Because water is 800 times denser and 50 times more viscous than air, it puts very strong demands on the feeding system of vertebrates. An aquatic predator that approaches a prey will generate bow waves that can either push the prey further away or along a predator's jaws. To avoid or compensate for those bow waves, we find two systems among aquatic vertebrates: filter feeding and suction feeding. However, aquatic snakes seem not able to perform filter- or suction feeding because of their very specialised head morphology (for the consumption of large prey). Still more than 300 snake species feed in an aquatic environment on a variety of prey and with a range of different feeding morphologies and behaviours.
High-speed video recordings and Particle Image Velocimetry on the strikes of Natrix maura and N. tesselata with altered predator and prey characteristics will allow us to gain insight in how the process of aquatic feeding in snakes precisely works and through which factors this process is influenced. This information will be completed with measurements on a physic snake model to look at the effects of a broader range of prey- and predator characteristics (functional morphology part). Finally we will try to consider if it is possible with the obtained insights, to link the large variation in head morphology and feeding behaviour among aquatic snakes, to the variety of different prey they eat (ecomorphological part). Data on the head morphology of aquatic snake species will be obtained by measuring museum species; data on the feeding behaviour and diet of aquatic snake species will be collected from literature.