High Calling Rates Research Articles

Antimasking aspects of harp seal (Pagophilus groenlandicus) underwater vocalizations.

Underwater sounds are very important in social communication of harp seals (Pagophilus groenlandicus) because they are the main means of long- and short-distance communication. Individual harp seals must try to avoid being masked and emit only those calls that will benefit them. Underwater vocalizations of harp seals were recorded during the breeding season. The physical characteristics associated with antimasking attributes of 16 call types were examined. Rising frequency or increasing amplitude within calls were not common. Most of the calls ended abruptly (range 145-966 dB/s), but call onset was more gradual. At high calling rates (95.1-135 calls/min) there were significantly more calls overlapping temporally than at medium (75.1-95 calls/min) or low (35-75 calls/min) calling rates, but even at the highest calling rates, 79.1% of the calls were not overlapped. When 2, 3, or 4 calls overlapped, there were significantly fewer frequency separations of less than 1/3 octave than would be expected by chance. This is important because sounds that are separated by less than 1/3 octave likely mask each other. When 2-4 calls are occurring simultaneously, only 4.5% to 14.2% are masked by virtue of being within 1/3 octave from their nearest neighbor. None of the overlappping calls was of the same type. This suggests that the seals are actively listening to each other's calls and are not randomly using the different call types. Harp seals use frequency and temporal separation in conjunction with a wide vocal repertoire to avoid masking each other.

ULTRASONIC CALLING IN ISOLATED INFANT PRAIRIE VOLES (MICROTUS OCHROGASTER) AND MONTANE VOLES (M. MONTANUS)

Abstract I compared number of ultrasonic calls infant prairie voles (Microtus ochrogaster) and montane voles (M. montanus) emit when isolated. Typically, murid infants produce ultrasonic calls when they cannot thermoregulate adequately. Infant prairie voles called much more than did infant montane voles (average of 954 versus 17 calls/20 min at ages 0–10 days, P < 0.001) and more than other murids. Prairie voles also differed from montane voles in calling at high rates from day of birth, which is not typical of murids. The 2 species developed thermoregulatory competency at the same ages, so differences in calling could not be explained by differences in ontogeny. I suggest that rates of calling are related to social organization for, unlike montane voles and most murid species, prairie voles display monogamous mating behavior and a high level of biparental care. High calling rates could be adaptive for infant prairie voles, as parents are near almost all the time and can retrieve them; in contrast, montan...

Diana monkeys, Cercopithecus diana , adjust their anti-predator response behaviour to human hunting strategies

In Taï National Park, Ivory Coast, humans with guns hunt monkeys for their meat. The poachers imitate animal calls to feign the presence of eagles or leopards, two predators to which monkeys react with high calling rates and approach. In the presence of humans, monkeys become silent and move off. A small area of the park is now avoided by poachers, due to the establishment of a field project on chimpanzees in 1979. This offered the opportunity to investigate whether sudden changes in predation pressure lead to a rapid alteration in prey behaviour. Playback experiments, using groups of Diana monkeys, Cercopithecus diana, as subjects, revealed that the poachers' strategy works well in the home range of the habituated chimpanzee group. However, monkeys which are frequently exposed to poachers are rarely fooled by the imitations. Adaptive discrimination abilities can thus be acquired or lost within the lifespan of individual monkeys.

Within-call repetition may be an anti-masking strategy in underwater calls of harp seals (Pagophilus groenlandicus)

Underwater vocalizations of harp seals (Pagophilus groenlandicus) were recorded in the Gulf of St. Lawrence, Canada, during the breeding season in March of 1999 and 2000. At high calling rates (&gt;95 calls/min) the background noise levels increase and individual calls may be masked. The purpose of the study was to determine if seals increase the number of elements per call in response to higher calling rates by conspecifics. Eight multi-element call types were analyzed. Six narrowband and one of two broadband multi-element call types showed a significant increase in the number of elements per call at higher calling rates. One broadband call type did not show a significant difference among the different calling rates. Our findings suggest that harp seals increase the number of elements per call in many call types to avoid having their calls masked by an increasing number of conspecific vocalizations.

Utilization of energy substrates during calling activity in tropical frogs

Calling activity in frogs is energetically demanding to males because they usually perform at or near their physiological capacities. Metabolic fuel for muscle contractions during bouts of aerobic calling activity comes from carbohydrates and lipids that are stored in the trunk muscles. I monitored nightly calling performance in males of seven tropical frog species from two families, Hylidae and Leptodactylidae, and compared levels of glycogen and lipid in the trunk muscles from males collected before and after a three-hour period of calling activity. Trunk muscles from late-evening males in five species had up to 63% less glycogen than the trunk muscles from early-evening males; relatively little depletion was observed in two other species. Overall, glycogen reserves and rates of depletion were highest in species with very high calling rates. It was not possible to measure changes in the relatively large stores of lipid in the trunk muscles after only 3 h of calling. Nevertheless, intramuscular lipid stores probably provide a greater percentage of the energy needed for sound production than glycogen stores, and are largest in species with high calling rates.

Biochemical Correlates of Calling Activity in Neotropical Frogs

Variation in behavioral performance among animals often is closely matched to the functional capacity of muscles that support the activity. In frogs, a general correlation exists between calling activity and characteristics of the trunk muscles that support call production. I determined hourly calling rates and call durations from males of six tropical hylid species and two leptodactylid species. Samples of trunk- and leg-muscle tissue were collected and assayed for activity levels of the catabolic enzymes citrate synthase (CS) and β-hydroxyacyl-CoA dehydrogenase (HOAD), which generally are correlated with tissue capacities for aerobic metabolism and fatty acid oxidation, respectively. Enzyme activity levels in the more aerobic trunk muscles were several times greater than in the more anaerobic leg muscle and were significantly correlated with average calling rates. Overall, species with higher calling rates had trunk muscles with higher enzyme activity levels. This study demonstrates a significant relati...

Localization of Insect Calls by the Bat Nyctophilus-Geoffroyi (Chiroptera, Vespertilionidae) - a Laboratory Study

Many insects use acoustic signals to attract mates but their calls may be exploited by predators. This laboratory study showed that the lesser long-eared bat, Nyctophilus geoffroyi, was attracted to both (a) calling tettigoniids and (b) synthesised calls broadcast through loud-speakers. Playback experiments, using synthetic calls, demonstrated that bats were more attracted to calls of longer duration than to calls of short duration, while high calling rates and high call intensities had no special attraction. Two-speaker choruses appeared to be more attractive than a single speaker. These results are discussed in the context of predation as a selective force on calling strategies.

Repetition enhances hearing detection thresholds in a harbour seal (Phoca vitulina)

Pure-tone hearing thresholds of a harbour seal (Phoca vitulina) were measured in air and underwater using behavioural psychophysical techniques. A 50-ms sinusoidal pulse was presented in both white-noise masked and unmasked situations at pulse repetition rates of 1, 2, 4, and 10/s. Test frequencies were 0.5, 1.0, 2.0, 4.0, and 8.0 kHz in air and 2.0, 4.0, 8.0, and 16.0 kHz underwater. Relative to 1 pulse/s, mean threshold shifts were −1, −3, and −5 dB at 2, 4, and 10 pulses/s, respectively. The threshold shifts from 1 to 10 pulses/s were significant (F = 12.457, df = 2,36, p &lt; 0.001) and there was no difference in the threshold shifts between the masked and unmasked situations (F = 2.585; df = 1,50; p &gt; 0.10). Broadband masking caused by meteorological or industrial sources will closely resemble the white-noise situation. At high calling rates, the numerous overlapping calls of some species (e.g., harp seal, Phoca groenlandica) present virtually continous "background noise" which also resembles the broadband white-noise masking situation. An implication of lower detection thresholds is that if a seal regularly repeats short vocalizations, the communication range of that call could be increased significantly (80% at 10 pulses/s). This could have important implications during the breeding season should storms or shipping noises occur or when some pinniped species become increasingly vocal and the background noise of conspecifics increases.

Distant and near-range functions of harp seal underwater calls

Underwater vocalizations of harp seal (Phoca groenlandica) in the Gulf of St. Lawrence, were obtained during 10 breeding seasons between 1968 and 1983. No changes in their vocal repertoire were found. At high calling rates, vocalizations overlapped and the average sound levels increased. An individual's calls may be partly masked under these conditions. Sound levels of 140 dB re 1 μPa were received with no seal closer than 2 m from the hydrophone. Such sounds should be detectable (by other seals) from a distance of at least 2 km (uner ice cover). Recordings at points progressively farther away from the main herd detected calls continuously over a 60-km distance. Seals were in the water along these transects and presumably were in acoustic contact with each other. A seal searching for the heard would thus be searching for a large acoustic target rather than the relatively smaller on-ice herd. Calls also may be associated with courtship or mating. These would be involved with close-range communication. Harp seal calls are typically repeated at least twice but often more than 10–20 times. This repetition, the loudness of some calls, and the possible incorporation of clues to aid directional hearing may help overcome the masking problem encountered by these shorter range courtship or mating calls.

Male Calling Behavior and Female Choice in the Neotropical Treefrog Hyla microcephala

AbstractThe effect of stimulus call complexity and calling rate on the vocal responses of males and female mate choice was studied in Hyla microcephala in Panama. Males increased the number of notes in their calls in response to increases in stimulus call complexity during both playback of 1 to 8‐note advertisement calls and during natural interactions. However, precise matching of the number of notes in stimuli and responses did not occur consistently. Males also increased calling rates if stimuli were presented above prestimulus rates. Two‐stimulus choice experiments demonstrated that females prefer both higher calling rates and greater call complexity, indicating that the ways males change their vocal behavior during interactions increases their attractiveness to potential mates. Tests in which the relative intensity of a high and low rate stimulus was varied indicated that females prefer stimuli with higher total sound energy. In a natural chorus, it is likely that females simply approach males giving the most conspicuous calls.

Calling behaviour of the Yellow-bellied Glider, Petaurus australis Shaw (Marsupialia: Petauridae).

Vocalizations of the Yellow-bellied Glider, Petaurus australis, were studied at Nadgee State Forest, near Eden, New South Wales. Six basic call types were recognized aurally and shown to have characteristic sonographs. Several short primary call components of high energy and relatively pure frequencies were identified. These were combined with medium frequency bands of lower energy to form calls of longer duration. High calling rates occurred early in the night and were associated with time of emergence from hollows, periods of gliding and food searching. During the months August to May, the pattern was similar. Calls were heard throughout the night but calling frequency declined after midnight. In June and July, few or no calls were heard. Reasons for the differential calling rate and the functions of various call types are discussed.