John M. Burt

Lesions of the anterior forebrain song control pathway in female canaries affect song perception in an operant task

We tested whether the avian anterior forebrain pathway functions in song perception in female canaries, and whether it is specialized for conspecific song perception or functions more generally in auditory perception. Using operant conditioning methods, we trained female canaries to discriminate among synthetic sound stimuli, canary songs, and song sparrow songs. We also trained each bird to discriminate among visual stimuli to test for general effects of lesions on performance. When canaries had learned the discrimination tasks, bilateral electrolytic lesions of the lateral portion of the magnocellular nucleus of the anterior neostriatum (lMAN) were made. The lesioned birds were then tested on the previously learned discrimination tasks. Lesions that destroyed most or all of lMAN decreased the ability of female canaries to discriminate between previously learned pairs of acoustic stimuli of all types, while visual discrimination was unaffected. These results suggest that the female canary anterior forebrain pathway contributes to the perception of acoustic stimuli, with this contribution including heterospecific song and other acoustic stimuli as well as canary song.

The Role of Social Interaction in Bird Song Learning

Bird song learning has become a powerful model system for studying learning because of its parallels with human speech learning, recent advances in understanding of its neurobiological basis, and the strong tradition of studying song learning in both the laboratory and the field. Most of the findings and concepts in the field derive from the tape-tutor experimental paradigm, in which the young bird is tutored by tape-recorded song delivered by a loudspeaker in an isolation chamber. This paradigm provides rigorous experimental control of auditory parameters, but strips song learning of any social context, and has slowed the realization that social factors might be critical to the process. In recent years, field research and lab studies using live birds as tutors have revealed that social factors play a preeminent role in song learning. In this article, we propose a new experimental paradigm—the virtual-tutor design, which permits precise manipulation of singing interactions between simulated tutors that the young bird “overhears,” as well as direct singing interactions between the young bird and the simulated tutors. We suggest that this approach may permit researchers to analyze social factors in bird song learning, particularly those relating to auditory interactions, that have been difficult to analyze heretofore.

Song sharing in two populations of song sparrows (Melospiza melodia)

Abstract Sharing song types with immediate neighbors is widespread in birds with song repertoires, and sharing songs may confer a selective advantage in some cases. Levels of song sharing vary between different geographical populations of several bird species, and ecological differences often correlate with differences in singing behavior; in particular, males in migratory subspecies often share fewer songs than males in resident subspecies. The song sparrow (Melospiza melodia) appears to fit this pattern: resident song sparrows in western North America generally share 20–40% of their repertoire (of about eight songs) with each neighbor, while migratory subspecies from eastern North America often share 10% or less. We compared song sharing in two populations within a single subspecies of song sparrow (M. m. morphna) in Washington State. These populations, separated by only 120 km, nonetheless differ in migratory tendencies and several other ecological and life history variables. We recorded complete song repertoires from 11 male song sparrows in a high-elevation, migrating population at Gold Creek in west-central Washington, and compared them to two samples (n = 15 and n = 36) from a coastal, resident population at Discovery Park, Seattle, Washington. Despite major differences in habitat, population density, and migratory tendencies, song sharing among Gold Creek males was as high as that among Discovery Park males. In both populations, sharing was highest between immediate neighbors, and declined with distance. We conclude that at the within-subspecies level, neither migration nor population density affect song sharing in song sparrows, a song repertoire species.

Regenerated hair cells in the European starling: are they more resistant to kanamycin ototoxicity than original hair cells?

Previous work from our laboratory [Marean et al. (1993) Hear. Res. 71, 125-136] has shown that a 10 day dose of 200 mg/kg/day kanamycin produced damage to the basal 34% of the starling basilar papilla. We also observed that repeating the dosing schedule following a 4 month survival period resulted in significantly less damage to the regenerated auditory epithelium. The present study investigated whether or not this apparent resistance was the result of a tendency for regenerated hair cells to be less susceptible to kanamycin ototoxicity, or if other, systemic factors may be involved. Eight European starlings were given subcutaneous injections of 200 mg/kg/day kanamycin for 10 days. Serum levels of kanamycin were measured at the time of sacrifice for all birds, and the basilar papillae of all birds were examined by scanning electron microscopy (SEM). Two of these birds (Group 1) were sacrificed immediately following the dosing period. Two of the birds were allowed to survive for 60 days (Group 2). Two of the birds were redosed with 200 mg/kg/day for 10 days after 60 days survival (Group 3). Finally, two birds were redosed with 250 mg/kg/day until serum levels of kanamycin were the same as Group 1 when sacrificed (> 9 micrograms/ml). The SEM results showed that the regenerated auditory epithelium of the birds dosed a second time sustained less damage compared to previously untreated ears, even though the dosing regimen was the same (Group 3 versus Group 1). The regenerated auditory epithelium of birds dosed a second time sustained the same damage as previously untreated animals when the dosage was increased to attain similar serum levels (Group 4 versus Group 1). These results suggest metabolic changes occur in the starling in response to the initial dose of kanamycin which do not necessarily involve changes in hair cell resistance to ototoxicity.

Auditory perception following hair cell regeneration in European starling (Sturnus vulgaris): Frequency and temporal resolution

Behavioral detection thresholds, auditory filter widths, and temporal modulation transfer functions were obtained from four starlings before, during and after 11 days of subcutaneous injections of kanamycin, an aminoglycoside antibiotic. Birds were operantly conditioned to respond to pure tones and amplitude modulated noises ranging in frequency from 0.25 to 7 kHz using adaptive staircase procedures and were tested daily for 92 days after the first injection of aminoglycoside. All birds had threshold shifts of at least -60 dB at frequencies above 4 kHz. Lower frequencies were affected in some birds, although none of the birds had hearing loss below 3 kHz. All four birds had wider auditory filters at 5 kHz immediately after the aminoglycoside series. Any changes in frequency resolution at frequencies below 5 kHz were slight, transitory, and rarely observed. Two of the four birds had permanently wider auditory filters at 5 kHz. Temporal modulation transfer functions were briefly affected in two birds during the time of greatest threshold shift. Recovery of detection thresholds began soon after the injections ceased and continued for approximately 60 days. Recovery in frequency resolution lagged behind auditory threshold by about 10 days. Normal temporal resolution was observed in the context of impaired intensity and frequency resolution. Changes in auditory threshold and frequency resolution were closely associated for all birds at 5 kHz, but were correlated with statistical significance in only two birds. Scanning electron microscopy was performed on all four birds after 90 days of recovery and confirmed that the extent of initial damage was consistent with the pattern of observed hearing loss.

What is the Function of Song Learning in Songbirds

In this paper we approach the question of the function of song learning in songbirds by addressing the more particular question of why a bird chooses the particular songs he does from among the many songs he hears during his song learning period. Our generalizations about song learning are derived from observations of a sedentary (nonmigratory) population of song sparrows (Melospiza melodia). We examine this question in the field, rather than in the laboratory, because we believe that the variables controlling song selection are social and ecological. We proceed from the hypothesis that song learning is an adaptive strategy, and attempt to identify the specific design features and overall function of this strategy in our particular study species. From our studies, we have identified several design features which, taken together, serve to maximize the number of songs the young bird will share with his neighbors, especially his near neighbors, in his first breeding season. Why should it be advantageous for the bird to have songs he shares with his neighbors? We suggest four possible, non-mutually exclusive advantages, and discuss the evidence in support of the fourth one. First, shared songs may be attractive to females. Second, shared songs may provide a mechanism by which two neighbors might effectively codefend their territories against other birds: each bird would effectively be mimicking the other while repelling prospective intruders. Third, shared songs may function as a “badge” of familiarity among territorial males; shared songs are a reliable signal of familiarity since they must be learned in the local neighborhood. Fourth, at least in song sparrows, shared songs appear to facilitate communication among neighboring birds. In particular, a bird uses the songs he shares with a neighbor to direct his song to that bird. We conclude by noting the paradox that songbirds have the ability to improvise new songs (demonstrated in lab experiments), yet in the field birds of most species faithfully copy the songs of their older neighbors. We suggest that song researchers need to ponder this paradox, and figure out why it is so important for a songbird to have the same songs as his neighbors.

Calibrating animal-borne proximity loggers

Summary Growing interest in the structure and dynamics of animal social networks has stimulated efforts to develop automated tracking technologies that can reliably record encounters in free‐ranging subjects. A particularly promising approach is the use of animal‐attached ‘proximity loggers’, which collect data on the incidence, duration and proximity of spatial associations through inter‐logger radio communication. While proximity logging is based on a straightforward physical principle – the attenuation of propagating radio waves with distance – calibrating systems for field deployment is challenging, since most study species roam across complex, heterogeneous environments. In this study, we calibrated a recently developed digital proximity‐logging system (‘Encounternet’) for deployment on a wild population of New Caledonian crows Corvus moneduloides. Our principal objective was to establish a quantitative model that enables robust post hoc estimation of logger‐to‐logger (and, hence, crow‐to‐crow) distances from logger‐recorded signal‐strength values. To achieve an accurate description of the radio communication between crow‐borne loggers, we conducted a calibration exercise that combines theoretical analyses, field experiments, statistical modelling, behavioural observations, and computer simulations. We show that, using signal‐strength information only, it is possible to assign crow encounters reliably to predefined distance classes, enabling powerful analyses of social dynamics. For example, raw data sets from field‐deployed loggers can be filtered at the analysis stage to include predominantly encounters where crows would have come to within a few metres of each other, and could therefore have socially learned new behaviours through direct observation. One of the main challenges for improving data classification further is the fact that crows – like most other study species – associate across a wide variety of habitats and behavioural contexts, with different signal‐attenuation properties. Our study demonstrates that well‐calibrated proximity‐logging systems can be used to chart social associations of free‐ranging animals over a range of biologically meaningful distances. At the same time, however, it highlights that considerable efforts are required to conduct study‐specific system calibrations that adequately account for the biological and technological complexities of field deployments. Although we report results from a particular case study, the basic rationale of our multi‐step calibration exercise applies to many other tracking systems and study species.

Performance of Encounternet Tags: Field Tests of Miniaturized Proximity Loggers for Use on Small Birds.

Proximity logging is a new tool for understanding social behavior as it allows for accurate quantification of social networks. We report results from field calibration and deployment tests of miniaturized proximity tags (Encounternet), digital transceivers that log encounters between tagged individuals. We examined radio signal behavior in relation to tag attachment (tag, tag on bird, tag on saline-filled balloon) to understand how radio signal strength is affected by the tag mounting technique used for calibration tests. We investigated inter-tag and inter-receiver station variability, and in each calibration test we accounted for the effects of antennae orientation. Additionally, we used data from a live deployment on breeding barn swallows (Hirundo rustica erythrogaster) to analyze the quality of the logs, including reciprocal agreement in dyadic logs. We evaluated the impact (in terms of mass changes) of tag attachment on the birds. We were able to statistically distinguish between RSSI values associated with different close-proximity (<5m) tag-tag distances regardless of antennae orientation. Inter-tag variability was low, but we did find significant inter-receiver station variability. Reciprocal agreement of dyadic logs was high and social networks were constructed from proximity tag logs based on two different RSSI thresholds. There was no evidence of significant mass loss in the time birds were wearing tags. We conclude that proximity loggers are accurate and effective for quantifying social behavior. However, because RSSI and distance cannot be perfectly resolved, data from proximity loggers are most appropriate for comparing networks based on specific RSSI thresholds. The Encounternet system is flexible and customizable, and tags are now light enough for use on small animals (<50g).

Immediate and long-term effects of testosterone on song plasticity and learning in juvenile song sparrows

Steroid sex hormones play critical roles in the development of brain regions used for vocal learning. It has been suggested that puberty-induced increases in circulating testosterone (T) levels crystallize a birds repertoire and inhibit future song learning. Previous studies show that early administration of T crystallizes song repertoires but have not addressed whether new songs can be learned after this premature crystallization. We brought 8 juvenile song sparrows (Melospiza melodia) into the laboratory in the late summer and implanted half of them with subcutaneous T pellets for a two week period in October. Birds treated with T tripled their singing rates and crystallized normal songs in 2 weeks. After T removal, subjects were tutored by 4 new adults. Birds previously treated with T tended toward learning fewer new songs post T, consistent with the hypothesis that T helps to close the song learning phase. However, one T-treated bird proceeded to learn several new songs in the spring, despite singing perfectly crystallized songs in the fall. His small crystallized fall repertoire and initial lag behind other subjects in song development suggest that this individual may have had limited early song learning experience. We conclude that an exposure to testosterone sufficient for crystallization of a normal song repertoire does not necessarily prevent future song learning and suggest that early social experiences might override the effects of hormones in closing song learning.

'Neurogame Therapy' for Improvement of Movement Coordination after Brain Injury: Developing a Wireless Biosignal Game Therapy System

Emerging technology holds tremendous promise for improving recovery following brain injury. Here we describe a home-based rehabilitation system for improving volitional control of hand movement. People with cerebral palsy and those recovering from stroke or traumatic brain injury often have difficulty producing coordinated movements of the hand and arm on one side of the body. Surface electromyography (sEMG) recorded over affected muscles is used to provide enhanced visual feedback via a computer game interface. Several weeks of practice using this system has resulted in improved muscle coordination. Preliminary results are shown from the next generation of this system, which will employ ultra-low power wireless sensors to transmit muscle activity to a home computer.