Popular version of paper 2pABa9, “The metabolic costs of producing clicks and social sounds differ in bottlenose dolphins (Tursiops truncatus).”
Presented Tuesday afternoon, November 3, 2015, 3:15, City Terrace room
170th ASA Meeting Jacksonville
Dolphins are known to be quite vocal, producing a variety of sounds described as whistles, squawks, barks, quacks, pops, buzzes and clicks. These sounds can be tonal (think whistle) or broadband (think buzz), short or long, or loud or not. Some sounds, such as whistles, are used in social contexts for communication. Other sounds, such as clicks and buzzes, are used for echolocation, a form of active biosonar that is important for hunting fish . Regardless of what type of sound a dolphin makes in its diverse vocal repertoire, sounds are generated in an anatomically unique way compared to other mammals. Most mammals, including humans, make sound in their throats or technically, in the larynx. In contrast, dolphins make sound in their nasal cavity via two sets of structures called the “phonic lips” .
All sound production comes at an energetic cost to the signaler . That is, when an animal produces sound, metabolic rate increases a certain amount above baseline or resting (metabolic) rate. Additionally, many vociferous animals, including dolphins and other marine mammals, modify their acoustic signals in noise. That is, they call louder, longer or more often in an attempt to be heard above the background din. Ocean noise levels are rising, particularly in some areas from shipping traffic and other anthropogenic activities and this motivated a series of recent studies to understand the metabolic costs of sound production and vocal modification in dolphins.
We recently measured the energetic cost for both social sound and click production in dolphins and determined if these costs increased when the animals increased the loudness or other parameters of their sounds [4,5]. Two bottlenose dolphins were trained to rest and vocalize under a specialized dome which allowed us to measure their metabolic rates while making different kinds of sounds and while resting (Figure 1). The dolphins also wore an underwater microphone (a hydrophone embedded in a suction cup) on their foreheads to keep track of vocal performance during trials. The amount of metabolic energy that the dolphins used increased as the total acoustic energy of the vocal bout increased regardless of the type of sound the dolphin made. The results clearly demonstrate that higher vocal effort results in higher energetic cost to the signaler.
Figure 1 – A dolphin participating in a trial to measure metabolic rates during sound production. Trials were conducted in Dr. Terrie Williams’ Mammalian Physiology lab at the University of California Santa Cruz. All procedures were approved by the UC Santa Cruz Institutional Animal Care and Use Committee and conducted under US National Marine Fisheries Service permit No.13602.
These recent results allow us to compare metabolic costs of production of different sound types. However, the average total energy content of the sounds produced per trial was different depending on the dolphin subject and whether the dolphins were producing social sounds or clicks. Since metabolic cost is dependent on vocal effort, metabolic cost comparisons across sound types need to be made for equal energy sound production.
The relationship between energetic cost and vocal effort for social sounds allowed us to predict metabolic costs of producing these sounds at the same sound energy as in click trials. The results, shown in Figure 2, demonstrate that bottlenose dolphins produce clicks at a very small fraction of the metabolic cost of producing whistles of equal energy. These findings are consistent with empirical observations demonstrating that considerably higher air pressure within the dolphin nasal passage is required to generate whistles compared to clicks . This pressurized air is what powers sound production in dolphins and toothed whales  and mechanistically explains the observed difference in metabolic cost between the different sound types.
Figure 2 – Metabolic costs of producing social sounds and clicks of equal energy content within a dolphin subject.
Differences in metabolic costs of whistling versus clicking have implications for understanding the biological consequences of behavioral responses to ocean noise. Across different sound types, metabolic costs depend on vocal effort. Yet, overall costs of producing clicks are substantially lower than costs of producing whistles. The results reported in this paper demonstrate that the biological consequences of vocal responses to noise can be quite different depending on the behavioral context of the animals affected, as well as the extent of the response.
Au, W. W. L. The Sonar of Dolphins, New York: Springer-Verlag.
Cranford, T. W., et al., Observation and analysis of sonar signal generation in the bottlenose dolphin (Tursiops truncatus): evidence for two sonar sources. Journal of Experimental Marine Biology and Ecology, 2011. 407: p. 81-96.
Ophir, A. G., Schrader, S. B. and Gillooly, J. F., Energetic cost of calling: general constraints and species-specific differences. Journal of Evolutionary Biology, 2010. 23: p. 1564-1569.
Noren, D. P., Holt, M. M., Dunkin, R. C. and Williams, T. M. The metabolic cost of communicative sound production in bottlenose dolphins (Tursiops truncatus). Journal of Experimental Biology, 2013. 216: 1624-1629.
Holt, M. M., Noren, D. P., Dunkin, R. C. and Williams, T. M. Vocal performance affects metabolic rate in dolphins: implication for animals communicating in noisy environments. Journal of Experimental Biology, 2015. 218: 1647-1654.
Popular version of paper 4aAB2, “Seemingly simple songs: Black-capped chickadee song revisited”
Presented Thursday morning, November 5, 8:55 AM, City Terrace Room
170th ASA Meeting, Jacksonville, Fl
Vocal communication is a mode of communication important to many animal species, including humans. Over the past 60 years, songbird vocal communication has been widely-studied, largely because the invention of the sound spectrograph allows researchers to visually represent vocalizations and make precise acoustic measurements. Black-capped chickadees (Poecile atricapillus; Figure 1) are one example of a songbird whose song has been well-studied. Black-capped chickadees produce a short (less than 2 seconds), whistled fee-bee song. Compared to the songs produced by many songbird species, which often contain numerous note types without a fixed order, black-capped chickadee song is relatively simple, containing two notes produced in the same order during each song rendition. Although the songs appear to be acoustically simple, they contain a rich variety of information about the singer including: dominance rank, geographic location, and individual identity [1,2,3].
Interestingly, while songbird song has been widely-examined, most of the focus (at least for North Temperate Zone species) has been on male-produced song, largely because it was thought that only males actually produced song. However, more recently, there has been mounting evidence that in many songbird species, both males and females produce song [4,5]. In the study of black-capped chickadees, the focus has also been on male-produced song. However, recently, we reported that female black-capped chickadees also produce fee-bee song. One possible reason that female song has not been extensively reported is that to human vision, male and female chickadees are visually identical, so females that are singing may be mistakenly identified as male. However, by identifying a bird’s sex (via DNA analysis) and recording both males and females, our work  has shown that female black-capped chickadees do produce fee-bee song. Additionally, these songs are overall acoustically similar to male song (songs of both sexes contain two whistled notes; see Figure 2), making vocal discrimination by humans difficult.
Our next objective was to determine if any acoustic features varied between male and female songs. Using bioacoustic techniques, we were able to demonstrate that there are acoustic differences in male and female song, with females producing songs that contain a greater frequency decrease in the first note compared to male songs (Figure 2). These results demonstrate that there are sufficient acoustic differences to allow birds to identify the sex of a signing individual even in the absence of visual cues. Because birds may live in densely wooded environments, in which visual, but not auditory, cues are often obscured, being able to identify the sex of a bird (and whether the singer is a potential mate or territory rival) would be an important ability.
Following our bioacoustic analysis, an important next step was to determine whether birds are able to distinguish between male and female songs. In order to examine this, we used a behavioral paradigm that is common in animal learning studies: operant conditioning. By using this task, we were able to demonstrate that birds can distinguish between male and female songs; however, the particular acoustic features birds use in order to discriminate between the sexes may depend on the sex of the bird that is listening to the song. Specifically, we found evidence that male subjects responded based on information in the song’s first note, while female subjects responded based on information in the song’s second note . One possible reason for this difference in responding is that in the wild, males need to quickly respond to a rival male that is a territory intruder, while females may assess the entire song to gather as much information about the singing individual (for example, information regarding a potential mate’s quality). While the exact function of female song is unknown, our studies clearly indicate that female black-capped chickadees produce songs and the birds themselves can perceive differences between male and female songs.
Figure 1. An image of a black-capped chickadee.
Figure 2. Spectrogram (x-axis: time; y-axis: frequency in kHz) on a male song (top) and female song (bottom).
Sound file 1. An example of a male fee-bee song.
Sound file 2. An example of a female fee-bee song.
Hoeschele, M., Moscicki, M.K., Otter, K.A., van Oort, H., Fort, K.T., Farrell, T.M., Lee, H., Robson, S.W.J., & Sturdy, C.B. (2010). Dominance signalled in an acoustic ornament. Animal Behaviour, 79, 657–664.
Hahn, A.H., Guillette, L.M., Hoeschele, M., Mennill, D.J., Otter, K.A., Grava, T., Ratcliffe, L.M., & Sturdy, C.B. (2013). Dominance and geographic information contained within black-capped chickadee (Poecile atricapillus) song. Behaviour, 150, 1601-1622.
Christie, P.J., Mennill, D.J., & Ratcliffe, L.M. (2004). Chickadee song structure is individually distinctive over long broadcast distances. Behaviour 141, 101–124.
Langmore, N.E. (1998). Functions of duet and solo songs of female birds. Trends in Ecology and Evolution, 13, 136–140.
Riebel, K. (2003). The “mute” sex revisited: vocal production and perception learning in female songbirds. Advances in the Study of Behavior, 33, 49–86
Hahn, A.H., Krysler, A., & Sturdy, C.B. (2013). Female song in black-capped chickadees (Poecile atricapillus): Acoustic song features that contain individual identity information and sex differences. Behavioural Processes, 98, 98-105.
Hahn, A.H., Hoang, J., McMillan, N., Campbell, K., Congdon, J., & Sturdy, C.B. (2015). Biological salience influences performance and acoustic mechanisms for the discrimination of male and female songs. Animal Behaviour, 104, 213-228.
Can a spider “sing”? If so, who might be listening?
Alexander L. Sweger – firstname.lastname@example.org
George W. Uetz – email@example.com
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
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.
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.