All “chick-a-dee” calls are not created equally

Black-capped chickadees (Poecile atricapillus) discriminate between naturally-ordered and scramble-ordered chick-a-dee calls and individual preference is related to rate of learning

Though many forms of animal communication are not reliant on the order in which components of signals are combined to be effective, there is evidence that order does matter for some communication systems. In the light of differential responding to calls of varying note-order observed in black-capped chickadees in the field, we set out to determine whether chickadees recognize syntactically-ordered and incorrectly-ordered chick-a-dee calls as separate and distinct conceptual categories using both an auditory preference task and go/no-go operant conditioning paradigm. Results show that chickadees spent more time on the perch that did not produce sound (i.e., silent perch) than on either of the acoustic perches (i.e., natural and scrambled order chick-a-dee call playback) and visited the perch associated with naturally-ordered calls more often than the perch associated with scrambled-order calls. Birds in both the True natural- and scrambled-order call groups continued to respond according to the contingencies that they learned in Discrimination training, indicating that black-capped chickadees are capable of perceiving and acting upon the categories of natural- versus scrambled-ordered calls.

Properties of an attention-grabbing motion signal: a comparison of tail and body movements in a lizard

Animals signals must be detected by receiver sensory systems, and overcome a variety of local ecological factors that could otherwise affect their transmission and reception. Habitat structure, competition, avoidance of unintended receivers and varying environmental conditions have all been shown to influence how animals signal. Environmental noise is also crucial, and animals modify their behavior in response to it. Animals generating movement-based visual signals have to contend with wind-blown plants that generate motion noise and can affect the detection of salient movements. The lizard Amphibolurus muricatus uses tail flicking at the start of displays to attract attention, and we hypothesized that tail movements are ideally suited to this function. We compared visual amplitudes generated by tail movements with push-ups, which are a key component of the rest of the display. We show that tail movement amplitudes are highly variable over the course of the display but consistently greater than amplitudes generated by push-ups and not constrained by viewing position. We suggest that these features, combined with the tail being a light structure that does not compromise other activities, provide an ideal introductory component for attracting attention in the ecological setting in which they are generated.

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.

Discrimination of acoustically similar conspecific and heterospecific vocalizations by black-capped chickadees (Poecile atricapillus)

Chickadees produce a multi-note chick-a-dee call in multiple socially relevant contexts. One component of this call is the D note, which is a low-frequency and acoustically complex note with a harmonic-like structure. In the current study, we tested black-capped chickadees on a between-category operant discrimination task using vocalizations with acoustic structures similar to black-capped chickadee D notes, but produced by various songbird species, in order to examine the role that phylogenetic distance plays in acoustic perception of vocal signals. We assessed the extent to which discrimination performance was influenced by the phylogenetic relatedness among the species producing the vocalizations and by the phylogenetic relatedness between the subjects' species (black-capped chickadees) and the vocalizers' species. We also conducted a bioacoustic analysis and discriminant function analysis in order to examine the acoustic similarities among the discrimination stimuli. A previous study has shown that neural activation in black-capped chickadee auditory and perceptual brain regions is similar following the presentation of these vocalization categories. However, we found that chickadees had difficulty discriminating between forward and reversed black-capped chickadee D notes, a result that directly corresponded to the bioacoustic analysis indicating that these stimulus categories were acoustically similar. In addition, our results suggest that the discrimination between vocalizations produced by two parid species (chestnut-backed chickadees and tufted titmice) is perceptually difficult for black-capped chickadees, a finding that is likely in part because these vocalizations contain acoustic similarities. Overall, our results provide evidence that black-capped chickadees' perceptual abilities are influenced by both phylogenetic relatedness and acoustic structure.

ZENK activation in the nidopallium of black-capped chickadees in response to both conspecific and heterospecific calls

Neuronal populations in the songbird nidopallium increase in activity the most to conspecific vocalizations relative to heterospecific songbird vocalizations or artificial stimuli such as tones. Here, we tested whether the difference in neural activity between conspecific and heterospecific vocalizations is due to acoustic differences or to the degree of phylogenetic relatedness of the species producing the vocalizations. To compare differences in neural responses of black-capped chickadees, Poecile atricapillus, to playback conditions we used a known marker for neural activity, ZENK, in the caudal medial nidopallium and caudomedial mesopallium. We used the acoustically complex 'dee' notes from chick-a-dee calls, and vocalizations from other heterospecific species similar in duration and spectral features. We tested the vocalizations from three heterospecific species (chestnut-backed chickadees, tufted titmice, and zebra finches), the vocalizations from conspecific individuals (black-capped chickadees), and reversed versions of the latter. There were no significant differences in the amount of expression between any of the groups except in the control condition, which resulted in significantly less neuronal activation. Our results suggest that, in certain cases, neuronal activity is not higher in response to conspecific than in response to heterospecific vocalizations for songbirds, but rather is sensitive to the acoustic features of the signal. Both acoustic features of the calls and the phylogenetic relationship between of the signaler and the receiver interact in the response of the nidopallium.

Linking social complexity and vocal complexity: a parid perspective

The Paridae family (chickadees, tits and titmice) is an interesting avian group in that species vary in important aspects of their social structure and many species have large and complex vocal repertoires. For this reason, parids represent an important set of species for testing the social complexity hypothesis for vocal communication--the notion that as groups increase in social complexity, there is a need for increased vocal complexity. Here, we describe the hypothesis and some of the early evidence that supported the hypothesis. Next, we review literature on social complexity and on vocal complexity in parids, and describe some of the studies that have made explicit tests of the social complexity hypothesis in one parid--Carolina chickadees, Poecile carolinensis. We conclude with a discussion, primarily from a parid perspective, of the benefits and costs of grouping and of physiological factors that might mediate the relationship between social complexity and changes in signalling behaviour.

Note types and coding in Parid vocalizations: the chick-a-dee call of the boreal chickadee (Poecile hudsonicus)

An important first step in characterizing a vocalization is to classify, describe, and measure the elements of that vocalization. Here, this methodology is employed to study the chick-a-dee call of the boreal chickadee (Poecile hudsonicus). The note types (A, B, C, D, and D(h)) in a sample of boreal chickadee calls are identified and described, spectral and temporal features of each note type are analyzed, and production phenomena in each note type are identified and quantified. Acoustic variability is compared across note types and individuals to determine potential features used for note-type and individual discrimination. Frequency measures appear to be the most useful features for identifying note types and individuals, though total duration may also be useful. Call syntax reveals that boreal chick-a-dee calls follow a general rule of note-type order, namely A-B-C-D(h)-D, and that any note type in this sequence may be repeated or omitted. This work provides a thorough description of the boreal chickadee chick-a-dee call and will serve as a foundation for future studies aimed at elucidating this call's functional significance within this species, as well as for studies comparing chick-a-dee calls across Poecile species.

Acoustic transmission of the chick-a-dee call of the Black-capped Chickadee (Poecile atricapillus): forest structure and note function

The acoustic adaptation hypothesis predicts that bird vocalizations will be structured to optimize their transmission through native vegetation. In cases where communication with distant individuals is needed, optimal transmission implies maximal propagation. In other cases, vocal signals are intended for nearby conspecifics and optimal transmission may be only a few metres. The “chick-a-dee” call of the Black-capped Chickadee ( Poecile atricapillus (L., 1766)) is a complex call used in both long- and short-range communication. Here we test whether this call transmits optimally in the locally preferred forests composed of a mix of deciduous and coniferous vegetation, or in either pure deciduous or coniferous forest stands. In addition, we examine whether notes that putatively function in short-range communication transmit shorter distances than those used in long-range communication. We found differential transmission rates for the highest and lowest frequencies in the chick-a-dee call in different forest types, and an overall improvement in call transmission in mixed forests. Note-type transmission correlated with putative note function with one notable exception. In summary, our results suggest that the chick-a-dee call conforms to the acoustic adaptation hypothesis, and that the forms of its note types are in line with their function.

Acoustic Mechanisms of a Species-Based Discrimination of the chick-a-dee Call in Sympatric Black-Capped (Poecile atricapillus) and Mountain Chickadees (P. gambeli)

Previous perceptual research with black-capped and mountain chickadees has demonstrated that these species treat each other's namesake chick-a-dee calls as belonging to separate, open-ended categories. Further, the terminal dee portion of the call has been implicated as the most prominent species marker. However, statistical classification using acoustic summary features suggests that all note-types contained within the chick-a-dee call should be sufficient for species classification. The current study seeks to better understand the note-type based mechanisms underlying species-based classification of the chick-a-dee call by black-capped and mountain chickadees. In two, complementary, operant discrimination experiments, both species were trained to discriminate the species of the signaler using either entire chick-a-dee calls, or individual note-types from chick-a-dee calls. In agreement with previous perceptual work we find that the D note had significant stimulus control over species-based discrimination. However, in line with statistical classifications, we find that all note-types carry species information. We discuss reasons why the most easily discriminated note-types are likely candidates to carry species-based cues.

Alert signals enhance animal communication in "noisy" environments

Environmental noise that reduces the probability that animals will detect communicative signals poses a special challenge for long-range communication. The application of signal-detection theory to animal communication lead to the prediction that signals directed at distant receivers in noisy environments will begin with conspicuous "alerting" components to attract the attention of receivers, before delivery of the information-rich portion of the signal. Whether animals actually adopt this strategy is not clear, despite suggestions that alerts might exist in a variety of taxa. By using a combination of behavioral observations and experimental manipulations with robotic lizard "playbacks," we show that free-living territorial Anolis lizards add an "alert" to visual displays when communicating to distant receivers in situations of poor visibility, and that these introductory alerts in turn enhance signal detection in adverse signaling conditions. Our results show that Anolis lizards are able to evaluate environmental conditions that affect the degradation of long-distance signals and adjust their behavior accordingly. This study demonstrates that free-living animals enhance the efficiency of long-range communication through the modulation of signal design and the facultative addition of an alert. Our findings confirm that alert signals are an important strategy for communicating in "noisy" conditions and suggest a reexamination of the existence of alerts in other animals relying on long-range communication.