SELECTION OF PREY FROM GROUPS: WATER SNAKES AND FISH
ADRIAN HAILEY* AND P. M. C. DAVIES
Zoology Department, University of Nottingham NG7 2RD, UK.
Present Address: Ecology Unit, Rutherford College Extension, University of Kent, Canterbury CT2 7NX, UK.
(Accepted 14.5.85)
ABSTRACT
This paper investigates the selection, ingestion and digestion of different sized goldfish by viperine water snakes Natrix maura. A previous study had suggested that sentinel foraging N. maura preferentially select medium sized fish to give the maximum rate of energy intake during ingestion. It was however found that snakes preferentially struck at the largest fish available in the range 1-20 per cent relative prey weight, even though these fish gave no advantage in ease of capture or rate of energy intake during ingestion or digestion. The advantage of this selection is shown to result from the schooling behaviour of fish and the low rates of capture during sentinel foraging. It was confirmed that snakes capture and attempt to ingest fish too large for them. A large fish provides an energy supply large in relation to the snake's requirements (covering about 60 days maintenance) compared to the small cost of handling before rejection. It would thus be better to handle all fish unless much too large, rather than rejecting those closer to the maximum and possibly making a mistake.