Peter Marler

Sound transmission and its significance for animal vocalization

Summary1.Sound transmission was measured in open fields, mixed decidous forest with and without leaves and coniferous forest in Dutchess County, New York. Attenuation of white noise and pure tones was measured between one microphone close to a loudspeaker and another microphone 100 m away, at the same height. Graphs of excess attenuation (E.A. in dB/100 m) against frequency were obtained at 0.15, 1, 2, 5, and 10 m above the ground. An analysis of variance was conducted to estimate effects of height, frequency and habitat.2.Height and frequency affect sound transmission more than habitat. With a sound source close to the ground (15 cm and 1 m) all frequencies were more attenuated than at greater heights. The patterns of E.A. as a function of sound frequency were basically similar in all habitats. At all source heights the lower the frequency the better the sound carried, with the exception that close to the ground, sounds below 2 kHz were excessively attenuated. Comparing open field and forest, trees improved transmission of frequencies below 3 kHz, especially close to the ground.3.Some general trends can be predicted for maximization of transmission distances of animal sounds in these habitats. For an animal vocalizing higher than 1 m above the ground, the lower the frequency the further the sound travels. Close to the ground, low frequencies are again preferred for maximization of transmission distances, but the frequencies must be pitched above a range of attenuated, low-pitched sounds, the limits of which vary to some extent with habitat, creating the ‘sound window’ of Morton. This ‘window’ of least-attenuated frequencies, only occurring close to the ground, tends to be pitched somewhat lower in forest than in open habitats. However, for an animal producing sounds in the habitats tested, perch height and sound frequency are more important than the habitat in determining how far the sound will carry.

Rhesus monkey (Macaca mulatta) screams : representational signalling in the recruitment of agonistic aid

Abstract Free-ranging rhesus monkeys on Cayo Santiago (Puerto Rico) give five acoustically distinct scream vocalizations during agonistic encounters. These calls are thought to be an important mechanism in the recruitment of support from allies against opponents. Alliance formation during agonistic encounters is known to vary with the dominance rank and matrilineal relatedness of opponents, as well as with the severity of aggression. In contrast to previous interpretations of screams as graded signals reflecting the level of arousal of the caller, we found these calls to be much more discrete, with each of the five acoustic types significantly associated with a particular class of opponent and level of physical aggression. We performed a series of field experiments in which tape-recorded screams of immature rhesus monkeys were played to their mothers in the absence of any other information. The results suggest that the information necessary for differential responses is conveyed by the scream vocalizations themselves. We conclude that screams are representational signals that refer to external objects and events and function in the system of agonistic alliance formation.

Issues in the Classification of Multimodal Communication Signals

Communication involves complex behavior in multiple sensory channels, or “modalities.” We provide an overview of multimodal communication and its costs and benefits, place examples of signals and displays from an array of taxa, sensory systems, and functions into our signal classification system, and consider issues surrounding the categorization of multimodal signals. The broadest level of classification is between signals with redundant and nonredundant components, with finer distinctions in each category. We recommend that researchers gather information on responses to each component of a multimodal signal as well as the response to the signal as a whole. We discuss the choice of categories, whether to categorize signals on the basis of the signal or the response, and how to classify signals if data are missing. The choice of behavioral assay may influence the outcome, as may the context of the communicative event. We also consider similarities and differences between multimodal and unimodal composite signals and signals that are sequentially, rather than simultaneously, multimodal.

Selective Vocal Learning in a Sparrow

Male swamp sparrows learn their songs; they fail to learn songs of the sympatric song sparrow. Syllables from tape recordings of both species of sparrow were spliced into an array of swamp sparrow-like and song sparrow-like temporal patterns. Swamp sparrows learned only those songs made of swamp sparrow syllables. They did so irrespective of whether the temporal pattern was swamp sparrow-like or song sparrow-like. Selectivity was retained by birds reared in total isolation from adult conspecific sounds.

Specific Distinctiveness in the Communication Signals of Birds

When using releasers in phylogenetic study, it is essential to consider whether the compared species are sympatric. If they are allopatric, it is often possible to find relationships between all releasers. If they are sympatric it is essential to know something of the function of the releasers, before their taxonomic value can be assessed. Signals that are in some way involved in reproductive isolation are likely to be highly divergent between closely allied sympatric species. They will therefore be useful as characters for specific diagnosis, but of limited value at higher levels of classification. In birds this group will include the male colours of most sexually dimorphic species, especially those that rely on visual recognition, have a short pair bond, and whose reproductive isolation is not yet complete (SIBLEY in press) : also advertisement, pair formation, courtship and some appeasement displays: songs, when they are loud and play an important part in pair-formation: some courtship and perhaps food and nest calls. Releasers of sympatric species whose function discourages specific distinctiveness, will often converge on common types, for the value either of mutually similar signals, or of signals that are for some extrinsic reason most efficient for the context. They are likely to be of limited taxonomic value, even at the specific level. This group includes colours of Batesian and Mullerian mimics; distraction, alarming and aggressive displays used against predators (LACK 1941), alarm calls and displays (HUXLEY 1938) and some nestling and fledgling calls. Releasers selected for moderate specific distinctiveness, with both intra- and inter-specific functions, diverge at a relatively slow rate. They are therefore of little use in specific diagnosis, but are valuable for classifying genera and families. This group includes cryptic colours, especially of female and young; mobbing, pre-flight and aggressive displays; flight and aggressive calls, and some owl-mobbing calls which have secondary functions. A similar moderate specific distinctiveness is found in close-range signals, again valuable in discerning relationships. This group includes colours of eggs and the nestling palate, and perhaps the eye, beak and face colours of adults; some copulatory, submissive and begging displays; soft calls, such as certain alarm cries, and songs which have no function in reproductive isolation, perhaps especially the songs and calls of densely colonial birds.

A Test for Responsiveness to Song Structure and Programming in Female Sparrows

Female song sparrows, primed with implants of estradiol, gave the solicitation display for copulation in response to acoustic stimulation with song. This technique demonstrated that female song sparrows respond more strongly to conspecific song than to alien songs, that they discriminate on the basis of both overall temporal pattern and syllabic structure, that they respond more to several song types than to repetitions of one song, and that they are most responsive to several song types if the songs are organized in bouts of a single type, as they are normally delivered by a male song sparrow. These results demonstrate a substantial correspondence between the structure and programming of the singing behavior of male birds and female responsiveness to song.

Species-universal microstructure in the learned song of the swamp sparrow (Melospiza georgiana)

Abstract A swamp sparrow song is a 2-s string of about 10 identical syllables, each made up of two to five distinct notes. Naturally-occurring syllables are highly polymorphic. The development of syllable patterning is strongly influenced by imitation. Analysis of 452 songs indicates that, whether simple or complex, all syllables were assembled from the same species-universal set of note types, consisting of six basic categories. Two populations studied intensively, 1000 km apart, differed in the number of notes per syllable and the ordering of note types within a syllable. It appears that song dialects can be defined in the swamp sparrow by reference to these features. The process of song learning in the swamp sparrow thus consists of the selection of a particular number, timing and sequence of notes from a limited set of types. While some degree of selection of within-type note variants is possible, the structure of the major categories of swamp sparrow note types is in large degree genetically preordained.

The logical analysis of animal communication.

Abstract An attempt has been made to describe some of the responses evoked by communication signals in certain animals and to infer the kind of information which the signals transmit. Using the methods developed by C. W. Morris 1946 for the logical analysis of human language, identiflors, designators, appraisors and prescriptors can be distinguished. Animal signals are rich in designative information, and five subcategories are distinguished: species-specific, sexual, individual, motivational and environmental information. The influence of natural selection upon the form of a signal will vary according to its information content. For example, the variable nature of some signals and the stereotypy of others can be related to the conveyance of different types of motivational information. A single signal often conveys several different items of information which are usually inherent in the whole signal and not represented by different parts of the signal. The form of some signals is arbitrary but the physical structure is often directly related to information content, in an iconic manner, or in other ways.

Vocal communication in the domestic chicken: I. Does a sender communicate information about the quality of a food referent to a receiver?

Abstract Male domestic chickens produce ‘food calls’, when they are presented with food. Experiments, conducted under controlled conditions, on the responses of cockerels to the presentation of various foods in the presence of a hen indicate that the rates and numbers of food calls vary with the preference ranking of the food. A hen is more likely to approach a male when he is calling than when he is silent. The probability of a hen approaching is greater when the male is calling to a highly preferred food than to a low-preference food. We conclude that male food calling communicates information about food quality to a female chicken, the signal receiver.

Vocal communication in the domestic chicken: II. Is a sender sensitive to the presence and nature of a receiver?

Abstract As a test of the automaticity of the food calling behaviour of cockerels, their sensitivity to the presence and nature of an audience was explored. Males were presented with either a highly preferred food or a non-food item in the presence of a familiar female, a strange female, a male, or with no audience at all. With food as a referent, there was significantly less food calling with no audience than in the presence of females, and even less with a male as a potential receiver. There was a significant amount of calling for the non-food item, especially in the presence of a strange female. Food calling to non-foods in certain social contexts is discussed as a case of deception. The modulation of signal production according to the nature of the receiver is considered in relation to the issue of intentionality in animal communication.