The New Zealand short-tailed bat Mystacina tuberculata

(Chiroptera: Mystacinidae) has been of great interest to biologists (see Lloyd, 2001 for a review). It is one of only two extant indigenous mammals in New Zealand, the other being the long-tailed bat Chalinolobus tuberculatus (O’Donnell, 2001). It therefore evolved in the absence of small terrestrial mammals and, until recent introductions of predators by humans, may have been exposed to few predators. The absence of small terrestrial mammals and reduced predation risk may have permitted the exploitation of terrestrial prey by M. tuberculata. Dietary analyses show that M. tuberculata is omnivorous, eating arthropods (many of which are nonflying), pollen, nectar (Arkins et al., 1999) and fruit (Daniel, 1979, 1990). While most bats capture prey in the air, or by briefly gleaning from surfaces, M. tuberculata is unusual in that it searches for both plant material (Daniel, 1979) and insects (Parsons, 1998) while on the ground. M. tuberculata shows several adaptations for terrestrial behaviour. Strong legs and feet confer considerable agility on the ground (Dwyer, 1962; Daniel, 1976), and basal talons on the claws may be used in burrowing (Daniel, 1979). Moreover, the bats can fold their wings tightly, allowing use of the forearms for terrestrial locomotion (Dwyer, 1962; Daniel, 1979). Indeed, Daniel (1979) speculated that M. tuberculata might spend up to 40% of its time foraging on terrestrial and arboreal invertebrates. The varied diet and terrestrial adaptations of M. tuberculata make it interesting from a sensory ecology perspective. M. tuberculata has relatively large ears (O’Donnell et al., 1999) and prominent nostrils (Daniel, 1979), implying that it may listen for prey-generated sounds and may use olfaction in the detection of food. Because the bats eat both volant and nonvolant arthropod prey (Arkins et al., 1999), we expect that they will face different sensory challenges for the detection and localization of prey in cluttered (clutter echoes are echoes other than those from the target of interest) and non-cluttered space (Faure and Barclay, 1994). In highly cluttered space, background echoes overlap with prey echoes, and masking of prey echoes by clutter echoes makes detection of prey problematic. Bats that emit frequency-modulated (FM) calls mainly use prey-generated acoustic cues for the detection and localization of prey in clutter (Schnitzler and Kalko, 1998). The Indian false vampire bat Megaderma lyra may use echolocation to detect prey in limited clutter (Schmidt et al., 4209 The Journal of Experimental Biology 206, 4209-4216 © 2003 The Company of Biologists Ltd doi:10.1242/jeb.00678