Effects of humidity on reproductive behavior in male and female zebra finches (Taeniopygia guttata).

Zebra finches (Taeniopygia guttata) are regarded as opportunistic breeders with reproductive behaviors mediated by short-term proximal environmental conditions. This article provides experimental evidence for the role of humidity in reproductive behaviors. Zebra finches were subjected to experimentally manipulated high levels of relative humidity. Males gathered more nest material and sang more. Females showed no relationship between humidity and gathering nest materials, egg laying, or changes in rates of vocalization.

Amplitude regulation of vocalizations in noise by a songbird, Taeniopygia guttata.

Bird vocalizations are produced under various noise conditions. It could therefore benefit birds to alter the amplitude of their signals as noise conditions change. We tested this by recording male and female zebra finches, Taeniopygia guttata, as they were subjected to various levels of white noise. Both sexes increased amplitude levels of vocalization in response to increased levels of noise. Similar results were obtained with humans (the 'Lombard effect'). The results are discussed in terms of the 'active space' of bird song and honest signalling. Copyright 1998 The Association for the Study of Animal Behaviour.

Conspecific and heterospecific song discrimination in male zebra finches with lesions in the anterior forebrain pathway.

Adult zebra finches can produce normal song in the absence of Area X, IMAN, or DLM, nuclei that constitute the anterior forebrain pathway of songbirds. Here, we address whether lesions involving Area X and IMAN affect adult male zebra finches' ability to discriminate between conspecific or heterospecific songs. Intact birds and lesioned birds were trained on an operant GO/NOGO conditioning paradigm to discriminate between hetero- or conspecific songs. Both lesioned and intact birds were able to learn all discriminations. Lesioned and intact birds performed equivalently on canary song discriminations. In contrast, discriminations involving bird's own song took significantly more trails to learn for lesioned birds than for intact birds. Discrimination between conspecific songs in general also took longer in the lesioned birds, but missed significance level. Birds with control lesions medial to Area X did not show any differences from intact animals. Our results suggest that an intact anterior forebrain pathway is not required to discriminate between heterospecific songs. In contrast, Area X and IMAN contribute to a male zebra finch's ability to discriminate between its own song and that of other zebra finches.

Conspecific song perception in zebra finches (Taeniopygia guttata).

Adult male and female zebra finches (Taeniopygia guttata), previously trained with operant conditioning to discriminate between conspecific songs, were tested to determine their dependence on 2 properties of songs, the presence of song syllables and the temporal order of songs. The removal of song syllables disrupted discrimination performance but usually only if the stimulus was the bird's own song. All birds initially failed to identify reversed songs correctly, but males relearned discriminations with reversed songs in fewer trials than did females. The results suggest that there are 3 levels of song perception: a bird's own song, other males' songs as processed by males, and songs as processed by females. Each of these levels correlates with the known electrophysiological and neuroanatomical properties of the song system and with the natural history of song.

Auditory frequency generalization and a failure to find octave generalization in a songbird, the European starling (Sturnus vulgaris).

Many species of songbirds have absolute pitch perception. They memorize tones when discriminating between sequences and fail to generalize to novel frequency ranges. I examined frequency generalization in starlings (Sturnus vulgaris) that were trained to discriminate between individual frequencies. Starlings were tested for frequency generalization after training on 2- and 3-tone discriminations. There was no evidence for octave generalization, which is a hallmark of human absolute pitch perception. This suggests that avian absolute pitch perception must not be interpreted as identical with that in humans. A control experiment with 1-tone discriminations indicated that the presence of lit response keys affects the shape of the generalization gradients. Lit response keys are a common feature in avian auditory perception experiments, and this control experiment cautions that results may be affected by this seemingly minor procedural change.

Role of gender, season, and familiarity in discrimination of conspecific song by zebra finches (Taeniopygia guttata).

Operant conditioning techniques were used to assess how gender and song familiarity affect song discrimination in adult zebra finches (Taeniopygia guttata). Twenty-five males and females, divided into five cohorts, were trained to discriminate between conspecific songs at different times of year. Males discriminating between their own and another song from their own aviary reached criterion in the fewest number of trials, followed by males discriminating between two songs from their own aviary, then by males discriminating between songs they had not heard before. Females discriminating between two songs from their own aviary required more trials than males to reach criterion, but, unlike in males, song familiarity did not have a significant effect on song discrimination by females. The number of trials required to reach criterion was greater in winter than in summer, suggesting a photoperiodic effect in what has been regarded as a nonphotoperiodic species. Gender, season, and familiarity appear to affect how zebra finches discriminate between conspecific songs.

Hemispheric differences in avian song discrimination.

Auditory input to the right or left forebrain of adult male zebra finches (Taeniopygia guttata) was disrupted by lesioning the ipsilateral auditory relay nucleus of the thalamus. These birds were then presented with two kinds of auditory discriminations: (i) between their own song and the song of a cage mate; (ii) between two versions of an unfamiliar zebra finch song that differed only in the harmonic profile of one of the syllables. Right-side lesion birds did better than left-side lesion ones at discriminating between their own song and the song of a cage mate; left-side lesion birds did better on the harmonic profile task. We suggest that the two halves of the zebra finch brain process conspecific sounds differently, as seems to be the case for humans.

Testosterone facilitates some conspecific song discriminations in castrated zebra finches (Taeniopygia guttata).

An experiment was designed to test for the influence of testosterone on song discriminations. We found that testosterone did have an effect, which interacted with practice and the nature of the stimuli. Fourteen adult castrated zebra finches (Taeniopygia guttata) were grouped into seven pairs. In each pair, one bird was implanted with a testosterone-filled silastic tube and the other was implanted with an empty silastic tube. They were then trained on a go/no-go operant task to discriminate between bird songs in six consecutive experiments. The songs to be discriminated were as follows: experiment 1, two canary song segments; experiment 2, the bird's own song and that of the other member of the pair; experiment 3, the same two songs as in experiment 2 but with reversed stimulus-response contingencies; experiment 4, two other zebra finch songs; experiment 5, another two zebra finch songs; and experiment 6, another two canary song segments. There were no reliable learning differences between birds treated with testosterone or with an empty silastic in experiments 1 and 3-6. However, in experiment 2, testosterone-treated birds mastered the discrimination between their own song and the song of the other member of the pair in fewer trials than birds treated with empty silastics. We suggest that a song's ability to control the behavior of male zebra finches is influenced by the nature of the song, prior experience with the training paradigm, and hormone levels.

Timbre discrimination in zebra finch (Taeniopygia guttata) song syllables.

Zebra finch (Taeniopygia guttata) songs include syllables of a fundamental frequency and harmonics. Individual harmonics in 1 syllable can be more or less emphasized. The functional role of this variability is unknown. These experiments provide evidence of how the phenomenon is perceived. We trained 12 male and female zebra finches on a go-no-go operant procedure to discriminate between 2 song syllables that varied only in the absence of the 2nd or 5th harmonic. Training involved many thousands of trials. Both sexes used the presence or absence of the 2nd harmonic as the sole discriminative cue. Females had more difficulty learning to perform the task when the presence of the 2nd harmonic was the go stimulus, which indicates that their use of the information was biased by stimulus-response contingencies. The results are discussed in terms of a broad strategy to understand how animals perceive sounds used in communication.

On variables that affect estimates of the true sizes and densities of radioactively labeled cell nuclei.

Tritiated thymidine has been widely used as a nuclear marker of cell birth. The true diameters and packing densities (nuclei/microns 3) of such radioactively labeled nuclei cannot be measured directly from tissue sections. Here we show that existing stereological corrections cannot be applied to data from radioactively labeled nuclei. We empirically measured the number of silver grains exposed by nuclei containing tritiated thymidine. The nuclei were separated from the photographic emulsion by known thicknesses of fixed, embedded avian telencephalon. The results of this experiment were used to develop an equation that estimates the number of silver grains exposed by a cell nucleus of any given diameter, containing a given amount of radioactive label, and located at any given distance from the photographic emulsion. The equation also allows one to calculate the probability that a label-containing nucleus will be correctly classified as labeled. Simulations of the equation revealed that not all label-containing nuclei are correctly classified by using commonly employed identification procedures and that larger nuclei are less likely to be correctly classified than smaller nuclei, given the same amount of label. The equation can be used to modify one class of existing stereological equations so as to be applicable to measurements of radioactively labeled nuclei. Finally, we discuss the assumptions and limitations of this modification.

Song learning in birds: the relation between perception and production.

The vocal control system of oscine songbirds has some perplexing properties--e.g. laterality, adult neurogenesis, neuronal replacement--that are not predicted by common views of how vocal learning takes place. Similarly, we do not understand the relation between the direct pathway for the control of learned song and the recursive pathway necessary for song learning. Some of the paradoxes of the vocal system of birds may disappear once the relation between the perception and production of learned vocalizations is better understood. To some extent, perception and production may be two closely related states of a same system.

Experimental determination of a unit of song production in the zebra finch (Taeniopygia guttata).

Zebra finch (Taeniopygia guttata) song is composed of syllables delivered in a set order. Little is known about the program that controls this temporal delivery. A decision to sing or not to sing may or may not affect the entire song. Song, once commenced, may continue or may halt. If song is halted, stops may occur only at certain points. Seven zebra finches were presented with short bursts of strobe light while engaged in song. The variables of interest were whether the birds stopped and where they stopped. The results can be summarized as follows: Ongoing zebra finch song can be interrupted, interruptions occur at discrete locations in song, and the locations almost always fall between song syllables. These results reveal a functional representation of song production and place constraints on possible neural mechanisms that underlie song production in zebra finches and probably other oscine species. The results also raise hypotheses about the elements of song perception and memory.

Timbre control in zebra finch (Taeniopygia guttata) song syllables.

Zebra finch (Taeniopygia guttata) song syllables often include harmonically related frequency components. These harmonics may be suppressed, and this differential emphasis varies between the syllables in a song and between individual birds' songs. These patterns of harmonic suppression are timbre. Individual syllables' patterns of harmonic suppression are constant with adult males' songs. Young males that imitate the songs of older males also imitate their patterns of harmonic suppression. Syringeal denervation distorts these patterns, which suggests that they are produced through active control of the vocal organ. The selective suppression and emphasis of some harmonics creates a great number of possible timbre variants for any one syllable. These add signal diversity to the limited array of frequency modulations and range of fundamental frequencies found in zebra finch song. Analyses of bird song that disregard timbre may overlook a feature that is important in vocal communication.

Relative pitch perception in the European starling (Sturnus vulgaris): further evidence for an elusive phenomenon.

Relative pitch perception in animals has been difficult to demonstrate. This failing is due in part to stimulus sets that make an absolute pitch solution viable. In Experiment 1, starlings failed to acquire a discrimination that could be solved only on the basis of relative pitch. In Experiment 2, starlings were trained on a smaller set of pitch patterns, for which both absolute and relative pitch solutions were available, then tested with three series of unreinforced probe stimuli. Series 1 assessed stimulus control by absolute pitch. In Series 2, absolute pitch cues dictated one response, and relative pitch cues dictated a different response. Results indicate that starlings extract relative pitch from artificial pitch patterns only after acquiring a discrimination that permits both absolute and relative pitch solutions. Results are discussed in terms of the relative salience of absolute and relative pitch.

Perception of missing fundamental by a species of songbird (Sturnus vulgaris).

Two experiments investigated whether a species of songbird perceives missing fundamentals in sounds containing complex frequencies. In Experiment 1, European starlings were trained to discriminate between two sinusoids. This discrimination persisted when the sinusoids were replaced with waveforms composed solely of four consecutive higher harmonics of the training frequencies. In Experiment 2, starlings trained to discriminate between two complex frequencies consisting of sets of higher harmonics transferred the discrimination to the sinusoidal fundamentals. The results demonstrate that starlings can perceive harmonic or periodic structure, and show that a species of songbird can use harmonic structure to gain information about its auditory environment. The findings, together with those obtained from fish and mammals, suggest that periodicity pitch perception may be a general process in vertebrate hearing.

A psychophysical measure of pitch discrimination loss resulting from a frequency range constraint in European starlings (Sturnus vulgaris).

Earlier research (Hulse & Cynx, 1985) revealed that a number of species of songbirds acquired a pitch discrimination between rising and falling sequences in an arbitrarily defined training range of frequencies, but then failed to generalize the discrimination to new frequency ranges--a frequency range constraint. The two experiments here provide a psychophysical estimate of how pitch discrimination deteriorated in one species as sequences were stepped out from the training range. The gradient showing loss of discrimination was much sharper than would have been anticipated by stimulus generalization or the training procedures, and appeared unaffected by the removal of rising and falling frequency information. The frequency range constraint and its psychophysical properties have implications both for the analysis of birdsong and the study of animal cognition.