. vipera is very low, with an index of 0.0476 Body condition index (BCI) of females that consumed nocturnally-active lizards did not differ from females that consumed diurnally-active lizards and, also, not from males. Sexual dietary differences may suggest eco-physiological causation for the sexual dichromatism, which may have forced males to shift into diurnal hunting.