Parus major L. III. Home range of the basic flocks

Transcription

1 Ecological study of social organization in the Great Tit, III Ecological study of social organization in the Great Tit, Parus major L. III. Home range of the basic flocks and dominance relationship of the members in a basic flock * Takashi Saitou ** Introduction Saitou (1978, 1979a) reported the basic structure and formation of the winter flocks in the Great Tit, Parus major L., and distinguished the basic flocks of constant composition from the compound flocks formed through the aggregation of two or more basic flocks. The basic flocks as the social unit in the non-breeding season have a well defined flock range, in which various relations of the members in a basic flock and between basic flocks are observed. Hence, it is necessary for understanding some aspects of flocks to obtain the knowledge of the home range of flocks. Hinde (1952) briefly described the home range of winter flocks in the Great Tit, but he did not distinguish the basic flocks from the compound flocks, so that the characteristic of home ranges of the basic flock is still unknown in detail. The first aim of this paper is to describe the difference between the range in which the basic flocks forage over by themselves and that they move about as compound flock, and to clarify the structure, basis and size of home ranges of basic flocks. Dominance-subordination relationship has been found in natural flocks of birds, especially in winter flocks of tits and chickadees (Colquhoun 1942, Hamerstrom 1942, Odum 1942, Brian 1949, Dixon 1963, 1965, Hartzler 1970, Glase 1973). There has been a problem on the dominance relationship of members in flocks of the genus Parus. Site-dependent dominance relationship was observed in the Blue Tit, P. caeruleus (Colquhoun 1942) and the Great Tit (Brian 1949), whereas unilateral and linear relationship was reported in the Carolina Chickadee, P. carolinensis (Dixon 1963), the Mountain Chickadee, P. gambeli (Dixon 1965) and the Black-capped Chickadee, P. atricapillus (Hartzler 1970, Glase 1973). The point in dispute is whether site-dependent dominance relationship exists in true natural flocks, because it was observed only in an aggregation of birds at an artificial feeding station. The second aim of this paper is to describe the dominance relationship of the members in a basic flock, and to discuss the factors affecting dominance relationship. Futhermore, an attempt is made to get at least a partial answer to the point in dispute. * This paper is a part of Dr. Sci. thesis submitted to the Tohoku University. ** Institute of Biological Sciences, The University of Tsukuba, Sakura-mura, Ibaraki , Japan.

2 Methods The field work was made from the spring of 1968 to the winter of , in the Akasaka Palace, Tokyo, Japan. The study area of about 37 ha mainly consisted of mixed evergreen and deciduous broad-leaved forest (Fig. 1). In the forest, nesting boxes had been Fig. 1. Study area. A is the main study area of territory. provided at a density of about ten per ha. Virtually all of the birds in the study area were individually marked by colour rings and their previous history was known. Observation of basic flocks was usually made from late September to the middle of March every year. Each flocks was followed at least for twenty minutes once a week, as a rule, but most of the flocks were usually observed every other day and their movements were plotted directly on a 1:2500 scale field map. Many such observations were then superimposed onto a map and the outermost points were connected with line so as to include all of the others. The obtained area was regarded as home range. With respect to the size of home ranges, most of the basic flocks extended their home range outside of the study area, so that the size was measured for 55 flocks whose home ranges were restricted within the study area.

3 Ecological study of social organization in the Great Tit, III The main study of breeding territory was carried out in the south-east part of the study area (Fig. 1-A). The area covered an area of about 7 ha and 9 to 12 pairs bred there every year. The method of observation was the same as that of flocks. Each pair was followed every other day and the territory was determined by connecting points at which chases and boundary clashes occurred within the home range of the pair. The size of territories was measured for a total of 71 pairs from 1968 to The Great Tits roost singly in natural holes or nesting boxes during autumn and winter. Observation of roost started in the winter of and was made from November to February. The birds return to the roosting area about one hour to half an hour before sunset. Some birds enter their roosting hole as soon as they arrive at the roosting site, but most of them stay at a branch near the roosting site for some minutes, uttering a particular call like the scolding call. During this period, the colour rings of the bird were birds roosted in nesting boxes. Nightly inspection of nesting boxes was not made by February, because it caused a bird change the roosting site. But, out of the roosing birds in nesting boxes, the birds not identified their colour rings by observation were captured in early February at night and identified. Dominance-subordination relationship was determined by supplanting attacks (Hinde 1952) in which one individual displaced another either from food or from feeding site. Whenever a supplanting attack took place during observation, the attacking and attacked birds were identified by their colour rings, and the site of the encounter was recorded on the field map. As supplanting attacks takes place in a moment, it is difficult to recognize the attacking and attacked birds individually when the attack occurs in dense bushes or foliage. The data collected were mainly of the supplanting attacks observed on the ground. Feeding stations were not set in the study area. Results 1. Home range of the basic flocks The basic flocks usually move about the forest by themselves, but they often unite each other to form the compound flock in mid-winter (Saitou 1978). In the home range of a basic flock, the area in which the basic flock foraged over by itself was different from that it moved about with other flocks as compound flock. The former consisted of the main area of home range and the basic flock spent much of its time there, whereas the latter was the secondary area that was temporarily utilized (Fig. 2). The home ranges were very different in size, which ranged from 0.7ha to 15.9ha, sizes in the scondary area. Since the compound flocks were formed through the aggregation of two or more basic flocks and foraged over the main area of each basic flock until they

4 Fig. 2. Home range of a basic flock. A, main area. B. secondary area. broke up, the size of secondary area in each basic flock varied with the number and combination of other basic flocks forming the compound flock. In fact, the size of home ranges tended to increase with the increase of the total number of flocks which united to form the compound flocks (Fig. 3). Therefore, further discussion about the home ranges will be focussed on the main area, which is called "basic flock range". During autumn and winter, the basic flocks spend much of their time in feeding and forage over their basic flock range. But the feeding places were not evenly distributed over the whole of the basic flock range. The cumulate feeding time of the flock was also different among the feeding places (Fig. 4). From the distribution of cumulate feeding time, the basic flock range can be divided into two parts; a central part and a peripheral Fig. 3. Relation between size of home range in a basic flock and total number of other flocks uniting the basic flock to form compound flocks. Vertical line, standard deviation. part. The former was more favourable feeding area with dense foliage or undergrowth than the latter, and was defined by connecting feeding places at which the cumulate feeding time was more than ten minutes. In the central part, the most favourable

5 Ecological study of social organization in the Great Tit, III Fig. 4. A basic flock range. Main area of home range in Fig. 1. Black circle, feeding place and cumulative feeding time. Area surrounded by dotted line, central part. A, feeding activity center. feeding place is termed "feeding activity center". The basic flock ranges were not defended against encroachment of neighbouring flocks. The basic flocks often encroached on the central part of neighbouring flocks in the absence of the home flocks. It was sometimes observed that, when the home flock returned, the intruding flock went back to its own central part of the flock range. However, it was very rare that actual skirmishes occurred between the flocks. Even in such cases, only the adult male of the home flock, that had bred in that area, chased the members of intruding flock away. Thus, the basic flock ranges were not the flock territory, but a well defined area throughout winter, though the peripheral part varied slightly with month, and the feeding activity centers of neighbouring flocks never overlapped each other (Fig. 5). ha. It is expected that the size of the range is related with the size of flocks. The average size seems to increase in proportion to the size of flocks, but the tendency is not so remarkable (Fig. 6). In the process of flock formation, adults, usually a previous breeding pair, remain on or near their previous breeding territory even after the breeding and the young unite them to form a basic flock (Saitou 1979a). This fact suggests that the basic flock range appears to be based on the previous breeding territory of the adults belonging to the flock. As set out in Fig. 7, it is clear that the basic flock range was mainly established on the basis of

6 Fig. 5. Basic flock ranges of neighbouring flocks and their feeding activity centers. Alphabet indicates each flock. Black circle, feeding activity center.

7 Ecological study of social organization in the Great Tit, III the previous breeding territory of the adults belonging to the flock. As mentioned above, the relation between the size of basic flock range and the flock size was not so remarkable. However, taking the relation between the basic flock range and the previous breeding territory of the adults belonged to the flock in consideration, the average size of the ranges seems to be related with the number of adults, particularly adult males in the flock. In 55 flocks measured for the size of basic flock ranges, they contained one to three adult males. The relation between the average size of basic flock ranges and the number of adult males in the flocks is remarkable (Fig. 8), as compared with Fig. 6. Fig. 6. Size of basic flock ranges and flock size. Vertical line, standard deviation. The Great Tits roost singly in holes, cracks in trees, nesting boxes or in other similar sites during autumn and winter. It is necessary to ascertain whether the members of a basic flock select their own roosting site within their basic flock range. Once the roosting site was selected, each bird occupied the same roosting site until the following spring if it was not disturbed by accidents, such as heavy rain or snow causing submergence of the cavity, and capture of the roosting bird in the nesting box at night. The Great Tits evidently preferred small natural holes as roosting site to nesting boxes. Whether the birds roost in nesting boxes or not is easily known by a regular inspection of all nesting boxes in the daytime, because they usually defecate in the roosting sites every day. Although nesting boxes were provided at a density of about ten per ha in the study area, only small proportion of the birds roosted in the nesting boxes. In the winter of , 149 birds consisted of 32 flocks and out of these birds, the roosting sites of 72 birds were found. Out of 72 birds, 20 birds (only 13.4 per cent of 149 birds) roosted in the nesting boxes, whereas other 52 birds roosted in the small holes or cracks of the oak, Shiia sieboldii, the ginkgo, Ginkgo biloba, the maple, Acer palmatum, and the zelkove, Zelkowa serrata. From the distribution of roosting sites, it is found that the members of a basic flock selected their own roosting site within their basic flock range, particularly in the central part of the flock range. The distance between roosting sites of the members, measured by the nearest distance form one roosting site to another in a basic flock, ranged from 0m (different holes in the same tree) to 120m (Fig. 9). selected their roosting site within 50m. It is noticeable that most of them The association of members in a basic flock primarily results from the overlap of

8

9 Ecological study of social organization in the Great Tit, III

10 Fig. 7. Previous breeding territories of adults belonging to the flock and basic flock ranges. Above, breeding territories. Below, basic flock ranges. Alphabet indicates each basic flock. Alphabet and figure indicate flock members. Dot, female. Territory in white, immigrant. Hatched area, grassland.

11 Ecological study of social organization in the Great Tit, III Fig. 8. Average size of basic flock ranges and number of adult males belonging to the flock. Vertical line, standard deviation. Fig. 9. Distance of roosting sites between members of a basic flock. settling areas between members (Saitou 1979a). This association continued not only for one winter, but also for two winters or more. Out of the previous members of a basic flock, two to seven birds survived until the following autumn and the total of these birds amounted to 192 during six years (Table 1). While 173 out of these 192 birds had bred in their previous basic flock range, 19 birds (5 males and 14 femates) had dispersed from their previous basic flock range to other parts of the study area after the basic flock broke up and joined other basic flocks there in the following autumn. Out of 173 birds, 20 males had belonged two by two to 10 previous basic flocks in previous winter, but joined different basic flock each other in the following autumn. Other 153 birds (88.4 per cent of 173 birds) Table 1. Association of previous flock members in the following autumn.

12 belonged again to the same basic flock in the following autumn. Therefore, most of the previous members in a basic flock rejoined with each other to form the basic flock in the following autumn as long as they survived. The fact suggests that after settling in an area, individuals remain there for the rest of their life. To ascertain this point, the feeding activity center of a basic flock range and the breeding site of each member of the flock are used as central base of individual's life in the non-breeding and breeding season, respectively. Each central base of an individual in successive years was restricted within an area. An example is given in Fig. 10. Then, distance Fig. 10. Central bases of each individual which survived two or more year in the south-east port of the study area. between central bases in successive years is measured for each individual. In their first autumn, most of the birds settled within an area 300m away from their birth place and bred within 100m from the feeding activity center of their basic flock range in the following spring. In the second autumn, they joined the basic flock having a feeding activity center within 100m from their breeding site and so on; the difference of the distance in successive years was only less than 100m (Fig. 11). Therefore, it is clear that after settling in an area, individuals remain there for the rest of their life. 2. Dominance relationship of the members in a basic flock When the flocks were feeding, particularly on the ground, it was observed that one bird attacked another in feeding and displaced it from food or from feeding site. As Hinde (1952) described, such supplanting attacks took place most often on a bird which was opening

13 Ecological study of social organization in the Great Tit, III Fig. 11. Average distance between feeding activity center and nest site of flock members in successive year. Bi, birth place. W, feeding activity center. B, nest site. Figure, year old. a nut, or had just dugged a pit among fallen leaves, or was feeding in some other way which involved its being in the same place for at least several seconds. The attacked bird flew away, abandoning the food or the feeding site, so that the supplanting attacks were always successful. From the outcome of supplanting attacks (Table 2), it is found that a dominance relationship was established among the members of a basic flock. Moreover, it, once formed, remained stable over the basic flock range and was maintained throughout the winter. Adults always dominated over young within a sex group. Adults were slightly larger than young Table 2. Dominance-subordination relationship between members of basic flocks. The figure is number of supplanting attacks.

14 Table 3. Difference of mean wing lengths (mm) between between age. S. D, standard deviation sex and Table 4. Difference of mean tail lengths (mm) between sexes and between ages. S. D, standard deviation Males were always dominant to females within an age group. Males were usually larger Moreover, the number of supplanting attacks of adult and young males was 5.2 and 6.3 times as large as those of adult and young females, respectively. It is considered that males are more aggressive than females. Most of the basic flocks contain one adult male and female, but about one third (53 flocks) of 169 flocks observed during six years contain two or more adult males and/or two or more adult females (Saitou 1978). In such flocks, a few supplanting attacks were observed between adults of the same sex. It was 17 times between adult males in 11 flocks and 6 times between adult females in 3 flocks. Nevertheless, it is noticeable that the attacking bird was always the previous owner of the area in which the flock was feeding at the time, irrespective of their age; the adults made the supplanting attacks on the others of the same sex in their previous breeding territory. The dominance relationship of young of the same sex seemed to be determined before the basic flock was formed. In the summer flocks (Saitou 1978), the supplanting attacks were observed frequently, and often developped into actual combats, as Hinde (1952) pointed out. In the case of the young mentioned in the process of flock formation (Saitou 1979a), three of four young males which belonged to the basic flock I appeared in the south-east part of the study area for the first time during early July. The difference of appearance

15 Ecological study of social organization in the Great Tit, III dates was only a week among them; I-16 in 3 July, I-17 in 8 July and I-18 in 10 July. During July and August, I-16 dominated over I-17 and 18, and I-18 dominated over I-17. The last I-20 appeared in 21 July and became subordinate to the others. Such dominance relationship remained stable from September onward. Similar result was obtained in other few cases. Adult males always dominate over young females, but dominance relationship between adult females and young males was not unilateral. It was observed that adult females attacks 10 times on young males and the latter attacked 13 times on the former. The age and number of the attacking females were five birds of second year old, two of third, one of fifth and two of 7th, whereas those of the attacked females were eight birds of second year old, four to third and one of fifth; the older females were not always more aggressive on young males than the younger ones. Hence, aggressiveness of adult females is probably not related with their age. Although the dominance relationship between adult females and young males was neither linear nor unilateral as a whole, the relation of particular individuals in a basic flock was unilateral; a particular adult female always dominated over a particular young male in one flock, while a particular young male was always dominant to a particular female in another flock. Discussion and conclusion Because the basic flock is the social unit of the Great Tit in the non-breeding season and temporarily unite each other to form the compound flocks (Saitou 1978), the home range of the basic flocks have a double structure; it consist of the main area in which the basic flocks forage over by themselves and the secondary area in which the flocks move about with others as the compound flock. Furthermore, the main area, that is the basic flock range, can be divided into the central part and the peripheral part. The double structure of home ranges gives a difficulty to a direct comparison of the size of home ranges between the present study and other studies. The reason is that the size, particularly of secondary area, varies largely with the number and combination of basic flocks forming the compound flocks. Hinde (1952) reported that the size of flock ranges was about 4 to 8 ha in a mixed broad-leaved forest. As the flocks reported by Hinde appear to correspond closely to the compound flocks in the present study (Saitou 1978), the flock ranges would include both the main and secondary area of home ranges. In the present study, the average size was 5.5ha, ranging from 0.7 to 15.9ha, in the mixed evergreen and deciduous broad-leaved forest. Such difference may be not only due to the difference of vegetations, but also to that of population density in the non-breeding season. It is better for analysis of flock ranges to adopt the basic flock ranges rather than the home ranges as a whole. The characteristic of the basic flock range is a well defined area throughout the winter. Moreover, the feeding activity centers of neighbouring flocks never

16 overlap, though the basic flock ranges themselves overlap extensively each other; taking the feeding activity center as a datumn point, some aspects of flocks or individuals can be analyzed. The basic flock range was based on the previous breeding territories of the adults belonging to the flock. Thus their size was not related with the size of flock which correlates mainly with the number of young in the flock (Saitou 1978), but with the number of adults, particularly of adult males in the flock. Although the basic flock range was based on the previous breeding territories of adults belonging to the flock, this does not imply that the basic flock range consist of only the previous breeding territories of the adults. In the process of flock formation, adults remain on or near their previous breeding territories even after the breeding and then young select there as their settling area. As a result, a basic flock is formed by individuals whose settling areas, including the previous breeding territories of adults, overlap (Saitou 1979a). Therefore, it is concluded that the basic flock range is an overlapping range of settling areas between members of the flock. The flock ranges of the Carolina Chickadee (Dixon 1963) and the Black-capped Chickadee (Hartzler 1970, Glase 1973) are also well defined, like the basic flock ranges of the Great Tit. However, there is a difference in respect to wheter the flocks defend their flock range or not. The flocks of the Great Tit do not defend their basic flock range against encroachment of neighbouring flocks, whereas those of Chickadees do so and the most dominant adult male of the flock, that has bred within the flock range, actively defends it. Apart from the defence of flock range, the base of flock ranges in the Chickadees is also the previous breeding territory of the adult male belonging to the flock, like the case of the Great Tit. Hence, it is considered that the flocks of constant composition in the species of Parus have the same base of flock ranges on establishment so long as information is available. The members of a basic flock selected their roosting site individually within the basic flock range, that is their settling area. Their roosting sites concentrated at the central part of the basic flock range within 50m each other. This concentration suggests the extensive overlap of settling areas between members of the flock. Similar concentration of roosting sites is reported in the Black-capped Chickdee (Odum 1942) and the Great Tit (Hinde 1952). The overlap of settling areas is an important factor in the association of members in a basic flock (Saitou 1979a). Such association continued for two winters or more. Most of the previous flock members rejoined together the basic flock in the following autumn as long as they survived. This results from that after settling in an area, individuals remain there for the rest of their life. Kratzig (1938) pointed out that 'titmice, after completing their first moult, reside in a certain part of their range for breeding and sleeping, and stay there for the rest of their life'. From the observations of breeding and roosting Great Tits in nesting boxes, Kluijver

17 Ecological study of social organization in the Great Tit, III (1951) reached at the same conclusion and termed the area for roosting and breeding "domicile". It seems that the concept of domicile has not been appreciated. However, the concept is of importance for understanding social organization of the Great Tit in the non-breeding season and breeding season. It applies very well to the result of the present study. Adopting the term domicile instead of settling area, it is concluded that the basic flocks consist of individuals whose domiciles overlap and have a well defined flock range including all of the domiciles of the members. 2. Dominance relationship of members in a basic flock The dominance-subordination relationship was observed among the members of a basic flock. Adults always dominated over young within a sex group. With respect to the factor affecting the dominance, no correlation exists between body size and dominance. Another possible factor is the difference of familiarlty of members with their basic flock range. The basic flock range is the overlapping range of domiciles between members, but the adults have settled there at least one year earlier than young. Moreover, the basic flock range is based on the previous breeding territory of the adults. Consequently, the adults are naturally familiar enough with the area. It is well known that the familiarity with an area is related with the attacking and fleeing drives of the individual; in the familiar area, the attacking drive increase, whereas the fleeing drive decrease. This was confirmed in the Great Tit by the experiment of Hinde (1952). Since the adults are more familiar with their basic flock range than the young, they must behave aggressively toward the young over there. Thus, it is concluded that the dominance of adults over young within a sex group is due to the difference of their familiarity with the basic flock range; the important factor is the prior occupancy of the area in adults. In the species of Parus, many studies (Colquhoun 1942, Homerstrom 1942, Odum 1942, Kluijver 1957, Dixon 1963, 1965, Hartzler 1970, Glase 1973) show a general tendency for males to dominate over females within an age group. In the present study, males always dominated over females within an age group. The dominance of males over females is probably due to more aggressiveness and larger body size of males. Within a sex and age group, the dominance relationship of young seems to be determined before the basic flocks are formed. There are at least three months from dispersal of the young to formation of basic flocks (Saitou 1979a). During this period, supplanting attacks were observed frequently among the young of summer flocks. The dominance relationship observed in this period remained stable after the basic flocks were formed. Since the young from early broods settled earlier than those from late broods, the former probably became dominant to the latter by their prior occupancy of the area. However, it seems that a slight difference of appearance date in the area would not influence on the dominance. In this case, body size may be related with the dominance, because it is an important factor in affecting the survival of young after leaveing the nest

18 (Lack 1964, 1966, Perrins 1965). In the study area, no correlation existed between body size and dominance. However, most of the young were captured and measured their body size in mid-winter. Since there was the time lag between arrival of the young and its subsequent capture, it is necessary to confirm whether the dominance relationship of the young correlates with their body size. Between sex and age group, the dominance of adult males over young females suggests that adult's prior occupancy of the area and dominance of the sex are important to determine the dominance of adult males. On the other hand, the dominance relationship between adult females and young males was more complex and not unilateral as a whole. It seems that the prior occupancy of the area in adult females counterbalances the dominance of the sex in young males. But the dominance relationship between a particular adult female and a particular young male was linear and unilateral in a basic flock. The factor affecting the dominance could not determined only by their previous history. Whether the prior occupancy of the area in adult females takes precedence of the dominance of the sex in young males or the reverse may be related with the individuality of the birds concerned. Kluijver (1957) described that 'many older females gain the victory over yearling males' at artificial feeding stations. This does not agree with the result of the present study. But it should be noted that the dominance relationship of birds observed at artificial feeding stations are often different from that of natural flocks, as will be discussed later. On the other hand, Glase (1973) reported the dominance of young males over adult females in the flocks of Black-capped Chickadee, and suggested that sex is a more important than age. With respect to the factor affecting the dominance relationship between adult females and young males, it seems to be better that a general conclusion should be suspended until further data are available. The dominance relationship was linear and unilateral in a basic flock. It was maintained throughout winter and stable over the basic flock range. Hinde (1952) found that supplanting attacks are so common and they occur with a greater frequency when food is scarce than when it is plentiful. Therefore, the dominance relationship of members must have a survival value. Moreover, it is important to pair formation and establishment of territory of members within the basic flock range (Saitou 1979b). As mentioned above, two types of dominance relationship have been observed in winter flocks of the genus Parus. The first is site dependent. Colquhoun (1942) first described this type in a flock of the Blue Tit at an artificial feeding station. Similar result was obtained for the Great Tit by Brian (1949). The second is linear and unilateral and was reported in the Black-capped Chickadee (Hartzler 1970, Glase 1973), the Carolina Chickadee (Dixon 1963) and the Mountain Chickadee (Dixon 1965). With respect of these two types of dominance relationship, a point in dispute is whether reversible, site dependent dominance relationship is formed in natural flocks. Dixon (1965), Hartzler (1970) and Glase (1973) insisted that such dominance relationship hardly plays an

19 Ecological study of social organization in the Great Tit, III effective role as a principle of organization for natural flocks. Concerning the dominance relationship reported by Colquhoun (1942) and Brian (1949), it seems to result from the observation at a single artificial feeding station. The flocks observed are probably not of constant composition, but merely aggregation of birds or flocks, because feeding aggregation of birds or flocks tends to be formed frequently at feeding station. It is found that the dominance relationship of members between flocks are site dependent, with members of a flock being dominant while they are in the flock's own range (Dixon 1965, Hartzler 1970, Glase 1973, Saitou in preparation). In the Great Tit, most of the flocks contained one adult male and/or one adult female and the dominance relationship was linear and unilateral. However, site dependent dominance relationship was observed in the basic flocks containing two or more adults of the same sex. As mentioned above, the basic flock ranges included all of the previous breeding territories of the adults belonged to the flock. When the flock was feeding on an area, the previous owner of the area was dominant to the others. Hence, it is clear that the dominance relationship of adult within a sex is due to site dependent. With respect to the number and breeding experience of adults in a flock, the basic flocks of the Great Tit are interesting contrast to the flocks of Chickadee. In the Black-capped Chickadee (Glase 1973), 9 out of 23 flocks contained two adults of the same sex. In these flocks, only two contained two adult males and two adult females which bred in the previous winter flock range. Excepting alpha male and its previous mate, the adults of other flocks remained in his study area, but spent throughout the previous summer as solitary bird. Similar result was obtained for the Mountain Chickadee by Dixon (1965). Glase suggested that breeding experience in the area is an important factor determining the amount of dominance status as individual attained. In the Carolina Chickadee (Dixon 1963), only a few flocks contained two adults of the same sex. Dixon considered the influence of 'seniority' on the dominance relationship of adult males since 'the alpha male was the male of longest residency and the older subordinate male was of longer tenure than some other members of the flock'. In the Great Tit, the flocks of two or more adult males and/or two or more adult females were about one third of 169 basic flocks during six years. The age of adults was not necessarily related with the dominance relationship. Once the birds established their territory and bred there, they must have prior occupancy of the area, as compared with adults bred in other area, irrespective of their age. Hence, the adults of the same sex in a basic flock are equal to each other about prior occupancy of their basic flock range and previous breeding experience, unlike the adults of the Chickadees. On such condition, it is reasonable to consider that no other factors have the precedence over effect of prior occupancy of adults in each part of the basic flock range, so site dependent dominance relationship should remain in these flocks. The behaviour of these flocks are similar to that of the flocks containing only one adult

20 male and/or one adult female; the members of the former kept strictly together throughout winter as well as those of the latter, and behaviour of flocks in the formation or break-up of compound flocks was not less integrated than that of the latter. Incidentally, there were very few aggressive encounters between adults of the same sex, so that some other mechanism may exist for the avoidance of such encounters and may play to organize these flocks. In any case, the flocks containing two or more adults of the same sex are integrated ones, involving site dependent dominance relationship between adults of the same sex. In the flocks of constant composition within the genus Parus, most of the flocks contain only one adult male and/or one adult female, particularly one adult male. The flocks of two or more adults of the same sex being equal status are found only in the Great Tit so long as information is available. It is interesting problem whether more organized mechanism will be developped in such flocks or the flocks will be gradually transformed into those of one adult male in future. When further data about many other species of Parus become available, the existence of these flocks should appear significance for the evolutionary process with the genus Parus of the social organization in the non-breeding season. Lastly, taking the dominance relationship into consideration, it is certain that the members of a basic flock recognized each other individually through learning. The individual recognition is important to understand the association of members in a basic flock. As mentioned above, the members of a basic flock are primarily associated with each other by the overlap of their domiciles. If the association of members was only due to the overlap of their domiciles, the change of members between neighbouring flocks may occur, since it is probable that the domiciles of members in one flock overlap those of members in neighbouring flock. But the composition of basic flocks never changed until the flocks broke up in early spring (Saitou 1978). Therefore, it is considered that the association of members primarily based on the overlap of their domiciles has to be solidified by the individual recognition between the members. Acknowledgement I am much indebted to Professor Y. Kurihara of the Tohoku University, for his discussion and criticism on the present study. I express appreciation to Dr. J. Mishima of the University of Tsukuba for his advice and encouragement. I wish to thank Professor M. Uramoto of the Wako University and Dr. M. Nishihira of the Kyoto University, who kindly read and offered critical comments of this paper. I am grateful to Mr. N. Abe for his discussion and to Miss Asakawa for her assistance of I would also like to thank Mr. S. Ohori for his assistance of 1973 onward and his discussion. Finally, I wish to express my thanks to the chamberlains of the Household of the Akasaka Palace, who gave me many kind of help. Summary 1. This paper describes home range of the basic flocks and the dominance relationship between the members of a basic flock, and attempts to clarify the structure, size and basic of home range

21 Ecological study of social organization in the Great Tit, III and the factors affecting dominance relationship of the members in a basic flock. 2. The field work was made from the spring of 1968 to the winter of in the Akasaka Palace, Tokyo, Japan. The study area of about 37 ha mainly consisted of mixed evergreen and deciduous broad-leaved forest. Virtually all of the birds were marked individually by colour rings and their previous history was known. 3. The home range of the basic flock can be divided into two area. The first is a main area in which the basic flock foraged over by itself. The second is a secondary area in which the flock moved about with other flocks as compound flock. The size of home range was, in average, 4. The main area is called "basic flock range". The basic flock range can be also divided into two parts; a central part and a peripheral part. The central part was more favourable feeding area than the peripheral one and contained a feeding activity center as most favourable feeding place. 5. The basic flock ranges overlapped each other extensively and were not defended against encroachment of neighbouring flocks. But they were well defined throughout winter and the feeding activity center of neighbouring flocks never overlapped each other. It was closely related with the number of adult males in the flock since the basic flock range was based on the previous breeding territories of adult males belonging to the flock. 7. In the process of flock formation, adults remained their domiciles even after breeding, and then young select the area as their domicile. Therefore, it is concluded that the basic flock consisted of individuals whose domiciles overlapped and the basic flock range was the overlapping range of domiciles between members of the flock. 8. Adults always dominated over young within a sex group. The important factor determining the dominance relationship was the prior occupancy of the basic flock range in adults. Males always dominated over females within an age group. This was due to more aggressiveness and larger body size of males. 9. The dominance relationship of young within a sex group seemed to be determined before the formation of the basic flock and remained stable after the flock were formed. The prior occupancy of the basic flock range and body size were probably important to determine the dominance relationship. 10. Adult males were always dominant to young females. This was due to the adult's prior occupancy of the basic flock range and the dominance of the sex. The dominance relationship between adult females and young males was not unilateral as a whole, but that between a particular adult female and a particular young male was linear and unilateral in a basic flock. The factor affecting such relation was unknown. 11. Although the dominance relationship of adults within a sex group was site dependent, most of the basic flocks contained one adult male and/or one female and the dominance relationship was linear and unilateral. The relationship was maintained throughout winter and stable over the basic flock range. 12. Taking the dominance relationship into consideration, it is certain that the members of a basic flock recognized each other individually. The association of members primarily based on the overlap of their domiciles has to be solidified by the individual recognition between the members. Reference Brian, A. D Dominance in the Great Tit. Scot. Naturalist 61: Colquhoun, M. K Notes on social behaviour of Blue Tits. Brit. Bird 35: Dixon, K. L Some aspects of the social organization of the Carolin Chickadee. Proc. Int. Ornith. Congr. 13:

22 Dixon, K. L Dominance subordinance relationship in the Mountain Chickadee (Parus gambeli). Condor 67: Glase, J. C Ecology of social organization in the Black-capped Chickadee. Living Bird 17: Hamerstrom, F Dominance in winter flocks of chickadee. Wilson Bull. 54: Hartzler, J. E Winter dominance relationship in Black-capped Chickadee. Wilson Bull. 82: Hinde, R. A The behaviour of the Great Tit (Parus major) and other related species. Behaviour Suppl. 2: Kluijver, H. N Roosting habits, sexual dominance and survival in the Great Tit. Cold Spring Harb. Symp. Quant. Biol. 22: Kratzig, H Untersuchungen zur Siedlungsbiologie waldbewohnender Hohlenbruter. Orn. Abhandlungen Heft 1. Lack, D A long-term study of the Great Tit (Parus major). J. Anim. Ecol. 33 (Jubilee Suppl.): Lack, D Population studies of birds. Oxford. Odum, E. P. Annual cycle of the Black-capped Chickadee. Auk 59: Perrins, C. M Population fluctuations and clutch-size in the Great Tit, Parus major. J. Anim. Ecol. 34: Saitou, T Ecological study of social organization in the Great Tit, Parus major L. I. Basic structure of the winter flocks. Jap. J. Ecol. 28: Saitou, T. 1979a. Ecological study of social organization in the Great Tit, Parus major L. II. Formation of the basic flocks. J. Yamashina Inst. Ornith. 11: Saitou, T. 1979b. Ecological study of social organization in the Great Tit, Parus major L. IV. Pair formation and establishment of territory in the members of basic flocks. J. Yamashina Inst. Ornith. 11:

23 Ecological study of social organization in the Great Tit, III