Tonal Calls Research Articles

The vocal repertoire of the Key Largo woodrat (Neotoma floridana smalli)

The Key Largo woodrat (Neotoma floridana smalli) is an endangered rodent endemic to the island of Key Largo, FL. There is little information on vocal communication in this species and descriptions of the acoustic structure of calls are lacking. A captive breeding program was established as part of the recovery plan for the species, providing the opportunity to investigate the vocal repertoire and acoustic structure of calls in both wild and captive contexts. Audio and video recordings were conducted at the Crocodile Lake National Wildlife Refuge in Key Largo and at Disney's Animal Kingdom(®). Analysis of the acoustic structure of calls resulted in four provisional call types: "Tonal calls" consisted of "ultrasonic vocalizations" (40 kHz fundamental frequency, F(0)), "high squeaks" (10 kHz F(0)), and "squeaks" (1.8 kHz F(0)). "Noisy," broadband calls known as "raspy" vocalizations did not exhibit fundamental frequencies, but contained several prominent spectral peaks (from 9 to 40 kHz). The social contexts of vocal production showed that all four call types were associated with pup need or interactions between pups and dams, and that raspy vocalizations were associated with courtship and copulation. Adults without pups exhibited little or no vocal activity, which may result from solitary lifestyles and predator avoidance.

Simple Syllabic Calls Accompany Discrete Behavior Patterns in CaptivePteronotus parnellii: An Illustration of the Motivation-Structure Hypothesis

Mustached bats, Pteronotus parnellii, are highly social and vocal. Individuals of this species roost in tight clusters, and emit an acoustically rich repertoire of calls whose behavioral significance is largely unknown. We recorded their social and vocal behaviors within a colony housed under semi-natural conditions. We also quantified the spatial spread of each bat's roosting location and discovered that this was relatively fixed and roughly confined to an individual's body width. The spatial precision in roosting was accompanied by an equally remarkable match between specific vocalizations and well-timed, discrete, identifiable postures/behaviors, as revealed by logistic regression analysis. The bodily behaviors included crouching, marking, yawning, nipping, flicking, fighting, kissing, inspecting, and fly-bys. Two echolocation-like calls were used to maintain spacing in the colony, two noisy broadband calls were emitted during fights, two tonal calls conveyed fear, and another tonal call signaled appeasement. Overall, the results establish that mustached bats exhibit complex social interactions common to other social mammals. The correspondence of relatively low frequency and noisy, broadband calls with aggression, and of tonal, high frequency calls with fear supports Morton's Motivation-Structure hypothesis, and establishes a link between motivation and the acoustic structure of social calls emitted by mustached bats.

Sound production behavior of individual North Atlantic right whales: implications for passive acoustic monitoring

Passive acoustic monitoring is being used to detect vocalizing marine mammals. Data on call types and individual rates of sound production are necessary to use passive acoustics to identify species, assess individual detectability, and estimate the number of individuals present. The present study describes the sound production behavior of endangered North Atlantic right whales Eubalaena glacialis in the Bay of Fundy, Canada, during July and August, recorded with suction cup archival tags (Dtag) in 2000 to 2002 and 2005. The Dtag simultaneously recorded acoustic data from a hydrophone along with the depth and orientation of the whale. Over 168 h of acoustic data were obtained from 46 tag deployments (35 ind.), with an average attachment dura- tion of 4.5 h. The rate of sound production was variable, ranging from 0 to 200 calls h �1 (mean ± SD: 6.4 ± 29.8 calls h �1 ), with 28 of the 46 tagged whales producing no calls (corresponding to 69/168 h of data). Right whale sounds from any whale in the area were recorded on most tag records, indicating that aggregations of whales may be detected more reliably than individuals. Calling rates were highest during surface activity and traveling and lowest during foraging and logging behavior. Whales of both sexes and all age-classes produced upcalls and other tonal calls, and 1 adult male produced gunshot sounds. The present study provides insight from the largest extant collection of recordings of individual North Atlantic right whales into the acoustic detectability of individual right whales and demonstrates that the behavioral state is the primary factor affecting calling rate.

Automated extraction of odontocete whistle contours

Many odontocetes produce frequency modulated tonal calls known as whistles. The ability to automatically determine time × frequency tracks corresponding to these vocalizations has numerous applications including species description, identification, and density estimation. This work develops and compares two algorithms on a common corpus of nearly one hour of data collected in the Southern California Bight and at Palmyra Atoll. The corpus contains over 3000 whistles from bottlenose dolphins, long- and short-beaked common dolphins, spinner dolphins, and melon-headed whales that have been annotated by a human, and released to the Moby Sound archive. Both algorithms use a common signal processing front end to determine time × frequency peaks from a spectrogram. In the first method, a particle filter performs Bayesian filtering, estimating the contour from the noisy spectral peaks. The second method uses an adaptive polynomial prediction to connect peaks into a graph, merging graphs when they cross. Whistle contours are extracted from graphs using information from both sides of crossings. The particle filter was able to retrieve 71.5% (recall) of the human annotated tonals with 60.8% of the detections being valid (precision). The graph algorithm's recall rate was 80.0% with a precision of 76.9%.

Dolphin whistles: a functional misnomer revealed by heliox breathing

Delphinids produce tonal whistles shaped by vocal learning for acoustic communication. Unlike terrestrial mammals, delphinid sound production is driven by pressurized air within a complex nasal system. It is unclear how fundamental whistle contours can be maintained across a large range of hydrostatic pressures and air sac volumes. Two opposing hypotheses propose that tonal sounds arise either from tissue vibrations or through actual whistle production from vortices stabilized by resonating nasal air volumes. Here, we use a trained bottlenose dolphin whistling in air and in heliox to test these hypotheses. The fundamental frequency contours of stereotyped whistles were unaffected by the higher sound speed in heliox. Therefore, the term whistle is a functional misnomer as dolphins actually do not whistle, but form the fundamental frequency contour of their tonal calls by pneumatically induced tissue vibrations analogous to the operation of vocal folds in terrestrial mammals and the syrinx in birds. This form of tonal sound production by nasal tissue vibrations has probably evolved in delphinids to enable impedance matching to the water, and to maintain tonal signature contours across changes in hydrostatic pressures, air density and relative nasal air volumes during dives.

Species-specific and shared features in vocal repertoires of three Eurasian ground squirrels (genus Spermophilus)

Along to alarm calls, Eurasian ground squirrels of the genus Spermophilus also produce other call types toward potential predators and rival conspecifics. Individually identified 50 speckled (Spermophilus suslicus), 18 European (S. citellus) and 59 yellow (S. fulvus) ground squirrels were examined for interspecies differences in their vocal repertoires. A separate sample of 116 (90 adult and 26 juvenile) S. suslicus was examined for presence of ultrasound in their alarm calls. In addition, all tonal calls in all the three species were checked for presence of nonlinear phenomena. Calls were elicited by approaching animals in live-traps or near burrows; some types of vocalizations were also recorded during handling. Eight call types, three tonal and five wideband ones, were described. Vocal repertoires were remarkably similar between species, excluding the alarm calls, which were species-specific. Alarm calls with ultrasonic components were found in two individuals of S. suslicus. Concerning nonlinear phenomena, biphonation in alarm calls of S. suslicus, frequency jumps and sidebands in screams of S. citellus, frequency jumps and subharmonics in screams of S. fulvus were found. Results are discussed with literature evidence on audible and ultrasonic vocalizations in ground squirrels.

Quality calls: phylogeny and biogeography of a new genus of neotropical katydid (Orthoptera: Tettigoniidae) with ultra pure-tone ultrasonics

This paper describes Artiotonus, a new genus of tropical katydid from Colombia and Ecuador. These acoustic ensiferans are represented by three species with a geographic distribution generally restricted to the rainforest of the Bolivar geosyncline of northwestern South America (Pacific). A phylogenetic analysis based on 28 morphological and six behavioural characters produced a tree (A. artius, (A. tinae, A. captivus)) with a consistency index of 0.9. All species are defined by a few autapomorphic changes. The most reliable character for identification is the temporal pattern of the calling song, suggesting a recent genetic divergence. Biogeographic analysis indicates that such genetic divergence began with geographic isolation produced before the Holocene transgression. Species of this genus are remarkable in that the calling song of males exhibits a narrow spectrum with a high quality factor (37–42), unusual values for such ultrasonic signals. A broad discussion on the evolution of tonal calls and pulse trains is offered.

A novel image-processing based method for the automatic detection, extraction and characterization of marine mammal tonal calls

A novel, automatic method for the detection, extraction and characterization of marine mammal tonal calls is presented. Signals are automatically detected from the spectrogram, isolated using region-based segmentation, extracted and finally characterized by means of a fixed number of radial basis function (RBF) coefficients. A total of sixteen RBF coefficients are sufficient to accurately capture the time–frequency information contained in the calls. These coefficients can be later used to classify signals based on their characteristics. New specific functions for contour extraction and cross-resolution have been developed. The performance of the method has been extensively tested using simulated signals and a set of recordings covering a significant range of situations that can be encountered at sea.

A graph search algorithm for delphinid whistle contours.

A graph search algorithm is presented to extract tonal contours from audio signals in a fully automated manner. The algorithm is capable of tracking multiple contours simultaneously. Search is done in the spectral domain, with contours being treated as paths through a phase‐magnitude space. A graph search formalism is combined with dynamic programming techniques to track candidate paths that may overlap or cross. Disambiguation of path crossings is accomplished by examining a combination of slope and the derivative of phase. The algorithm is general in nature and applicable to tonal calls from many animals with little modification. We target this work specifically toward delphinid whistles and demonstrate its efficacy on calls from bottlenose (Tursiops truncatus), short‐ and long‐beaked common (Delphinus delphis and D. capensis), and Risso’s (Grampus griseus) dolphins recorded in the Southern California Bight. Characterizing the complete contour will permit the development of call comparison techniques that take into account finer grained detail than the typically used contour statistics (e.g., number of inflection points, minimum, and maximum frequencies). [This work is sponsored by the Office of Naval Research.]

Simultaneous acoustic tag and seafloor acoustic recorder detection of right whale calls in the Bay of Fundy.

Passive acoustic monitoring is playing a growing role in marine mammal detection. Determining the range of detection for calls of a particular species in a particular location is important to assess the regional coverage provided by individual recording units. This study describes the comparison of right whale calls recorded by digital acoustic recording tags (Dtags) attached with suction cups to North Atlantic right whales and the detection of the same calls using a dispersed seafloor array of autonomous recorders. The seafloor array consisted of 5 units, spaced 6–10 km apart, continuously recording from July 29– August 17, 2005. Dtags were attached to a total of 14 individual right whales during this time period and 7 of these individuals produced a total of 88 tonal calls during tag attachment. The tag and related tracking of the whale provided information on call type, and the timing, depth, and approximate location of the whale producing the call. Tagged whale calls were audible on the seafloor array, and whale-recorder distances provided estimates of the acoustic detection range for right whales in the Bay of Fundy, Canada.

VOCALISATIONS OF THE SILVERY MOLE-RAT: COMPARISON OF VOCAL REPERTOIRES IN SUBTERRANEAN RODENTS WITH DIFFERENT SOCIAL SYSTEMS

ABSTRACT We examined vocalisations of a solitary subterranean rodent, the Silvery Mole-rat Heliophobius argenteocinereus (Bathyergidae). Seven true vocalisations and one mechanical vocalisation were identified. The main frequencies of the analysed sounds (0.34–13.17 kHz) match to a great extent the frequency range suitable for transmission in underground burrows. Due to the narrow frequency range of vocalisations, motivation is predominantly expressed by the rate of tonality rather than by frequency changes. The vocal repertoire of the Silvery Mole-rat perfectly matches to Morton's MS rules, i.e. that low-frequency and harsh vocalisations indicate hostility whereas high tonal calls signalise appeasement or fear. In comparison with social species, this solitary bathyergid produces fewer calls. It lacks contact and alarm calls, but has a rich repertoire of mating calls (mating ends with duet vocalization of male and female). Acoustic signals seem to play a major role in lowering natural aggressiveness during the mating period.

NORTH AMERICAN ELK BUGLE VOCALIZATIONS: MALE AND FEMALE BUGLE CALL STRUCTURE AND CONTEXT

Bugle calls of male North American elk (Cervus elaphus) are common sounds during fall in the Canadian and United States Rocky Mountains. In contrast, bugle calls of female elk are rarely heard. We quantified the acoustic structure of elk bugle calls, which is an essential 1st step to understanding of the function of the call. We also investigated whether motivation‐structural rules apply to these long-distance calls. We measured male elk bugle calls in Rocky Mountain National Park, Colorado, during autumn of 1998 and 1999 and we measured female elk bugle calls on 2 Colorado elk ranches (private establishments that raise elk for commercial purposes) during spring of 2001 and 2002. All bugle calls had 3 segments: on-glide, whistle, and off-glide. Male bugle calls were longer in duration than female bugle calls (P , 0.01). Bugle calls emitted in aggressive interactions had 4 or 5 low-frequency formants, resulting in harsher, wider bandwidth bugles (P , 0.001) compared to the tonal calls emitted in nonaggressive contexts, which lacked formants. Thus, elk bugle calls appear to conform to motivation‐structural rules.

Blue whale calling in Australian waters

Calling from the Antarctic true blue whale (Balaenoptera musculus intermedia) and the tropical subspecies (brevicauda, or pygmy blue) have been recorded across southern Australia with the pygmy blue calls also recorded along the Western Australian (WA) coast. The subspecies have a believed common downsweep and markedly different longer, tonal calls. The frequency of most energy in the tonal calls is offset between the subspecies suggesting sound-space partitioning. The pygmy blue three-part tonal call is typically 120 s long repeated every 200 s, has several variants, and includes a complex two-source component. The nature of the pygmy blue call allows counts of instantaneous calling individuals, giving relative abundance. These estimates in the Perth Canyon, a localized seasonal feeding area, show patterns in usage of space and through time within and between seasons, such as the sudden departure of animals at a season end, which varies by approximately 2 weeks between years. Sea noise records along the WA coast indicate south-traveling animals arrive midway along the coast in October to November, animals fan out across southern Australian over December through May, then move north in the Austral winter. We have begun converting abundance estimates from relative to absolute for pygmy blue calling rates.

BLUE WHALE (BALAENOPTERA MUSCULUS) SIGHTINGS AND RECORDINGS SOUTH OF THE ALEUTIAN ISLANDS

Blue whales have been sighted throughout the North Pacific Ocean (Mizroch et al. 1984), and were harvested around the Pacific Rim from Mexico to Japan (Fig. 1). The International Whaling Commission (IWC) currently recognizes only one stock of blue whales in the North Pacific (Donovan 1991); however, there may be up to five (reviewed in Stafford 2003). While past shipboard and aerial surveys in the Aleutian Island chain found no blue whales (Rice and Wolman 1982, Stewart et al. 1987), their contemporary presence in this area has been well documented by acoustic monitoring (Watkins et al. 2000, Stafford et al. 2001). In this note we present the results of a shipboard survey during which blue whales were seen south of the Aleutian Islands and recordings of blue whale vocalizations were obtained. Blue whale calls vary geographically (Thompson et al. 1996), and these geographic differences may be useful in discriminating different populations of blue whales. Two geographically and spectrographically distinct blue whale call types have been recorded in the North Pacific. The northeastern Pacific blue whale call type is well known and has been recorded from locations in the northeast Pacific, ranging from the equator along the west coast of North America up to the Gulf of Alaska (Stafford 2003). The northwestern Pacific blue whale call type is less well known, but has been recorded from remote hydrophones near Kaneohe, Hawaii, Midway Island, and locations along the Aleutian Islands and northwest Pacific and Gulf of Alaska (Northrup et al. 1971, Thompson and Friedl 1982, Stafford et al. 2001, Stafford 2003). This call type is recorded annually from June through December by seafloor hydrophones just south of the central Aleutian Islands (Stafford et al. 2001). Prior to this report, the western calls had never been visually linked to a blue whale. The calls have nevertheless been attributed to blue whales based on their similarity to other blue whale calls worldwide: they are long (>10 s), low-frequency (fundamental <100 Hz), frequency-modulated (FM) tonal calls (Thompson et al. 1996, Stafford et al. 2001, Stafford 2003, Rankin et al. 2005). Although fin whale calls are also low

Sei whale sounds recorded in the Antarctic

Sei whales are the least well known acoustically of all the rorquals, with only two brief descriptions of their calls previously reported. Recordings of low-frequency tonal and frequency swept calls were made near a group of four or five sei whales in waters west of the Antarctic Peninsula on 19 February 2003. These whales also produced broadband sounds which can be described as growls or whooshes. Many of the tonal and frequency swept calls (30 out of 68) consist of multiple parts with a frequency step between the two parts, this being the most unique characteristic of the calls, allowing them to be distinguished from the calls of other whale species. The average duration of the tonal calls is 0.45 +/- 0.3 s and the average frequency is 433 +/- 192 Hz. Using a calibrated seafloor recorder to determine the absolute calibration of a sonobuoy system, the maximum source level of the tonal calls was 156 +/- 3.6 dB re 1 microPa at 1 m. Each call had different character and there was no temporal pattern in the calling.

Sound production by North Atlantic right whales (Eubalaena glacialis) in surface active groups

The surface active group (SAG) is the most commonly observed surface social behavior of North Atlantic right whales. Recordings were made from 52 SAGs in the Bay of Fundy, Canada between July and September, from 1999 to 2002. The call types recorded from these groups were similar to those described previously for Southern right whales (Eubalaena australis), with six major call types being termed scream, gunshot, blow, upcall, warble, and downcall. The percentage of total calls of each call type depended on the group size and composition. The most common call type recorded was the scream call. The scream calls were produced by the focal female in a SAG. Production of other sound types can be attributed to whales other than the focal female, with gunshot and upcalls produced by males, and warble calls produced by female calves. The source levels for these sounds range from 137 to 162 dB rms re 1 ,tPa-m for tonal calls and 174 to 192 dB rms for broadband gunshot sounds.

Function of male song in the greater white-lined bat, Saccopteryx bilineata

The use of vocalizations by males to attract mates and defend territories is widespread in birds but uncommon in mammals. In the greater white-lined bat, males defend small territories in tree buttresses and produce complex audible vocalizations. During the day, females roost within these territories, and males with females in their territories have higher reproductive success than males without females. To determine call function, we recorded male vocalizations on the island of Trinidad and made behavioural observations of the focal male and nearby bats at the time the calls were given. Noisy broadband calls were directed mainly at other males whereas tonal calls were used primarily in interactions with females. Two other types of calls were given independently of any observable context and may be involved in territorial defence or conspecific notification. Poisson regression showed that males with song repertoires that contained more unique types of composite syllables had more females in their territories. In addition, several acoustic features of one common call type significantly correlated with the number of females on a territory. Male vocalizations may, therefore, transfer information to colony members about male quality or fighting ability.

INDIVIDUAL VOCAL TRAITS OF MOTHER AND PUP FUR SEALS

ABSTRACT This study investigates individual vocal traits in three species of fur seal: Antarctic fur seal Arctocephalus gazella, Subantarctic fur seal A. tropicalis, New Zealand fur seal A. forsteri and their hybrids. The attraction calls of mothers and pups were highly stereotyped within each individual and markedly different between individuals. Pup attraction calls (emitted by females) were more variable between individual A. tropicalis and A. forsteri than between individual hybrids and A. gazella. However, such a pattern was not evident for female attraction calls (emitted by pups). Pup attraction calls and female attraction calls were both generally tonal calls overlain with regions of pulses. Female attraction calls had relatively high fundamental frequencies. The importance of individual vocalisations for mothers and pups is best appreciated in relation to maternal fitness and offspring survival: individual vocalisations are favoured by natural selection as they facilitate rapid reunion when mothers return from foraging trips, ensuring maternal resources are not invested in unrelated pups.

Female Courtship Call of the Iberian Midwife Toad (Alytes cisternasii)

We describe a female courtship call, a vocalization produced before amplexus, by female Iberian midwife toads as a response recorded a large sample of femae responses to synthetic calls imitating male calls in two-speaker phonotaxis playback tests. Female courtship calls were tonal calls similar to male advertisement calls but shorter in duration. Courtship call duration by both sexes was negatively correlated with body temperature of toads. Unlike male advertisement calls, which were always a single note, female courtship calls comprised a sequence of 1-5 different notes; note duration of the last note was longest Both duration and dominant frequency were much more variable in female court- ship calls than in male advertisement calls. No correlations were found between female body size and call characteristics.

ACOUSTIC CHARACTERISTICS OF WHITE-NOSED COATI VOCALIZATIONS: A TEST OF MOTIVATION-STRUCTURAL RULES

Vocalizations of white-nosed coatis (Nasua narica) emitted in nonaggressive and aggressive contexts were measured and compared to determine if these calls exhibited acoustic characteristics in accordance with motivation-structural (MS) rules. “Chirp” and “squawk” calls were compared spectrographically using 11 coatis from 3 zoos. Chirps were short-duration (68.6–212.0 ms), high–maximum frequency (16.2–17.9 kHz), tonal calls with frequency modulations. Squawks were longer-duration (177.9–546.5 ms), low–maximum frequency (8.4–13.2 kHz), wide-bandwidth calls with 6 resonances and little frequency modulation. Squawks differed from chirps in duration, maximum frequency, and change in frequency (P < 0.001). Chirps were emitted during nonaggressive behaviors, whereas squawks were emitted during agonistic encounters. Squawks conformed to MS rule predictions for aggressive calls, and chirps supported MS rule predictions for nonaggressive contexts, but some exceptional characteristics were noted in chirps. Many chirps (67.7%) concluded with a short-duration, broad-bandwidth sound with high energy in low frequencies, and may represent variations of a graded call.