Differential immediate early gene activity revealed by playback of male and female incomplete chick-a-dee calls.

In both humans and animals, biological differences between males and females has long been a topic of research. In songbirds, sexual dimorphisms can be seen in many species' plumage and heard in some species' songs. However, not all songbirds have such overt phenotypic sexual differences, leading to the question: are all vocalizations dimorphic? One of the most used and versatile vocalizations of the black-capped chickadee (Poecile atricapillus) is their namesake chick-a-dee call, that is produced by both sexes. This call is composed of four note types: A, B, C (together chick-a), and D (dee). Previous research has found that A notes contain information regarding the sex of the caller. However, chickadees do not categorize full chick-a-dee calls, or altered chick-a calls, based on the sex of the caller. Here we presented both male and female chickadees with altered chick-a calls (dee portion removed) of both sexes and measured the number of ZENK labeled cells in auditory nuclei. We found that calls produced by males and females had more ZENK labeled cells than the control condition; however, there was no significant difference in ZENK labeled cells between male and female listeners. Overall, our results suggest that black-capped chickadees do not perceive sexual differences in the production of chick-a calls.

Mitigating road impacts on animals through learning principles.

Roads are a nearly ubiquitous feature of the developed world, but their presence does not come without consequences. Many mammals, birds, reptiles, and amphibians suffer high rates of mortality through collision with motor vehicles, while other species treat roads as barriers that reduce gene flow between populations. Road effects extend beyond the pavement, where traffic noise is altering communities of songbirds, insects, and some mammals. Traditional methods of mitigation along roads include the creation of quieter pavement and tires and the construction of physical barriers to reduce sound transmission and movement. While effective, these forms of mitigation are costly and time-consuming. One alternative is the use of learning principles to create or extinguish aversive behaviors in animals living near roads. Classical and operant conditioning are well-documented techniques for altering behavior in response to novel cues and signals. Behavioral ecologists have used conditioning techniques to mitigate human-wildlife conflict challenges, alter predator-prey interactions, and facilitate reintroduction efforts. Yet, these principles have rarely been applied in the context of roads. We suggest that the field of road ecology is ripe with opportunity for experimentation with learning principles. We present tangible ways that learning techniques could be utilized to mitigate negative roadside behaviors, address the importance of evaluating fitness within these contexts, and evaluate the longevity of learned behaviors. This review serves as an invitation for empirical studies that test the effectiveness of learning paradigms as a mitigation tool in the context of roads.

Fast- and slow-exploring pigeons differ in how they use previously learned rules.

Several studies report a correlation between exploratory behaviour and performance on tests of cognitive ability. Exploration may influence learning because less exploratory animals are less likely to come in contact with to-be-learned stimuli. Alternatively, the way information available in the environment is processed could influence the rate of exploration. Pigeons are one of the most-studied species used to examine the mechanisms underlying cognitive abilities, but have not been used to examine the relationship between these abilities and animal personality. Here, twelve pigeons were first tested in a novel environment to assess repeatability in exploratory behaviour. Pigeons were then trained to discriminate between two visual stimuli: lines oriented at 90° (vertical, the S+) and 135° (the S-). After training pigeons underwent generalization testing with ten additional visual line orientation stimuli. We found exploratory behaviour was related to generalization performance: fast-explorers had steeper generalization gradients compared to slow-explorers. This effect was only seen in the direction towards the S-. These results suggest that birds with different exploratory styles differ in how they use previously learned information. Further testing is needed to confirm which cue(s) (S+ or S-) control the behaviour of fast-explorers.

Differential effects of vocalization type, singer and listener on ZENK immediate early gene response in black-capped chickadees (Poecile atricapillus).

Here we examined immediate early gene (ZENK) induction to vocalizations in the ascending auditory pathway of black-capped chickadees (Poecile atricapillus) to assess the impact that the sex of the producer and perceiver has on ZENK induction. We manipulated the playback by both the vocal type (song/call) and sex of producer (male/female), and then presented these stimuli classes to either male or female black-capped chickadees. Neural response to the stimulus was quantified by the amount of protein of the IEG ZENK (also known as zif-268, egr-1, ngf-Ia and krox-24) in the caudal medial nidopallium (NCM) and caudomedial mesopallium (CMM). Overall, there was more ZENK induction in CMM and the dorsal parts of the caudal medial nidopallium (NCMd) than in the ventral parts of the caudal medial nidopallium (NCMv) and males had more ZENK induction than females. CMM had the most complex responding of ZENK induction to stimuli such that vocalization type, sex of producer, and sex of perceiver all affected ZENK induction. The silence controls had the least ZENK induction compared to any other group.

All "chick-a-dee" calls are not created equally. Part II. Mechanisms for discrimination by sympatric and allopatric chickadees.

The 'chick-a-dee' call, common to all members of the genus Poecile, is used by both sexes throughout the year to putatively co-ordinate flock movements and register alarm. In some regions, two or more chickadee species occupy overlapping territories, and therefore it is essential that these sympatric species learn to discriminate between the acoustically similar calls of the species. Previous work from our laboratory has shown that black-capped (P. atricapillus) and mountain chickadees (P. gambeli) discriminate between the species' calls and treat each species' calls as belonging to separate open-ended categories. In the current set of experiments we use an operant conditioning paradigm to gain an understanding of (1) how the birds perform this discrimination and (2) whether birds with different levels of experience with heterospecific calls perform this task differently. We use natural recordings of chick-a-dee calls and perform several manipulations to test the importance of the introductory 'chick-a' portion and the terminal 'dee' portion for discriminating among the calls of the two species. Evidence suggests that birds mainly use the terminal 'dee' portion, as all groups of birds responded similarly to these probe stimuli and control chick-a-dee calls. We propose that the terminal 'dee' portion, consisting of lower frequency notes, is more likely to be resistant to degradation, and therefore a more reliable species-specific marker.

A bird's eye view: top down intracellular analyses of auditory selectivity for learned vocalizations.

The "song system" refers to a group of interconnected brain nuclei necessary for the utterance of learned song and for the generation of vocal plasticity important to both song learning and adult song maintenance. Although song learning and, in some species, song maintenance depend on auditory feedback, how audition influences vocalization remains unknown. One attractive idea is that auditory signals propagate directly to those telencephalic nuclei implicated in song patterning, providing a convenient substrate for sensorimotor integration. Consistent with this idea, auditory neurons highly selective for the bird's own song have been detected in telencephalic song nuclei, and lesions of these structures can impair song perception as well as song production. This review discusses evidence for an auditory-perceptual role of the song system, the anatomical pathways by which auditory information enters the song system, the synaptic events underlying highly selective action potential responses to learned song, and the possible roles such activity could play in song learning and maintenance.

Bird communication: two voices are better than one.

How do emperor penguins find their mates on a featureless ice flow, packed at densities of ten animals per square meter? A recent study has revealed how use of their 'two-voice' calls enables emperor penguins to locate their mates and chicks under some of nature's most extreme conditions.

Call-note discriminations in black-capped chickadees (Poecile atricapillus).

Bioacousticians (M.S. Ficken, S. R. Ficken, & S. R. Witken, 1978) classified black-capped chickadee call notes from the chick-a-dee call complex into 4 note types (A, B, C, and D) identified from sound spectrograms. In Experiment 1, chickadees (Poecile atricapillus) learned operant auditory discriminations both within and between the 4 note types but learned the between note-type discrimination significantly faster. In Experiment 2, when the original, unrewarded between-category exemplars were replaced with novel, rewarded exemplars of these same categories, chickadees showed transfer of inhibitory stimulus control to the novel exemplars. In Experiment 3, when novel exemplars were replaced by the original exemplars, chickadees showed propagation of positive stimulus control back to the original exemplars. This evidence suggests that chickadees and bioacousticians accurately sort conspecific call notes into the same open-ended categories (R. J. Herrnstein, 1990).

Timing and classifying brief acoustic stimuli by songbirds and humans.

The durations of animals' brief vocalizations provide conspecifics with important recognition cues. In the present experiments, zebra finches and humans (trained musicians) were rewarded for responding after S+ (standard) auditory signals from 56 to 663 ms and not for responding after shorter or longer S- (comparison) durations from 10 to 3684 ms. With either a single standard (Experiment 1) or multiple standards (Experiment 2), both zebra finches and humans timed brief signals to about the same level of accuracy. The results were in qualitative agreement with predictions from scalar timing theory and its connectionist implementation in both experiments. The connectionist model provides a good quantitative account of temporal gradients with a single standard (Experiment 1) but not with multiple standards (Experiment 2).

Frequency-range discriminations: special and general abilities in zebra finches (Taeniopygia guttata) and humans (Homo sapiens).

The acoustic frequency ranges in birdsongs and human speech can provide important pitch cues for recognition. Zebra finches and humans were trained to sort contiguous frequencies into 3 or 8 ranges, based on associations between the ranges and reward. The 3-range task was conducted separately in 3 spectral regions. Zebra finches discriminated 3 ranges in the medium and high spectral regions faster than in the low region and discriminated 8 ranges with precision. Humans discriminated 3 ranges in all 3 spectral regions to the same modest standard and acquired only a crude discrimination of the lowest and highest of 8 ranges. The results indicate that songbirds have a special sensitivity to the pitches in conspecific songs and, relative to humans, have a remarkable general ability to sort pitches into ranges.