Multimodal cues improve prey localization under complex environmental conditions

Abstract

Predators often eavesdrop on sexual displays of their prey. These displays can provide multimodal cues that aid predators, but the benefits in attending to them should depend on the environmental sensory conditions under which they forage. We assessed whether bats hunting for frogs use multimodal cues to locate their prey and whether their use varies with ambient conditions. We used a robotic set-up mimicking the sexual display of a male tú ngara frog (Physalaemus pustulosus) to test prey assessment by fringe-lipped bats (Trachops cirrhosus). These predatory bats primarily use sound of the frog's call to find their prey, but the bats also use echolocation cues returning from the frog's dynamically moving vocal sac. In the first experiment, we show that multimodal cues affect attack behaviour: bats made narrower flank attack angles on multimodal trials compared with unimodal trials during which they could only rely on the sound of the frog. In the second experiment, we explored the bat's use of prey cues in an acoustically more complex environment. Tú ngara frogs often form mixed-species choruses with other frogs, including the hourglass frog (Dendropsophus ebraccatus). Using a multi-speaker set-up, we tested bat approaches and attacks on the robofrog under three different levels of acoustic complexity: no calling D. ebraccatus males, two calling D. ebraccatus males and five D. ebraccatus males. We found that bats are more directional in their approach to the robofrog when more D. ebraccatus males were calling. Thus, bats seemed to benefit more from multimodal cues when confronted with increased levels of acoustic complexity in their foraging environments. Our data have important consequences for our understanding of the evolution of multimodal sexual displays as they reveal how environmental conditions can alter the natural selection pressures acting on them.

Collateral damage or a shadow of safety? The effects of signalling heterospecific neighbours on the risks of parasitism and predation

“…A previous study with captive bats suggests that heterospecific signallers could affect the evolution of signal structure by producing considerable acoustic noise [15]. This may result in increased reliance on active echolocation of motion cues produced by prey and selection against the associated visual signal components.…”

“…It remains plausible, however, that collateral damage or shadow of safety effects exist for other species calling in mixed-species choruses, especially when one prey species is highly preferred. Furthermore, the preferences of fringe-lipped bats for prey can change seasonally [35]; and these bats have been shown to alter their foraging behaviour in captivity when prey cues from multiple modalities are present, or if trained only to approach tú ngara frog calls, when hourglass treefrog calls are also played nearby [15]. A temporary or permanent change in preference across the population could give rise to risk transfer due to the collateral damage or shadow of safety effects.…”

“…High call rates or signal complexity, for example, increase attractiveness to predators and parasites [4,[9][10][11]. Likewise, proximity to signalling conspecifics can alter selective pressures acting on a calling individual through the dilution of risks posed by signal-oriented predators and parasites, or by increasing the perceptual challenges faced by such eavesdroppers [12][13][14][15].…”

Toward Testing for Multimodal Perception of Mating Signals

“…There are plenty of examples of multisensory processing in animals-predators, such as bats, locate their prey faster if they can use information in more than one modality (Rhebergen et al, 2015;Leavell et al, 2018). Bumblebees learn new food sources faster if they can combine visual and weakly electric signals of flowers (Clarke et al, 2013).…”

How do predators and scavengers locate resource hotspots within a tropical forest?

“…Knowledge of the cues used by different animals to exploit resources is important not only for understanding ecosystem function (Koski et al 2015;Rhebergen et al 2015), but also for management (Ward-Fear et al in press). For example, knowledge of attractant cues can facilitate control of problem fauna by identifying effective cues for trapping (Crossland et al 2012), and minimizing cues that attract those taxa to areas where they are especially problematic (Rodda et al 1999).…”