Snakes are important predators that have radiated throughout many ecosystems, and constriction was important in their radiation. Constrictors immobilize and kill prey by using body loops to exert pressure on their prey. Despite its importance, little is known about constriction performance or its full effects on prey. We studied the scaling of constriction performance in two species of giant pythons (Python reticulatus and Python molurus bivittatus) and propose a new mechanism of prey death by constriction. In both species, peak constriction pressure increased significantly with snake diameter. These and other constrictors can exert pressures dramatically higher than their prey's blood pressure, suggesting that constriction can stop circulatory function and perhaps kill prey rapidly by over-pressurizing the brain and disrupting neural function. We propose the latter 'redout effect' as another possible mechanism of prey death from constriction. These effects may be important to recognize and treat properly in rare cases when constrictors injure humans.

Constriction is a prey-immobilization technique used by many snakes and is hypothesized to have been important to the evolution and diversification of snakes. However, very few studies have examined the factors that affect constriction performance. We investigated constriction performance in ball pythons (Python regius) by evaluating how peak constriction pressure is affected by snake size, sex, and experience. In one experiment, we tested the ontogenetic scaling of constriction performance and found that snake diameter was the only significant factor determining peak constriction pressure. The number of loops applied in a coil and its interaction with snake diameter did not significantly affect constriction performance. Constriction performance in ball pythons scaled differently than in other snakes that have been studied, and medium to large ball pythons are capable of exerting significantly higher pressures than those shown to cause circulatory arrest in prey. In a second experiment, we tested the effects of experience on constriction performance in hatchling ball pythons over 10 feeding events. By allowing snakes in one test group to gain constriction experience, and manually feeding snakes under sedation in another test group, we showed that experience did not affect constriction performance. During their final (10th) feedings, all pythons constricted similarly and with sufficiently high pressures to kill prey rapidly. At the end of the 10 feeding trials, snakes that were allowed to constrict were significantly smaller than their non-constricting counterparts.

We investigated how exposure duration (time that two individuals initially interact) and separation interval (time between the initial interaction and a subsequent interaction) affect recognition memory of conspecifics in male red-backed salamanders Plethodon cinereus. Previous studies have demonstrated that this species aggressively defends territories. We recorded aggressive behavior to assess recognition memory, because aggression is more intense toward previously unencountered individuals compared to previously encountered individuals in this species. We found that with 15-min exposures and 5-day separation intervals, focal males did not spend significantly more time threatening ‘unfamiliar’ intruders than ‘familiar’ intruders. After either 8-hour exposures and 5-day separation intervals and 5-day exposures and 5-day separation intervals, focal males spent significantly more time threatening unfamiliar intruders than familiar intruders. These results suggest that male red-backed salamanders can remember familiar conspecifics (e.g., territorial neighbors) after at least an 8-hour exposure duration and that memory persists at least as long as 5 days. After 5-day exposure and 15-day separation intervals, we found no significant difference in aggressive behavior toward familiar and unfamiliar intruders. Long separation intervals (15 days) may lead either to loss of memory of previously familiar individuals or, alternatively, aggressive reassessment of individuals as only a change in behavior indicates positively that memory has occurred. Thus, variance in territorial defense within an individual may depend on its ability to recognize conspecific males.

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