4pAB3 – Can a spider “sing”? If so, who might be listening?

Alexander L. Sweger – swegeral@mail.uc.edu
George W. Uetz – uetzgw@ucmail.uc.edu
University of Cincinnati
Department of Biological Sciences
2600 Clifton Ave, Cincinnati OH 45221

Popular version of paper 4pAB3, “the potential for acoustic communication in the ‘purring’ wolf spider’
Presented Thursday afternoon, May 21, 2015, 2:40 PM, Rivers room
169th ASA Meeting, Pittsburgh
Click here to read the abstract

While we are familiar with a wide variety of animals that use sound to communicate- birds, frogs, crickets, etc.- there are thousands of animal species that use vibration as their primary means of communication. Since sound and vibration are physically very similar, the two are inextricable connected, but biologically they are still somewhat separate modes of communication. Within the field of bioacoustics, we are beginning to fully realize how prevalent vibration is as a mode of animal communication, and how interconnected vibration and sound are for many species.

Wolf spiders are one group that heavily utilizes vibration as a means of communication, and they have very sensitive structures for “listening” to vibrations. However, despite the numerous vibrations that are involved in spider communication, they are not known for creating audible sounds. While a lot of species that use vibration will simultaneously use airborne sound, spiders do not possess structures for hearing sound, and it is generally assumed that they do not use acoustic communication in conjunction with vibration.

The “purring” wolf spider (Gladicosa gulosa) may be a unique exception to this assumption. Males create vibrations when they communicate with potential mates in a manner very similar to other wolf spider species, but unlike other wolf spider species, they also create airborne sounds during this communication. Both the vibrations and the sounds produced by this species are of higher amplitude than other wolf spider species, both larger and smaller, meaning this phenomenon is independent of species size. While other acoustically communicating species like crickets and katydids have evolved structures for producing sound, these spiders are vibrating structures in their environment (dead leaves) to create sound. Since we know spiders do not possess typical “ears” for hearing these sounds, we are interested in finding out if females or other males are able to use these sounds in communication. If they do, then this species could be used as an unusual model for the evolution of acoustic communication.

An image of a male "purring" wolf spider, Gladicosa gulosa, and the spectrogram of his accompanied vibration. Listen to a recording of the vibration here,

Figure 1: An image of a male “purring” wolf spider, Gladicosa gulosa, and the spectrogram of his accompanied vibration. Listen to a recording of the vibration here,

and the accompanying sound here.

Our work has shown that the leaves themselves are vital to the use of acoustic communication in this species. Males can only produce the sounds when they are on a surface that vibrates (like a leaf) and females will only respond to the sounds when they are on a similar surface. When we remove the vibration and only provide the acoustic signal, females still show a significant response and males do not, suggesting that the sounds produced by males may play a part in communicating specifically with females.

So, the next question is- how are females responding to the airborne sound without ears? Despite the relatively low volume of the sounds produced, they can still create a vibration in a very thin surface like a leaf. This creates a complex method of communication- a male makes a vibration in a leaf that creates a sound, which then travels to another leaf and creates a new vibration, which a female can then hear. While relatively “primitive” compared to the highly-evolved acoustic communication in birds, frogs, insects, and other species, this unique usage of the environment may create opportunities for studying the evolution of sound as a mode of animal communication.

Robotic Sonar System Inspired by Bats

Robotic Sonar System Inspired by Bats

Team at Virginia Tech hopes to create small, efficient sonar systems that use less power than current arrays

WASHINGTON, D.C., May 20, 2015 — Engineers at Virginia Tech have taken the first steps toward building a novel dynamic sonar system inspired by horseshoe bats that could be more efficient and take up less space than current man-made sonar arrays. They are presenting a prototype of their “dynamic biomimetic sonar” at the 169th Meeting of the Acoustical Society of America in Pittsburg, Penn.

Bats use biological sonar, called echolocation, to navigate and hunt, and horseshoe bats are especially skilled at using sounds to sense their environment. “Not all bats are equal when it comes to biosonar,” said Rolf Müller, a mechanical engineer at Virginia Tech. “Horseshoe bats hunt in very dense forests, and they are able to navigate and capture prey without bumping into anything. In general, they are able to cope with difficult sonar sensing environments much better than we currently can.”

To uncover the secrets behind the animal’s abilities, Müller and his team studied the ears and noses of bats in the laboratory. Using the same motion-capture technology used in Hollywood films, the team revealed that the bats rapidly deform their outer ear shapes to filter sounds according to frequency and direction and to suit different sensing tasks.

“They can switch between different ear configurations in only a tenth of a second – three times faster than a person can blink their eyes,” said Philip Caspers, a graduate student in Müller’s lab.

Unlike bat species that employ a less sophisticated sonar system, horseshoe bats emit ultrasound squeaks through their noses rather than their mouths. Using laser-Doppler measurements that detect velocity, the team showed that the noses of horseshoe bats also deform during echolocation–much like a megaphone whose walls are moving as the sound comes out.

The team has now applied the insights they’ve gathered about horseshoe bat echolocation to develop a robotic sonar system. The team’s sonar system incorporates two receiving channels and one emitting channel that are able to replicate some of the key motions in the bat’s ears and nose. For comparison, modern naval sonar arrays can have receivers that measure several meters across and many hundreds of separate receiving elements for detecting incoming signals.

By reducing the number of elements in their prototype, the team hopes to create small, efficient sonar systems that use less power and computing resources than current arrays. “Instead of getting one huge signal and letting a supercomputer churn away at it, we want to focus on getting the right signal,” Müller said.

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On Bleats, in the Year of the Sheep

David G. Browning, 139 Old North Road, Kingston, RI 02881 decibeldb@aol.com

Peter M. Scheifele, Dept. of Communication Science, Univ. of Cincinnati, Cincinnati, OH 45267
Click here to read the abstract

A bleat is usually defined as the cry of a sheep or goat but they are just two voices in a large worldwide animal chorus that we are just starting to understand.

A bleat is a simple short burst of sound comprised of harmonic tones. It is easily voiced by young or small animals, who are the majority of the bleaters. From deer to polar bears; muskoxen to sea lions, the young bleats produce a sound of enough character to allow easy detection and possible identification by concerned mothers. As these animals mature usually their voices shift lower, longer, and louder and a vocabulary of other vocalizations are developed.

But for some notable exceptions this is not the case. For example, sheep and goats retain their bleating structure as their principal vocalization through adulthood – hence bleating is usually associated with them. Their bleats have been the most studied and show a characteristic varietal structure and at least a limited ability for maternal recognition of specific individuals.

For another example, at least four small varieties of toad, such as the Australian Bleating Toad and in America, the Eastern Narrow Mouthed Toad are strong bleaters through their entire life. Bleats provide them a signature signal that carries in the night and is easily repeatable and sustainable. But why these four amphibians? Our lack of an answer speaks to our still limited knowledge of the vast field of animal communication.

Perhaps most interestingly, the Giant Panda retains bleating while developing a complex mix of other vocalizations. It is probably the case that in the visually challenging environment of a dense bamboo thicket they must retain all possible vocal tools to communicate. Researchers link their bleating to male size and female age.

In summary, bleating is an important aspect of youth for many animals; for some it is the principal vocalization for life; and, for a few, a retained tool among many.

2pAB9 – Vocal behavior of Southeast Alaskan humpback whales: context matters

Michelle Fournet – michelle.fournet@gmail.com
Oregon State University
425 SE Bridgeway Ave
Corvallis, OR 97333

David K. Mellinger – david.k.mellinger@noaa.gov
Cooperative Institute for Marine Resources Studies, Oregon State University
NOAA Pacific Marine Environmental Laboratory
2030 SE Marine Science Dr.
Newport, OR 97365

Lay language paper 2pAB9
Presented Tuesday Afternoon, October 28th, 2014
168th ASA Meeting, Indianapolis

Humpback whales (Megaptera novaeangliae) were made famous by the discovery that male whales sing long complex songs on the breeding grounds[1]. Humpbacks, however, also produce a wide range of sounds throughout their range—purrs, shrieks, whups, moans, and more—that have received considerably less attention[2-5]. Unlike song, which is produced exclusively by male whales and serves a presumptive breeding purpose, males, females, and juveniles all produce these ‘non-song vocalizations’ [3, 4, 6-10], although the context under which these sounds are used remains largely unknown.

The ocean is getting louder. As shipping throughout the North Pacific, and the world, continues to increase humpback whales, and many other acoustically oriented marine animals, run the risk of being negatively impacted by an inundation of man-made (anthropogenic) noise. Large vessel noise from shipping in particular may have the ability to acoustically mask humpback whale vocalizations, preventing animals from being able to detect one another (Figure 1).

Fournet_Figure1

Figure 1 – Humpback whales increasingly share the ocean with vessels ranging in size from cruise ships to zodiacs. All motorized vessels have the potential to input some sort of noise into the marine environment. As acoustically oriented animals humpbacks whales produce a wide range of vocalizations to communicate, though their function is not yet understood.

The ability to adapt to these changing ocean conditions may be critical for the success of the species, and the ecosystems they inhabit. Recognizing adaptation in the face of a changing ocean is contingent on understanding vocal behavior now in a relatively quiet ocean, and comparing it to future behavior. Understanding patterns of use and the role of non-song vocal behavior in humpback whale communication allows for a more comprehensive assessment of the potential risks of increasing man-made (anthropogenic) noise.

Fournet_Figure2 - Southeast Alaskan humpback whales

Figure 2 – A recent study of Southeast Alaskan humpback whales found that whales produce at least 16 unique call types that fall into one of four vocal classes. Example spectrograms (visual representations of sound) of calls from each class are shown above: (L-R) Low-Frequency Harmonic, Pulsed, Noisy/Complex, Tonal.

Sound File 1 – An example of a Southeast Alaskan ‘whup’ call (file missing)
Sound File 2 – An example of a Southeast Alaskan ‘swop’ call

Sound File 3 –  An example of a Southeast Alaskan ‘Ascending Shriek’ (file missing)
Sound File 4 – An example of a Southeast Alaskan ‘Feeding Call’

In Southeast Alaska humpback whales are known to produce at least sixteen unique vocalizations that fall into four vocal classes (Figure 2, Sounds 1-4). In this study we investigated whether call types from each vocal class were used equally, and what impact social interaction between animals may have on vocal behavior. What we found was that unlike song, which is highly stereotyped and repeated throughout the breeding season, the use of non-song calls on foraging grounds is at least somewhat context driven and may be spatially mediated. For example, the use of pulsed (P) calls, including wops, swops, and horse calls, increased as whale clustered together on a foraging ground. Furthermore, as clustering increased the vocal behavior of the whales grew more diverse; indicating that as the opportunity for close range interaction increased the amount of information conveyed with vocalizations grew more complex

Not all calls were used equally; some calls, like the Southeast Alaskan “Growl” and “Whup” calls, dominated the soundscape, while other calls with structure more reminiscent of song were relatively uncommon. The whup and growl calls, which have been proposed as contact calls, made up more than half of the vocalizations detected throughout the study. While the discrete function of these and other non-song vocalizations is still unknown, this study indicates that non-song vocalizations serve a communicative function that may be social in nature. Work like this lays the foundation for investigation into discrete call function and vocal resilience; two topics which will play a key role in understanding the vocal behavior of humpback whales and how they respond to increasing anthropogenic noise in our world’s oceans. (Figure 3)

Fournet_figure3 - Humpback whales

Figure 3 – Humpback whales are considered a medium sized baleen whale, weighing in at approximately 35 tons in weight and reaching lengths of 30-50 feet.

  1. Payne, R.S. and S. McVay, Songs of humpback whales. Science, 1971. 173(3397): p. 585-597.
  2. Dunlop, R.A., D.H. Cato, and M.J. Noad, Non-song acoustic communication in migrating humpback whales (Megaptera novaeangliae). Marine Mammal Science, 2008. 24(3): p. 613-629.
  3. Stimpert, A.K., et al., Common humpback whale (Megaptera novaeangliae) sound types for passive acoustic monitoring. Journal of the Acoustical Society of America, 2011. 129(1): p. 476-82.
  4. Fournet, M., Vocal repertoire of Southeast Alaska humpback whales (Megaptera novaeangliae), in Marine Resource Management2014, Oregon State University.
  5. Rekdahl, M.L., et al., Temporal stability and change in the social call repertoire of migrating humpback whales. Journal of the Acoustical Society of America, 2013. 133(3): p. 1785-1795.
  6. Dunlop, R.A., et al., The social vocalization repertoire of east Australian migrating humpback whales (Megaptera novaeangliae). Journal of the Acoustical Society of America, 2007. 122(5): p. 2893-905.
  7. Silber, G.K., The relationship of social vocalizations to surface behavior and aggression in the Hawaiian humpback whale (Megaptera novaeangliae). Canadian Journal of Zoology, 1986. 64(10): p. 2075-2080.
  8. Cerchio, S. and M. Dalheim, Variations in feeding vocalizations of humpback whales (Megaptera novaeangliae) from southeast Alaska. Bioacoustics, 2001. 11/4(11 4): p. 277-295.
  9. Stimpert, A.K., et al., ‘Megapclicks’: acoustic click trains and buzzes produced during night-time foraging of humpback whales (Megaptera novaeangliae). Biology letters, 2007. 3(5): p. 467-70.
  10. Zoidis, A.M., et al., Vocalizations produced by humpback whale (Megaptera novaeangliae) calves recorded in Hawaii. Journal of the Acoustical Society of America, 2008. 123(3): p. 1737-46.

1aAB11 – A New Dimension to Bat Biosonar

Rolf Müller – rolf.mueller@vt.edu
Anupam K. Gupta – anupamkg@vt.edu
Yanqing Fu – fyq@vt.edu
Uzair Gillani – uzair@vt.edu
Hongxiao Zhu – hongxiao@vt.edu

Virginia Tech
1075 Life Science Circle
Blacksburg, VA 24061

Popular version of paper 1aAB11
Presented Monday morning, October 27, 2014
168th ASA Meeting, Indianapolis

Sonar is a sensing modality that is found in engineering as well as in nature. Man-made sonar systems can be found in places that include the bows of nuclear submarines and the bumpers of passenger cars. Likewise, natural sonar systems can be found in toothed whales that can weigh over 50 tons as well as in tiny bats that weigh just a few grams. All these systems have in common that they emit ultrasonic waves and listen to the returning echoes for clues as to what may be going on in their environments.

Beyond these basic commonalities, man-made and biological sonar systems differ radically in their approach to emitting and receiving the ultrasonic waves. Human sonar engineers tend to favor large numbers of simple elements distributed over a wide area. For example, sonar engineers fit hundreds of emitting and receiving elements into the bow of a nuclear submarine and even automotive engineers often arrange a handful of elements along the bumper of a car. As small flying mammals, bats did not have the option of distributing a large number of sonar elements over wide areas. Instead, they were forced to take a radically different approach. This biological approach has led to sonar systems that are based on a small number of highly complex emitting and receiving elements. At the same time, they have achieved levels of performance that remain unmatched by their man-made peers.

Bat biosonar has only one emitting element, in some bat species this is the mouth and in other, nasally emitting species, the nose. In all bat species, the echoes are received through two receiving elements, i.e., the two ears. But where is the complexity that allows these three elements to vastly outperform naval sonars with hundreds of emitting and receiving elements?

Over the past few years, research on two groups (families) of bats with particularly sophisticated sonar systems has yielded clues to the existence of a new functional dimension in bat biosonar that could be a key factor behind the remaining performance gap between engineered sonar and biosonar. Horseshoe bats (Rhinolophidae) and Old World leaf-nosed bats (Hipposideridae) emit their biosonar pulses nasally and have elaborate baffle shapes (so-called “noseleaves”) that surround the nostrils and can be seen to act as miniature megaphones.
Old World leaf-nosed bat
Figure 1. Noseleaves (“miniature megaphones”) and outer ears of Old World leaf-nosed bats.

Close-up studies of live bats have shown that the noseleaves and the outer ears of these species are both highly dynamic structures. The noseleaves of these bats, for example, have not only much greater geometric complexity than man-made megaphones, but most intriguingly their walls are dynamic: Each time the bat emits an ultrasonic wave packet through its nostrils, it can set the walls of its noseleaf in motion. Hence, the outgoing ultrasonic wave interacts with a changing surface geometry. On the reception side, certain horseshoe bats, for example, have been shown to change the shape of their outer ears within one tenth of second. This is about three times as fast as the proverbial blink of an eye. As for the noseleaf, these changes in shape can take place as the bat receives the ultrasonic echoes.

Figure 2 (video). Motions of the outer ear in an Old World leaf-nosed bats (landmarks added for tracking purposes).

While it is still not certain whether these dynamic features in the sonar system of bats have a function and help the animals to improve their sensory abilities, there is a growing body of evidence that suggests that these fast changes are more than just an oddity. The shape changes in the noseleaves and outer ears are the results of a highly specialized muscular machinery that is unlikely to have evolved without a significant functional advantage acting as a driving force. The resulting changes in shape are big enough to have an impact on the interaction between surface geometry and the passing ultrasonic waves and indeed acoustic impacts have been demonstrated using numerical as well as experimental methods. Finally, dynamic effects are wide-spread among bats with sophisticated sonar systems and are even found in unrelated species that are most likely to have acquired them in response to parallel evolutionary pressures.