Winter Flocks Research Articles

A UNIQUE LOCAL CALL IN THE WILLOW TIT PARUS MONTANOS

ABSTRACT A unique up-slurred call of the willow tit Parus montanus, rendered pui or plui, was discovered at a locality in the birch alpine region of central Norway in the summer of 1987 when three neighbouring pairs shared this call. Up to 1996 inclusive an additional number of 19 pui-calling individuals were found. Typically, these birds were either offspring of birds already uttering the call, or members of winter flocks in which the dominant adults possessed the call. The call is evidently acquired by learning and serves as an alternative alarm call. It is suggested that rudimentary pui-calls are a normal component in babbling series of young willow tits in general and that the development of these into full calls depends on appropriate tutors. It should be emphasized that the pui-call does not replace another call in the repertoire, but is an extra call adding to the repertoire. It is probably the first time that such a phenomenon has been reported in birds. The expectation that the call would spread in the population has so far proved wrong.

Fattening strategies in dominance-structured greenfinch ( Carduelis chloris ) flocks in winter

Relationships between social status and levels of body reserves stored by members of greenfinch (Carduelis chloris) flocks in winter were investigated. In addition, the adjustment of reserves by birds of different rank to experimental changes in food predictability and to changed weather conditions were examined. Birds with low social status carried overall larger body reserves than high-ranked birds. The results of the experiments suggest that this was mainly because subordinates, due to their low priority to food access, perceived future foraging success as less predictable than dominants. In response to severe weather, which probably increased the risk of starvation for birds, dominants temporarily increased their reserves more than subordinates. This response also indicated that birds with low social status carried larger reserves than high-ranked birds, and demonstrated that dominants could increase food intake when there was a risk of energetic shortfall. The results suggest that fattening strategies in greenfinches depend on social status. In winter, subordinates may be forced to carry larger reserves than dominants to safeguard against social constraints in access to food during critical times. As body reserves may be costly to carry and acquire, this should reduce the probability of surviving the winter for subordinates compared to dominants.

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

Wind Stress Affects Foraging Site Competition between Crested Tits and Willow Tits

Crested Parus cristatus and Willow tits P. montanus are severe food competitors owing to their similar body size, diet and foraging sites. In Belgium, they occupy overlapping territories and form mixed-species winter flocks. Earlier, we found environmental stress to govern foraging strategies of first-year Crested Tits (subordinates) in unispecific flocks. I here test whether niche shifts of Willow Tits (subordinates) in mixed flocks with Crested Tits (dominants) are in the direction expected if interspecific competition governs foraging site segregation when wind velocity increases.

Social Unit of the Alpine Accentor Prunella collaris in the Non-breeding Season

The breeding unit of the Alpine Accentor Prunella collaris is a territorial group consisting of seven unrelated members. Within the group, cooperative polygynandry is common; females copulate with several male members and the males help to feed the chicks of the several females with whom they have copulated. Do Alpine Accentors, like typical cooperative breeders, maintain the membership of the group throughout the year? The social unit in winter and the wintering ecology were studied at Ashio in 1989-95, Yoshino in 1990-93 and Misaka-Pass in 1992-95. At each site, one or two (total of four) individuals banded at a breeding site, Mt. Norikura, wintered. They exhibited wintering site fidelity within seasons and between years. They were recorded singly or in flocks with less than ten unhanded birds. The unhanded birds were not members of their breeding group, which means that the breeding group was broken' up in winter. We also found no evidence of extended bonds between parents and their offspring in winter flocks. Flocks were less cohesive and their membership often changed day by day. Linear dominance hierarchies were observed within a flock. Individual activities were concentrated in particular areas, but they frequently associated with other conspecifics without aggression. Wintering individuals spent, on average, 78.1% and 17.3% of their total activity foraging and perching, respectively. Information at other wintering sites also shows that Alpine Accentors live in less cohesive small flocks but can readily switch from solitary living to flocking. We conclude that the breeding group and the winter flock in Alpine Accentors are independent of each other because there was no evidence that individual associations (group composition and family bonds) were maintained between breeding and, wintering sites.

Correlation between two components of parental investment: nest defence intensity and nestling provisioning effort of willow tits.

Nest defence intensity and nestling provisioning effort of female willow tits (Parus montanus) were significantly correlated at the end of nestling period: well-fed young were defended most intensely. Increased effort was rewarded, since broods with the highest female per-offspring provisioning rates were the most likely to produce local recruits. This suggests that the feeding ability is an important cue for parental investment decisions, at least in a species like the willow tit which has adopted the clutch adjustment strategy. Thus, the most valuable broods would not necessarily be the largest ones, but the ones in which the original number of young could be fed most adequately. However, no associations were found between the level of parental effort and offspring weight, size or condition, nor did the broods producing recruits differ from other broods in timing of breeding or number and size of offspring. The female behaviour may suggest that they invest the most time, energy and risk in the young whose chances of joining the winter flock are the best. The first well-fed young also gain an advantage of prior residency in joining the flock. The first to join normally obtain higher social status, and hence better winter survival, than latecomers. The corresponding patterns in male parental investment behaviour were weak or absent, which suggested that the male effort was affected by the female behaviour. Males seemed to invest in nestling provisioning in such a way as to supplement the female effort. During nest defence action males also seemed to invest in protection of females against predation.

Genetic Structure of Reintroduced Rio Grande Wild Turkeys in Kansas

We investigated genetic structure within and among wintering flocks of Rio Grande wild turkeys (Meleagris gallopavo intermedia) to assess the importance of local individual flocks to managing and conserving genetic diversity of the wild turkey. We documented genetic differences among 4 local flocks of female turkeys reintroduced in south-central Kansas. We estimated that ≥2% (P < 0.001) of the total genetic variation observed is partitioned among the 4 wintering flocks sampled. Analysis of a wintering flock sampled in 1991 and 1992 indicated no change in gene frequencies between years (P = 0.65). Spatial genetic differentiation of Rio Grande turkeys may be the result of breeding tactics and occurrence of family groups on wintering areas. In this study genetic variation appeared to be conserved within flocks of Rio Grande wild turkeys.

Territorial defence is the major function of female song in the superb fairy-wren, Malurus cyaneus

Unlike most passerines, female superb fairy-wrens are prolific solo singers. Four hypotheses for the function of female song were evaluated: (1) to defend territories; (2) to maintain contact with mates; (3) to assess the amount of time mates are spending on the territory; and (4) to solicit displays from extra-group males. Female song rates increased as fairy-wrens reasserted territorial boundaries after a period of communal winter flocking. Song rates were not affected by the age of the female, the time she had been paired to her current mate, the time her mate had been the dominant male on the territory, or the composition of her group. However, females that had recently established territories, or had undergone significant changes in territorial borders, sang at higher rates than females that had been established in their territories for many years. Playback experiments revealed that: (1) females were more likely to sing in response to songs of male or female neighbours than to songs of their mates or their own song; (2) females responded more intensely to songs of female strangers than to songs of female neighbours; (3) extra-group males did not respond with extra-group courtship displays when a female's song was played back from her territory, although some territorial responses were elicited. The stronger response to neighbours indicates that mate location and mate assessment are not major functions of female song. The display solicitation hypothesis can be rejected because extra-group males did not respond to playbacks of females, and there was no correlation between female song rate and the incidence of male display. In contrast, the results suggest that the major function of female song is territorial defence, and that receivers use variation in the song to discriminate between different classes of individuals (self, mate, neighbour, stranger).

Nest-building by crested tit Parus cristatus males: an analysis of costs and benefits

In a population of crested tits in Belgium, one out of three breeding males participated in nest-building. Since variation in the amount of nest-building among 11 building males was low, analysis of male nest-building allowed a logistic regression design. The probability of building increased with male condition and for late nests. The effect of male condition decreased with date, and date was the only factor predicting nest-building for repeat broods. The effect of male condition on nest-building suggests that building entails important costs for males. Based on correlative data, we argue that building by males shortens the interval between the start of nest-building and the onset of egg-laying by about 5 days. Since clutch size, incubation and nestling time did not differ between early and late broods, male nest-building apparently affects fledging date. Since early fledgers (early dispersers) are more likely to settle in future winter flocks, building behaviour by crested tit males should be favoured by natural selection. So far, male nest-building in hole-breeding birds might have been overlooked due to the widespread use of artificial nest-boxes in behavioural studies.

Causes of divorce in the monogamous willow tit, Parus montanus, and consequences for reproductive success

Abstract. Divorce rates were measured in a population of willow tits, in which the size of some broods was manipulated. The population, with annual survival rates of ca 63 and 64% for females and males, respectively, had a relatively low divorce rate of 12·0%. The experiments on altered breeding success did not support the hypothesis that poor success is likely to initiate divorce. Most variation in reproductive success of the pairs differing in breeding history was attributable to the age of the female, yearling females being least successful. Yearling birds split up more often than older birds. Divorced females usually paired with older, and divorced males with younger, mates than their previous ones. With a new mate, divorced females bred successfully and advanced their laying date more than widowed females indicating that divorce was beneficial. The success of divorced males was low and some even remained unpaired in the season after splitting up. Divorce thus seems to be a strategy chosen by females to increase future reproductive success. The decision seems to be initiated when a female can obtain a higher-ranked mate among the birds in her own or in a neighbouring winter flock.

Age-Related Hoarding Strategies in the Crested Tit Parus cristatus: Should the Cost of Subordination be Re-Assessed?

1. In a population of crested tits Parus cristatus in northern Belgium, living in group territories outside the breeding season, food was mainly stored during October and November, a time when territorial flocks are split up in age-specific subflocks. 2. First-year flock members frequently stored in the upper and outermost parts of the trees, whereas adults consistently hoarded and foraged in protected sites near the trunk. The outermost, predator-exposed sites were only used by first-year foragers in mixed-age winter flocks with adults, as a result of site competition within flocks on cold days. 3. Consequently, the overlap between foraging sites (protected) and hoarding sites (exposed) of first-year birds was small during autumn, but large during winter

Conflict of interest between the sexes in Siberian jay winter flocks

Conflict of interest between the sexes in Siberian jay winter flocks

Effects of habitat fragmentation on the timing of Crested Tit Parus cristatus natal dispersal

Crested Tit Parus cristatus young from first broods dispersed 1 week later if they were born in small isolated pine plots (‘habitat fragments’) compared with individuals in a large pine forest (‘continuous habitat’). This delay in dispersal was caused by an extended period between fledging and dispersal. In second broods, the delay was even longer due to the interbrood interval being 9 days longer in habitat fragments. As nestlings in habitat fragments had a lower body‐mass, and age at dispersal was negatively correlated with nestling body‐mass within each nest, the postponed dispersal from fragments might be explained partly by a lower body‐mass. Alternatively, postponed dispersal from fragments could result from a barrier effect caused by reluctance to cross inhospitable habitat.Immigration by young from first broods into habitat fragments was delayed by approximately 3 weeks, and proportionally more second brood emigrants were recovered in this type of habitat. These results are in agreement with the hypothesis that fragments are second‐choice habitat. Early immigrants into continuous habitat had a higher probability of settlement in winter flocks compared with late ones, independent of condition or age. Therefore, Crested Tits born in habitat fragments probably have a lower chance of settling in first‐choice habitat.

Extra-Pair Paternity in the Black-Capped Chickadee

Studies of the mating strategies of birds are increasingly shifting their focus to the role that females take in controlling copulation (Hunter et al. 1993, Petrie 1992, Birkhead and Moller 1993). In some avian species, females appear able to control whether copulations occur by accepting or rejecting copulation attempts (BjSrklund et al. 1992, Lifjeld and Robertson 1992, Westneat 1992). Similarly, females of some species actively solicit copulations by seeking the extra-pair male in his own territory (Smith 1988, Kempenaers et al. 1992, Venier et al. 1993). In species where females do control the outcome of copulation attempts, there is a need to, first, determine the extent that extra-pair copulations (EPCs) lead to fertilizations and, second, establish potential benefits that a female may obtain by engaging in EPCs. Smith (1988) reported that female Black-capped Chickadees, Parus atricapillus, seek EPCs from males on territories adjacent to the territory defended by the female's mate. Interestingly, Smith observed that females preferentially sought males for EPCs that held higher dominance rank than the female's mate in the preceding winter's flock. Thus, female Black-capped Chickadees may be engaging in a mixed reproductive strategy of social monogamy while increasing reproductive success by extra-pair copulations with males of higher genetic quality than their own mate (Trivers 1972, Smith 1988, Hamilton 1990). Females may also benefit from engaging in EPCs with dominant males if, by doing so, this facilitates rapid pair bonding with the dominant male in the event that his mate dies. There is a need for data on whether EPCs are resulting in extra-pair paternity of the nestlings in order to imply a fitness benefit to the female's behavior. In this study we document rates of extra-pair paternity in an Ontario population of Black-capped Chickadees, using DNA fingerprinting, and provide support for Smith's hypothesis by showing that extra-pair males were of higher dominance rank than the female's mate. We also suggest a paternity-related explanation for occasional observations ofpolyandry in chickadees (Waterman et al. 1989, Howitz 1991).

Variation in initiator strategy in fighting by silvereyes

Abstract. Silvereyes, Zosterops lateralis, initiate agonistic interactions for access to food using 10 different elements of threat display, attack, vocalization and aerial combat. Qualitative variation in the strategies used by initiators was examined in interactions, after short-term food deprivation, between members of 10 caged winter flocks in which membership and dominance relationships had been stable for 3 months. Differences in strategy were independent of initiator rank per se but were related to the dominance relationship and rank distance between initiator and opponent. Hunger motivation and the degree of familiarity of contestants were also significant influences. An experimental manipulation of flock membership confirmed that strategy changed as position in the hierarchy changed. Threat display and attack are alternative strategies adopted in different situations and are associated with different probabilities of winning. A model based on a multidimensional scaling analysis of the patterns of co-occurrence of the 10 elements is reported. It is concluded that costs and benefits of participating in an interaction differ for individuals and that those costs are associated with performance, the probability of submission or retaliation by the opponent and, thus, access to food. Different elements of threat display and attack signal variations in the ratio of potential and actual costs and benefits of fighting to the initiating individual.

Food exploitation by a winter flock of greylag geese: behavioral dynamics, competition and social status

To investigate the dynamics of the winter flock patch exploitation, feeding experiments were performed with 140 semi-tame, free-roaming greylag geese (Anser anser). Three different initial densities of barley were offered on a 50-m2 patch: low (1600 grains/m2), intermediate (3300/m2) and high (I 1500/m2). Goose numbers on the patch, peck rates, and frequencies of agonistic encounters and of alert postures were observed by scanning the flock and in focal individuals. At low and intermediate initial food densities, peck rates decreased with food density, whereas at high food density, peck rates decreased only slightly over the feeding bout. Agonistic interactions increased as food decreased. A switch from exploitation to interference competition occurred at a threshold of approximately 900 remaining grains per square meter. With high initial food density, agonistic encounters began to increase gradually after 20–30 min. The same general patterns were observed for frequency of alertness. Family members occupied the patch for the longest time periods. The family female and the offspring fed most intensely. The family gander however, fed significantly less but was more aggressive and vigilant than all other social categories. Solitary geese spent their time on the patch doing little else but feeding and were the first to leave. It seems that high-ranking families and low-ranking singles adopt different competitive strategies, the former being superior interference competitors whereas the latter are forced scramble competitors.

Individual variation in mate care by alpha males in crested tit winter flocks

Winter flocks of crested tits Parus cristatus, typically consisting of two adults and one or two non-kin 1st-year birds, were observed to split up into subflocks in a way related to ambient temperature. On warm days, when they were foraging in subflocks without 1 st-year birds, alpha males always occupied the most preferred upper foraging sites, as expected from their top dominance rank. On cold days, when foraging in flocks with 1st-year birds, 8 out of 13 alpha males shifted to lower (less preferred) positions below their alpha mates while allowing the latter to forage at the best sites. As enhanced access to preferred microsites on days with high energy stress is believed to increase overwinter survival probability, this shifting behaviour of alpha males can be considered as a form of mate care. Out of 13 alpha males, however, 5 did not shift and always occupied the best foraging sites irrespective of flock composition. As (i) these non-shifting males were in poorer physical condition than shifting males, (ii) they scanned significantly less for predators than either females or shifting males when foraging in the uppermost tree parts, and (iii) four out of five non-shifting males were replaced by immigrants in early spring, absence of mate care during winter may be caused by constraints due to condition. High-quality-territory owners in poor condition at the end of autumn were most vulnerable to replacement by immigrants. Therefore, as four out of five replacements affected high-quality territories, selective intrusion by immigrants is suggested.

Predation Risk and the Organization of the Parus Guild

Many studies indicate that interspecific competition restricts the use of foraging sites in mixed-species winter flocks of tits. However, predation is a strong mortality factor for members of the tit guild and predation risk may restrict the selection of foraging sites and organisation of the mixed-species tit flock. We evaluated pygmy owl (Glaucidium passerinum) predation can North European tits and goldcrests. A literature analysis of six areas showed clearly that pygmy owls feed more heavily on those species that forage on exterior tree parts (coal tit P. ater and golderest Regulus regulus)

Behavioral and Physiological Adjustments of Birds Living in Winter Flocks

Behavioral and Physiological Adjustments of Birds Living in Winter Flocks

Ontogeny of food storing in titmice Parus spp.

The ontogeny of food storage in Crested Tits Parus cristatus and Willow Tits P. montanus starts during the period of parental care after the young have left the nest and develops gradually. In southern Norway, the storing behaviour becomes fully developed during August‐September, i.e. at a time when most juveniles have completed their dispersal period and settled in permanent winter flocks. The food storing behaviour is largely innate, but is improved by practice and experience.