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Point counts are widely used for conducting ecological surveys of wild birds. Vocal output of birds varies with time of day, and therefore the results of ecological surveys should also vary with time of day. We modeled how males' singing rates change over the morning. We calculated song rates in 3 min sampling periods (the standard sampling period used by the north American breeding bird Survey) and compared how detection rates vary as sampling period increases. We recorded singing activity in 15 neighbourhoods of breeding black-capped Chickadees (Poecile atricapillus) with 16-element microphone arrays that recorded every song from every male in every neighbourhood. We calculated the proportion of males that produced one or more songs during 3, 5, and 10 min count periods between nautical twilight and late morning. our results show a strong peak in singing activity just before sunrise followed by a steady decline in singing activity over the course of the morning. We found that longer sampling periods yielded significantly higher detection rates at all times after sunrise. After sunrise, detection rates never exceeded 60%, even with 10 min sampling periods. We found that unpaired males had significantly higher detection rates than paired males but we found no difference between paired males with fertile versus incubating mates. our results provide strong evidence that, for black-capped Chickadees, surveys during the dawn chorus provide the most comprehensive assessment of the number of birds present, and that longer sampling periods yield significantly better estimates of population sizes at all times after sunrise. [ABSTRACT FROM AUTHOR]

In songbirds, male song is an acoustic signal used to attract mates and defend territories. Typically, song is an acoustically complex signal; however, the fee-bee song of the black-capped chickadee is relatively simple. Despite this relative simplicity, two previous studies (Christie et al., 2004b: Hoeschele et al., 2010) found acoustic features within the fee-bee song that contain information regarding an individual's dominance rank: however each of these studies reported a different dominance-related acoustic cue. Specifically, the relative amplitude of the two notes differed between the songs of dominant and subordinate males from northern British Columbia, while the interval pitch ratio differed between the songs of dominant and subordinate males from eastern Ontario. In the current study, we examined six acoustic features within songs from both of the chickadee populations (northern British Columbia and eastern Ontario) examined in these previ-ous studies and used bioacoustic analyses and discriminant function analyses to determine whether there is a consistent dominance-related acoustic cue across both, or in each of these populations. Consistent with the previous findings, the current results indicate that relative amplitude differs based on dominance status in the songs from British Columbia; however, our results failed to reach significance with songs from Ontario. These results suggest that acoustic cues that signal a male's dominance in this species vary with geographic location. Furthermore, examining songs from these two locations and one additional location in northern British Columbia, we found that discriminant function analyses could correctly classify songs based on geographic location. Considering the broad extent of the species' range, black-capped chickadee song is considered relatively invariant; however, our results suggest that there is geographic variation in songs, although the differences are subtle compared to geographic song variation in other species. [ABSTRACT FROM AUTHOR]

Animals eavesdrop on dyadic interactions between other individuals to gather information for future mate choice and territory defense decisions. The capacity for eavesdroppers to combine information gathered from overhearing multiple two-way interactions is poorly studied. We tested whether inexperienced (second year) and older (after second year) male black-capped chickadees (Poecile atricapillus) eavesdrop on rivals' song contests to evaluate the relative threat levels of multiple unfamiliar territorial intruders. We used a multiple speaker playback experiment to simulate 3 male territorial intruders (A, B, and C) engaging in 2 successive dyadic song contests, presenting focal males with the information that A was more threatening than B, and B was more threatening than C. We then assayed the response of focal males when presented with simulated intruders A and C without relative information. We predicted that males would defend against the intruder perceived to be the greater threat. Focal males initially responded toward the more threatening intruder (A) significantly more than the less threatening intruder (C), consistent with our predictions. Older birds approached the more threatening intruder (A) significantly more than the less threatening intruder (C), whereas young males showed more variable responses. Our results suggest that male chickadees were able to acquire relative threat information from separate song contests that influenced their responses toward rivals paired in novel contests. These findings indicate that territorial songbirds in communication networks may be capable of integrating information gathered through eavesdropping on multiple interactions. [ABSTRACT FROM PUBLISHER]

Animals can encode information into signals using at least 2 basic mechanisms. First, signalers can repeat their signals, encoding information into sequence-level parameters, such as signaling rate. Second, signalers can encode information into the fine structural variation of individual signals. This mechanism requires sophisticated encoding and decoding but potentially affords more rapid or efficient information transfer. The chick-a-dee call of Parid birds is a structurally complex signal that conveys food- and predator-related information to both conspecific and heterospecific receivers. However, the basic mechanism by which it communicates information is unclear. Previous research suggests that variation in the number of terminal notes is important, but this structural trait has not been manipulated independently from other structural traits or from sequence-level parameters, such as total duty cycle. We independently manipulated the fine structure and duty cycle of the calls of Black-capped Chickadees (Poecile atricapillus) and then broadcast them to potential receivers. Both conspecific and heterospecific receivers ignored manipulations to the fine structure of individual calls when the duty cycle of the signaling sequences was held constant. In marked contrast, receivers exhibited significantly stronger responses when the duty cycle was experimentally increased, and the fine structure of individual calls was held constant. Specifically, signaling sequences with a high duty cycle attracted more conspecific and heterospecific receivers and caused those receivers to approach the speaker more quickly, to approach the speaker more closely, and to remain within 10 m of the speaker for longer. These findings show that receivers respond to a simple sequence-level trait in a structurally complex avian signal. [ABSTRACT FROM PUBLISHER]

The dawn chorus of songbirds provides an ideal opportunity to study communication networks because multiple singers are within signalling range of each other, permitting eavesdropping by both males and females. Using an Acoustic Location System, we examined the dawn chorus singing behaviour of male black-capped chickadees (Poecile atricapillus) in 15 neighbourhoods to determine whether singing behaviour is consistent with the communication network model. We calculated levels of frequency matching for 19 focal males and all of their neighbours. The observed level of frequency matching was greater than expected by chance. All males were involved in multi-way matching at dawn and often matched two or three neighbours simultaneously. The identity of individuals involved in three-way matches was related to both previous winter-flock membership and the relative dominance rank of the interacting males. We show that male black-capped chickadee dawn choruses are interactive communication networks where males are involved in high levels of matching with neighbours, and they match multiple individuals both simultaneously and sequentially. Additionally, the existence of multi-way matching and the identities of individuals involved suggest that individual males may eavesdrop at dawn. This is the first study to quantify network communication during the dawn chorus in multiple neighbourhoods. [ABSTRACT FROM AUTHOR]

The ability to discriminate among signallers and to respond to them on an individual basis provides receivers with substantial benefits. For example, discriminating among signallers allows receivers to ignore unreliable individuals or to focus their territorial defence on unfamiliar intruders. Such discrimination requires signals to be individually distinctive; that is, signals must vary more among than within individuals. Furthermore, receivers must be able to discriminate among the signals of different individuals. In this study, we used fine structural analysis to show that the simple songs of male black-capped chickadees are individually distinctive, but that substantial variation exists both within and among recordings of the same individual. This finding emphasizes the need for multiple recordings of each individual in studies of individual distinctiveness, since failing to measure variation across recordings of the same individual can make it difficult to determine whether signals vary among individuals or whether they simply vary among different recording sessions. To test whether chickadees discriminate among the signals of different individuals, we used a playback experiment in which we broadcast priming and discrimination stimuli to 45 territorial males. When individuals heard the playback of two different males, they produced more songs and remained near the loudspeaker for a longer period than when they heard two different exemplars from the same male. Chickadees can therefore discriminate among singers based exclusively on their songs, which may help to explain how chickadees eavesdrop on singing contests and subsequently select extrapair mates on the basis of song contest performance. [Copyright &y& Elsevier]

Our understanding of animal communication is expanding from a dyadic framework of one signaler and one receiver to a broader communication network model, yet empirical studies of communication networks are scarce. To investigate whether territorial males eavesdrop on interactions occurring outside of their territory boundaries and to quantify the neighborhood-level effects of song contests, we simulated diurnal dyadic countersinging exchanges in the undefended spaces between established territories of black-capped chickadees (Poecile atricapillus). In each of 10 neighborhoods, we used stereo playback to simulate interactions between 2 unknown rivals. We simulated 2 types of song contests that differed only in the relative timing and patterning of the songs of the contestants; aggressive treatments contained frequency matching and song overlapping, whereas submissive treatments contained neither matching nor overlapping. We used a 16-microphone acoustic location system to record males in the neighborhood surrounding the playback apparatus. Territorial chickadees responded more intensely to the aggressive treatments than the submissive treatments. Neighborhood song output (number of songs produced by all individuals in the recording area) was twice as high after aggressive playback than after submissive playback. Males with territories bordering the playback apparatus had higher song output than males who were more than one territory removed from the playback apparatus. We did not find an influence of male dominance rank on playback responses. Our results reveal that territorial male chickadees eavesdrop on and respond to interactions occurring outside of their territory boundaries. [ABSTRACT FROM PUBLISHER]

Dominance relationships structure many animal societies, yet the process of rank attainment is poorly understood. We investigated acquisition of social dominance in winter flocks and its fitness consequences in male black-capped chickadees (Poecile atricapillus) over a 10-year period. Age was the best predictor of rank, and paired comparisons showed high-ranked males to be older than their low-ranked flock-mates. When controlling for age, morphological variables did not predict male social rank, but high-ranked males were heavier, had lower fat scores and were in leaner condition than low-ranked males. Males that survived between years tended to increase in rank over time; however, the rate of rank advancement varied individually. Rank reversals between familiar contestants were rare, and changes in male social rank were associated with changes in flock membership. Average lifetime reproductive success (LRS) of males and females was variable and best predicted by lifespan. Male rank history also influenced realized reproductive success. Birds with higher average rank over their lifespan were more likely to reproduce successfully. However, among successful birds, average rank did not significantly predict LRS. Thus, birds that lived longer and attained high social rank earlier had higher fitness, but this effect was not manifested as fine-scale differences among successful individuals. Taken together, these findings demonstrate the importance of social factors influencing individual fitness. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90, 85–95. [ABSTRACT FROM AUTHOR]

Birds that nest in cavities may regulate nest microclimate by orienting their nest entrance relative to the sun or prevailing winds. Alternatively, birds may orient their nest entrance relative to conspecific individuals around them, especially if the acoustic properties of cavities permit nesting birds to better hear individuals in front of their nest. We measured the cavity entrance orientation of 132 nests and 234 excavations in a colour-banded population of black-capped chickadeesPoecile atricapillusfor which the reproductive behaviour of nesting females was known. Most chickadees excavated cavities in rotten birchBetula papyrifera, aspenPopulus tremuloidesand mapleAcer saccharum. Nest cavities showed random compass orientation around 360° demonstrating that chickadees do not orient their cavities relative to the sun or prevailing winds. We also presented chickadees with nest boxes arranged in groups of four, oriented at 90° intervals around the same tree. Nests constructed in these nest box quartets also showed random compass orientation. To test the acoustic properties of nest cavities, we conducted a sound transmission experiment using a microphone mounted inside a chickadee nest. Re-recorded songs demonstrate that chickadee nest cavities have directional acoustic properties; songs recorded with the cavity entrance oriented towards the loudspeaker were louder than songs recorded with the cavity entrance oriented away from the loudspeaker. Thus, female chickadees, who roost inside their nest cavity in the early morning during their fertile period, should be better able to hear males singing the dawn chorus in front of their nest cavity. Using GIS analyses we tested for angular-angular correlation between actual nest cavity orientation and the azimuth from the nest tree to the territories and nest cavities of nearby males. In general, nest cavity entrances showed no angular-angular correlation with neighbourhood territory features. However, among birds who followed a mixed reproductive strategy and nested in the soft wood of birch and aspen trees, nest cavity entrances were oriented towards their extra-pair partners. We conclude that nest cavity orientation in birds may be influenced by both ecological and social factors. [ABSTRACT FROM AUTHOR]

Optimal sex allocation for individuals can be predicted from a number of different hypotheses. Fisherian models of sex allocation predict equal investment in males and females up to the end of parental care and predict brood compositions based on the relative costs of producing males and females. The Trivers-Willard hypothesis predicts that individual females should alter the sex ratio of their broods based on their own condition if it has a differential impact on the lifetime reproductive success of their sons and daughters. The Charnov model of sex allocation predicts that females should alter sex allocation based on paternal attributes that may differentially benefit sons versus daughters. Because females are the heterogametic sex in birds, many recent studies have focussed on primary sex ratio biases. In black-capped chickadees Poecile atricapilla , males are larger than females suggesting they may be more costly to raise than females. Female condition affects competitive ability in contests for mates, and thus may be related to variance in fecundity. Females prefer high-ranking males as both social and extrapair partners. These observations suggest that females might vary the sex ratio of their broods based on the predictions of any of the above models. Here, we report on the results of PCR based sex determination of 1093 nestlings in 175 broods sampled from 1992 to 2001. Population-wide, we found a mean brood sex ratio of 0.525±0.016, with no significant deviation from a predicted binomial distribution. We found no effect of clutch size, female condition, hatch date, parental rank or paternity. Our results reject the idea that female black-capped chickadees systematically vary sex allocation in their broods. [ABSTRACT FROM AUTHOR]

Many animals produce sounds that overlap the sounds of others. In some animals, overlapping is thought to be an aggressive signal important in resource defence. Yet, overlapping can also occur by chance, and therefore its function is controversial. In this study, we conducted two experiments to test the function of overlapping in black-capped chickadees, Poecile atricapillus . In experiment 1, we simulated territorial intrusions by broadcasting songs inside established chickadee territories. Resident males overlapped the playback-simulated intruders significantly less than expected by chance, as in most species in which overlapping has been described. Chickadees also overlapped more when they were farther from the intruder. This pattern suggests that chickadees avoid overlapping as a mechanism for reducing acoustic interference (‘interference avoidance hypothesis’). However, the pattern could also constitute submissive signalling if chickadees signal de-escalation (associated with greater distance between opponents) through increasing rates of overlapping (‘submissive signalling hypothesis’). Therefore, in experiment 2, we contrasted these two hypotheses by comparing responses to playback stimuli with low or high interference potential and low or high signal value. We manipulated interference potential by broadcasting stimuli at different amplitudes. We manipulated signal value by broadcasting either song stimuli, which elicit aggression, or white noise stimuli with matching time-amplitude characteristics. If overlapping is a submissive signal, then we predicted that chickadees would avoid overlapping song stimuli, but not white noise stimuli, which lack signal value. Contrary to this prediction, chickadees overlapped song and white noise stimuli equally often, but significantly less often than expected by chance. Furthermore, chickadees overlapped both types of stimuli more often when they were broadcast at lower amplitudes (i.e. lower interference potential). Together, these findings provide compelling evidence that overlapping is not a signal in this species, and that chickadees avoid overlapping both biotic and abiotic sounds as a mechanism for reducing interference. [ABSTRACT FROM AUTHOR]

Animals use a variety of aggressive signals to mediate territorial interactions. Often these signals can be sufficient to ward off potential rivals, thus minimizing the chance of injury due to physical encounters. Yet not all behaviours produced during territorial interactions are aggressive signals. In this investigation, we examined the aggressive signals of black-capped chickadees, Poecile atricapillus, by determining which signals predict attack on a competitor. We used a recently developed playback protocol involving a loudspeaker and a taxidermic mount to simulate an intruder on males'' breeding territories. We examined males'' behaviours prior to any physical attack on the mount, both in the minute before attack and the time period preceding this minute. In the minute before attack, we found that gargle calls consistently predicted attack. In the preceding time period, we found that high song rate predicted attack. Surprisingly, we found that attack and the behaviours associated with attack were not significantly correlated with male dominance status. We conclude that song rate and gargle calling behaviour communicate intent to attack during territorial interactions in black-capped chickadees. These results expand our knowledge of aggressive signals during territorial encounters by revealing novel vocalizations used to communicate an animal’s probability to attack an opponent. [Copyright &y& Elsevier]

Variation in the level of competition for mates and territories is likely to influence the behaviour of competitors. The start of the dawn chorus in songbirds is influenced by a variety of internal factors (e.g. circadian rhythms) and external factors (e.g. light levels, social cues). Here we investigate whether the start time of the dawn chorus is influenced by the singing behaviour of conspecific competitors. Using an Acoustic Location System, we recorded the dawn chorus in neighbourhoods of 5–10 black-capped chickadees, Poecile atricapillus. We used playback to simulate an unfamiliar male performing a dawn song bout within an existing male’s territory. Playback began 15min before the earliest song sung by any male on the preceding day. Focal males began singing a mean±SE of 4.3±1.6min earlier on the day of playback (time relative to sunrise), significantly earlier than on the previous day. We also found a significant communication network level response where neighbouring males began singing 2.3±0.8min earlier in response to playback. Dawn song bouts of males that received playback were longer, but ended at a similar point relative to sunrise. As this effect of a simulated conspecific on chorus start time is on the scale of only a few minutes, other factors probably play a significant role in shaping the timing of dawn chorus onset. Our results show that animals adjust the timing of their sexual communication in response to increased levels of competition. [ABSTRACT FROM AUTHOR]

The two-note fee bee song of the black-capped chickadee ( Poecile atricapillus ) is sung at many different absolute frequencies, but the relative frequencies between the start and end of the fee note (the glissando) and between the fee and the bee notes (the inter-note ratio) are preserved regardless of absolute frequency. If these relative frequencies are experimentally manipulated, birds exhibit reduced behavioural responses to playback of altered songs both in field studies and laboratory studies. Interestingly, males appear to be sensitive to alterations in the glissando, while females appear to be sensitive to alterations in both the glissando and the inter-note ratio. In this study, we sought to determine whether the behaviour of male and female chickadees corresponds to differences in zenk protein immunoreactivity (ZENK-ir) in auditory perceptual regions following playback of fee bee songs with typical and altered pitch ratios. Overall, there was a small but significant sex difference in ZENK-ir (females > males), but altering relative frequencies did not reduce ZENK-ir compared to typical song. Birds did vocalize less in response to playback of songs that lacked an inter-note interval, but amount of singing fee bee song, chick-a-dee calls, or gargles was not correlated with ZENK-ir in perceptual regions (caudomedial nidopallium, NCM and caudomedial mesopallium, CMM) or in HVC, which is part of the song system. Our results confirm that ZENK-ir in NCM and CMM is not involved in fine-grain perceptual discrimination, however it did not support the idea that increased vocalizing increases ZENK-ir in HVC. [ABSTRACT FROM AUTHOR]

The songs of many songbird species vary geographically, yet, the songs of black-capped chickadees, Poecile atricapillus , show remarkable consistency across most of the species' North American range. Previous research has described subtle variations in the song of this species by comparing songs produced by males at distant parts of the species' range (British Columbia and Ontario). In the current study, we used an operant discrimination task to examine whether birds classify the songs produced by males in these two previously studied locations as belonging to distinct open-ended categories. In both experiments, when birds were presented with new songs, they continued to respond to songs from the same geographical location as the songs that were reinforced during initial discrimination training, suggesting that birds were using open-ended categorization. We also presented birds with songs in which we manipulated acoustic features in order to examine the acoustic mechanisms used during discrimination; results provide support that birds use the duration of the song when discriminating, but the results also suggest that birds used additional acoustic features. Taken together, these experiments show that black-capped chickadees classify songs into open-ended, geography-based categories, and provide compelling evidence that perceptible acoustic differences exist in a vocalization that is seemingly consistent across the species' range. [ABSTRACT FROM AUTHOR]

Animal signalling contests are used by males to advertise to choosy females and to repel male competitors. During countersinging interactions in songbirds, males vary the type and timing of songs with respect to their opponent''s behaviour. In black-capped chickadees, Poecile atricapillus, frequency matching and song overlapping appear to be important in territory defence and mate attraction. We studied frequency matching and overlapping behaviour during 100 naturally occurring diurnal song contests among male chickadees using an Acoustic Location System (ALS). The ALS consisted of 16 microphones that recorded countersinging interactions across multiple territories simultaneously, allowing us to triangulate the position of individuals based on delays in sound arrival at each microphone. We used the ALS to record 10 neighbourhoods of chickadees whose relative dominance status had been tabulated during the preceding winter. In 80% of contests there was at least one instance of overlapping between the contestants. In 37% of contests, the contestants were frequency matched within 50Hz. Neither overlapping nor matching occurred at levels different from those expected by chance. However, contests that contained frequency matching had significantly more instances of overlapping than nonmatched contests. There were no rank-related differences in the proportion of opponents'' songs that were frequency matched or overlapped. In using an Acoustic Location System to record entire neighbourhoods of territorial songbirds, this study is the first to quantify song matching and overlapping by free-living animals in the context of natural countersinging exchanges between familiar territorial neighbours. [Copyright &y& Elsevier]