Syntactical Organization of the Gargle Vocalization of the Black-capped Chickadee,Parus atricapillus

The gargle is a complex call of the black-capped chickadee Parus atricapillus associated with agonistic interactions. A large sample of calls was recorded from five sites in southeastern Wisconsin. Three sites were near one another and the other two with a different dialect pattern were more distant (all sites were within 15 km of each other). A typical call consists of about 6 notes selected from an array of about 15 different note-types that are shared among individuals in the same population. Note-types are given in many combinations, and any individual may deliver many different variations. Analysis of two- and three-note sequences shows a syntactical organization with certain note-types much more likely to precede or follow than others. In some cases linkage between note-types was nearly complete. Some differences occurred among individuals and sites, but general organizational rules were similar. One effect on ordering was acoustical structure of the notes. Higher pitched, shorter duration notes were more likely at the beginning than the end of the call which often consisted of trills. Organization of the gargle was compared to that of the chick-a-dee call of the same species. Similarities include recombinant properties, general acoustic rules and syntax. A major difference may be that in chick-a-dee calls various note combinations constituting a call have different meanings, while the various note combinations comprising an individual's repertoire of gargles may be functionally equivalent.     

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.     

Dawn chorus and female behaviour in the Willow Tit Parus montanus

We studied the effect of female behaviour on the dawn chorus of Willow Tits Parus montanus. Ten females were temporarily kept in their nest holes in order to delay their dawn emergence. Simultaneously, their mates' singing behaviour was measured. We compared the control dawn behaviour (during which the females emerged when they wanted) with that during the experimental delay. The dawn song by the males lasted longer when the females' emergences were delayed. Our results show that the duration of the dawn chorus is directly related to the female's behaviour. We suggest that at least one function of the dawn song is intrapair signalling, which is often linked to sperm competition.     

Age-Related Microhabitat Segregation in Willow Tit Parus montanus Winter Flocks

It is expected that through flexibility in behaviour, flock living birds respond to the asymmetries in resource access derived from dominance relationships. We analysed the microhabitat use of willow tits in winter flocks and assessed possible factors which shape habitat segregation between adults and juveniles in different temperature regimes. When foraging in mild conditions (ambient temperature > 0°C), flocks split up into subgroups with adults foraging in inner parts of trees more often than juveniles. However, no differences were recorded in the vertical position occupied in trees. In harsh conditions (< ? 4°C), flocks re‐united and juveniles further moved to outer parts of trees, increasing horizontal segregation between age classes. In mild conditions, vigilance behaviour was not related to the position of birds in trees, but in harsh conditions, scanning frequency was higher in outer parts of trees only for adults. In mild weather, juvenile position in trees was associated with body size and mass. The foraging microhabitat segregation detected in harsh conditions fits the age‐related hoarding distribution previously described in the same population. This supports the hypothesis that hoarded food is important in determining future foraging habitat use. Adult preference and intraspecific competition for safer or richer inner parts of trees as foraging sites during harsh conditions seems to determine the habitat segregation between adults and juveniles. Furthermore, we suggest that in mild weather, when foraging in the absence of adults, juveniles balance the costs of using a potentially dangerous microhabitat with the benefits of building energetically cheap and large food reserves through hoarding. The expected patterns of microhabitat segregation may differ in parids, depending on whether predation risk or other factors such as food availability are the main factors controlling habitat quality.     

Cost of reproduction: parental survival and production of recruits in the Willow Tit Parus montanus

Summary Brood sizes of the Willow Tit were altered experimentally by subtracting or adding two nestlings in 1986 and 1987 in the vicinity of Oulu, northern Finland. The manipulated broods were within the normal range observed in natural conditions. Unaltered broods were used as controls. Data from natural broods from 1978–1985 were available for comparison. When the nestlings were 13 days old they were ringed and weighed and their tarsus, wing, and tail lengths were measured. On the same day the parents were caught, weighed, and measured. In 1986 there were no differences in nestling mortality between the reduced, control, or enlarged broods; i.e. parents were able to fledge the two extra young. In 1987 starvation was most pronounced in the enlarged broods. This resulted in the number of fledglings being practically the same in each manipulation category. Especially the body weight, but also the other indices of body size, decreased as a function of the brood size category, suggesting that there may be quality differences between the young reared in different experimental groups. In 1986 there was a non-significant trend towards lower body weight of the parents attending reduced, control, or enlarged broods, in that order. In 1987 the differences were much smaller. These results were not due to size differences between the groups, so possibly the increased reproductive effort of raising extra young was responsible for the trend observed in 1986. There were no significant differences in parental survival associated with the manipulation category, although the trend in the females was consistent with the hypothesis of reproductive cost. It is possible that environmental conditions in 1986 were so favourable that the tits were not unduly stressed even when attending two extra young. Correlative data from 1978–1985 did not support the cost hypothesis either. A non-significant trend towards reduced post-fledging survival and recruitment of the young was observed with increased brood size. The average fitness value of parents, incorporating parental survival and number of recruits, showed that the success of the adults raising enlarged broods may be lower than that of others. It seems that the reproductive cost, if it exists, decreases individual fitness value by reducing the chances of recruiting descendants into the next generation. The reproductive stress may be insufficient to reduce the subsequent survival of parents. More data are however needed to confirm these results.     

Brood size manipulations within the natural range did not reveal intragenerational cost of reproduction in the Willow Tit Parus montanus

To test for the existence of a reproductive cost, we manipulated brood sizes (-2 and +2 nestlings) over 6 years in a northern population of Willow Tits Parus montanus breeding in natural holes. Possible effects were sought in subsequent survival and fecundity of the parents. Parents given extra chicks made more feeding visits than did parents with reduced and control broods. However, this was not reflected in differences in parental body-weight between groups at the end of the nestling period. Brood size manipulation did not significantly affect female or male survival. In 4 out of 6 years, there was a weak and nonsignificant effect on male survival, consistent with a cost of reproduction. Female and male fecundity in the year following the experiment was not affected by the manipulations. Thus, the data do not give evidence of an intragenerational cost of reproduction in the Willow Tit. Parents appeared unwilling to increase their breeding effort to a level which jeopardized their own survival or future breeding success. It is possible that, because of the time constraints in northern latitudes, females work under their capacity and lay smaller clutches than would otherwise be most profitable. Thus, no costs to the parents would be expected as a consequence of manipulations. These results suggest that the current reproductive rate is not maintained by reproductive cost in the Willow Tit. However, the results do not rule out the possibility that selection has operated outside the current range of reproductive rates during evolutionary history of the species.     

Matched Counter-singing Signals Escalation of Aggression in Black-capped Chickadees (Parus atricapillus)

Black-capped chickadees (Parus atricapillus) have the ability to shift their songs up and down over a wide range of absolute frequencies. Males can shift their songs over 465 ± 52.9 (SE) Hz. During the dawn chorus, males shift their songs by 80 Hz or more every 41 ± 8.8 (SE) songs, but it appears that males can sing at any frequency within their range. Frequency shifting may allow males to match counter-sing with rival males; that is, to switch song output to match that of a rival. During simultaneously recorded dawn choruses, however, there was no correlation over time in the frequency of neighbouring males' songs, nor was there a correlation over time in the size of shifts between their songs. Moreover, males did not match the frequencies of songs presented on a played-back tape at the edge of their territories during the dawn chorus. Matching was observed during some bouts of counter-singing between males. In these cases, matched counter-singing was highly associated with escalation of the conflict. We suggest that frequency matching in this species may be a graded signal that allows the singer to direct aggression towards a particular rival.     

Phylogeography of the Eurasian Willow Tit (Parus montanus) based on DNA sequences of the mitochondrial cytochrome b gene

The phylogeographic relationships of the trans-Palearctic Willow Tit assemblage were studied by obtaining sequence data from the mitochondrial cytochrome b gene from 34 specimens representing nine subspecies from across the species range. Four distinct genetic groups were identified: Parus montanus weigoldicus, P. m. affinis, P. m. songarus, and a clade containing six Eurasian subspecies (ssp. baicalensis, borealis, montanus, restrictus, rhenanus, and sachalinensis). P. m. weigoldicus, P. m. affinis, and P. m. songarus were reciprocally monophyletic and separated from each other and other subspecies by uncorrected genetic distances between 1.9 and 5.8%. The remaining six subspecies were closely related and shared mitochondrial haplotypes, despite marked morphological and acoustical differences, suggesting a rapid evolution of distinct vocalization patterns. The current classification splitting the species into the songarus and montanus subspecies groups is not concordant with our phylogeny. Also, the four regiolect groups, Lowland, Alpine, Siberian, and Sino-Japanese, are not fully mirrored in the phylogeny. Our data suggest that the mono-frequency song type may be ancestral and was retained over a long evolutionary time in certain populations, but was altered or camouflaged by learning processes in others.     

Initial winter flock formation in the Willow Tit Parus montanus. Do immigrating juveniles assess the quality of territorial adults?

In the Willow Tit Parus montanus , forming of winter flocks starts shortly after the juveniles have become independent of their parents. In the early phase of flock formation the juveniles roam about prospecting for suitable winter territories. They visit several occupied territories in succession and seek contact with the territory holders. I describe the behaviour of juveniles during such encounters with adult conspecifics. I suggest that, by approaching adults closely and behaving specifically, juveniles gain important information on the adults' innate qualities; this may affect the settling juveniles' future survival.     

Social rank in winter flocks of Willow Tits Parus montanus

The social hierarchies in winter of ten flocks of Willow Tits Parus montanus were studied when the birds were foraging naturally and when visiting feeders. All the flocks consisted of one adult mated pair together with two juvenile males and two juvenile females (probably pairs). All flocks studied had a stable composition and the hierarchies remained constant throughout the study period. The hierarchies were linear and unilateral. The adults of each sex dominated the respective juveniles and within each age group the male dominated the female. The dominance relationships between the age and sex groups were not consistent. Although the males dominated all the females in six flocks, in one flock the adult female dominated both the juvenile males, but only one of them in three other flocks. The degree of aggression between flock-members was 0.8 encounters per hour, and males initiated 94% of all attacks. Body-weight explained 77% of the variation in dominance rank. It is suggested that the dominance rank of a male is also a function of his seniority, while the rank of a juvenile female is correlated with the rank of her mate.     

Social rank and antipredator behaviour of Willow Tits Parus montanus in winter flocks

Field experiments on three free-ranging Willow Tit winter flocks, each consisting of one adult pair and two male and two female juveniles (first-year birds), were performed to examine whether preferences for feeding site and antipredator behaviour are related to social rank. The dominance structure was the same in all flocks; adult male > juvenile male 1 > juvenile male 2 > adult female > juvenile female 1 > juvenile female 2.
The proportion of time spent scanning for predators was positively correlated with distance from cover, and adults scanned relatively more than juveniles at the same controlled distance from cover, especially in the afternoon. Given a choice between feeders placed 1 m, 3 m, 5 m, 10 m and 20 m from the forest edge, the tits preferred feeders close to cover. Low-ranking individuals used feeders farther from cover indicating that higher ranked tits prevented them from using the feeders close to cover by means of social dominance. When only the 10m and 20 m feeders were baited, only low-ranked juveniles visited the feeders, subordinate females slightly more than males. The subordinate juveniles increased their use of exposed feeders at low ambient temperature, suggesting that they are prepared to take greater risks during cold periods.
The sequence of return to a feeder, after a life-like stuffed predator model mounted 1 m from a feeder opening was removed, was positively correlated with dominance status, revealing that subordinates take the greatest predation risks.     

Winter survival and breeding success of dominant and subordinate Willow Tits Parus montanus

We studied the effect of winter rank on survival rate and reproductive success in Willow Tits Parus montanus, a resident passerine living in dominance-structured flocks during the nonbreeding season, in 6 years. Winter survival was dependent on both the birds' age and rank. Adults survived better than first-year birds, and within first-year males, dominants survived better than subordinates. In other sex and age classes, rank did not contribute to survival. Although first-year males were in excess among nonbreeders, no connection existed between breeding status and rank. Female rank did not explain the variation in the start of laying, clutch size, number of fledglings or recruit production. We conclude that social status in Willow Tits affects individual fitness mainly through rank-dependent survival. Acquiring a high rank position seems to be most important for first-year birds, especially first-year males.     

Factors influencing Willow Tit Poecile montanus site occupancy: a comparison of abandoned and occupied woods

The British Willow Tit Poecile montanus kleinschmidti underwent a decline of 85% between 1970 and 2003. The cause of this decline is unknown. However, several hypotheses have been put forward to account for it: competition from other tit species, predation by Great Spotted Woodpeckers Dendrocopos major and habitat change. In order to test these, woods that are currently occupied by Willow Tits were paired with woods (within 50 km) that had been abandoned by Willow Tits five or more years previously. Point counts for other tit species (potential competitors) and woodpecker species (potential predators) were carried out at ten evenly spaced points throughout each wood. Habitat variables were collected within a 50-m radius of where a Willow Tit was located (in the occupied woods) or where maps showed a Willow Tit had been located (for abandoned woods). No evidence was found for differences in numbers of potential competitor or potential predator species in abandoned and occupied woods. Soil water content was found to be higher at occupied sites. No other habitat features differed between the two categories of site. The drying up of British woods could therefore be implicated in the Willow Tit decline and this warrants further investigation.     

Social dominance in free-living Willow Tits Parus montanus: determinants and some implications of hierarchy

Several features of social dominance among Willow Tit Parus montanus winter flocks were examined during a four-winter study. Birds of both sexes were evenly distributed over the 33 flocks studied. In nearly half of the flocks there was an adult pair accompanied by yearlings, but one-third of the flocks consisted of more than two adults with yearlings. Males were found to be dominant over and larger than females. Within a sex, yearlings were usually subordinate to adults. The effect of size on dominance, after controlled for sex and age, remained obscure in our field data. The hierarchical status of an individual was found to rise or at least stay the same in different years, which supports the "hopeful dominants" hypothesis, i.e. birds stay in flocks hoping to achieve a higher status in the future. The ranks of mates correlated highly significantly, implying that high-ranking birds were paired with other high-ranking birds and low-ranking birds with other low-ranking birds. Birds of different age and sex did not show any differences in the proportion of initiated aggressive encounters directed at other individuals. However, males were more aggressive to other males than to females and also tended to behave less aggressively towards their own mates than towards other individuals in the flock. This could be a male strategy to strengthen the pair-bond and to enhance mate protection described earlier in     

Age Differences in the Response of Willow Tits (Parus montanus) to Conspecific Alarm Calls

Predation is an important mortality factor in wintering birds. To counter this, birds produce alarm calls in the presence of predators which serve to warn conspecifics. In social hierarchical bird flocks, adults survive the winter better than juveniles and therefore survival strategies probably vary with social status. This study examined the differential responses to alarm calls by free-living willow tits, Parus montanus, in dominance-structured winter flocks in Finland. To explore the age-dependent differences in response to conspecific alarm calls, a series with three alarm calls was played to focal adults and juveniles while they sat in the middle section of a spruce branch. Immediately after the playback, juvenile willow tits moved more often, flew longer distances and changed branches more often than did adults. Previous mammal studies have shown that juveniles are more likely to flee than adults after hearing conspecific alarm calls. The current study demonstrates that similar age-dependent responses to conspecific alarm calls occur in birds also. These findings reflect an increased vulnerability to predators or lack of experience of young birds.     

Long‐Distance Calling by the Willow Tit,Poecile montanus,Facilitates Formation of Mixed‐Species Foraging Flocks

The occurrence of mixed‐species foraging flocks is a worldwide phenomenon in terrestrial bird communities. Previous studies suggest that individuals participating in flocks might derive benefits in terms of improved feeding efficiency and/or reduced risk of predation. However, very little is known about how individuals establish mixed‐species flocks. Here, I provide the first experimental evidence that long‐distance calling by the willow tit, Poecile montanus, facilitates the establishment of mixed‐species flocks at a foraging patch. Observations at experimental foraging patches showed that willow tits that find a food source produce long‐distance calls, particularly when they are isolated from conspecific flockmates. The probability of long‐distance calling was negatively correlated with the number of heterospecific foraging individuals near the food source. A playback experiment confirmed that calls attract both conspecific and heterospecific members of foraging flocks. This study demonstrates that willow tits use long‐distance calls to attract conspecific flockmates to foraging patches, and these calls can also facilitate the formation of mixed‐species flocks on patches.     

Seeing without being seen: a removal experiment with mixed flocks of Willow and Crested Tits Parus montanus and cristatus

This paper tests the hypothesis that foraging site selection reflects a trade-off between the various needs for concealment from predators, to find food, and for the individual to maintain some view of its surroundings. After removal of Crested Tits Parus cristatus (the dominant species in mixed flocks), Willow Tits P. montanus did not decrease their foraging heights as expected but remained in the most exposed parts of young pines. In contrast, after removal of Willow Tits, Crested Tits increased their foraging height from the sheltered lower canopy to sites previously occupied by Willow Tits. When flock size was reduced, the birds maintained the same high levels of vigilance without concealing themselves in dense vegetation. I suggest that flock members may benefit from foraging in sites that afford good anti-predator vigilance.