Michael D. Beecher

Sociobiology of Bank Swallows: Reproductive Strategy of the Male

Male bank swallows pursue a mixed reproductive strategy. As previously documented, they form monogamous pair bonds with females with whom they will share parental duties of nest-building, incubation, and feeding of the young. In addition, however, they routinely seek promiscuous copulations with other females, both before and after pair-bonding.

Signalling systems for individual recognition: an information theory approach

Abstract This paper develops a quantitative method for measuring the information capacity of an animals ‘signature system’, i.e. the set of cues by which individuals are identified. The information measure (Hs) is derived by applying Shannons measure for the information in a continuous variable to a simple linear model. The model is essentially the analysis of variance model II (random effects), and is implicit in the many ANOVAs and discriminant function analyses that have been done on the signature systems of animals. For multivariate measurements, a principal components transformation of the data permits the information in the independent components to be added to give the total information. An analysis of illustrative data sets reveals a close correlation between Hs and the probability of a correct classification of an individual (P) obtained by discriminant function analysis. Hs has the advantage, however, that it is a population estimate whereas the value of P is tied to the number of individuals in the sample. The information analysis approach may prove valuable for comparative analyses where evolutionary hypotheses predict one species to have a better developed signature system than another.

Repertoire matching between neighbouring song sparrows

A male song sparrow,Melospiza melodia, has a song repertoire of about eight or nine distinct song types, and he typically shares several of these song types with each of his several neighbours. In the prevailing theoretical view, the song types in a birds repertoire are interchangeable and multiple song types exist primarily to provide diversity. The present study was designed to test a contrary hypothesis concerning one particular context, counter-singing between neighbours. Specifically, the hypothesis was tested that song sparrows reply to the songs of particular neighbours with particular songs from their repertoire: they select a song type they share with that neighbour (‘repertoire matching’). In a field experiment, neighbour song was played to the subject from just inside the neighbours territory. Subjects responded with a song shared with that neighbour in 87.5% of trials (chance expectation for this sample is 42%). In control trials, where stranger song was presented from the same location, subjects responded with songs shared with the neighbour at that location in only 17% of the trials. It is suggested that ‘repertoire matching’ may be one advantage of a song learning strategy that produces song sharing between neighbours.

Song learning in birds: diversity and plasticity, opportunities and challenges

A common trend in neuroscience is convergence on selected model systems. Underlying this approach is an often implicit assumption that mechanisms observed in one species are characteristic of all related species. Although the model system approach has been extremely productive, it might not account for all of the mechanistic differences between species that differ behaviourally. Using the neural system that regulates song learning in songbirds as an example, we demonstrate how integrating model system and comparative approaches can lead to a more complete picture of neural mechanisms, and can resolve issues raised by a focus on selected species.

Territory tenure in song sparrows is related to song sharing with neighbours, but not to repertoire size

Song repertoires may be a product of sexual selection and several studies have reported correlations of repertoire size and reproductive success in male songbirds. This hypothesis and the reported correlations, however, are not sufficient to explain the observation that most species have small song repertoire sizes (usually fewer than 10, often fewer than five song types). We examined a second important aspect of a males song repertoire, the extent to which he shares songs with his neighbours. Song sharing has not been measured in previous studies and it may be partially confounded with repertoire size. We hypothesized that in song sparrows, Melospiza melodia, song sharing rather than repertoire size per se is crucial for male territorial success. Our longitudinal study of 45 song sparrows followed from their first year on territory showed that the number of songs a bird shares with his neighbourhood group is a better predictor of lifetime territory tenure than is his repertoire size. We also found that song sharing increases with repertoire size up to but not beyond eight to nine song types, which are the most common repertoire sizes in the population (range in our sample 5-13). This partial confound of song sharing and repertoire size may account for some earlier findings of territory tenure-repertoire size correlations in this species and other species having small- or medium-sized repertoires. Copyright 2000 The Association for the Study of Animal Behaviour.

Perception of Conspecific Vocalizations by Japanese Macaques

Japanese macaques (Macaca fuscata) and control species (vervet, pigtailed macaque, bonnet macaque) were trained for food to respond to one class of recorded fuscata vocalizations an

Recognition of individual neighbors by song in the song sparrow, a species with song repertoires

SummaryPrevious theory and research have suggested that bird species with song repertoires in general, and song sparrows (Melospiza melodia) in particular, cannot readily discriminate between the songs of neighbors and strangers. In a recent study (Stoddard et al. 1991) we showed that song sparrows can in fact discriminate neighbors from strangers on the basis of song. In this study we sought to demonstrate that song sparrows can make the finer discrimination between individual neighbors and that they can do so on the basis of a single song type. We compared the response of territorial males to song playback of neighbors and strangers at three locations: the neighbors regular boundary, the opposite boundary, and the center of the territory. The birds showed strong neighbor-stranger discrimination at the regular boundary but not at the opposite boundary, nor in the center of the territory. The differences in song discrimination between different boundary locations indicate that song sparrows associate particular songs with particular territories, effectively discriminating between individual neighbors on the basis of song. Song repertoires themselves do not interfere with neighbor recognition to the extent originally postulated. As speakers are moved inside the territory from the border, however, the degree of discrimination diminishes. We believe that differences in speaker placement may have contributed to the variability in neighbor-stranger discrimination observed in previous studies of the song sparrow and perhaps other repertoire species as well. This interpretation is consistent with data from another song sparrow population showing that half the territory takeovers are by immediate neighbors.

Kin recognition in birds

I develop the argument that for a true kin recognition system to evolve, selection must act on both parties: not only must recognition be favored in the donor of care, but reliable identification must be favored in the potential recipient of the care. This perspective suggests two complementary hypotheses, which I discuss and evaluate with data drawn from studies of birds. According to thesignature adaptation hypothesis, when the sender benefits by reliably identifying itself, selection will act directly on phenotypic characters so as to enhance their signature properties. I summarize our studies on parent-offspring recognition in four species of swallows which are consistent with this hypothesis. In particular, acoustical and perceptual analyses of chick calls show that the calls of colonial swallows are more individually distinctive than are the chick calls of noncolonial swallows. According to theantirecognition hypothesis, when the sender doesnot benefit by reliably identifying itself, selection will act so as to minimize signature characteristics. I suggest two contexts for research on this hypothesis. The first context occurs when parentage is uncertain due to extrapair copulations and/or egg-dumping, and the second context occurs when there is a long period between the onset of chick mobility and chick fledging, as occurs typically in gulls. In both instances, parents will be favored to recognize genetic relatedness of offspring but offspring will be favored to conceal it. To date, data from bird studies are consistent with the prediction that the interests of chicks win out in this situation.

Response of territorial male song sparrows to song types and variations

SummaryThe song repertoires of male song sparrows (Melospiza melodia) are comprised of distinct song types and many overlapping variations within each type. This study examines the sensitivity of territorial male song sparrows to both multiple song types and variation within types. A playback experiment was conducted using stimulus tapes that had either single songs (but not variations), song variations (but not types) or a single song. Response during playback was similar for all three stimulus groups, but diminished sooner after playback for the single-song tape. Thus our results indicate that male song sparrows are sensitive to song variability both within and among song types.

MEMORY DOES NOT CONSTRAIN INDIVIDUAL RECOGNITION IN A BIRD WITH SONG REPERTOIRES

Summary We tested the hypothesis that memory or perceptual limitations imposed by song repertoires contrain the ability of song birds to recognize their neighbours by song. Using operant conditioning procedures, we trained male song sparrows (Melospiza melodia) (median repertoire size = 8) to discriminate between two artificial song sparrow repertoires of 32 songs each (64 songs total). Both song sparrows learned to discriminate concurrently between all 32 song pairs. The birds learned later songs as quickly as they learned earlier songs. These results suggest that song sparrows are capable of memorizing the full song repertoire of their neighbours under natural conditions. In a second experiment we found that song sparrows readily generalize from one exemplar of a song type to other variations of that song type. We conclude that the evolution of song repertoires of song sparrows have neither constrained nor been constrained by individual recognition of neighbours by song.