Chick-a-dee call variation in Carolina chickadees and recruiting flockmates to food

The "chick-a-dee" call of many Paridae species (titmice, tits,and chickadees) is structurally complex and functions in socialcohesion. Studies with different Parid species suggest thatvariation in the note composition of calls relates to a widevariety of contexts. An earlier study with Carolina chickadees(Poecile carolinensis), the focal species of the present study,found that receivers responded differently to playback callsdiffering in note composition in feeding contexts. Here, weaddressed whether signalers actually produce calls differingin note composition in feeding contexts and whether those callsmight serve a recruitment function. In a first study, we foundthat the first chickadee to take seed from a feeding stationproduced calls with a greater number of D notes before the secondchickadee arrived to take seed, compared with after the secondchickadee arrived to take seed. This suggests that calls witha large number of D notes might serve a general recruitmentfunction. We tested this idea in a second study, using playbacksof calls containing a large number of D notes or a small numberof D notes at different sites. We found that the latency fora first chickadee to come into a site and take seed was shorterfor playback variants containing a large number of D notes.Thus, in Carolina chickadees, chick-a-dee calls containing alarge number of D notes may function to recruit other flockmembers to a discovered food source.     

Call Variation in Tufted Titmice (Baeolophus bicolor) in a Distress Context: Potential Sex Differences

Tufted titmice, Baeolophus bicolor, produce calls in the contexts related to threat and approach of, and capture by, a predator. In titmice, these calls transition from the chick‐a‐dee call, used in a wide range of social contexts, to ‘distress’ calls that are produced by birds when captured and held by a predator or human observer. A recent study indicated that titmice modify the note composition of their calls in the presence of such threatening stimuli. Here, we tested whether female and male titmice differed in their calling behavior, as relatively few sex differences have been documented in calls shared by female and male songbirds. Individual titmice were captured in walk‐in treadle traps, and we gradually increased the level of fear or arousal by approaching and finally capturing the bird in the hand. Male titmice produced more chick‐a‐dee calls than females as the level of threat increased, up to the point of capturing the bird in the hand. Furthermore, the note composition of calls produced by males differed from that of calls produced by females. A limitation to our study is that our method did not allow us to rule out the possibility that size or dominance differences, rather than sex, were the main reason for the differences in calling we detected. However, increased size generally was not associated with increased calling. We discuss some possible explanations for variation in distress calling behavior in titmice.     

Social context affects risk taking by a satellite species in a mixed-species foraging group

Mixed-species flocks of birds form during winter in the easterndeciduous forests of North America. These flocks consist oftwo flock-leading nuclear species, tufted titmouse (Baeolophusbicolor) and Carolina chickadee (Poecile carolinensis), andseveral follower, or satellite, species, including downy woodpecker(Picoides pubescens) and white-breasted nuthatch (Sitta carolinensis).Hypotheses explaining the adaptiveness of participation in suchmixed-species foraging groups have focused on increased foragingsuccess and/or decreased predation risk. We tested the predictionthat if nuthatches join nuclear species to reduce predationrisk, they should be more reluctant to visit an exposed feederin the absence of titmice than in their presence. When the feederwas positioned 16 m from forest cover, latency to visit thefeeder was greater for both male and female nuthatches whentitmice were absent. Removal of titmice had no effect on latencyat 8 m. In the absence of titmice, nuthatches visited the feederless frequently at both distances. These results indicate thatreduced predation risk is a benefit that satellite species gainby flocking with nuclear species.     

Variation in Note Composition of Chick‐a‐dee Calls is Associated with Signaler Flight in Carolina Chickadees,Poecile carolinensis

Chick‐a‐dee calls are used in a wide range of social contexts in Poecile (chickadee) species. These calls comprise a number of distinct note types. Earlier naturalistic observational studies suggested that the ‘C’ note type was used frequently in calls of Carolina chickadees (P. carolinensis) in the context of flight. We conducted three field studies with Carolina chickadees to test in more experimentally manipulative ways whether Chick‐a‐dee calls with more ‘C’ notes were associated with flight. The three studies differed in how they elicited flight behavior from chickadees, as well as in the likely arousal levels experienced by the birds. First, we captured chickadees and released them, recording any calls they produced in flight or when later perched after escape. Second, we approached chickadees that were foraging near the ground in field settings and recorded any calls they produced when perched compared to when they were in flight. Third, from a distant blind, we recorded chickadees flying to and from feeding stations, in which the closest perching substrate/cover was at least 2 m away from the feeding station, thus requiring flight. In all three studies, calls contained more ‘C’ notes when birds were in flight compared to when they were perched. This work expands our understanding of variation in note composition of chick‐a‐dee calls beyond the contexts of food and predator detection to the context of movement. Studies are now needed to test whether such variation in chick‐a‐dee calls brings about group cohesion.     

Geographic Variation in Note Composition and Use of chick‐a‐dee Calls of Carolina Chickadees (Poecile carolinensis)

The aim of this study was to determine whether geographic variation exists in the composition of note types in the chick‐a‐dee call of Carolina chickadees. This determination is of interest for two reasons: earlier studies with a related species suggested minimal geographic variation in note composition, and geographic variation in social signals may represent important developmental or selection processes shaping signal use. Carolina chickadees were recorded in a naturalistic observation study in west‐central Indiana. Chick‐a‐dee calls were analyzed and compared to calls from an eastern Tennessee population that had been described in a previously published study (Auk, 125, 2008, 896). Despite much similarity in the basic rules by which notes are organized to compose calls, there were several significant differences in how calls of the two populations were structured. Furthermore, birds from Indiana used their chick‐a‐dee calls in certain contexts in different ways compared to birds from Tennessee. These findings suggest interesting population‐level variation in this call system, and future research should be able to determine whether these differences are driven by evolutionary, ecological, or developmental factors, or some combination of these factors.     

The versatility of graded acoustic measures in classification of predation threats by the tufted titmouse Baeolophus bicolor: exploring a mixed framework for threat communication

Many mammal and bird species respond to predator encounters with alarm vocalizations that generate risk‐appropriate responses in listeners. Two conceptual frameworks are typically applied to the information encoded in alarm calls and to associated anti‐predator behaviors. ‘Functionally referential’ alarm systems encode nominal classes or categories of risk in distinct call types that refer to distinct predation‐risk situations. ‘Risk‐based’ alarms encode graded or ranked threat‐levels by varying the production patterns of the same call types as the urgency of predation threat changes. Recent work suggests that viewing alarm‐response interactions as either referential or risk‐based may oversimplify how animals use information in decision‐making. Specifically, we explore whether graded alarm cues may be useful in classifying risks, supporting a referential decision‐making framework. We presented predator (hawk, owl, cat, snake) and control treatments to captive adult tufted titmice Baeolophus bicolor and recorded their vocalizations, which included ‘chick‐a‐dee’ mobbing calls (composed of chick and D notes), ‘seet’ notes, two types of contact notes (‘chip’, ‘chink’), and song. No single call type was uniquely associated with any treatment and the majority of acoustic measures varied significantly among treatments (46 of 60). The strongest models (ANOVA and classification tree analysis) grouped hawk with cat and owl, and control with snake, and were based on the number or proportion of a) chick and D notes per chick‐a‐dee call, b) chip versus chink notes produced following treatment exposure, and c) the frequency metrics of other note types. We conclude that (1) the predation‐threat information available in complex titmouse alarm calls was largely encoded in graded acoustic measures that were (2) numerous and variable across treatments and (3) could be used singly or in combinations for either ranking or classification of threats. We call attention to the potential use of mixed threat identification strategies, where risk‐based signal information may be used in referential decision‐making contexts.     

Dual Function of Chip Calls Depending on Changing Call Rate Related to Risk Level in Territorial Pairs of White‐Eared Ground‐Sparrows

Different mechanisms have been proposed for encoding information into vocalizations: variation of frequency or temporal characteristics, variation in the rate of vocalization production, and use of different vocalization types. We analyze the effect of rate variation on the dual function of chip calls (contact and alarm) produced by White‐eared Ground‐sparrows (Melozone leucotis). We conducted an acoustic playback experiment where we played back 1 min of four chip call rates (12, 36, 60, 84 calls/min). We measured the response of territorial pairs using behavioral responses, and fine structural features of calls produced in response to those playbacks. White‐eared Ground‐sparrows showed more intense behavioral responses to higher than lower call rate playbacks. Both individuals of the pair approached the source of the playback stimulus faster, produced the first vocalization faster, produced more vocalizations, and spent more time close to the stimulus in higher call rate than in lower call rate playbacks. Frequency and duration characteristics of calls (chip and tseet) were similar in response to all call rate playbacks. Our playback experiment elicited different intensity of behavioral responses, suggesting that risk‐based information is encoded in call rate. Our results suggest that variation in the rate of chip call production serves a dual function in this species; calls are used at lower rates for pair contact and at higher rates for alarm/mobbing signals.     

Traffic noise and responses to a simulated approaching avian predator in mixed-species flocks of chickadees,titmice, and nuthatches

Traffic noise likely reaches a wide range of species and populations throughout the world, but we still know relatively little about how it affects anti-predator behavior of populations. We tested for possible effects of traffic noise on responses to predator acoustic cues in Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis) near 14 independent feeding stations in eastern Tennessee. We compared anti-predator calling and seed-taking behavior in response to playbacks of predator stimuli (screech owl calls) at sites naturally exposed to traffic noise and at sites that faced relatively little traffic noise. The screech owl call playback was designed to simulate the approach of this dangerous predator to a feeder being used by these small songbirds. We found that chickadees responded consistently to the owl stimuli across different levels of traffic noise. However, titmice, and nuthatches exhibited different behavioral responses to the predator stimulus, suggesting that traffic noise masked these low-frequency predator calls. Overall, chickadees and nuthatches showed the broadest anti-predator behavioral responses in comparison to titmice, corroborating earlier published work with an Indiana population. Finally, populations exposed to traffic noise overall seemed less able to detect predator cues potentially masked by that noise, and future work will need to assess likely seasonal variation in these responses as well as species-level variation in anti-predator responses in mixed-species groups.     

Titmice are a better indicator of bird density in Northern European than in Western European forests

Population sizes of many birds are declining alarmingly and methods for estimating fluctuations in species’ abundances at a large spatial scale are needed. The possibility to derive indicators from the tendency of specific species to co‐occur with others has been overlooked. Here, we tested whether the abundance of resident titmice can act as a general ecological indicator of forest bird density in European forests. Titmice species are easily identifiable and have a wide distribution, which makes them potentially useful ecological indicators. Migratory birds often use information on the density of resident birds, such as titmice, as a cue for habitat selection. Thus, the density of residents may potentially affect community dynamics. We examined spatio‐temporal variation in titmouse abundance and total bird abundance, each measured as biomass, by using long‐term citizen science data on breeding forest birds in Finland and France. We analyzed the variation in observed forest bird density (excluding titmice) in relation to titmouse abundance. In Finland, forest bird density linearly increased with titmouse abundance. In France, forest bird density nonlinearly increased with titmouse abundance, the association weakening toward high titmouse abundance. We then analyzed whether the abundance (measured as biomass) of random species sets could predict forest bird density better than titmouse abundance. Random species sets outperformed titmice as an indicator of forest bird density only in 4.4% and 24.2% of the random draws, in Finland and France, respectively. Overall, the results suggest that titmice could act as an indicator of bird density in Northern European forest bird communities, encouraging the use of titmice observations by even less‐experienced observers in citizen science monitoring of general forest bird density.     

Production and perception of sex differences in vocalizations of Wied's black‐tufted‐ear marmosets (Callithrix kuhlii)

Males and females from many species produce distinct acoustic variations of functionally identical call types. Social behavior may be primed by sex‐specific variation in acoustic features of calls. We present a series of acoustic analyses and playback experiments as methods for investigating this subject. Acoustic parameters of phee calls produced by Wied's black‐tufted‐ear marmosets (Callithrix kuhlii) were analyzed for sex differences. Discriminant function analyses showed that calls contained sufficient acoustic variation to predict the sex of the caller. Several frequency variables differed significantly between the sexes. Natural and synthesized calls were presented to male–female pairs. Calls elicited differential behavioral responses based on the sex of the caller. Marmosets became significantly more vigilant following the playback of male phee calls (both natural and synthetic) than following female phee calls. In a second playback experiment, synthesized calls were modified by independently manipulating three parameters that were known to differ between the sexes (low‐, peak‐, and end‐frequency). When end‐frequency‐modified calls were presented, responsiveness was differentiable by sex of caller but did not differ from responses to natural calls. This suggests that marmosets did not use end‐frequency to determine the sex of the caller. Manipulation of peak‐and low‐frequency parameters eliminated the discrete behavioral responses to male and female calls. Together, these parameters may be important features that encode for the sex‐specific signal. Recognition of sex by acoustic cues seems to be a multivariate process that depends on the congruency of acoustic features. Am. J. Primatol. 71:324–332, 2009. © 2008 Wiley‐Liss, Inc.     

Advertisement calls of two anuran amphibians,Rana tigrina andTomopterna breviceps

Rana tigrina andTomopterna breviceps occur as sympatric species at Dharwad, India. Sexually mature males produce advertisement calls. The advertisement call of both the species consist of a number of calls produced in series forming a call group. Each call group ofRana tigrina comprises 10–40 calls, whereas that ofTomopterna breviceps consists 13–141 calls. Each call consists of a pulse group with variable number of pulses which lack pulse interval. Calls of both the species exhibit similarities in (i) call consisting of series of calls with a pulse group in each call, (ii) absence of pulse interval within the pulse group, (iii) the amplitude of the first pulse being always small, and (iv) the frequency spectrum beginning from 200 Hz. Based on the similarities in the spectral features of the calls, it is suggested that the two species may be closely related to each other.     

Bioacoustic analysis of frog calls from northeast India

Mating calls of three frog species abundant in northeast IndiaRana tigerina,Rana cyanophlyctis andRana limnocharis were recorded in the fields of Assam and Meghalaya during their breeding season (July-August, 1991). The calls were analysed for their temporal and spectral characters. They were species specific, with distinct call duration and call period, number of pulses per call and interpulse interval, and dominant frequency and frequency domain. A comparison of the mating calls ofRana cyanophlyctis with those of the siblingRana ehrenbergi from Yemen showed differences in their temporal and spectral characters, supporting the suggestion that these two species are distinct species, rather than subspecies of the same species. Differences in the temporal and spectral pattern were found in the mating calls of morphologically alike specimens ofRana limnocharis, indicating that the present morphotypeRana limnocharis in northeast India is composed of several species.     

Acoustic Preference of Frog‐Biting Midges (Corethrella spp) Attacking Túngara Frogs in their Natural Habitat

In many animals, males aggregate to produce mating signals that attract conspecific females. These leks, however, also attract eavesdropping predators and parasites lured by the mating signal. This study investigates the acoustic preferences of eavesdroppers attracted to natural choruses in a Neotropical frog, the túngara frog (Engystomops pustulosus). In particular, we examined the responses of frog‐biting midges to natural variation in call properties and signaling rates of males in the chorus. These midges use the mating calls of the frogs to localize them and obtain a blood meal. Although it is known that the midges prefer complex over simple túngara frog calls, it is unclear how these eavesdroppers respond to natural call variation when confronted with multiple males in a chorus. We investigated the acoustic preference of the midges using calling frogs in their natural environment and thus accounted for natural variation in their call properties. We performed field recordings using a sound imaging system to quantify the temporal call properties of males in small choruses. During these recordings, we also collected frog‐biting midges attacking calling males. Our results revealed that, in a given chorus, male frogs calling at higher rates and with higher call complexity attracted a larger number of frog‐biting midges. Call rate was particularly important at increasing the number of midges attracted when males produced calls of lower complexity. Similarly, call complexity increased attractiveness to the midges especially when males produced calls at a low repetition rate. Given that female túngara frogs prefer calls produced at higher repetition rates and higher complexity, this study highlights the challenge faced by signalers when increasing attractiveness of the signal to their intended receivers.     

No evidence of eavesdropping on heterospecific alarm calls by captive zebra finches recently descended from wild birds

Alarm calls are vocalisations animals give in response to predators which mainly function to alert conspecifics of danger. Studies show that numerous species eavesdrop on heterospecific calls to gain information about predator presence. Responding to heterospecific calls may be a learned or innate response, determined by whether the response occurs with or without prior exposure to the call. In this study, we investigated the presence of eavesdropping behaviour in zebra finches Taeniopygia guttata. This species is not known to possess a distinct alarm call to warn adult conspecifics of a threat, and could be relying on alarm calls of nearby heterospecifics for predator information. We used a playback experiment to expose captive zebra finches to three heterospecific sounds: an unfamiliar alarm call (from the chestnut‐rumped thornbill Acanthiza uropygialis), a familiar alarm call, and a familiar control (both from the noisy miner Manorina melanocephala). These calls were chosen to test if the birds had learnt to distinguish between the function of the two familiar calls, and if the acoustic properties of the unfamiliar alarm indicated presence of a threat to the finches. Our results showed that in response to the thornbill alarm, the birds reduced the rate of production of short calls. However, this decrease was also seen when considering both short and distance calls in response to the control sound. An increase in latency to call was also seen after the control stimulus when compared to the miner alarm. The time spent scanning increased in response to all three stimuli, but this did not differ between stimuli. There were no significant differences when considering the stimulus by time interaction for any of the three vigilance measures. Overall, no strong evidence was found to indicate that the captive zebra finches were responding to the heterospecific alarm stimuli with anti‐predator behaviour.     

Development of Early Vocalizations and the Chick-a-dee Call in the Black-capped Chickadee,Parus atricapillus

The chick-a-dee call of the black-capped chickadee (Parus atricapillus) is composed of discrete elements, or notes, that are combined to form hundreds of different calls. To investigate the development of this complex call, 12 families of color-marked chickadees were observed and recorded in the wild. Vocalizations were monitored for 18 d in the nest and 14–18 d postfledging. Most vocalizations of nestlings and fledglings were associated with feeding. At hatching, vocalizations consisted of a structurally simple note type that became more complex and variable with age. Around 9–12 d, the development of the call occurred, when single notes became organized into a multiple-note unit. Notes within the call differentiated into higher frequency, rapidly modulated initial note types and a lower frequency, moderately modulated terminal note type, features also present in adult chick-a-dee calls. Several adult-like calls including chick-a-dee calls, fee-bee songs, and a subsong-like vocalization developed prior to fledgling dispersal. Based on resemblances of note structure and general call structure, the chick-a-dee call appeared to develop from calls of nestlings and fledglings, although not necessarily in a chronologically linear progression. Some features of the chick-a-dee call closely resembled features of older nestling and fledgling calls, while other features more closely resembled the sounds of very young nestlings. Vocal development in the chickadee is compared with song and call development in other species, and the possible significance of acoustic resemblances between chick-a-dee calls and the food-associated calls of nestlings and fledglings is discussed.     

Geographical variation in male advertisement calls and female preference of the wide‐ranging canyon treefrog,Hyla arenicolor

We surveyed the geographical variation in male advertisement calls of the wide‐ranging canyon treefrog, Hyla arenicolor, and found large call differences among geographically distant lineages that had been characterized by a recent phylogeographical study. To test whether these call differences were biologically relevant and could allow reproductive isolation of different lineages should they come into secondary contact, we assessed female preference in a lineage occurring in southern Utah and north‐western Arizona, USA. These females exhibited a strong preference for their own lineage's call type over the calls of two Mexican lineages, but not over the calls from the geographically nearest lineage. We also identified traits that female frogs probably use to discriminate between lineage‐specific advertisement calls. Our behavioural results, together with recent molecular estimates of phylogenetic relationships among lineages, will guide future work addressing the evolutionary forces that have led to this biologically significant variation in male sexual signals. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

Geographic variation in advertisement calls of a Microhylid frog – testing the role of drift and ecology

Acoustic signals for mating are important traits that could drive population differentiation and speciation. Ecology may play a role in acoustic divergence through direct selection (e.g., local adaptation to abiotic environment), constraint of correlated traits (e.g., acoustic traits linked to another trait under selection), and/or interspecific competition (e.g., character displacement). However, genetic drift alone can also drive acoustic divergence. It is not always easy to differentiate the role of ecology versus drift in acoustic divergence. In this study, we tested the role of ecology and drift in shaping geographic variation in the advertisement calls of Microhyla fissipes. We examined three predictions based on ecological processes: (1) the correlation between temperature and call properties across M. fissipes populations; (2) the correlation between call properties and body size across M. fissipes populations; and (3) reproductive character displacement (RCD) in call properties between M. fissipes populations that are sympatric with and allopatric to a congener M. heymonsi. To test genetic drift, we examined correlations among call divergence, geographic distance, and genetic distance across M. fissipes populations. We recorded the advertisement calls from 11 populations of M. fissipes in Taiwan, five of which are sympatrically distributed with M. heymonsi. We found geographic variation in both temporal and spectral properties of the advertisement calls of M. fissipes. However, the call properties were not correlated with local temperature or the callers' body size. Furthermore, we did not detect RCD. By contrast, call divergence, geographic distance, and genetic distance between M. fissipes populations were all positively correlated. The comparisons between phenotypic Q_st (P_st) and F_st values did not show significant differences, suggesting a role of drift. We concluded that genetic drift, rather than ecological processes, is the more likely driver for the geographic variation in the advertisement calls of M. fissipes.     

Polymorphic microsatellite loci from the American goldfinch (Carduelis tristis) and their cross‐amplification in a variety of passerine species

Cardueline finches have become important models in studies of sexual selection. Here I describe eight polymorphic microsatellite loci isolated from the American goldfinch (Carduelis tristis) that are useful in parentage and heterozygosity studies. The number of alleles per locus ranged from eight to 38 based on 252 goldfinches. The markers are polymorphic in at least four other Cardueline finch species, and several amplify in nonfinch passerines including red‐winged blackbird (Agelaius phoeniceus), black‐throated blue warbler (Dendroica caerulescens) and tufted titmouse (Baeolophus bicolor), indicating they should be useful in paternity and population studies of a variety of species.     

Similarity in the begging calls of nestling Red‐winged Blackbirds

ABSTRACT Although individually distinct begging calls may permit parents to recognize their offspring, birds nesting in dense breeding colonies where fledglings intermingle might benefit from additional adaptations. For example, if the calls of all nestlings in a brood were similar, parents would need to recognize only one brood call instead of the identity calls of each nestling. We recorded nestling Red‐winged Blackbirds (Agelaius phoeniceus) to determine whether their calls function to identify individuals (identity call hypothesis) or broods (brood call hypothesis). We used spectrogram cross‐correlation and dynamic time warping as well as call duration, peak frequency, and frequency range to estimate the similarity of begging calls of nestling Red‐winged Blackbirds. We recorded individual nestlings on day 5 and on day 9 of the nestling period to determine whether calls of individuals were more similar than calls of different nestlings, and whether calls of broodmates were more similar than calls of nestlings from different broods. We found that calls of 8‐d‐old individuals were more similar than calls of different nestlings, but the calls of broodmates were not more similar than those of nestlings from different broods. These results were consistent with the identity call hypothesis. We then compared begging calls of pairs of nestlings recorded separately and together on day 9. We found that the calls of 8‐d‐old nestlings recorded together were more similar than when they were recorded separately. In addition, using playback of begging calls from normal broods and artificial “broods” constructed from the calls of single nestlings, we found that females returned with food sooner in response to the calls of single nestlings (with enhanced call similarity) than to those of normal broods. Our results suggest that similar begging calls may be beneficial for both nestlings and parents, with broodmates fed at higher rates when their calls are more similar and, after fledging, parents needing to recognize only one brood call instead of the identity calls of each fledgling.