Morphology, echolocation and foraging behaviour in two sympatric sibling species of bat (Tylonycteris pachypus and Tylonycteris robustula) (Chiroptera: Vespertilionidae)

We studied the wing morphology, echolocation calls, foraging behaviour and flight speed of Tylonycteris pachypus and Tylonycteris robustula in Longzhou County, South China during the summer (June–August) of 2005. The wingspan, wing loading and aspect ratio of the two species were relatively low, and those of T. pachypus were lower compared with T. robustula . The echolocation calls of T. pachypus and T. robustula consist of a broadband frequency modulated (FM) sweep followed by a short narrowband FM sweep. The dominant frequency of calls of T. pachypus was 65.1 kHz, whereas that of T. robustula was 57.7 kHz. The call frequencies (including highest frequency of the call, lowest frequency of the call and frequency of the call that contained most energy) of T. pachypus were higher than those of T. robustula , and the pulse duration of the former was longer than that of the latter. The inter-pulse interval and bandwidth of the calls were not significantly different between the two species. Tylonycteris pachypus foraged in more complex environments than T. robustula , although the two species were both netted in edge habitats (around trees or houses), along pathways and in the tops of trees. Tylonycteris pachypus flew slower (straight level flight speed, 4.3 m s⁻¹) than T. robustula (straight level flight speed, 4.8 m s⁻¹). We discuss the relationship between wing morphology, echolocation calls, foraging behaviour and flight speed, and demonstrate resource partitioning between these two species in terms of morphological and behavioural factors.     

Acoustic Repertoire of Spawning Cod, Gadus morhua

We examine the vocal repertoire of spawning cod, Gadus morhua. Fish captured in northern Norway were allowed to spawn in tanks and we recorded sound during the spawning period. The cod's grunt repertoire contained more variation than previously suggested. Half of the grunts lasted more than 200ms including one grunt lasting nearly 1s and consisting of 52 pulses, which is far beyond previous reports. Moreover, increasing repetition period and increasing duration of pulses within a grunt from the first pulse towards pulses at the end of the grunt, has previously not been described. On the other hand, no knocks or series of knocks, and on average only one grunt per hour suggest that cod are less versatile vocalists than closely related gadid species, such as haddock, Melanogrammus aeglefinus.     

Sound production and reproductive behaviour of the armoured catfish Corydoras paleatus (Callichthyidae)

Sound production during reproductive behaviour, dyadic encounters and distress situations was investigated in the callichthyid catfish Corydoras paleatus. Sounds were broad-band, pulsed, acoustic signals produced during abduction of the pectoral spines. Only males emitted trains of sounds during courting and trains of sounds of shorter duration during dyadic encounters. Several males, which are usually smaller than females, courted one gravid female without obvious cooperation or competition between them. During mating, one previously vocalizing male clasped the female's barbels with one pectoral spine and inseminated the eggs. The number of successful spawnings, days until spawning, and number of eggs laid was not related to the number of males (one, two or three) combined with one female. Males did not behave aggressively towards each other during courting or in dyadic encounters. In distress situations, when fish were hand held, both sexes and juveniles produced single sounds. The dominant frequency was negatively correlated with body size and the sound duration was positively correlated with relative length of pectoral spines (standardized to body length). This acoustical behaviour in C. paleatus differs considerably from Hoplosternum thoracatum, a representative of the callichthyine subfamily, in which vocalization was observed during territorial behaviour in males and aggressive behaviour in both sexes. This is the first report of a major difference in vocalizing behaviour within one teleost family.     

Food-associated calls in rhesus macaques (Macaca mulatta): I. Socioecological factors

Upon discovering food, free-living rhesus macaques (Macaca mulatta)on the island of Cayo Santiago, Puerto Rico, produce a complexof vocal signals consisting of five acoustically distinguishablecalls. This report examines the socioecological factors elicitingcall production and the information protentially conveyed toothers. The primary contexts for three vocalizations ("warbles," "harmonicarches, " and "chirps") are encounters with rareand highly preferred foods (e.g., coconut). Two other vocalizations("coos" and "grunts") are produced both in food (primarily provisionedchow) and in nonfood contexts, such as during mother-infantseparation and grooming interactions. Grunts given upon encounteringfood are acoustically distinct from those given in nonfood contexts.In contrast, coos associated with food are statistically indistinguishablefrom coos given in other contexts. When conspecitics hear thesefood-associated calls, they typically approach the caller. Coosare less likely to lead to approach than other food-associatedcalls, Results from all-day follows on adult males and adultfemales reveal that changes in hunger level influence call ratebut not call type; the different call types are produced throughoutthe day. We infer that the structure of food-associated callsprovides information about the quality of the food discovered,whereas call rate conveys information about the relative hungerlevel of the caller. In this population, adult males give fewerfood-associated calls than adult females. In addition, femaleswithin large matrilines call more than females within smallermatrilines, and males who are resident in a group are more vocalthan peripheral males.     

Infant distress vocalizations in the Southern African Lesser Bushbaby (Galago moholi)

Infant lesser bushbabies are typically able, from the earliest age, to utter distress vocalizations which appear to have major adaptive significance. Distress vocalizations of infant G. moholi were analyzed by means of a digital storage oscilloscope. Three kinds of sound analyses were carried out: analysis of the sound wave signal, sequential spectrum analysis, and fast Fourier transformation. We emphasize analysis of the frequency spectrum. Three distress calls were identified-the click call, the crackle, and the chirp-which we report for the first time. Click calls were typically composed of short, high-pitched pulses (clicks) uttered in fast, repetitive sequences with a broad band frequency spectrum containing frequencies up to 60 kHz. These acoustic characteristics appear to be particularly well suited for accurate spatial localization of the sound source. The main function of the click call is apparently to alert and to guide the mother to a lost or endangered infant. These basic acoustic characteristics-related to sound localization-are shared to some extent, with the other two distress calls. However, the three calls appear to represent different degrees of distress, with the click call being the basic, call, the crackle corresponding to a greater degree of distress, and the chirp possibly signaling extreme distress such as physical pain.We prefer the specific name,Galago moholi (A. Smith, 1836), for the southern African lesser bushbaby [instead ofGalago senegalensis moholi (A. Smith, 1839)] according to the new classification proposed by Olson (1979, 1986) and Nashet al. (1989).     

Vocal Communication in a Fission-Fusion Society: Do Spider Monkeys Stay in Touch With Close Associates?

In fission-fusion societies, in which animals from the same group may spend long periods of time apart from each other, individuals could use long-distance vocalizations to maintain contact with others. This could be achieved with vocalizations that simply carried information about the caller's identity and location. I explored this possibility using observations and experiments from a 3-year field study of spider monkeys (Ateles geoffroyi) in Punta Laguna, México, analyzing the use of the species' most frequent vocalization, the whinny. By following 2 subgroups simultaneously, I found that subgroups that were within the active space of the whinny approached each other more often than subgroups that were farther apart. Individual adults in these subgroups also emitted more whinnies when they were within hearing range of another subgroup than when farther apart. I used a paired playback design to determine whether whinnies could influence the behavior of close associates as opposed to nonassociated individuals. Although nonassociates were as likely as close associates to respond vocally to playbacks of whinnies, only a close associate ever approached the speaker. Collectively, the results suggest that whinnies are used by spider monkeys to achieve flexibility in spacing while maintaining specific social relationships.     

Grouping in auditory temporal perception and vocal production is mutually adapted: the case of wriggling calls of mice

Auditory Gestalt perception by grouping of species-specific vocalizations to a perceptual stream with a defined meaning is typical for human speech perception but has not been studied in non-human mammals so far. Here we use synthesized models of vocalizations (series of wriggling calls) of mouse pups (Mus domesticus) and show that their mothers perceive the call series as a meaningful Gestalt for the release of instinctive maternal behavior, if the inter-call intervals have durations of 100–400 ms. Shorter or longer inter-call intervals significantly reduce the maternal responsiveness. We also show that series of natural wriggling calls have inter-call intervals mainly in the range of 100–400 ms. Thus, series of natural wriggling calls of pups match the time-domain auditory filters of their mothers in order to be optimally perceived and recognized. A similar time window exists for the production of human speech and the perception of series of sounds by humans. Neural mechanisms for setting the boundaries of the time window are discussed.     

Geographic variation in female preference functions and male songs of the field cricket Teleogryllus oceanicus

Male crickets (Teleogryllus oceanicus) produce a complex call consisting of two elements, the long chirp (three to eight sound pulses) followed by a series of short chirps (each with two sound pulses). There is significant geographic variation in the temporal structure of calls, and the long chirp is selected against by acoustically orienting parasitoids in some populations. Here we examine geographic variation in female preference functions for the amount of long chirp. In general, females prefer calls with greater proportions of long chirp, although the strength and nature of selection varied across populations. Variation in preference functions did not match variation in call structure. There was a mismatch between the proportion of long chirp produced by males in a population and the proportion of long chirp preferred by females. The convergent preferences of predators and females are likely to maintain genetic variation in song traits in parasitized populations. The apparent mismatch between preference and trait is discussed in relation to theoretical models of preference evolution.     

Female preference functions based on call duration in the gray tree frog (Hyla versicolor)

Preference functions, which quantify preference strength relativeto variation in male traits or signals, are central to understandingmechanisms and consequences of female choice. Female tree frogs(Hyla versicolor) choose mates on the basis of advertisementcalls and prefer long calls to short calls. Here we show, intwo experimental designs, that preference strength increasedsignificantly as the difference in call duration was increasedonly if the absolute durations of alternative stimuli were below average. Hence preference strength was a non-linear functionof duration, and females did not base preferences solely onthe percentage difference in duration. In experiments simulatingcostly choice (unequal playback levels), non-linear effectswere more pronounced than in the conventional design (equal playback levels). Repeated estimates of preference strengthusing the unequal-playback design revealed significant among-femalevariation. These patterns of preference suggest that selectionby female choice for males producing calls of average durationover males producing very short calls is stronger than selectionfor males producing very long calls over males producing callsof average duration. Female preferences, especially in tests simulating a potentially costly choice, could reflect differencesin the net benefits to females of mating with males producingcalls of different duration.