Exposure to seismic survey alters blue whale acoustic communication

The ability to perceive biologically important sounds is critical to marine mammals, and acoustic disturbance through human-generated noise can interfere with their natural functions. Sounds from seismic surveys are intense and have peak frequency bands overlapping those used by baleen whales, but evidence of interference with baleen whale acoustic communication is sparse. Here we investigated whether blue whales (Balaenoptera musculus) changed their vocal behaviour during a seismic survey that deployed a low-medium power technology (sparker). We found that blue whales called consistently more on seismic exploration days than on non-exploration days as well as during periods within a seismic survey day when the sparker was operating. This increase was observed for the discrete, audible calls that are emitted during social encounters and feeding. This response presumably represents a compensatory behaviour to the elevated ambient noise from seismic survey operations.     

Wild squirrel monkey (Saimiri sciureus) “caregiver” calls: Contexts and acoustic structure

A field study of the vocal behavior of 22 wild adult female squirrel monkeys (Saimiri sciureus) in Parque Nacional del Manu, Peru, found that 21% of vocalizations were “caregiver” calls. Caregiver calls are brief, low frequency calls, often with numerous harmonics, that are addressed by caregivers to their own infants in three contexts: 1) prenurse, signalling the caregiver's location and willingness to nurse; 2) nurse, while nursing; and 3) end nurse, indicating the end of the nursing bout. Three measures (start, end, and peak frequency) of the acoustic structure of the fundamental frequency of the caregiver calls significantly differed across the contexts. Duration of caregiver calls, however, was not distinguished by context. Compared to other primate taxa, the specificity and importance of caregiver calls in squirrel monkey vocal behavior appears unusual, if not unique. That S. sciureus caregiver calls are highly developed and employed so extensively probably follows from an unusual combination of ecological and life history factors. These factors include delayed weaning and large infant body size, high levels of indirect foraging competition which encourages spatial separation, susceptibility to predation, and specialization on a densely foliated, branch-end microhabitat in which visual contact is often impeded. © 1995 Wiley-Liss, Inc.     

Loud calls ofGalago crassicaudatus andG. garnettii and their relation to habitat structure

Long distance vocalizations have been shown to be good indicators of genetic species in primates. Here the loud calls of two recently identified greater galago taxa —Galago crassicaudatus andG. garnettii — are compared and analyzed statistically. Observed differences in call structures are investigated further as potential indicators of differences in the structures of habitats frequented by the two species. Although the calls share a repetitive structure, and show similar dominant frequency bands (1,000 – 1,500 Hz), they differ significantly in the number of units per call, unit duration, inter-unit interval, highest frequency, lowest frequency, dominant frequency band, first harmonic, and call duration. The duration of theG. crassicaudatus call is more than twice that ofG. garnettii. Strong intraspecific consistency is seen in the most energetic frequency bands (dominant frequency band and first harmonic), and durations of the individual units and inter-unit intervals. Information important to species recognition is thus most likely to be contained in these features. Individual recognition may be encoded in the relative emphasis of higher level harmonics. The frequency structures of the calls will reflect requirements for acoustical transmission in a forest environment, as well as structural constraints imposed by body size. Higher frequencies detected in theG. garnettii call (up to 8,500 Hz) may have a functional significance related to distance estimation, or may simply be a reflection of smaller body size. The greater modulation of theG. garnettii call suggests that its habitat constitutes a denser or more turbulent medium for sound transmission than does the habitat ofG. crassicaudatus.     

Acoustic preferences and localization performance of blood-sucking flies (Corethrella Coquillett) to tungara frog calls

Mating signals that increase attractiveness of males to femalescan also increase conspicuousness of the signaler to predatorsand parasites. We investigated the acoustic preference of speciesof blood-sucking flies of the genus Corethrella (Diptera: Corethrellidae),which eavesdrop on the sexual advertisement signals of túngarafrogs (Physalaemus pustulosus). Male frogs of this species facultativelyproduce 2 types of mating calls: simple (whines alone) and complex(whines and chucks). We tested the acoustic preference of theflies and their ability to locate their host when the frogsproduce simple or complex calls. The flies exhibited phonotaxisto both types of calls but were preferentially attracted tocomplex calls. We show that acoustic information alone is sufficientfor the flies' accurate localization of calling frogs. Complexcalls, however, were not approached at closer distance or withdecreased landing error (i.e., proportion of landings outsidethe target) than simple calls, suggesting that call structuredoes not influence localization performance. Female túngarafrogs and frog-eating bats (Trachops cirrhosus) also prefercomplex to simple túngara frog calls. Thus, intendedand unintended receivers with different ear morphologies exhibitthe same preference for a specific túngara frog calltype. This result is discussed in the context of the evolutionof call attractiveness in a communication network.