Niche-specific cognitive strategies: object memory interferes with spatial memory in the predatory bat, Myotis nattereri

Abstract

Related species with different diets are predicted to rely on different cognitive strategies: those best suited for locating available and appropriate foods. Here we tested two predictions of the nichespecific cognitive strategies hypothesis in bats, which suggests that predatory species should rely more on object memory than on spatial memory for finding food and that the opposite is true of frugivorous and nectivorous species. Specifically, we predicted that: (1) predatory bats would readily learn to associate shapes with palatable prey and (2) once bats had made such associations, these would interfere with their subsequent learning of a spatial memory task. We trained freeflying Myotis nattereri to approach palatable and unpalatable insect prey suspended below polystyrene objects. Experimentally naïve bats learned to associate different objects with palatable and unpalatable prey but performed no better than chance in a subsequent spatial memory experiment. Because experimental sequence was predicted to be of consequence, we introduced a second group of bats first to the spatial memory experiment. These bats learned to associate prey position with palatability. Control trials indicated that bats made their decisions based on information acquired through echolocation. Previous studies have shown that bat species that eat mainly nectar and fruit rely heavily on spatial memory, reflecting the relative consistency of distribution of fruit and nectar compared with insects. Our results support the niche-specific cognitive strategies hypothesis and suggest that for gleaning and clutter-resistant aerial hawking bats, learning to associate shape with food interferes with subsequent spatial memory learning.

Bats are still not birds in the digital era: echolocation call variation and why it matters for bat species identification

“…Based on acoustic tomography representations of prey resting on substrate, Clare and Holderied (2015) proposed that bats perceive changes in the depth profile and acoustic shadows cast by prey, especially when the surface ensonified is smooth (detection would be more difficult for cluttered surfaces, where prey might be concealed acoustically). Echolocation may also be used by gleaners to recognize the shape of specific plant species that are likely to host prey (Siemers 2001;Hulgard and Ratcliffe 2014).…”

Echolocating bats inspect and discriminate landmark features to guide navigation

“…When tested in a twochoice task with a novel feeder of a different shape, these bats flew repeatedly to the trained round-shaped feeder, even though it was empty. Furthermore, Hulgard and Ratcliffe (2014) reported that object feature learning can inhibit later spatial location learning in M. nattereri. In our study, the insectivorous big brown bat (E. fuscus) learned to use the features of a landmark to guide its navigation, despite the changing landmark position across trials.…”

“…When tested in cue-conflicting conditions with no reward, both nectarivorous and frugivorous bat species preferred to visit the feeder consistent with the spatial cues (Carter et al, 2010;Thiele and Winter, 2005). By contrast, studies of insectivorous species (Myotis nattereri), which normally chase moving prey, showed that bats can rely on feature cues to locate food (Hulgard and Ratcliffe, 2014;Siemers, 2001). Siemers (2001) trained gleaning bats (Myotis nattereri) to feed in a round-shaped feeder.…”

“…Nectarivorous and frugivorous bats rely preferentially on spatial location cues over stimulus cues when feeder locations remain constant on a wall during training (Carter et al, 2010;Thiele and Winter, 2005). However, in conditions under which feeding locations were not constant across trials during training, insectivorous bats instead learned to use object features to find a goal (Hulgard and Ratcliffe, 2014;Siemers, 2001). Additionally, insectivorous big brown bats can learn to rely on the location of a moving landmark to guide navigation (Jensen et al, 2005).…”

Free-ranging bats combine three different cognitive processes for roost localization

“…A hierarchical use of spatial memory over associative learning has also been observed in the foraging behavior of nectar-feeding animals such as carpenter bees (Orth and Waddington 1997), hummingbirds (Hurly and Healy 1996) and bats (Thiele and Winter 2005;Stich and Winter 2006;Carter et al 2010) whose foraging resources are also relatively predictable in space and time. On the contrary, animals preying on unpredictable resources (e.g., swarms of insects) rely more on associative learning than on spatial memory to localize known resources (Hulgard and Ratcliffe 2014).…”