The social behaviour of the Common Buzzard Robin J. Prytherch ABSTRACT During a long-term study of the Common Buzzard Buteo buteo in Avon, special emphasis was placed on social behaviour.This is shown to be more complex than previously thought, with several new behaviours being described. Furthermore, flight behaviours are shown to be distinctive for the two components of a resident population: territorial pairs and unpaired (non- breeding), mostly one- to three-year-old birds. Buzzards defend their territories from intruding birds by using assertive postures initially. If necessary, further, more demonstrative, behaviours are directed at intruders. These behaviours help the birds to avoid fighting, but this does happen rarely. These and other behaviours serve to advertise the presence of a pair in a territory and are important in pair-bonding. For breeding pairs, activity is normally restricted to the territory, but some males engage in extra-territorial chases, which may involve a form of reciprocal altruism. Some unpaired young birds defend territories, but do not use the full repertoire of behaviours. Some aspects of pair formation and relations within the family group are described, as well as perched postures.The behaviour of juveniles is distinctive especially with regard to play, an activity that can be easily confused with adult behaviours. A few exceptions are described. Suggestions for the origins of the displays are made.

crucial aspect of my long-term study seven and 28 visits per month, most visits lasting of the Common Buzzard Buteo buteo some 3–8 hours. Visits were carried out in all A in Avon has been an attempt to unravel months, although less frequently in winter. Early the intricate nature of the species’ social in the year, I check all territories for occupancy behaviour, the results of which I present here. and then check nest-sites during March and Other aspects of the study, which commenced in April. This is when most territorial behaviour is 1980 and still continues, concern population seen, although it can be observed at other times. monitoring, territory size and topography, When entering my study area, observations breeding biology, nest-sites, and individual life often start opportunistically; otherwise, I watch histories, all gathered during over 18,000 hours a single territory or go to a regular observation of fieldwork in my 75-km2 study plot, which lies point (usually at low elevation), from where I just west of Bristol. The area comprises a can monitor several territories. All observations mixture of woodland (mostly deciduous), are noted, timed and attributed to the relevant grassland (meadows for cattle, horses and pairs/territories. I aim to spend a minimum of sheep) and some arable land, and rises from sea 25 minutes in a territory, in order to gain level through wide, low-lying valleys to ridges knowledge about conspicuousness, time and plateaus up to about 180 m. There are many budgets, etc., as well as social and other villages, as well as three large conurbations behaviours. adjacent to the area. At the start of my study, I was heavily To gather information, I spent up to 1,200 dependent on the work already carried out by hours in the field each year, making between Colin Tubbs (1974) and Douglas Weir and Nick

© British Birds 102 • May 2009 • 247–273 247 The social behaviour of the Common Buzzard

Picozzi (1975), as well as the account given in Structure of the study population Vol. 2 of BWP (Cramp & Simmons 1980), based In my study area, all the breeding adults were largely on the previous two studies. Soon I sedentary, and defended their territories began to realise the value of following individual throughout the year. They comprised the bulk of birds; by knowing their sex and/or age I was the population: 13 pairs in 1982, rising to 97 learning so much more as they interacted with pairs in 2008, with up to 107 juveniles by late others. It was also quickly apparent that the summer, in addition to non-breeders (a group studies mentioned above were far from of unknown size, but probably fewer than 30). complete, as the social signals that the birds use Most of the juveniles dispersed out of the area by to mark their territories are both complex and early autumn, but were replaced to some extent subtle. by juveniles from elsewhere. Many of these Common Buzzards (hereafter referred to juveniles may subsequently have returned to simply as ‘Buzzards’) vary greatly, not only in settle close to their natal area (Davis & Davis their plumages, among individuals and age 1992; Walls & Kenward 1998). Some juveniles classes (see below), but to a lesser extent also in were initially sedentary (remaining in their terms of voice, ‘personality’ and shape. All of parents’ territory for much of their first year and these features helped me to attribute particular rarely much longer) but most of them, and behaviours to individual birds and therefore to almost all other non-breeders, were wanderers interpret their purpose (I have identified as or ‘floaters’ – settling for a period (from a few individuals at least 60 birds during the study days to several months) in locations free of period, by a mixture of plumage and other breeding birds, but often adjacent to an characters). In this paper, I describe first the occupied territory. Many of these birds, like various behaviours of both breeding (territorial) some breeders, became very inconspicuous in and non-breeding birds, and then describe their midsummer. function and how the behaviours relate to each Before leaving the natal territory, juveniles other. The social behaviour of territorial, can be identified quite easily: they are tolerated breeding pairs is distinct from that of other by their parents, and also call distinctively when Buzzards and is crucial in interpreting the in the territory. The call is usually a double or activities of a group of two or more interacting triple ‘ki-ki’ or ‘pi-ya – pi-ya – pi-ya’ (but very birds. Indeed, breeding and non-breeding birds variable), rather higher pitched and shriller can be described as forming two components of than the better-known adult calls (which I the population. usually note as ‘ca-au’, but these are also highly variable). The calls of juveniles are commonly thought to denote hunger, but they also act to appease their parents; once fledged, juven- iles normally call only when a parent is in view, and do so even when the caller has a full crop. Later, when making their first flights beyond the territory, they often call on their return as they cross

Robin Prytherch the boundary, as if 132. Part of the study area in Avon: a view from Clevedon looking east-northeast to repress any attack along the Gordano Valley (which forms the western third of the study area); from a parent (see autumn 1994. It is an area of mixed woodland (mostly deciduous), damp also below). Having meadows separated by ditches, and a small amount of arable land. Much of the flat area is within the Gordano Valley National Nature Reserve. abandoned the natal

248 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard territory, a juvenile will normally cease to call, Age classes and ‘basic’ flight behaviour unless attacked (by another Buzzard), when it Adult Buzzards are distinguishable from juvenile might squeal shrilly, until it occupies a territory and some 2Y birds in terms of plumage of its own two to three or more years later. characters (see Appendix 1). Nonetheless, Once independent, juveniles did not plumage variation is such that some juveniles appear to defend the areas in which they (especially dark ones) can look very similar to settled and so these were not obvious older birds. Furthermore, in silhouette, which is territories. In this they differed from many a typical view of a flying Buzzard, plumage 2nd-year (2Y) or older birds, which settled in features are of limited value. There are, however, a territory of their own. (Note that I use ‘bird subtle structural differences and, more years’ rather than calendar-years to importantly, postural differences that help, and distinguish age classes, since the major moult which lead neatly into social behaviour. takes place from May/June in juveniles and Almost all the territorial interactions are not from July/August in most adults, and lasts for between adjacent pairs, as might be expected, at least four months.) Third-year and older but between a pair and non-breeding (mostly birds could be referred to as adults, and were juvenile), intruding birds. There are some rarely unpaired. Intruders were chased out of exceptions, which I will describe later. A pair in these single-bird territories, but the full its territory dominates all others that enter it repertoire of behaviour (see below) was not (including its own young, some of which may used. Single-bird territories were usually held remain in the territory for variable periods after from a few months to a year or more, until a fledging). The residents signal their status to mate arrived or the bird moved on. Territorial intruders by a distinctive assertive body pairs usually comprised two adults but, rarely, language. The intruders, regardless of their age, one of the pair was a juvenile or 2Y bird. adopt passive postures. These are most often These paired youngsters exhibited most of the demonstrated in flight but equivalent signals are behaviours of older birds, but often in a less given by perched birds. Flapping flight, circle- demonstrative way (particularly juveniles). and slope-soaring, sailing and gliding all have Four of my territories have been occupied by their distinctive forms (fig. 1). (When circle- three adults (one male and two females in and slope-soaring, birds ascend; when gliding, each case; see below) and for three, five, six birds descend; but when sailing, birds drift and seven years, with the last three still about maintaining roughly the same level. Such present in 2008. sailing flights may include a few flaps or single I recorded the plumage details of many individual paired birds and found this a crucial aid to the study, enabling intruders (especially juveniles) to be identified quickly. Knowing how to age birds in the field was therefore important. Plumage and structural differ- ences between age classes, together with basic flight postures,

are discussed in this Robin Prytherch paper because of their 133. Part of the study area in Avon: the Gordano Valley, looking southeast towards importance in under- Cadbury Camp (with the M5 viaduct just visible); September 2003.Woodland on standing other behav- the slopes gives way to improved or unimproved grasslands and wet meadows plus wooded hedgerows.The majority of the wet meadows form part of the iours. Gordano Valley NNR or reserves of the Avon Wildlife Trust.

British Birds 102 • May 2009 • 247–273 249 The social behaviour of the Common Buzzard

h

a j e

b

c f d

g i Robin Prytherch Fig. 1. Basic flight behaviour and two age classes of the Common Buzzard Buteo buteo.Top right,Juvenile/1Y (a) above an adult (b) as in circling or sailing. Note the slimmer wings and relatively longer tail of the juvenile, and the lack of an obvious dark subterminal bar along the trailing edge of the wings and tail, although in some dark youngsters this can be hard to see. Rely then on the different proportions, which are obvious even in silhouette. Below these are the equivalent views from the front.The juvenile (c), above the adult (d), tends to hold the wings flatter, but may vary somewhat, especially when alone, raising the wings in a shallow V but always looking more rakish. Centre and top left, juvenile (e) above adult (f) in the gliding posture.The juvenile looks slimmer and more rakish as in the small image below right (g).Top centre, head-on view of a gliding bird (h), although often wings are raised a little. Below left, an adult (i) in the rarer passive, flat-winged, circle/sail attitude.The other small image, upper left (j), shows the usual going-away glide. See text for further explanations.

circles. When slope-soaring, birds may ‘hang’ on relaxed, flight postures. Flapping is less rigid, an updraft or hover.) slower and with a rather paddle-like effect. In flapping flight, adults beat their wings When soaring or gliding, a juvenile intruder rapidly on stiff wings. This may be interspersed holds its wings less stiffly and in a slightly more with circle-soaring, slope-soaring or sailing, raked posture compared with an adult. Second- when the wings will be held in a slight dihedral year or older intruders also adopt passive (raised from the body to the tips and forming a postures, but because of their more adult-like shallow ‘V’). In a close territorial encounter, the proportions (see Appendix 1) these are less wings are held more stiffly, although the obvious. difference can be quite subtle and varies with the If an intruder is not threatened by adults, strength of uplift and, particularly, between these postures are often not so obvious, individuals. These are assertive postures. especially for distant birds, when it is difficult to However, when an adult is moving casually be sure of the status of some individuals. In through the territory at low level, flapping flight general, though, when young birds are involved may be more relaxed; in particular, the wings are in a territorial encounter, their relaxed, passive held in a flatter, more relaxed, slightly raked wing action is different from the adults’ posture (wings slightly tucked in towards the assertive, stiff-winged, rapid-flapping flight. So, body with the hand pointing slightly back; see in such an encounter, the intruding bird would fig. 1) when gliding but also, occasionally, when seem to be signalling the passive nature of its soaring and sailing (see also Combridge 2000). presence, while the adult is making it equally Intruding birds almost always adopt passive, clear to the intruder that it should move on.

250 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard

Should this basic signalling fail to have effect, the adult has a choice of other behaviours to draw upon to reinforce its message. Pairs mostly restrict their territorial activity to the confines of their own terri- tory, but temporarily they Robin Prytherch may become wind-drifted Fig. 2. Assertive bow. Moving into a horizontal posture, the adult lowers its over the adjacent part of head, sleeking the head feathers, with the base of the upper neck raised (right), their neighbours’ territory. sometimes with the secondaries flared slightly. Invariably, the bird calls (left), There are exceptions, which looking up at the intruder that has stimulated the display.The posture is I will describe below. In usually held for a few seconds, rarely longer, before the bird relaxes or flies off. reality, the observer will often recognise territo- In the accounts that follow, ‘adult’ will refer rial activity part way through an encounter, or to a territory-holder, ‘intruder’ to any other lose track of the action before it is over. It is Buzzard not holding a breeding territory. The only through regular watching over long latter comprise mostly juveniles but also 2Ys and periods that it is possible to stitch together the a few older birds in adult plumage. In this paper various elements of the behaviour. I introduce a new terminology for some of the behaviours so, where necessary and for the sake Territorial behaviours of clarity, I will also give the terms used in BWP Behaviours are described below in an idealised in parentheses. order from the moment that a perched adult first spots an intruder, through a chase sequence Conspicuous perching and assertive bow to evict it, then the basic displays as the adult (perch-and-call display, high perching) returns to a perch. This is followed by Buzzards spend the majority of their time descriptions of variations and other displays perched, in trees and bushes, on fences, poles, that might occur as more intruders arrive and etc., as well as on the ground. Here they ‘rest’ and complicate the situation. Finally, I describe some carry out routine behaviour such as preening, other perched postures, the behaviour of as well as using the perch to hunt from. juveniles and, briefly, expand on the exceptions Throughout the year, but most obviously in referred to above. winter and spring, when foliage is absent, adults Although territories are defended through- will perch conspicuously. This will often be high out the year, there is a distinct peak of activity in up, typically in a tree (preferably on a dead spring, from mid March to mid April, and a bough) or on a pylon. Such a position will give trough in summer, when birds can be very the bird a good view over its territory. To the inconspicuous. Territorial behaviour increases casual observer the bird may appear to be quite again in the autumn as the juveniles disperse, relaxed, but this is deceptive; an adult Buzzard is but during the depths of winter the birds spend always alert. most of their time hunting and feeding, and From such a location, an intruder entering intruders are chased out promptly (or almost the territory is readily spotted. If this should ignored if they pass over quickly). Some displays happen, the adult will call ‘ca-au’ (the familiar may be used, especially display stoops (see and widely known call, sometimes written as below). From February onwards, displaying ‘pei-eu’ or other variants) and may adopt the birds are seen more frequently. These timings assertive bow (fig. 2). This serves as a warning to are only approximate and are weather- the intruder: ‘get out or further action will dependent. Fine days with a mixture of follow’. The intensity of this behaviour varies sunshine, cloud cover and moderate winds seem greatly, but usually the bird adopts an almost to be best for observing display. In winter, horizontal stance with the head lowered and activity can be seen at almost any time of the day head feathers sleeked. This produces a slightly and occasionally in poor weather. Otherwise, hump-like effect at the base of the neck/top of most activity takes place between mid morning the back. At its least intense just the head is and mid afternoon. lowered slightly, whereas at the other extreme,

British Birds 102 • May 2009 • 247–273 251 The social behaviour of the Common Buzzard Robin Prytherch Fig. 4. Adult below/left, escorting a juvenile intruder out of its territory. Note that the adult retains a broader-winged appearance in the glide posture. The adult will normally turn back as soon as it Robin Prytherch reaches the edge of its territory. Fig. 3. Adult (below) engages juvenile in circling flight, the latter holding its wings passively in a flattish, usually be wind-drifted to the edge of the slightly raked posture.The adult is holding its wings territory (fig. 3). At this point, the adult will assertively, somewhat stiffly and raised in a shallow V. The adult starts much lower than the intruding bird. turn, usually to glide back down to perch as the intruder continues beyond the territory. with body level, the wings are drooped (see pp. Alternatively, at some point the intruder may 263–264 and figs. 16 & 17, perched postures). stop circling to glide, heading into the wind. The The posture may be held for a few seconds adult will then follow the intruder, usually before the bird relaxes or flies off, calling. If the somewhat lower, or alternatively the adult may intruder has turned and is heading out of the take the lead. During this glide the intruder will territory, or is high and moving fast across the usually adopt a slightly more raked wing posture territory, the adult relaxes. If the intruder than the adult, which adopts a fuller-winged remains in the territory and shows no sign of gliding posture (fig. 4). Again, once the intruder leaving, the adult will take flight, often calling. leaves the territory the adult will turn, On other occasions, an adult may remain sometimes to circle and then glide back down. perched while calling, sometimes with its mate At times, the birds will rise to over 1,370 m and perched nearby, also calling. One can regularly to over 900 m. On one occasion, I occasionally also hear a bird from a watched an adult male and intruder disappear neighbouring pair calling. The purpose of this momentarily into the cloud base before gliding calling is not entirely clear, unless to draw the out, whereupon the male, having reached the attention of an intruder to the resident. But it edge of his territory, dived down directly to his often becomes clear that an intruder is perched nesting wood, just 17 m above sea level. The within view (but unseen by a human observer), cloud base recorded on that day, 14th May 1997, as eventually one of the adults flies off into cover by the Bristol Weather Centre, was between to emerge quickly chasing an intruder. 1,295 m and 1,370 m. At this height, from When a feeding bird is approached by almost sea level, the birds appear tiny to the another, it will mantle the prey and the head is human eye (and still rather small through 10x sometimes sleeked and lowered, as in the binoculars). This suggests that the territory assertive bow. ‘ceiling’ is not a specific height above the ground, but is related to prevailing weather Engage and escort conditions. There is urgency in the initial, rapid flapping but This is the least aggressive form of territorial the adult (male or female, but usually the encounter, but is usually the prelude to any of former) soon circle-soars assertively, calling, the following behaviours. rising fast towards the intruder. As the adult approaches the intruder, the differences in flight Attack and chase posture are most obvious. As they circle up, the Almost invariably, an intruder may appear to intruder higher, circling passively, they will show some reluctance to leave a territory. In this

252 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard

Fig. 5. Attack and chase. An adult (top right) is attacking a juvenile intruder (top left) that, once the adult gets close, will dive down to avoid contact. The adult dives after the intruder as it continues the attack, but they split apart. Invariably, the adult chases the intruder and the action may be repeated several times before the latter is expelled from the territory. Adults will sometimes dive from a much higher position when they spot an intruder below, which will then take similar avoiding action. Robin Prytherch

wildly. Such a fall varies in length but the birds usually break apart after a few seconds and the chase continues. Exceptionally, birds that ‘lock talons’ may fall to the ground, where I have seen them remain locked, the adult on top of the intruder, until the latter manages to escape. It is on such occasions that birds may be damaged, or even killed. I know of at least one juvenile and an adult male that were almost certainly killed by another Buzzard, and a female that strained a leg when fighting with a juvenile. The juvenile escaped with a few broken feathers and the female’s leg appeared to have recovered within three days. It is interesting that males seem to attack some intruders with much more energy than others. Whether these are persistent intruders or dominant individuals is difficult to tell. Certainly, 2Y or older intruders are usually dealt case the adult may decide to press home an with aggressively and promptly. attack. To do so it will have to ascend to be level Frequently but not invariably, the male takes with, or above, the intruder. The adult usually the lead in an attack and chase, and the female circle-soars assertively, occasionally flapping up may remain perched. If she does take flight, she strongly. It can then fly powerfully at the may rise up, as mentioned above, or circle low intruder, causing it to flee – initially by flapping for a while before dropping down, with lowered and then, as the adult gets closer, by diving talons, to a perch where, on settling in a down, followed closely by the adult (fig. 5). They conspicuous position, she wing-waves (see then split apart quickly, swooping up again, below). Otherwise she lands rather heavily, when another dive might follow. Usually, briefly adopting the assertive bow. though, the adult will chase after the intruder, Once the intruder (or intruders, since there the latter occasionally weaving from side to side are often two or three, sometimes more) has left or down to avoid contact until it leaves the the territory, the adult (or pair) may circle or sail territory. During such an attack the adult will about before dropping down to perch. It is just often lower its talons. This is an aggressive signal as likely, however, that the adult will perform (as indicated below). At any time the adult’s several display stoops (see below) after any mate may circle up assertively, calling ‘ca-au’, encounter with an intruder. sometimes joining its mate in a two-pronged attack on the intruder. During close encounters Wing-waving the adult will usually lash out with its talons, the This display is given on a conspicuous perch (see intruder responding likewise. On very rare above), which might also be an old nest (of their occasions the adult and intruder may ‘lock own or that of a corvid), most often by a female talons’, whereupon they spiral down, flapping when her mate is involved in aerial activity with

British Birds 102 • May 2009 • 247–273 253 The social behaviour of the Common Buzzard

into a territory, before any aerial activity has taken place. This conspicuous behaviour serves to warn an intruder that it is in an occupied territory or to reinforce the message during an encounter between its mate and an intruder. (See also pp. 263–264 for other perched postures.) The ‘heavy landing’ mentioned above is distinct from the normal method of landing

Robin Prytherch where the bird approaches from below and Fig. 6. Wing-waving is given from a conspicuous sweeps up with wings fully spread to settle perch, usually by a female. The waving action is gently on its chosen perch. In a heavy landing, quite rapid, which, together with the calling, the bird approaches the perch at the same level makes the bird obvious to an intruder. or from slightly above, before settling. intruders. The perch will be approached from nearby cover or from above, if in flight. Talons Display stooping, display dive (roller-coaster are lowered during the approach and on settling, flight, sky dance display flight, undulating flight usually rather heavily, the head is lowered (as in and deep dive flight) the assertive bow), the wings remain partly open The stooping display is perhaps the one most and are flapped rapidly (but not raised high) for familiar to the casual Buzzard watcher and is the several seconds, the tail fanned (fig. 6). The bird most frequently performed of all the aerial will call loudly (‘ca-au’ or a more abrupt, displays. It is, however, highly variable, owing repeated,‘cau, cau, cau...’),cocking its head up to to different intensities of action and strength check on the action above, and then slowly of wind. It also occurs in two basic forms. The subside into a normal posture. The display is first serves mainly as the culmination to a terri- also rarely given on the arrival of an intruder torial encounter (above), affirming territory

a

b

c e

d Robin Prytherch Fig. 7. Display stooping. A schematic outline of several versions of this variable display. Having seen off an intruder, the adult glides over the territory (a) then suddenly closes its wings (sometimes after rising slightly) and dives down (b). It soon pulls up and after rising, at the point of stall (c), it continues into the second stoop of four it performs before gliding off to settle near its mate. Alternatively, after two stoops it changes direction, performs two more rather shallow stoops before dropping down to settle near its mate. Otherwise it may circle up (d) then sail off over the territory, or display dive down to settle close to its mate (e).The number and intensity of the stoops can vary greatly even within a series. See also figs. 8 and 9.

254 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard occupation, which is dealt with here; the other, may glide or circle over the territory, then at aggressive form is dealt with later. some point, usually when heading into the wind, The action is distinctive and conspicuous, the display stoops may start (fig. 8): the bird will occurring from c. 1,300 m down to treetop level either (a) suddenly close its wings and dive; or (fig. 7). Having expelled the intruder, the adult (b) rise up slightly, tail usually closed, then

b

a

e

d f

c Robin Prytherch Fig. 8. One display stoop to reveal the detail.The full explanation is given in the text.The degree of closure of the wings at (a) is highly variable (both within and between series) and some display stoops will be so shallow that the wings will not close more than shown at (c).The display dive posture is shown in (f).

d

c

g Robin Prytherch Fig. 9. The aggressive form of the display stoop varies from the normal form in two ways. (The bird at (c) matches that in fig. 8c.) Firstly, at (d), the bird flaps its wings wildly a couple of times and calls, with talons lowered.Then, at the end of the stoop, as it levels out, it lowers its talons and may continue calling as it sails off (g).The bird at bottom right is a front view of the same action as at bottom left.

British Birds 102 • May 2009 • 247–273 255 The social behaviour of the Common Buzzard suddenly close its wings and dive down. The display stoops will rarely all be of the same closed wings are usually held slightly out at the intensity, starting at low intensity and carpal joint, often with the alula feathers developing into higher intensity or vice versa. protruding. The tail is often fanned initially, but Each series is usually distinct but may be broken soon closes. During the dive the bird gathers by a long glide between two stoops within the speed, the angle of descent being very variable series. Many series end at low level with the bird (see below). After only one or a few seconds, the disappearing into the canopy. Occasionally, the wings open (c) as the bird then swings through final stoop converts into a display dive (see the base of the stoop and rises up. In the final below), which may take the displaying bird part of the rise, the wings will be fully extended, 100 m or more down into woodland or to a tail closed, and may end with the bird travelling conspicuous perch (see above). Otherwise the near vertically upwards. When almost stalled displaying bird will simply revert to gliding, (d), the bird will close its wings again as it peaks sailing or circling. Generally, a series of display and continues into the second display stoop.The stoops will cause the displaying bird to descend bird may perform just one stoop, although a gradually, but over a slope with a strong updraft series is more typical. A series of 3–5 is common the displaying bird may rise as much as it but this can be extended up to 12 and rarely to descends during the dive, and thus maintain over 20. The display usually ends after point (c), height. If both members of a pair continue to at the base of the stoop, as the bird levels off to circle or sail after a territorial encounter, they glide or circle, or to drop down to a perch if it may both display stoop down together, either has ended near ground level. The displaying bird one taking the lead with the other following. will often call, usually just before or at point (d). The displaying bird demonstrates a thrilling During such high-level displays, it is often combination of grace and tremendous élan. It difficult to be sure when the calls are made, if gives the impression of great fitness, and this indeed they can be heard at all. message is presumably transmitted to its mate At the display’s least intensive, the angle of and to any other Buzzards in the vicinity. It must dive and rise and the extent of closure of the be remembered that this display occurs after any wings are considerably less, so that the bird intruding birds have left the territory, even appears to undulate gently. Such mild displays though it/they may still be visible. are usually composed of only two or three linked Display stoops which occur during a stoops. During more intensive displays, the dive territorial encounter take a different, aggressive and rise can be marked, as the bird performs a form (fig. 9). This is much as above except that deep ‘U’, wings well open at the base but closing at point (d), at the top of the rise, the bird makes just before the peak, the bird twisting over to a couple of exaggerated flaps with talons dive, more or less at the stall point (d). lowered before dropping into the next stoop. Occasionally the bird changes direction here, The displaying bird, however, rarely performs rather than continue down in the same more than two or three stoops in a series. direction. To achieve this, the bird may briefly During the flaps the wings are raised high, throw out one wing in order to turn to the new exposing the undersides. This is probably a brief course. Display stooping is initiated into the wind form of display flapping (see below). As and the bird can use the wind to subtly change mentioned, aggressive display stooping occurs the direction of each stoop so that it ends up only in the presence of intruding birds displaying downwind. Between the mild and (commonly when there are several) and the more intensive forms there is much variation, displayer (or pair) usually seems to be highly with stoops deepening and wings more closed excited, giving repeated ‘ca-au’ calls. At the end with increasing intensity of the display. of the display, the bird may also level out from The most intensive form of display stooping the dive with lowered talons (g), sometimes even differs from the others towards the end of the dropping down to a perch to wing-wave (see rise, after a deep dive. Instead of closing the above). Talon lowering is a vital action, which wings just before or at the stall, the bird keeps distinguishes aggressive forms of several them closed as it rises vertically, carried by the behaviours. momentum created during the dive (e). Only A display dive (fig. 8f) commences just like a when close to stalling does it peak to continue display stoop but then the dive, with almost into another stoop. Even within a series, the closed wings, alulas protruding, continues down

256 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard Robin Prytherch Fig. 10. Display flapping is performed at the start of, or during, a territorial encounter.This shows the wings at the highest and lowest points of the flap in its most intense form. At lower intensity the wings are raised less. The display is often accompanied by calls. at high speed in a straight line to a perch. action may be less intense, at times appearing Although usually performed as the final dive of almost lackadaisical. a series of display stoops, it also occurs on its Display flapping is occasionally combined own, after a bird has been up high for some with other behaviours, particularly the display time, and for no apparent reason, but also bank (see below), which causes a rapid change of during a territorial encounter. If a female is up, direction. I have occasionally seen a female but below her mate, who is engaged with one or display flapping, but only at low level and more intruders, she might suddenly display dive usually at low intensity. During its first year in a down and leave her mate to deal with the territory, the male will sometimes display flap trouble. frequently when his mate is nearby. This behaviour is demonstrated when I enter Display flapping (deep wing-beat flight, some territories to inspect nests. Birds will slow-flapping display-flight) watch me, display flap and then (very rarely) This behaviour is performed at the start of, or dive at me, with much calling (a sure sign, at the during a territorial encounter. Used almost appropriate time, that the nest has chicks). exclusively by the male, this distinctive flight can occur at treetop height or high in the sky. The Display bank, and sailing and banking display bird will suddenly interrupt circling or gliding Although Buzzards will sometimes tilt over with a series of 4–7 very pronounced wingbeats, when circle-soaring in a strong wind, this is with the wings raised higher than normal never as marked as in a display bank. In this between each powerful, downward flap. The action, the Buzzard turns sharply with wings bird is propelled rapidly, often making excited held stiffly, the bird tilted over so that the wings ‘ca-au’ calls; the tail is usually closed (fig. 10). are held almost vertically and usually flattened Display flapping will often be performed soon (fig. 11). The tail is usually closed. Furthermore, after an intruder is spotted over, or approaching, this action is not associated with normal the territory. The male (or female) will call as it circling. It is used mainly in conjunction with leaves its perch, soon display flapping one or other displays, especially display flapping several times before circling up assertively. He (above). A bird will also sometimes display bank may then perform display flaps again at a higher at the ‘top’ of a display stoop in order to change level, particularly if his mate suddenly appears direction. Rarely, birds display bank at the end of in flight below. Alternatively, the male may each of a series of shallow downward dives, already be high in the sky ‘waiting’,as he watches which is part of the sailing and banking display. other distant pairs engaged in territorial activity. This display usually includes frequent display Then, invariably when an intruder makes an flaps. The impression given is of a more dashing approach, he will suddenly display flap several version of display stooping, but when the bird times. banks the wings are swept up a little, rather than This display serves to draw the attention of held stiffly. This is an extraordinarily graceful approaching intruders to the presence of adults and swift flying display, which also seems to in a territory. The male usually gives the reflect anxiety but to a higher degree. It is impression of being highly excited, but the interesting that this display is associated with action is very variable. Sometimes the flight males when they are new in a territory and must seems rather wavering and the actual flapping therefore feel the pressure from both adjacent

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approach the adult, which will adopt the assertive flight posture again; this might develop into the aggressive form of this display, which simply involves the addition of talon lowering (figs. 12 & 13a). The adult may then suddenly flick over to attack the intruder with its talons, which remain lowered for several seconds (fig. 13b), but then a chase might follow. On such occasions, the intruder does sometimes seem

Robin Prytherch to be ‘attracted’ to the Fig. 11. The display bank display is always used in conjunction with display flapping adult and gives the and more rarely with display stooping. Note that the wings are often held flat (but strong impression of sometimes swept up by the force of the turn) with the tail closed. It is not a part of normal circling. making a mock attack, despite the obvious established pairs and intruders. I also have the threatening signals. Both sexes will adopt this impression that some young males have not posture, sometimes as a pair. quite resolved the distinctive nature of the various parts of the separate displays (i.e. display Dive-on, turn-over display flapping, banking and stooping) and they get This behaviour involves the pair and occurs in them mixed up in their excitement. two forms: passive and aggressive. Typically, after a territorial encounter and as the pair sail Assertive flight posture overhead, the male positions himself above and Following a territorial encounter, an adult may behind his mate. He then dives fast towards her circle and sail about high in the sky, often and on arrival over her drops his talons as she because it can see some action in an adjacent turns over and raises hers. The talons rarely, if territory. Then if an intruder approaches, the ever, touch. The female immediately rights adult will sometimes call and adopt the assertive herself and both retract their talons to sail or flight posture (if it does not display flap) as soon glide on as before (fig. 14). The action may be as the intruder enters the territory (fig. 12). This repeated once or twice soon after. The female action is subtle and quite brief. The wings are will occasionally roll over (through 360°) during held stiffly and usually flat (though sometimes this display. This is the passive form of the raised slightly), with all feathers fanned to give display and may serve to maintain the pair bond maximum spread; the tail may be fanned or (see below). The pair will, however, perform a closed. The head is lowered slightly with the modified aggressive form of this display during feathers sleeked and a small hump appears a territorial encounter when several birds are between the neck and the back. This is, involved (i.e. at a territory boundary when both therefore, an aerial version of the assertive bow adjacent pairs and several intruders are and seems to have the same function of a together). During the melee of dive-chasing, warning. The posture is held for just a few circling and so on, the male may dive on his mate seconds before the adult relaxes to circle or sail as in the passive form but after the turn over the assertively. The intruder may then fly on, out of talons remain lowered. The lowered talons the territory, and the episode is quickly over. indicate the aggressive intent and at the same Occasionally, however, the intruder may time signal that they are a pair. This display can

258 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard Robin Prytherch Fig. 12. Assertive flight posture as seen from below (right) with, above it, the view from the side to show the lowered and sleeked head. All the flight feathers are spread to the maximum extent, usually with the wings flattened, although sometimes the tail remains closed. The aggressive form of the display is shown below left; the lowered talons are stimulated by the closeness of the intruder (above left). See also fig. 13.

ǩ

ǩ

Ǩ Ǩ a b Robin Prytherch Fig. 13. The aggressive form of the assertive flight posture is indicated by the lowered talons, as in (a), where an intruding juvenile dives slightly hesitantly down to an adult male, with its mate circling below and beyond, which also lowers its talons. This is followed (b) by the male flipping over to attack the intruder, which flees instantly.This is often followed by a chase.The roles of the sexes may be reversed. These actions could be mistaken for the dive-on, turn-over display of a pair (see fig. 14). be difficult to pick out among the dive-chases In late summer and autumn, when a juvenile that are also occurring during a mass encounter, is flying over the natal territory, it may approach especially as (rarely) the male from one territory a parent in flight and ‘mob’ it. The parent (male may dive at the female from another. The point or female) may then quickly flick over in an to note is that an intruder flees when attacked effort to fend off their pestering offspring. The (even if, momentarily, it turns and flicks up its juvenile will usually give its distinctive call talons), but a territorial female does not. Such during this action, but nevertheless it can be situations involving several birds can be very mistaken for the full dive-on, turn-over display confusing, even to the practised eye. of the pair if the observer is not familiar with the

British Birds 102 • May 2009 • 247–273 259 The social behaviour of the Common Buzzard

ǩ ǩ Ǩ a

Ǩ b

ǩ

ǩ

Ǩ Ǩ

c d Robin Prytherch Fig. 14. The dive-on, turn-over display is performed by a pair, often after a territorial encounter.The male dives towards the female from behind (a), usually at a fairly shallow angle. As he arrives over her (b), he lowers his talons as she turns over and raises hers, but usually avoiding contact.The male sails on (c), perhaps turning back to repeat the procedure once or twice more. An aggressive form is used when intruders are still in the territory. In this case the talons remain lowered (d). Sometimes, as here, the male has combined the action with the assertive flight posture as revealed by his lowered and sleeked head.

b

c

ǩ a d

f e

Ǩ Robin Prytherch Fig. 15. An example of how various displays can be combined. In this case, the pair is gliding down after a territorial encounter with two intruders (which have just left the territory). The male suddenly display banked (a) and display flapped (b), then performed one display stoop (c) before display diving (d) down to the female and they performed the dive-on, turn-over display (e). Note that the talons are tucked away since the intruders are no longer present. The pair continued on to settle in one of their nest woods (f).

260 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard status of the birds involved. stage, although usually less) and returns to his The dive-on, turn-over display will rarely territory. I once saw a neighbouring male ‘escort’ culminate a series of other displays after a period the intruding male back to his territory. They of territorial activity (fig. 15). flew close together, with the occasional mild jostle but no obvious aggression. On arriving Copulation back at the territory, the male will often display From early March (rarely earlier), Buzzard pairs stoop several times (occasionally calling) as he copulate frequently and continue to do so until drops down to perch. after the egg-laying period (all the pairs in my Such behaviour is clearly rare, but that it study area, with few exceptions, appear to happens at all is interesting, and appears to be a produce eggs each year). This behaviour peaks form of reciprocal altruism. There is normally in early April, when the pair may perform more little or no territorial interaction between than two copulations per hour. The action is adjacent pairs, and they clearly ‘know’ their conspicuous and can occur anywhere in the neighbours and other pairs beyond. It is possible territory – high in a tree, on an electricity pylon, that neighbours of a male involved in an extra- on the ground, etc. Even within the woodland territorial chase will recognise what is canopy, the flashing of the white under- happening. Furthermore, since most dispersing primaries of the male as he balances on the juveniles settle close to their natal territories female show through the branches and twigs, (occasionally adjacent) (Davis & Davis 1992), especially on a sunny day. Many copulations they could be closely related. ‘Helping’ occur when intruders are present, or neighbours on rare occasions may not, immediately after they are expelled from the therefore, be a disadvantage, as long as the territory. Typically, when territorial action is neighbours reciprocate. high in the sky and the female has dropped Although even more unusual, a pair may down to a perch, the male will suddenly close his make an extra-territorial flight. They may circle wings and dive or glide down to her, even up, drift out of their territory, then glide on away though the intruder(s) may not have left the from it, passing over several other territories to territory. He usually arrives with talons slightly eventually circle again, rising very high before lowered, directly onto the female’s back (she slowly gliding/sailing back. On their return they may or may not have solicited by lowering her may display stoop/dive down in several stoops to head). The male makes a rather quiet call, ‘eez- perch. During the ‘outing’, other territory ka’,during copulation, which is rarely audible to occupiers seem to ignore them and if an adult human observers. He then flies off from his does circle up to them there is no obvious mate’s back to circle or sail up again, or perch territorial response. It is impossible to hear either next to her or nearby. On other occasions, whether the pairs call at each other, but I think when the intruder is much lower, the male will that it is likely. break off the chase, drop down to the female, copulate, then fly off, with loud calling, after the Single-bird and three-bird territories intruder to continue the chase. I suggest that the In my study population there have occasionally birds are using the conspicuous behaviour of been single birds holding a small territory. The copulation for a secondary purpose, to signal birds are usually in their second or third year, clearly to an intruder that here is a pair on rarely fully adult. When defending their territory. territories they restrict their behaviour mainly to assertive bows, engage and escort and wing- Extra-territorial chases and flights waving, accompanied by calls. The actions are all Generally, a pair confines its territorial activities rather low-key. A crippled female, which within the territory. There are occasional defended a territory for over five years until her exceptions when the male leaves his territory – death, never attracted a mate. She also display- usually when engaged in a prolonged, high-level stooped and was generally more conspicuous. chase that extends across adjacent territories. Three-bird territories are created when a The other pairs below call excitedly, sometimes juvenile stays with its parents for over a year. flapping around at low level, but do not usually Even a young juvenile will occasionally help to get involved further. Eventually, the chasing chase out an intruder, but not usually on its male gives up (he may be up to 2 km away at this own. As it gets older it tends to keep a low

British Birds 102 • May 2009 • 247–273 261 The social behaviour of the Common Buzzard profile, but will occasionally join its parents in will often fly to perch next to its mate, causing some territorial behaviour. Very rarely, a young the other to fly to another perch (each time the female will stay on into adulthood, remaining birds will briefly adopt the assertive bow on with her parents. I have recorded only one case settling). This may happen several times and of polygyny in my study (which involved one indicates a low level of residual anxiety. male defending two territories, with two females Established pairs often perch close together, fully – a mother and daughter – in one and a single relaxed. female in the other). Relations within the family group Pair formation After the young have fledged, they usually spend Generally, a new (or replacement) pair of about six weeks with their parents before Buzzards appears on territory without obvious dispersing. At the end of this period, and for signs of pair formation. This might seem longer if one or more of the juveniles remain in surprising for a long-lived species which the territory, confusion is possible as the frequently has pair bonds that last up to 20 juveniles interact with their parents. The years. I have, however, seen pair formation in hunger/appeasement calling of juveniles can be single-bird territories. The incumbent has been so incessant that the adult will fly away to ‘hide’ a male, obviously highly excited/anxious by the from its noisy offspring, but is otherwise quite arrival of an adult female. He demonstrates by quiet and not always easily heard. The adults calling as he display flaps wildly near the female, normally do not fly at a juvenile to flush it away, then settles to watch her. It could be that he is although I have rarely seen this. Typically, somewhat nervous, and torn between chasing though, the juvenile will fly at its parent, which her off and accepting her. The female appears it displaces. This might be repeated if the adult totally unconcerned, or may fly to the male and does not move far. This action is identical to that displace him from his perch – females usually used by new pairs, when the female might dominate males. Then the male may fly fast repeatedly displace the male, and to that by towards the female and attempt to displace her; young birds feeding in a large group when they rather than be displaced she merely flicks her occasionally displace each other (see below). wings or ignores him. Alternatively, the male From time to time (especially in winter and may veer away just as he arrives at the female, or spring), the pair will often perch very close to brake to a hover before gliding away. In some each other, occasionally almost touching, but cases, the male may fly so hard at the female that regularly about 30 cm apart. The second to she is forced to jump up to present her talons arrive usually briefly adopts the assertive bow as (collapsing back onto the branches). The male it lands close to its mate; this is more common in usually makes two or three of these flights in new pairs, and probably reflects a mildly fairly quick succession. One single male made aggressive (or even nervous) reaction. I have rather timid approaches to a new female, who seen an old female settle thus next to her left within a week. Then another female arrived daughter (by now a full adult, sharing the same and he immediately behaved more aggressively mate) but, while in the assertive bow, she towards her; she stayed. It appears that the instantly turned her head through 90° for a female is judging the aggressiveness of the male, couple of seconds before relaxing. My impression which may relate to the male’s ability as a was that this had a ‘switching-off’ effect, hunter; that will be confirmed during the mate- cancelling any unintended aggressive message. feeding behaviour prior to breeding (see below). When apart, the pair will occasionally call quietly The similarity of this action to the dive-on, to each other – ‘cau, cau...’ – and at times this turn-over display by established pairs is obvious, seems to be a contact call associated with food. and (the latter) probably serves to reinforce the Females will call like this from the nest. original pair bond. The display flapping indicates confusion on the male’s part between mate Mate feeding attraction and intruder expulsion. This During the month or so before eggs are laid, behaviour is also difficult for humans to male Buzzards start to provide food for their interpret, especially when there is no knowledge mate (Hinde 1985). The term ‘courtship of the status of the birds involved. Furthermore, feeding’, which often refers to this behaviour, is once the pair seems to have settled, one partner misleading for Buzzards as the behaviour

262 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard

a b c d

e f Robin Prytherch Fig. 16. Various perched postures. These show relaxed adults (a) and (d), the former in cold weather, with most of the legs and feet hidden in the plumage. In (b), the adult has become more alert. The other alert adult (c) has spotted possible prey (or an intruder), which it is straining to see beyond a nearby obstruction. The juvenile at (e) is sleeked in a leaning posture owing to a strong wind, and the one at (f) is sleeked on the approach of a territorial adult.

a

b c Robin Prytherch Fig. 17. Perched postures during aggressive interactions with intruders. In (a), an adult runs in the assertive bow at a large juvenile female, which flapped off to avoid physical contact. More extreme versions of the assertive bow are also shown, with the secondaries flared (b), and the secondaries flared even more (c), causing the primaries to lower, and the head is lowered further, rarely almost to the ground. continues throughout incubation and the early a strong breeze (fig. 16e). Otherwise, when part of chick-rearing. Thereafter, the behaviour relaxed, they sit in a squat, hunched posture changes slightly and the male often takes the (figs. 16a,d) with (in cold weather) the body food directly to the nest, although he does not feathers fluffed out, covering the legs and most usually feed the chicks. of the feet (fig. 16a). If a bird becomes aware of a hidden disturbance nearby, its first reaction is Perched postures to ‘stand up’, sleeking the plumage (fig. 16b), Two perched postures, the assertive bow and looking intently towards the noise. If nothing wing-waving, have already been mentioned, but transpires, the bird quickly relaxes. It may have Buzzards assume a variety of postures when spotted possible prey, in which case it may perched (fig. 16). If the birds are hunting in the stretch up as high as possible (fig. 16c), rather open, their plumage is more or less sleeked and than move. If an intruder suddenly appears, the the body vertical, or tilted forward if facing into adult will instantly call and adopt the assertive

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bow (fig. 2), and then fly towards the intruder, as young birds dispersed in all directions at dusk described earlier. Similarly, an intruder perched and did not seem to be involved in a communal in a territory will sleek its plumage as soon as it roost. It appears that these young birds are sees the approaching adult, before flying off (fig. already showing signs of being solitary, which 16f). typifies the adults’ behaviour (see also Glutz von Groups of juveniles with some 2Y or older Blotzheim et al. 1971). birds will gather on bare, tilled land in ‘no-man’s- land’ between territories to feed, particularly on Behaviour of independent juveniles earthworms Lumbricus (see also below). The Having left their natal territory in their first adjacent adults will also be feeding in such areas autumn, juveniles seldom settle in defended and checking any straying intruders. An adult territories, but wander over a larger area. They will fly at such an intruder to displace it; if the may stay in an area where there is an abundant latter does not move well away, the adult may run food supply, congregating with other juveniles. (fig. 17a) or sidle up to it adopting the assertive Here, they will feed in close proximity (within bow in an extreme form. In this case, the adult 20 m) without interacting. The most frequent turns side-on to the intruder and flares its interaction is when one flies low to displace secondaries (fig. 17b). The amount of flaring is another from its feeding place. The latter may variable and has the effect of ‘pushing’ the not submit but turn to engage the new arrival by primaries down so that they touch the ground jumping up and resettling, then rushing at the (fig. 17c; ‘wing-drag walk’ in BWP), with the other, whereupon they lock talons or stand close head lowered even further. Usually, only the wing together and adopt angel postures (Weir & facing the intruder is flared, although both wings Picozzi 1975), one ‘fully spread’ (pseudo- may be flared at times. This has the effect of dominant), the other either ‘half’ or ‘fallen’ making the adult look larger and more (submissive) (fig. 18). Head feathers are intimidating. As a final resort, the adult might sometimes raised and, although I have never lunge at the intruder. When the pressure of a been sure of seeing the crest raised purposefully large number of feeding intruders is too great, (Weir & Picozzi 1975), I have seen the same the pair has to give way to them (I have seen up effect caused by wind blowing the feathers up. to 60 spread over c. 10 ha), although feeding These scuffles usually break up quickly. I have pairs usually keep a clear area around them. In only ever seen juveniles perform these angel such cases, an abundant food supply and postures, never an adult. On one occasion, when pressure from other Buzzards has forced the a juvenile walked within a few metres of a 2Y on territory holders to relax their defensive a fence post, the latter dropped onto the behaviour. Interestingly, the large gatherings of juvenile, which flattened into a fallen angel (fig.

a

b

c Robin Prytherch Fig. 18. The angel postures used by juveniles. Initially (a), having rushed together, wings are opened and the birds may jump up, or one attacks the other, they lock talons and one falls into the fallen angel (b). A 2Y attacks a juvenile, which immediately adopted the fallen angel posture, with the 2Y looking on (c). These episodes are normally fairly brief.

264 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard

18c). Another juvenile, attacked by an adult several minutes to around half an hour. If the female on the edge of a territory, refused to group strays too far into a territory, one of the move off. The female approached again, in an adults (usually the male) will approach, often assertive bow; the juvenile adopted a half angel adopting an assertive flight posture, and even and stepped backwards, whereupon the female dive at or chase the nearest bird, but I have never walked away. The angel postures apparently seen an adult fully engage in play. Eventually, the serve to appease an attacker and are submissive juveniles circle up, glide or sail off in ones or – but with a hierarchy from least submissive twos in various directions and the episode is (full) to total submission (fallen). over. When hunting on the ground, a juvenile will occasionally rush at something (e.g. a clod Play of earth, a piece of vegetation), pounce on it and Juveniles often gather in small groups (up to then jump up, drop it, jump up again, tossing about seven) in flight, often above a hilly bluff the object about and clearly playing with it. After forming a boundary between two territories, a few seconds, the bird will return to hunting and engage in apparent play activities (fig. 19). proper. They circle, dive on others, chase, settle and displace (actions sometimes reciprocated), often Exceptions weaving through the treetops at great speed. Interactions between pairs They will also fly at and grab a cone or small As emphasised above, during social behaviour twig (items that may be mistaken for prey by it is intruding non-breeders that stimulate observers), which is carried aloft and dropped, territorial adults to rise up and evict them. Many followed by a zigzagging chase to recapture it, new pairs that take up a territory adjacent to one unless another bird intercepts it. These activities or more established pairs experience no conflict appear to be ‘without purpose’ and to represent with the older birds. On some occasions, the classic play behaviour exhibited by the young however, the male from the older territory will of many birds and mammals (Immelman 1985); fly over the new territory and engage with one of this appears not to have been recorded in the the new birds, even diving at it. Both will circle Buzzard before. Such episodes may last from assertively and/or adopt the assertive flight

b a

c

d Robin Prytherch Fig. 19. Play behaviour of juveniles. This involves much chasing, including when one has a play object (a). Birds will dive at branch tips to detach items such as cones (b), which may be dropped and dived after (c). On the ground any small, loose object may be dashed at, dislodged or thrown up (d). Up to seven birds were involved in the flight episodes observed in this study, which mostly happened at treetop level and sometimes lasted over half an hour.

British Birds 102 • May 2009 • 247–273 265 The social behaviour of the Common Buzzard posture. Normally this activity will diminish passes over quickly, otherwise (usually) it takes quickly and within a few weeks the pairs more or flight with rapid, stiff-winged beats, sometimes less ignore each other. display flapping. The adult, usually the male, Aggressive interactions between well- then circles assertively up to the intruder, which established pairs occur only rarely. On one circles above in a more relaxed passive posture. If occasion, I watched a female sail into her the intruder is persistent, the adult may chase it neighbours’ territory where she was attacked by and dive at it aggressively before circling the male, after which she was soon back over her resumes. Once the intruder glides off, the adult own territory. The neighbours had young chicks will follow it, somewhat below and behind, until still branching (when the chicks wander from the former leaves the territory. The adult will the nest but before they are capable of flight) then turn back, dropping down to a perch in a and this may have caused the unusually steep glide, or it may display stoop a few times. aggressive reaction. Alternatively, the adult may stay aloft, sailing about or circling. If another intruder Persistent adult intruders approaches, the adult may display flap and call A similar activity might involve an adult ‘ca-au’. If the intruder enters the territory, the intruder that attacks and chases a resident adult adult might adopt the assertive flight posture, (i.e. male on male). This could result in the perhaps calling again. If the intruder approaches intruder killing the resident and thus effect a the adult, by sailing towards it, or by diving mate change. These ‘battles’ can last, down to it, the adult will briefly lower its talons intermittently, for two weeks or more before into the aggressive form of the assertive flight being resolved, but are rarely observed, at least posture, even rolling to direct its talons towards in my study. the intruder. By now the adult’s mate (the female) may have appeared, circling up to the Adult-like behaviour of juveniles action, perhaps briefly display flapping and Towards the end of their first year, some calling. It may also adopt the assertive flight juveniles may (rarely) show signs of adult-like posture, aggressively if necessary. One or both behaviour. I have seen one dive down members of the pair may then chase the aggressively, with talons lowered and toes intruder out of the territory. The pair might spread, among a small group of other youngsters then, after a period of circling, perform the dive- and an adult. It quickly assumed the expected on, turn-over display two or three times in passive glide and relaxed flapping as the adult moderately quick succession before circling sailed assertively towards it. On another again. occasion, a lone juvenile had been using the One or both adults might then display stoop corner of a grass field to feed in for a week or so. down to the trees, or they may glide to meet yet When another juvenile arrived, the first bird more intruders, perhaps at the territory adopted the assertive posture, with secondaries boundary where neighbours are engaged with flared. The first bird was simply showing its them. As they join in the circling melee, which dominance over the second, which soon flew off. could now involve eight or more birds, the Such events probably happen fairly frequently. pair(s) will engage in display flapping, and aggressive forms of assertive flight posture, Summary of territorial flight behaviours display stooping and dive on, turn overs, Having described in detail all the various seemingly throwing themselves about in the sky displays and postures, this summary is intended with abandon. The female might dive down, to help underline the relationships between with talons dangling, to settle conspicuously, them and make their purpose clearer. This will from where she calls and wing-waves. Once the be a hypothetical description since in reality birds have risen to well over 1,000 m, quite most actions may involve only some of the suddenly the sky empties as the intruders glide behaviours, and there is great variation in off fast and the adults drop down to the trees. individual behaviours both within and between This might be by one fast display dive or a series episodes. of display stoops, the pair doing so close to each Once a perched adult spots an intruder flying other, but rarely synchronised. over, it may call ‘ca-au’ as it adopts the assertive All these behaviours are concerned with bow. It may remain perched if the intruder territory defence (and advertisement): the birds

266 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard are signalling ‘get out’ and, once the intruders avoid overt aggression. Significant physical have gone, the display stooping and dive on, turn contact is unusual and will often occur only overs reinforce the pair bond. during an attack (involving talon-locking, culminating as a fight on the ground). The angel Discussion postures exhibited by juveniles are primarily In this section, I refer to previous key studies in concerned with determining hierarchy, although abbreviated form: BWP (Cramp & Simmons damage might occur. 1980), GvB et al. (Glutz von Blotzheim et al. Without this vital background knowledge, 1971), Tubbs (Tubbs 1974) and W&P (Weir & many behaviours can be easily misinterpreted; I Picozzi 1975). My study reveals new information certainly did so early in my study. This is about the social behaviour of Buzzards, some of demonstrated by the widespread misunder- which conflicts with previous work. In trying to standing of the most basic of observations, that explain these differences, it is worth considering when two Buzzards circle together it is the male several general points. I have put in far more that circles above (or ‘leads’) the female (quoted effort (see p. 247) than the other studies. Even by or suggested by all the above accounts). This though Tubbs’s main study lasted ten years, he may be so if it is the pair which is circling, but it had sparse information to work from, and the is more likely to be an intruding juvenile (male same applies to W&P, whose study lasted only or female) above an adult male. The impression three years. These and other accounts failed to of smallness is, of course, due to the slightly recognise that any resident population of smaller size and slimmer proportions of the Buzzards comprises two components (territorial young bird. This will be emphasised if the adult breeding adults and unpaired birds), as I have female is escorting a young intruder. described, which reveals not only separate basic There are many suggestions in the key flight postures for the two age classes, but that literature that behaviours are related to the social behaviour which determines territory ‘courtship’; this is misleading, in my view, marking is confined to the older (breeding especially where it concerns attracting a mate. adult) component. Similarly, the significance of This aspect of social behaviour in the Buzzard the distinction between ‘passive’ (or submissive) seems to be very perfunctory. Pairing appears to and ‘assertive’ (or aggressive) behaviours was take place very quickly and once a pair is settled not fully realised. Some of these facts have been in a territory the two birds are usually together implied by other studies (see BWP and GvB et for life. There may be some changes in the first al.) but not stated specifically. year, although these are rare and I have Behaviours including conspicuous perching witnessed only one ‘divorce’.Should one partner and assertive bow, engage and escort/chase, die, replacement can be rapid, often within a display flapping, and display stooping and dive week, but may take several months. But have been described in earlier accounts but not suddenly the new bird is there and behaving as if always clearly understood. I have chosen new it had been in the territory for years. names for some of the behaviours for the sake of The calling contests described by Tubbs as simplicity. Wing-waving is described clearly in between pairs are, in my view, always directed at BWP but not identified as a discrete behaviour. an intruder, even if it is not visible to the human Behaviours that have not been described before observer. One pair might start the calling and are assertive flight posture, display banking, alert the other pair to a ‘problem’, perhaps an banking and sailing display, and dive on, turn intruding bird (or even a human observer) on over, as well as the aggressive forms of display their common border or in a narrow strip of stooping, assertive flight posture and dive on, turn ‘no-man’s-land’. over. It is clear to me that the dive-on, turn-over The catalyst for all of the loud calling and display (not recorded by other observers) has subsequent territorial activity by adult birds is been mistaken for an adult chasing an intruder. an intruder. The progression of behaviours from Certainly it can be difficult to distinguish this the first sighting of an intruder through to its behaviour if it occurs in a large group high in departure from the territory has not previously the sky involved in all sorts of activities. been described (see summary above). Most of Similarly, mock dives by a juvenile on an adult this behaviour is effectively a highly that is in the assertive flight posture can be sophisticated form of signalling designed to construed as an adult diving on a juvenile (if one

British Birds 102 • May 2009 • 247–273 267 The social behaviour of the Common Buzzard is not familiar with the detail of the behaviour) When unchallenged by intruders, adult and may also account for W&P’s ‘wing- Buzzards will fly about their territory in a touching’, which I have otherwise never seen. relaxed mode, with the wings often slightly I have never seen adults use angel postures raked and sometimes held quite flat or, more when involved in antagonistic encounters. This usually, slightly raised at the tips; flaps will also has only ever involved juvenile and 2Y birds, and be rather relaxed. Most commonly though, the even the latter do not get fully involved. W&P,in adults are flying because an intruder has been using a captive bird, may well have observed spotted, in which case they switch to the actions that may be less likely in the wild. assertive modes of flight. Wings are held more Continental writers (see BWP, GvB et al.) may stiffly, the dihedral is more obvious, and flaps have seen interactions involving adults (i.e. are more rapid. In other words, this is an where migrants and residents mix in winter), exaggerated form of the normal flight. This but this is not clear. GvB et al. described a bird certainly makes them look bigger, with the flight making ‘pecking movements towards the feathers spread to maximum effect. These are ground’ and attributed it to ‘displacement- the most basic signals, together with calls, that activity’. I have never seen this but I suspect that adults use to indicate that they are in a territory. the action described may have been an extreme Intruders acknowledge the submissive nature of form of the assertive bow. their flight by maintaining relaxed postures, Tubbs discussed the likely vertical dimension which also helps to make them look smaller; of a Buzzard territory and estimated that the large birds dominate smaller ones. ceiling would be c. 160 m in the New Forest Intention to take flight is not always obvious, (Hampshire) and c. 250 m above the valley but birds will momentarily adopt a horizontal floors in south-central Wales. These estimates posture at take-off. Frequently, the most obvious are far too low and, as suggested above, the intention movement is to defecate. This ceiling height is probably determined by weather naturally puts the bird in a horizontal posture conditions. I have seen birds above 1,400 m, and, after a short delay, it flies (if it does not level with the cloud base, and they may well go relax). This appears to be the root of the assertive higher on fine, cloudless days. bow. The lowering of the head, with sleeked I have described a wide selection of head plumage, seems to be a modification to behaviours, which also vary in intensity with amplify the action. This latter action is also an extraordinary subtlety. Buzzards can be highly important part of the aerial form of the display, aggressive, a trait necessary for catching large the assertive flight posture. prey, but also useful in the defence of territories. Display flapping is almost identical to the However, attacking another Buzzard has to be a flapping flight used in a low-level hunting flight last resort and many of the displays and other towards prey. For the display, the flight is behaviours seem designed to avoid this while modified to give a slightly wavering effect and still deterring intruders. The appearance of an can be made more conspicuous with the intruding Buzzard stimulates most of the addition of display banks, which are modified behaviours described and, without such from a part of normal circling flight. The stimulus, pairs spend hours below canopy level banking action is steeper than in normal and dispense with rising high into the sky. In circling, the tail is closed and the turn is summer (with nests to attend to), and even in restricted to about 180°. winter, they can be very inconspicuous. Display stooping seems to be based on two separate actions that have been combined, Origins of the displays namely a hunting stoop and normal landing on Why has this species developed such a wide a raised perch. Hunting stoops are rarely as repertoire of social signals? The fact that impressive as the display version, which territorial adults will go to great lengths to evict emphasises (in the most intense forms) the intruders without resorting to physical contact closed wings (briefly held with the carpal area is clearly significant. The evolution of such pushed out, sometimes with alulas spread, and signalling is complex but it may be related to wing-tips over the tail) and speed of the stoop. If basic autonomic actions such as intention a hunting stoop is aborted near the ground, the movements, flight (hunting and casual) and bird sweeps up on spread wings and this is feeding movements (Krebs & Davies 1981). mimicked in the display stoop at the end of each

268 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard downward dive section. But this also mimics the open wings as it lurches at an interloper. It is upward sweep to a normal landing on a raised possible that this flapping action has been perch, all the more so since the bird often closes exaggerated to produce this very conspicuous its wings as it lands deftly, almost at the moment display. of stall. In the most intense form of the display The full angel posture adopted by fighting stoop, in the final rising section of the stoop, the juveniles is exactly the same as the posture at the bird closes its wings before reaching the stall moment of ‘capture’ of a prey item on the point and peaks before stooping again. In this ground, especially where the bird seems not to way, the Buzzard has neatly combined two be sure whether the item is in its talons, as it commonly used parts of routine behaviour to looks down intently. This seems to indicate a create one of its most impressive displays. conflict of aggression (needed to catch the prey) Display dives are also derived from the hunting with anxiety (or fear) of the possible retaliation stoop. of the prey (which must happen often). When The two parts of the dive-on, turn-over two fighting birds make contact (usually talon to display appear to have evolved from different talon), one soon relaxes slightly or even but related behaviours. The dive on by the male collapses on its back to indicate submission. seems to be a simple modification of the chasing This seems to be enough to ‘switch off’ the action of an adult on an intruder. The turn over dominant individual and the birds soon by the female is a barely altered action normally separate, the submissive bird fleeing. used by both sexes when they are mobbed by conspecifics, corvids or other raptors. In both Acknowledgments cases, however, the talons appear to be clenched, This paper is dedicated to my late friend Ken (K. E. L.) hiding the claws. The talon lowering that occurs Simmons, who showed me how much more fulfilling birdwatching can be by taking an interest in what birds do, briefly is a normal part of the separate actions that is, watching their behaviour. Without his example and (except that then the claws may be exposed) and interest, I would not be writing these words now. I have signals their aggressive origins. However, in this many other people to thank, simply for encouraging me and taking an interest in my studies. More specifically, I case, between members of a pair, the male is thank Mike Wilson for providing me with a translation of signalling his aggressiveness to the female and the relevant parts from Glutz von Blotzheim et al., and Ian she her dominance, as she does not flee. The Newton for his encouragement and for reading and mutual confidence signalled by this action could commenting on a draft of this paper that resulted in many improvements. also indicate compatibility in the pair. In the aggressive forms of display stooping References and diving, assertive flight posture and dive on, Combridge, P.2000. Common Buzzard soaring on flat turn over the talons are lowered; the birds are wings. Brit. Birds 93: 644. thus signalling with their lethal weapons! Cramp, S., & Simmons, K. E. L. (eds.) 1980. The Birds of the Western Palearctic. Vol. 2. OUP,Oxford. Although talons are also lowered briefly during Davis, P.E., & Davis, J. E. 1992. Dispersal and age of first aerial attacks by adults on intruders, in the breeding of Buzzards in Central Wales. Brit. Birds 85: aggressive displays the talon lowering is more 578–587. prolonged. All these actions must have their Glutz von Blotzheim, U. N., Bauer, K. M., & Bezzel, E. 1971. Handbuch der Vögel Mitteleuropas.Vol. 4. Akademische origins in a hunting strike, when the talons are Verlagsgesellschaft, Frankfurt am Main. usually lowered and thrust forward at the last Hinde, R. A. 1985.‘Courtship feeding.’ In: Campbell, B., & moment before the capture of prey. Lack, E. (eds.), A Dictionary of Birds. Poyser, Calton. Immelman, K. 1985.‘Development of behaviour.’ In: Wing-waving also has an aggressive element, Campbell, B., & Lack, E. (eds.), A Dictionary of Birds. revealed by the flying bird as it approaches a Poyser, Calton. perch with lowered talons and then lands heavily Krebs, J. R., & Davies, N. B. 1981. An Introduction to (without the usual sweep up from below), as if Behavioural Ecology. Blackwell, Oxford. Tubbs, C. R. 1974. The Buzzard. David & Charles, onto prey. The wing-waving which then follows Newton Abbot. is probably a modification of mantling – the Walls, S. S., & Kenward, R. E. 1998. Movements of radio- partly spread wing posture used when a feeding tagged Buzzards Buteo buteo in early life. Ibis 140: 561–568. bird is approached by another intent on stealing Weir, D., & Picozzi, N. 1975. Aspects of social behaviour in the prey. The mantling bird may flap its partly the Buzzard. Brit. Birds 68: 125–141.

Robin J. Prytherch, 23 Caledonia Place, Clifton, Bristol BS8 4DL

British Birds 102 • May 2009 • 247–273 269 The social behaviour of the Common Buzzard

Appendix 1. Key to identifying age classes of nominate Common Buzzard Buteo b. buteo

This deals with the features that are most underwing. On the inner primaries, the bar is helpful; these are not full descriptions. The narrower and not well demarcated – this is the darkest adults have a dark breast with, below the best section of the wing to concentrate on for a pale crescent (which may be almost absent on bird that is difficult to age. Overall, juveniles the darkest birds), heavily barred belly and flanks. look immaculate, although some flight feathers The barring can be fine or bold and often the may get broken as time passes. By the end of flanks – and even the belly – appear uniformly their first year, often during May, they will start dark at a distance. From these darkest birds their first moult, usually indicated by a missing there is a cline through almost limitless variation inner primary or outer secondary. Buzzards to the palest, which may have just a few streaks never undergo a complete moult (i.e. all the on the sides of the breast, but the belly and feathers replaced at one time), so after this point flanks will usually show some fine or faint all birds will show a plumage with feathers of barring. Intermediate individuals (the majority) mixed ages. will always show barring on the belly and flanks Second-year birds retain many juvenile but the breast may be blotchy, speckled, streaked feathers, which gradually become extremely or a mix of these. The eyes are dark. In flight, a bleached and faded. As new median and lesser broad, dark subterminal bar is visible along the coverts appear, they are strikingly darker and are trailing edge of the secondaries and inner often obvious on perched birds. Many of the primaries, clearly demarcated from the other, inner greater coverts are retained and these often much finer barring on the underside of the contrast markedly with replaced, outer feathers, flight feathers. This bar is also apparent on the which are longer and darker. All the inner upperwing of most individuals but is usually primaries are usually replaced and the new difficult to see in normal viewing. The tail is feathers have a broad, dark subterminal bar of similarly marked but the width of the adult type, distinctively different from that of a subterminal bar is more variable. juvenile. Because the feathers are longer, they Buzzards fledge with a distinctive juvenile/1Y also change the proportions of the wing-tip. The plumage, different from that which, after 2–3 retained outermost (‘fingered’) primaries are years, they will retain, through moults, for the short and worn; the effect is to make the wing- rest of their lives. The remiges are narrower and tip look broader and more square-ended. Some shorter than those of adults. This gives juveniles of the outer secondaries are renewed but most of a narrower-winged, relatively longer-tailed the inner ones are retained. This gives an uneven appearance than adults. Juvenile plumage is appearance to the trailing edge, with the inner paler than the corresponding adult plumage (of wing ‘pinched in’. The 2Y wing is therefore whichever morph), but nonetheless some distinctive, although not always completely individuals can be very dark. The eyes are pale obvious! Initially, the eyes of most 2Ys will show grey or pale yellow and can be difficult to see on some paleness but the vast majority have dark a distant bird, giving a rather plain-faced eyes by the next summer, when they are two appearance. The scapulars and wing-coverts are years old. tipped pale (whitish or buff); the greater-covert Virtually all third-year birds are inseparable tips usually show up as a pale bar and this may from adults. During the second moult, almost be a useful ageing feature on both perched and all the retained juvenile feathers will be renewed. flying birds (note that some adults show this The odd feather retained for a second year may feature, but on them it is less obvious). The be invisible, but occasionally the outermost underparts are streaked, rarely with some rather primaries and/or the outer tail feathers will be blotchy barring on the flanks and ‘trousers’ old, and obvious with an appropriate view of the (upper leg feathers). The dark subterminal bar bird. Exceptionally, an individual may retain a on the tail is usually the same width as the other few juvenile median wing-coverts and an odd bars, occasionally slightly wider. The equivalent greater covert, which stand out as very pale bar on the secondaries is more variable in width against the new, darker feathers. In all these but rarely well demarcated, so that the dark birds, though, the trailing edge of the wing will trailing edge fades into the rest of the be neat (barring any damaged feathers).

270 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard Robin Prytherch 134. This 2Y Common Buzzard Buteo buteo (photographed in the study area in November 2005) shows a bewildering mix of juvenile and new feathers following its first moult. The mix of older (shorter)

and newer (darker and longer) feathers is most Robin Prytherch obvious in the greater coverts and secondaries. 135. The age of this 2Y Common Buzzard Buteo There is a mix of old and new feathers on the body, buteo (photographed in the study area in October but especially on the median and lesser coverts. The 2008) is revealed by the four shorter, paler, eye is exceptionally pale for a 2Y (although this may greater coverts. Some pale juvenile lesser coverts be partly caused by the low sun).This is a particularly also remain, but this bird is much smarter than many scruffy individual, and many are much neater – see 2Ys. This bird was hunting, and is therefore sleeked, plate 135, right.The chestnut colour on the undertail- thus hiding the secondaries. As yet, no barring is coverts is staining from the soil, via the talons. visible on the crescent. Robin Prytherch 136. This Common Buzzard Buteo buteo, observed in the study area in January 2006, is a tricky individual to age, since the barred flanks and dark eye suggest full adult plumage. But note the two pale, shorter,

juvenile greater coverts, which, together with two Markus Varesvuo ages of feather in the remainder of the greater- 137. This is a dark adult Common Buzzard covert tract, confirm that this bird is a 3Y Buteo buteo, yet the pale crescent below the (i.e. is in its fourth calendar-year). breast is still present; Latvia, April 2004.

British Birds 102 • May 2009 • 247–273 271 The social behaviour of the Common Buzzard Markus Varesvuo 138 & 139. Common Buzzard Buteo buteo, juvenile (above) and adult (below); both Sweden, September 2005. These two together make a fine comparison.The most conspicuous difference is the dark trailing edge to the flight feathers, being bolder and more sharply delineated on the adult.This juvenile is typical but on some this feature may be even less obvious and on others more so.The subterminal tail bar is more obvious on this juvenile than usual. Markus Varesvuo

272 British Birds 102 • May 2009 • 247–273 The social behaviour of the Common Buzzard Markus Varesvuo 140 & 141. Common Buzzard Buteo buteo, juvenile (above, Finland, November 2005) and adult (below, Sweden, September 2004). From above, the most obvious difference between these individuals is in the tail, with the dark subterminal bar present on the adult, but not on the juvenile. Unusually, the juvenile’s greater coverts are not clearly marked with pale buff tips. Markus Varesvuo

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