TY - JOUR T1 - Does bat response to traffic noise support the misleading cue hypothesis?Abstract Y1 - 2019 A1 - Geipel, Inga A1 - Amin, Bawan A1 - Rachel A. Page A1 - Halfwerk, Wouter ED - Candolin, Ulrika KW - anthropogenic noise KW - bats KW - evolutionary trap KW - Micronycteris microtis KW - misleading cues KW - Traffic noise AB -

The world has become a noisier place due to the increase in urbanization. Noise is generally considered an impediment, altering an animal’s behavior through masking or distraction. But noise can also provide useful information about the environment. For animals that rely on natural environmental noise as an indicator of favorable foraging conditions, increasing levels of anthropogenic noise might mislead informed decision-making. Bats use rain noise, a natural environmental cue, to delay their emergence from the roost, presumably to avoid sensory and metabolic costs associated with foraging in heavy rain. Here we tested the “misleading cue hypothesis,” asking whether traffic noise is mistaken for rain noise by bats. Given the acoustic similarity between rain noise and traffic noise, we predicted that bats would confuse the two. We conducted a playback experiment using rain, traffic, and ambient noise at natural roosts of common big-eared bats (Micronycteris microtis, Phyllostomidae) and recorded bat emergence behavior. In contrast to their response to rain noise, the bats did not delay roost emergence in response to traffic noise. Thus, we found that bats were able to discriminate between traffic noise and rain noise and were not misled by similarity in acoustic parameters in the two noise types, when emerging from their roost. Emerging bats did show more exploration flights during traffic noise than during rain noise, but not during ambient noise, suggesting that they perceive traffic noise as a novel acoustic cue. Our data provide new insights into perception of traffic noise by bats.

UR - https://academic.oup.com/beheco/article/30/6/1775/5574811 ER - TY - CHAP T1 - Be loved, be prey, be eaten Y1 - 2014 A1 - Rachel A. Page A1 - Michael J. Ryan A1 - Ximena E. Bernal AB -

Animal communication is one of the most fundamental of all social behaviors. It modulates interactions among neighbors and strangers, siblings and parents, and individuals and their prospective mates. One of the most fundamental functions of communication is to enhance the sender’s conspicuousness, to cause the sender to stand out against the background so it can be detected by the receiver. This is a challenge for signals that function over long distances, such as those that function in territorial advertisement and mate attraction, because signal intensity and fidelity decrease with distance from the sender. At longer distances a signal is less likely to be above the receiver’s threshold for detection and recognition, and it is also more likely to be masked by noise as the intensity of noise at the receiver is independent of its distance from the sender.

Another type of noise is generated by conspecifics signaling in the same channel. We may perceive a chorus of frogs or insects as a melodious, even co- operative unit. But to members of the chorus the calls of their neighbors are every bit as deleterious to their own call’s ability to be detected as is environ- mental noise. There is also “noise” within the perceptual systems of the receiver that ameliorates signal detection. One example is habituation. Upon continual exposure to a signal, an animal will tend to ignore it, and some of the animal’s neurons will cease to fire. Another type of perceptual noise is incremental forgetting of a signal once it is perceived. Some signals are more memorable than others, surviving longer in the receiver’s memory. The importance of conspecific noise and perceptual noise is usually less appreciated in animal communication studies than is environmental noise.

Selection often will favor senders to produce communication signals that stand out against these three types of background noise. Conspicuousness is accomplished in a variety of ways. In the acoustic domain animals can use fre- quency bands that contain less noise; they can call longer, at a faster rate, or at a higher amplitude; they can call during periods when others are silent; and they can produce calls that are more complex. Visual signals can stand out more against background when their spectral properties and spatial patterns differ from those in the background, when colors are brighter and patterns are more complex, and when motion patterns associated with the signal, such as push-up displays in lizards, are different than the pattern of background movement, such as vegetation being blow in the wind (e.g., Fleishman, 1992). Increasing signal complexity in both the acoustic and visual domains can to some extent remedy the receiver habituating to and forgetting a signal. There is less known about how chemical, tactile, and electrical signals can enhance contrast with the background.

In a survey of preferences for sexual signals, Michael Ryan and Anne Keddy-Hector (1992) showed that across modalities prospective mates tended to prefer sexual signals that were greater in magnitude: longer and louder, faster and brighter, more complex and with more background contrast. Although there were numerous cases in which prospective mates preferred signals that were near the population mean, there were few cases in which there was a preference for signals of lesser magnitude. A simple rule of thumb for sexual signals is that more is better. Selection for signal efficacy, however, creates a dilemma for the sender: the curse of unintended receivers. In general, each signal has evolved under selection to communi- cate with a specific intended receiver. In the case of sexual advertisement sig- nals, the intended receivers are prospective mates, usually female conspecifics. Other receivers can also detect and respond to signals even if there was no selection on the sender to communicate with them. We refer to these receivers as eavesdroppers or unintended receivers. It is important to note that the terms intended and unintended should not imply intention- ality but instead refer to hypotheses about the selection forces that favored the evolution of these signals. With few exceptions, senders and receivers do not communicate in a private channel. The world is populated by unin- tended receivers, eavesdroppers who are attendant to the signals of senders, often to the demise of senders. In this chapter we explore the tension that exists in sexual communication systems between being conspicuous to potential mates and attracting eavesdroppers, between being loved, being prey, and being eaten.

ER - TY - JOUR T1 - Synchronized mating signals in a communication network: the challenge of avoiding predators while attracting mates Y1 - 2019 A1 - Legett, Henry D. A1 - Rachel A. Page A1 - Ximena E. Bernal KW - acoustic communication KW - communication network KW - eavesdroppers KW - relaxed selection KW - synchrony AB -

Conspicuous mating signals attract mates but also expose signallers to predators and parasites. Signal evolution, therefore, is driven by conflicting selective pressures from multiple receivers, both target and non-target. Synchronization of mating signals, for example, is an evolutionary puzzle, given the assumed high cost of reduced female attraction when signals over- lap. Synchronization may be beneficial, however, if overlapping signals reduce attraction of non-target receivers. We investigate how signal synchro- nization is shaped by the trade-off between natural and sexual selection in two anuran species: pug-nosed tree frogs (Smilisca sila), in which males pro- duce mating calls in near-perfect synchrony, and túngara frogs (Engystomops pustulosus), in which males alternate their calls. To examine the trade-off imposed by signal synchronization, we conducted field and laboratory play- back experiments on eavesdropping enemies (bats and midges) and target receivers (female frogs). Our results suggest that, while synchronization can be a general strategy for signallers to reduce their exposure to eavesdrop- pers, relaxed selection by females for unsynchronized calls is key to the evolution and maintenance of signal synchrony. This study highlights the role of relaxed selection in our understanding of the origin of mating signals and displays.

UR - https://royalsocietypublishing.org/doi/10.1098/rspb.2019.1067 ER - TY - JOUR T1 - Noise as an informational cue for decision-making: the sound of rain delays bat emergence JF - The Journal of Experimental Biology Y1 - 2019 A1 - Geipel, Inga A1 - Smeekes, Marcus J. A1 - Halfwerk, Wouter A1 - Rachel A. Page KW - bats KW - decision-making KW - foraging KW - information cues KW - Noise KW - rain AB -

Background noise can have strong negative consequences on animals, reducing individual fitness by masking communication signals, impeding prey detection and increasing predation risk. While the negative impacts of noise across taxa have been well documented, the use of noise as an informational cue, providing animals with reliable information on environmental conditions has been less well studied. In the tropical rainforest, downpours can be intense and frequent. Strong rainfall may impede efficient orientation and foraging for bats that need echolocation to both navigate and detect prey, and can result in higher flight costs due to increased metabolic rates. Using playback experiments at natural roosts we tested whether two bat species, differing in their hunting strategies and foraging habitats, use rain noise as a cue to delay emergence from their roosts. We found that both species significantly delayed their emergence time during rain noise playbacks compared to silence and ambient noise controls. We conclude that bats can use background noise, here the acoustic component of rainfall, as a reliable informational cue to make informed decisions, here about whether to initiate foraging trips or remain in the shelter of their roosts. Our findings suggest that environmental background noise can sometimes be beneficial to animals, in particular in situations where other sensory cues may be absent.

UR - http://jeb.biologists.org/lookup/doi/10.1242/jeb.192005https://syndication.highwire.org/content/doi/10.1242/jeb.192005https://syndication.highwire.org/content/doi/10.1242/jeb.192005 JO - J Exp Biol ER - TY - JOUR T1 - Cognitive constraints on optimal foraging in frog-eating bats JF - Animal Behaviour Y1 - 2018 A1 - Hemingway, Claire T. A1 - Michael J. Ryan A1 - Rachel A. Page KW - Decision making KW - foraging KW - frog-eating bat KW - patch choice KW - proportional processing KW - tĂșngara frog AB -

Animals are expected to optimize energy intake when choosing between different foraging options. A common explanation for deviations from optimal economic decisions is that there is an imperfect relationship between physical reality and an animal's perceptual processes, which can constrain assessment of profitability. One such phenomenon that is apparently ubiquitous across taxa is proportional processing, where a perceived change in a stimulus is proportional to the change in stimulus magnitude. In this study, we investigated whether proportional processing explains how frog-eating bats, Trachops cirrhosus, discriminate between patches of frog choruses that vary in their number of calling frogs. To test this, we created artificial choruses consisting of one to six calling frogs. In the flight cage, we then tested the preference of bats (N = 17) with every pairwise combination of chorus size. We found that while bats generally preferred larger choruses, preferences for larger choruses were better explained by the relative, not absolute, differences in chorus sizes. This indicates that T. cirrhosus is perceptually limited in its ability to discriminate between choruses of varying size as the choruses increase in size. Foragers are likely to be less choosy when choosing among larger patches.

VL - 143 UR - https://linkinghub.elsevier.com/retrieve/pii/S0003347218302227https://api.elsevier.com/content/article/PII:S0003347218302227?httpAccept=text/xmlhttps://api.elsevier.com/content/article/PII:S0003347218302227?httpAccept=text/plain JO - Animal Behaviour ER - TY - JOUR T1 - Interactions between complex multisensory signal components result in unexpected mate choice responses JF - Animal Behaviour Y1 - 2017 A1 - Stange, Nicole A1 - Rachel A. Page A1 - Michael J. Ryan A1 - Taylor, Ryan C. KW - anurans KW - mate choice KW - multimodal signalling KW - nonlinear interactions KW - sexual selection KW - signal weighting KW - tĂșngara frog KW - vocal sac AB -

Multimodal (multisensory) signalling is common in many species and often facilitates communication. How receivers integrate individual signal components of multisensory displays, especially with regard to variance in signal complexity, has received relatively little attention. In nature, male túngara frogs, Physalaemus pustulosus, produce multisensory courtship signals by vocalizing and presenting their inflating and deflating vocal sac as a visual cue. Males can produce a simple call (whine only) or a complex call (whine þ one or more chucks). In a series of two-choice experiments, we tested female preferences for variation in acoustic call complexity and amplitude (unimodal signals). We then tested preferences for the same calls when a dynamic robotic frog was added to one call, generating a multi- modal stimulus. Females preferred a complex call to a simple call; when both calls contained at least one chuck, additional numbers of chucks did not further increase attractiveness. When calls contained zero or one chuck, the visual stimulus of the robofrog increased call attractiveness. When calls contained multiple chucks, however, the visual component failed to enhance call attractiveness. Females also preferred higher amplitude calls and the addition of the visual component to a lower amplitude call did not alter this preference. At relatively small amplitude differences, however, the visual signal increased overall discrimination between the calls. These results indicate that the visual signal component does not provide simple enhancement of call attractiveness. Instead, females integrate multisensory components in a nonlinear fashion. The resulting perception and behavioural response to complex signals probably evolved in response to animals that communicate in noisy environments.

VL - 134 UR - http://linkinghub.elsevier.com/retrieve/pii/S000334721630121X JO - Animal Behaviour ER -