The Role of Sensory Receptors in the Predatory Behavior of the Brown Tree Snake, Boiga irregularis (Squamata: Colubridae)

Abstract

The brown tree snake (Boiga irregularis) is indigenous to parts of costal Australia, New Guinea, and the Solomon Islands (McCoy, 1980; Cogger, 1983). It can be found in a variety of habitats (Fritts, 1988), but it is arboreal and most common in primary and secondary growth forests (Savidge, 1986, 1987; Fritts et al., 1987). Its dentition is usually referred to as rear fanged, in which one or two posterior maxillary teeth are enlarged and bear on their labial faces an open groove associated with a connecting duct from Duvernoy's gland. The snakes appear to feed opportunistically: stomach and intestinal content analyses reveal a diet of birds and their eggs, lizards and their eggs, and small mammals (Savidge, 1988). The diets of males and females are the same, but medium to large snakes (over 120 cm SVL) tend to consume a larger proportion of birds, bird eggs, and mammals (Savidge, 1988). They are considered nocturnal in their natural habitat (Fritts, 1988; Chiszar, 1990), an activity continued in captivity (Chiszar et al., 1985). The eyes of the brown tree snake are large and the pupils are slit-like. A vomeronasal organ is present, but like other colubrid snakes, the brown tree snake lacks anatomically distinct thermosensitive facial pits. Eyes, chemosensory receptors (olfactory epithelium, vomeronasal organ), and thermosensitive pits are known to be important in the predatory behavior of certain venomous snakes (de Cock Buning, 1983). When denied visual information, pit vipers can still uccessfully strike prey, presumably by compensating with thermosensitive receptors (Noble and Schmidt, 1937; Dullemeijer, 1961). However, without such alternative sensory receptors the brown tree snake would seem to require alternative sensory input to compensate for loss of visual information during nocturnal forays for food. To assess feeding performance in the absence of visual information, prey capture success of brown tree snakes with and without blindfolds was compared. The purposes of this experiment were to describe the changes in predatory behavior (normal and blindfolded), and to produce hypotheses about how the sensory versatility of the nervous system might modulate the strike based upon alternative routes of sensory input. All brown tree snakes used were collected on Guam.