O. G. Dely szerk.: Vertebrata Hungarica 21. (Budapest, 1982)

Ananjeva, N.B. ; Orlov, N.L.: Feeding behaviour of snakes 25-32. o.

for water, etc. (SCUDDER et al. 1980). A search Involving active use of Jacobson organ proceeds up to the Instant of sighting the prey. 4. Vision is involved, the snake begins an active pursuit of the prey or seeks to strike. A venomous snake chooses an appropriate moment and strikes the prey by stabbing its fangs, while pythons or Colubridae seek to attack the prey, i.e. "to fix" it; Jacobson organ is again involved if the prey is lost to vision. In certain situations, after olfactory response snakes (many Boldae and Crotalldae) pass on to thermoreceptor orientation rather than visual (particularly so in the dark). 5. Then follows a lunge in non-venomous snakes (many batrachophages - Natrl

x, Nerodi

a, Thamnophi

s) and swallowing the prey alive or killing It first shortly after the strike. Venomous snakes start trailing the perished prey by olfactory reception exclusively, although in the case of small non-dangerous animal or bird prey which when stricken can run or fly a long way, the latter is not released until dying. The snake then releases the dead prey on the substrate, unmistakingly identifies the head and swallows the prey head first. Non-venomous snakes which constrict their prey (Pytho

n, Bo

a, Elaphe

) also lay it on the substrate after constriction and swallow it head first. This "ideal" picture of the hunting sequence is actually never demonstrated by one animal. Normally, certain behavioural actions in a particular situation appear to be irrelevant and are therefore omitted. It should be noted that discrimination of the prey objects is extremely high. The food item is discriminated by 1) movement pattern (DIEFENBACH & EMSLIE 1971, SMITH & WATSON 1972, HERZOG & BURGHARDT 1974), 2 ) size and shape (WIEDEMANN 1931), 3) smell (WIEDEMANN 1931), BURGHARDT 1967, 1968, 1973, 1977), 4) colour (SMITH & WATSON 1972), 4a) extent of the irradiated infra-red (when thermoreception is available, NOBLE & SCHMIDT 1937, GAMOV & HARRIS 1973), 5) "age". We have repeatedly observed in many snakes (Naja oxiana, Vipera lebetln

a, Coluber jugulari

s, Python reglus

) their ability to identify the age of the food item (in the context of imminent danger). Small blind mouse neonates were eaten without caution, swallowed alive, without being constricted or bitten, while adult mice capable of biting are constricted (or bitten by venomous snakes). The older the prey, the more cautious is the hunting. When Vipera lebetin

a, Vipera kaznakovl, Llasis macklot

i, Elaphe schrenk

l are presented with mouse neonates and adult mice, all the snakes kill and swallow adult rodents first, the swallowing of neonates comes after again. The same snakes show a differentiated approach when offered furred little mice, which can see and are capable of movements and defence (i.e. biting) as well as neonate blind rats (three times the size of mice). The snakes kill, then swallow smaller yet more adult mice, while they swallow alive helpless, though bigger, rats or else passively constrict and engulf them half-alive. When Python reglu

s, Python moluru

s and Eunectes notaeu

s are presented with grown up rats and neonate rabbits, which are 2-3 times bigger than rats, the pythons and anaconda attack and constrict the rats. However they crawl calmly towards the rabbits and swallow them. The amazing ability of snakes to identify the prey head after killing (even by neonate Elaphe and Lampropeltl

s - KLEIN & LOOP 1975) to facilitate the swallowing is due to olfactory and visual orientation (DIEFENBACH & EMSLIE 1971, HERZOG & BURGHARDT 1974, DUVALL et al. 1980). Direction of the fur as well as the presence of vibrisses also play a role. The snakes sometimes "blunder" in finding the right direction of engulfment and swallow the medial or posterior end first. A much higher percentage of error was observed by us in the snakes swallowing of newborn naked animals of a fairly large size. A strong odour producing a powerful olfactory effect makes the choice of direction of swallowing difficult as in the case of skin incision in the posterior end of the prey body ("blood smell"), which is misguiding. Olfactory reorientation resulting in error seems more likely in this situation. In "age" determination the snakes may be guided by the milk smell of neonate rodents. REFERENCES BISWAS, S., ACHARJIO, L.N. & MOHAPATRA, S. (1977): Observation on the feeding habit of the tree snake, common Indian Bronzeback, Dendrelaspis tristis (Daudin). - J.Bombay nat.Hist. Soc., 74 (3): 539-540.