Notes on the breeding biology of the Buzzard

Geoffrey Fryer

uring the 1970s and up to 1985, I made casual observations on the D breeding behaviour of the Buzzard Buteo buteo. Most of these were in the southern part of the Lake District, Cumbria, but others made elsewhere during the same period are also referred to here. Although various aspects of the breeding behaviour of the Buzzard are well documented (e.g. Melde 1971; Picozzi & Weir 1974; Tubbs 1974; Cramp & Simmons 1980), my observations revealed several apparently little-known or undescribed facets. Nest-site marking by crag nesters The habit of'decorating' the nest with fresh sprays of green leaves is well known, but some generalised statements are not always factually correct and its significance is still subject to debate. The repairing and maintaining of old nests in seasons when they are not in use is also well known. What seems not to be recorded is that actual sites, at least crag sites, may be marked by depositing green material there, even though no nest is constructed. In 1971, a pair of Buzzards nested on a crag in a Lakeland valley and raised one chick. This site was not used from 1972 to 1975, but, apart from noting the fact, I paid no attention to the nest ledge save recording that, on 26th April 1974, the nest was 'a wreck and not repaired at all'. On 21st April 1976, however, several shoots of holly Ilex aquifolium had been placed on the site. No attempt had been made to rebuild the nest, of which no more than a few old sticks persisted on the ledge. On 15th May, I found that, while one or two sticks had apparently been brought, no attempt had been made at nest rebuilding, yet several sprays of rowan Sorbus aucuparia had been placed on the site. On 22nd April 1977, no nest building had taken place, but two fresh green sprays of holly and one faded spray that had clearly been there longer were present; on 21st May, no additional material was present. On 23rd April 1978, on which date occupancy of another site within this territory was confirmed, two or three stalks of heather vulgaris had been brought and a few green holly shoots placed on the site. By 13th May, at least one further holly spray had been added, this despite a nest elsewhere in the territory having been occupied continuously since the first shoots were noted. This hints at the male being the bringer of the greenery, the female being usually otherwise'engaged at this stage of breeding. Males certainly bring green sprays to occupied nests, although MacNally (1962) saw only the female do so during the post-hatching phase at a Scottish nest. On 18th April 1979, a first, very rough attempt at remaking this nest had begun, and fresh

18 [fin/. 79: 18-28, January 1986] Breeding biology of the Buzzard 19 holly shoots (not an integral part of the structure) were again present. On 6th May, the nest was complete and contained what proved to be the full clutch of two eggs. The same ledge was thus re-used after seven years of disuse, though not complete abandonment. The position of the nest was virtually identical on each occasion. These observations show, incidentally, how quickly Buzzards can make a nest: not always is it completed 'long before they lay their eggs' (Bannerman 1956). The marking of incomplete or vestigial nests with greenery and the phenomenon of nests being completed but not used had already been observed at alternative sites in this same valley. A well-fashioned nest found in 1970 was visited by a Buzzard which, however, used an alternative site. On 13th May 1971, the unused 1970 nest, although incomplete, was marked by three sprays of rowan which had obviously not long been in position. It was not used in 1972 and 1973 (no details kept of its condition). In 1974, it received some attention, but was not lined; on 29th March, however, several holly sprays were present, the nearest source being about 500 m distant, and on 26th April sprays of fresh rowan had been added. On 25th April 1975, sprays of holly were present, and on 20th May the nest had been made up and the female was brooding two eggs; one young was eventually reared. On 28th March 1976, two fern fronds (species not ascertained) lay on the unrepaired remains of this nest. On 21st April, these had withered, but no further green material had been added, nor was any found in 1977-85, and, following desultory repairs in 1977, the site appears to have been abandoned. On 30th April 1983, a visit to a crag to which one of a pair of circling Buzzards had been seen to plunge directly and steeply some two weeks previously revealed a newly constructed, but incomplete, unlined, nest. Lying on it was a tuft of great wood-rush Luzula sylvatka, partly green, partly brown; two heather tufts, one greener than the other; and a green spike of whorled leaves, seen only through binoculars, possibly of fir clubmoss Lycopodiwn selago. Very little of the heather in the vicinity was green at this time in a late season, and the tufts present must have been assiduously sought. On 25th May 1977, sprays of rowan were also found at a derelict nest visited by a Buzzard elsewhere in this valley, but such behaviour was not confined to one area. In an entirely different part of the Lake District, a nest used in 1973 (not examined in 1974) showed no sign of being remade on 26th April 1975, but a few fronds of polypody Polypodium vulgare had been placed at its centre. Particularly gratifying was a visit made on 29th April 1977, specifically to check this behaviour, to a crag site in a different Lakeland Valley where Buzzards reared two young in 1974, but which was known to have been unoccupied in 1975 and 1976. There, although some attention had possibly been paid to the sticks still present, no real attempt at nest making had been made, but three fresh sprays of holly had been placed on the ledge; these, but no additional green material, were still present on 20th May. A nest in a yet different valley produced one young from a single egg in 1982; in 1983, it retained much of its shape but was unrepaired, though a freshly severed spray of juniper Juniperus communis had been placed at its centre by 4th May, on which date the pair was occupying an adjacent, newly built, nest containing two eggs. By 29th April 1984, the same nest, still in good shape but unrepaired, had been marked by three separate sprays of juniper and a dead fern frond, and on 10th May 1985—by which date a few heather stalks had been added to the rim—the unlined nest cup again had a spray ofjunipe r in its centre. Juniper grows nearby. In another valley, a nest which in 1981 failed at the egg stage was not used in 1982, but on 8th May four faded holly sprays and a wilted, but clearly more recently placed rowan branch with a stem at least 8 mm in diameter was present on the unrepaired nest, and several tufts of mat-grass Nardus stricta (see below) were also present. As this nest never became badly trampled, the latter could conceivably have persisted from the previous year, or could have been added with the green material. In a different valley, a nest discovered on 1st June 1985, to which some attention had probably been paid in that year, had a fresh frond of rowan at its centre and a similar, withered, frond at its rim. The placing of green material at nest sites or incomplete nests was established on a total of at least 22 separate occasions, involving nine sites and several seasons. The number of visits on which this was brought must have been greater: for example, the four holly sprays at one site presumably involved four separate visits (not necessarily on the same day). That fresh greenery, sometimes unaccompanied by faded material, was seen on dates 20 Breeding biology of the Buzzard ranging from 28th March to 1st June also hints at the possibility of renewal. Conclusive proof of the placing of greenery leading ultimately to nest making and egg laying, sometimes in subsequent years, was obtained at some sites. Equally conclusive proof of green material being placed on a previously used site that could not be used that year was also obtained, such material certainly being deposited at one site after nesting had begun elsewhere in the territory. Nevertheless, site-marking is by no means invariably practised. The first-mentioned site remained unused from 1980 to 1985, but no marking was observed. That the birds were aware of the site can hardly be doubted: a Buzzard was seen perched close to it early in the 1981 breeding season, leading me to suspect either nesting or at least marking, though neither occurred and no physical attention was paid to the site. I have seen a fern frond on an unrepaired tree nest used in the previous season—a parallel to the marking of crag sites—but in trees such marking is possible only when a remnant of an old nest survives. I can find no reference to the use of green material on what are sometimes nestless crag sites, but Blezard (1933) noted that 'the earliest sign of activity sometimes is a leafy spray placed on an old nest'.

Function of marking Both Tubbs (1974) and Newton (1979) tentatively suggested that greenery may advertise territorial ownership, a conclusion also drawn by Blezard (1933) regarding leafy sprays on old nests and one which I had reached as a result of my own observations. Indeed, 'decoration' of sites on crags provides stronger support for this idea than does the marking of an actual nest. Greenery on a nest could conceivably serve other purposes, but it is difficult to envisage another function for sprays placed on a crag ledge. It is suggested that its employment is analogous to that of pheromones as territorial markers by mammals, in keeping with the dominance of the visual sense in birds and the olfactory in mammals. Indeed, the evidence is perhaps better than that for scent-marking in mammals, the significance of which is often ambiguous. The take-over of nests of other species and their decoration by Buzzards that do not lay in them is also in harmony with this theory. I have seen the crag nest of a Raven Corvus corax so bedecked with greenery; and, once, the nest of a Carrion Crow C. corone in an ash tree Fraxinus excelsior, in the territory of a pair of Buzzards which nested successfully on an adjacent crag, was completely lined with green sprays of ash, but was not otherwise used. It is difficult to accept that the ultimate function of green material is to provide a soft bed of leaves on which the eggs are laid (e.g. Brown 1976), and BWP (Cramp & Simmons 1980) is misleading when it refers to the nestcup as being 'lined with green foliage prior to or during laying' as if this were invariably the case. Some nests are so lined, and indeed Picozzi & Weir (1974) used the lining of die nestcup with green material as one of the criteria for attempted nesting, but crag nests in the Lake District are generally not so lined. In fact, I have recorded only four cases of green material in the lining and never has the entire lining been so comprised. A Breeding biology of the Buzzard 21 nest on a crag in the vicinity of which larches Larix were numerous was partially lined with larch shoots. Another was lined exclusively with great wood-rush, mostly brown leaves but including one large partly green tuft, presumably pulled from the base of a growing plant, incorporated near the edge of the cup; the solitary egg lay entirely on brown leaves. In another, a spray of Scots pine Pinus sylvestris was included among otherwise dead material, and a further case involved the incorporation of a few soft, newly opened leaves of sycamore Acer pseudoplatanus. The experience of Blezard (1933) was evidently similar: he referred to 'grass, dead bracken and wood-rush' being used to line nests in the Lakeland Fells. It may be significant that my observations refer essentially to crag nests and those of Picozzi & Weir (1974), with one exception, to tree nests, but I doubt this, as even tree nests are not always so lined in the Lake District. Thus, in contrast to the crag nest that contained some larch shoots, a nest with two eggs built in a larch tree, and easily observable from the top of the crag on which the nest tree and other larches grew, included no larch shoots, nor any odier green material, in the nestcup. While my data for tree nests are scanty in this respect, this is not the only case in which the eggs rested in a cup without any trace of greenery. This is sometimes also so in Denmark (see photograph in Wenzel 1959). Furthermore, the case of the usurped Carrion Crow nest, the only instance of green lining recorded, suggests that this need not necessarily be an indication of attempted nesting. In Lake District crag nests, green material, which frequently includes tough, sharp-spined holly leaves quite unsuitable for providing a soft receptacle for the eggs, is generally placed at the margin of the nest in the early phases of nesting, not woven into its structure as Tubbs (1974) reported for the New Forest and as I have seen in Lakeland tree nests. It is much more usual to find green material, sometimes in copious amounts, laid across the nest when young are present, a situation quite contrary to the impression given in Cramp & Simmons (1980) that material may be added 'during incubation and even fledging periods'. Generalisation is clearly dangerous.

Other evidence of site ownership That Buzzards sometimes take a proprietary interest in old nest sites is indicated both by their visiting such sites in years when they are not used, which I have observed on several occasions, and by behaviour of a different kind. On one occasion, before egg laying could be expected, as I scrambled to an ancient and clearly long-disused site on a small low crag, on which no greenery was found, an airborne Buzzard began to call persistently. In some circumstances this could have indicated an undetected nest nearby, but in this case this was certainly not so, and I had a very strong impression that the 'resented' intrusion onto its 'property', although that property was untenanted and had been for some time. Several years later, in 1983, Buzzards again used this small crag, three eggs being found in a nest on another ledge. I have also seen Buzzards either perched near or 'playing' in the vicinity of old nest sites on crags where the nest was unrepaired in that breeding season. In one such case, in a valley different from any mentioned 22 Breeding biology of the Buzzard above, this was followed by the discovery later in the season of a nest containing two eggs about 200 m away.

Nests and sites While most crag nests conform broadly to descriptions in the literature, their structure is not rigidly stereotyped, nor is it necessarily determined by the accessibility of materials. A Buzzard nest is by no means always the 'substantial structure' described by Cramp & Simmons (1980). A southern Scottish nest with two small young was on a grassy ledge on which the eggs must have been laid directly, such hollowing as was apparent being no more than would result from brooding activities and the consequent killing of the grass. Two or three stalks of heather were present, but no nest at all had been constructed. Although the area was largely treeless, heather stalks were readily available, so the lack of sticks was not dictated by circum­ stances. The 'Additions & Corrections' to The Handbook (Witherby et al. 1944) mention the nest as 'occasionally very slight', while Blezard (1933, 1946a) reported flimsy nests consisting of 'a few scraps of plant stalks surrounding a hollow in turf and referred to a ground nest that was 'simply a scrape lined with tufts of grass' (Blezard 1946b). A nest that I found on a broad grassy ledge in the Howgill Fells consisted essentially of a lined hollow, with no more than a few token sticks around it, that in no way resembled a true stick nest. Similar nests, but with rather more sticks, have been seen in the Lake District. Where the nestcup occupies a natural hollow (or one resulting from long usage?) on the ledge, the sticks may be no more than a perhaps functionless adornment of a rim of earthy or rooted plant material. When the nestcup abuts the crag face, sticks may be used only on the outer side, where they form a more or less semicircular rim. They may be scanty, or sufficiently numerous to make a veritable barricade. Other nests have a large, almost perfectly circular, peripheral array of sticks. The central cup, when present, is variable in diameter: in one nest, built of large sticks, it barely encircled the three eggs; in others, it is larger.

Nest-lining material Notwithstanding the emphatic denial of Walpole-Bond (1914), sheep's wool may be incorporated into the lining, although this is not common. It may also sometimes be found at the edge of the central cup, and I have seen a little added with green material in a nest that held well-feathered young. Philipson (1948) also noted the occasional presence of'a little wool' in the nest lining in Lakeland nests, and wool has been found in the lining of Pennine nests (Blezard 1933; Brown 1974). On several occasions, a newly built nest has contained the basal parts of one or more dead tufts of mat-grass. Some nests are partially lined with such tufts, which may conceivably act as markers as well as lining material. Tufts commonly lie about on hillsides, and must be easily acquired. I have also seen tufts of mat-grass at the edge of a crag nest containing young in Scotland, as well as in northern England. Breeding biology of the Buzzard 23 Altitude Lake District nests with two eggs at about 1,900 feet (579 m) and at just over 2,000 feet (610m), respectively, and one with three eggs, all of which hatched, at about 2,100 feet (640 m), all in the same territory, appear to be above the usual limits there. Blezard etal. (1943) stated that crag-nesting in the area occurs 'up to 1500 feet [460 m] and occasionally up to 1750 [530 m]', but Brown (1974) reported breeding at up to 2,000 feet. The next highest site that I have found was at about 1,800 feet (550 m), but the nest held no eggs or young; another site, used twice, was at over 1,700 feet (520 m). Farther north, Weir & Picozzi (1983) recorded 380 m (1,250 feet) as the upper limit of altitude for the nest of a Buzzard in Speyside. Altitudes of Lake District nests, plus one from the adjacent Howgill Fells, that I have seen and for which data are recorded are shown in table 1. The highest tree nest was in a downy birch Betulapubescens in a sheltered ravine. Table 1. Altitudes of nest sites of Buzzards Butto buleo in the Lake District, Cumbria (plus one Howgill Fells crag site), 1970s-1985 Heights of trees ignored Crag nests Tree nests

No. nests 38 (8 not in use) 54 (13 not in use' ft 550-2,100 460-1,500 Range m 168-640 140-457 1,267 685 Mean 386 209 No. (%) at 1,000 ft (305 m) or above 29 (76%) 3 (6%)

Tree species used Tree nesters are reputed to show a preference for conifers (e.g. Brown 1976; Cramp & Simmons 1980), but availability (Melde 1971) and individual idiosyncracies are clearly involved. In one territory, I have seen three different occupied nests in a rather small group of larches, but an oak Quercus at the edge of this group has also been used. An unoccupied nest was in a solitary sycamore in the middle of a small plantation of apparently suitable larches. Trees seen to be used in the Lake District, so far as they were recorded, are indicated in table 2. Table 2. Trees used for nesting by Buzzards Buteo huteoin the Lake District, Cumbria, for which records were kept, 1970s-1985 The oaks were almost certainly all sessile oak Q.petraea, and the larches probably all L. europaea Tree species No. nests

Oak Quercus 19 Larch Larix 9 Scots pine Pinus sylvestris 8 Downy birch Betulapubescens 3 Ash Fraxinus excelsior 3 Beech Fagus sylvatica 2 Sycamore Acerpseudoplatanus 2 Fir Abies 2 Alder Alnus glutinosa 1 24 Breeding biology of the Buzzard Crags versus trees My observations do not support the suggestion of Tubbs (1974) that trees appear to be favoured as nest sites where they are available, nor his inference from BTO nest record cards that sites other than those in woodland tend to be used of necessity rather than from preference. Brown (1976) made even more categorical assertions of the same kind. The lowest- lying Lake District sites, in Borrowdale at about 550 feet (168 m) and in Dunnerdale at 600 feet (183 m), offered abundant alternatives in trees, and a nest in Longsleddale at 620 feet (189 m) was on a small rocky outcrop surrounded by suitable trees. Three other crag sites, all below 1,000 feet (305 m), had tree nests nearby. At two of these, adjacent tree and crag nests were certainly used in consecutive years; in one case, the same female, recognised by her aggressive behaviour, was almost certainly involved (Fryer 1974).

Periodicity of occupation Lakeland crag nests seem generally to be vacated after a year's use, although, as some sites were checked only intermittently or never revisited, examples of use in the following year may have been missed. While information is sporadic, I have details of 23 crag sites used in one year but not the next, but none of use in two successive years. A tree nest in an oak, however, was used for at least nine and probably ten consecutive years since first found, and could have been in use before this. Particularly noteworthy is that the sixth year of occupancy (1980) followed failure from an unknown cause in 1979, while fidelity to this site was demonstrated even more strongly by the return of the pair to the same nest in 1983, following human interference and desertion in 1982. Holdsworth (1971) noted that re-use was more likely after success than after failure. A pair was present for the tenth consecutive year early in the 1984 season, one of the birds being seen at the decorated nest, but laying was not proved and the nest was later deserted for reasons unknown; in 1985, the nest was repaired and decorated, but only a single bird was ever seen there. Whether this persistent occupancy always involved one or more of the previous year's users is not known. By contrast, the nearest neighbours of this pair used six different tree nests in eight years, and only once used the same nest in two consecutive years. Perhaps as a result of tree-felling, this pair was not located in the ninth year of observations, but it nested again in the same wood in 1984, after an absence of four years.

Passerine nestlings as prey Although Cramp & Simmons (1980) mentioned 'nestlings and just-fledged young', without clear distinction, as prey of the Buzzard, there seem to be very few published references to nestlings and even less information on the age of such prey. Tubbs (1974) recorded just one nestling Redstart Pkoenicurus phoenicurus among the large number of items brought to 81 Buzzard nests over a nine-year period in the New Forest, Hampshire, where avian prey is unusually important. Being of a hole-nesting species, however, and presumably sufficiently well feathered to permit recognition, Breeding biology of the Buzzard 25 this bird seems unlikely to have been taken from a nest. Newly fledged small are certainly captured, and it is not always possible to ascertain whether young birds brought to a Buzzard nest were removed from their own nest or taken after fledging. Although MacNally (1970) referred to the taking of nestlings, this seems to have been inferred from a curious case where the nest, but no young, of a Chaffinch Fringilla coelebs was found at a Buzzard nest, and he listed no nestling among over 200 prey items recorded at nests, though these included several fledglings. A related case of apparent nest plundering, for which the evidence is also somewhat circum­ stantial, refers to the apparent taking of embryonated eggs of a Blackbird Turdus merula (Streeck 1969). There is, however, one positive report of the taking of naked nestlings. Among prey found at Buzzard nests, VVendland (1933) reported three unfledged thrushes, possibly Mistle Thrushes T. viscivorus, about 8-10 days old, and also two headless, naked young birds. On five occasions in four different years, naked or near-naked nestlings were seen at the nests of Lakeland Buzzards; some, probably all, were Meadow Anthus pratensis, and all were intact. On each occasion, the recipient Buzzards were downy young. In one case, a nest containing one chick aged less than two days old and a hatching egg had been provisioned with two naked Meadow nestlings; one such nestling was seen at the same nest when the young were about seven and five days old. At another nest containing one young Buzzard about four days old, three naked nestlings were present (presumably the product of one nest). Two nearly naked Meadow Pipit nestlings were present at a nest containing a Buzzard chick about five days old and an unhatched egg (plate 34); just over four hours later these had gone, presumably having been fed to the chick, and had been replaced by the fragmentary remains of a pigeon Columba, probably a scavenged kill of a Peregrine Falco peregrinus. At another nest, a Buzzard no more than 14-15 days old was seen to swallow such a nestling unaided: it seized the nestling and several times flung back its head, the prey's legs flopping back at each fling. According to Tubbs (1974), young Buzzards can swallow small rodents whole at the age of one month, but they can perform even this feat much earlier than this (see Wenzel 1959). The ingestion of a small nestling must present fewer problems. It may be coincidental that such prey were recorded only at nests containing small young. If brought later (and Meadow Pipits are usually at least double-brooded), such items may be quickly swallowed and therefore missed by the casual observer. On the other hand, there may be a corre­ lation between the collection of very soft morsels and the needs and abilities of small young. Indeed, such items would make but a small contribution to the needs of large young. A somewhat older nestling (a Meadow Pipit?) whose wing quills were just developing was also seen at a nest containing two young Buzzards about four and two days old and a hatching egg. Remains of feathered Meadow Pipits, in one case possibly obtained from a nest, were also seen among the prey. Uttendorfer (1952) noted that many of the avian prey at Buzzard nests are young birds. This is not surprising, as the Buzzard's breeding season coincides with the time when young, inex­ perienced birds are particularly abundant. 26 Breeding biology of the Buzzard

34. Crag nest of Buzzard Buleo buleo with near-naked nestlings of Meadow Pipit Anthus pratensis (arrowed) at margin, and Buzzard chick about five days old and infertile egg; much use of tufts of mat-grass Nardus stricta at margin of nest cup (see text), Cumbria, May 1985 (G. Fryer)

That young are sometimes seized from the nests of larger birds is shown by several incidents. E. Taylforth (in litt.) saw a Buzzard fly to the tree nest of a Carrion Crow and 'hook out' a young bird, which fell to the ground. The parent crows, with others attracted by their calls, drove ofT the attacker. When examined, the victim was found to be dead and to have 'a hole in its neck', presumably made by the claw of the Buzzard. I observed what was conceivably a similar sortie by a Buzzard which dived into the wooded side of a valley; where it disappeared, a cacophony of frenzied Breeding biology of the Buzzard 27 alarm calls of Carrion Crows immediately arose. Coombs (1978) recorded that in 1955, when Buzzards were experiencing a severe food shortage following the effects of myxomatosis on the population of rabbits Oryctolagus cuniculus, 'well-grown nestling rooks [Corvus frugilegus] were repeatedly taken from the nest and tree branches at a rookery ... in Cornwall'. A case of a Buzzard at the nest of a Magpie Pica pica is reported elsewhere (Fryer 1986). Remains of feathered young crows were seen several times at Buzzard nests. Some could conceivably have been taken before fledging, but there is no proof of this, and I have on several occasions known Carrion Crows to nest, apparently unmolested, sometimes in open sites, in the territory of a pair of Buzzards. Richmond (1959) also mentioned Wood- pigeon Columba palumbus squabs brought to the nest.

Acknowledgments I am grateful to Dr D. A. RatclifFe and D. A. Christie for helpful comments on the original typescript, and to the former for drawing my attention to an early paper by E. Blezard. Summary During the 1970s and up to 1985, casual observations were made on breeding Buzzards Buteo buteo in the Lake District, Cumbria. Details are given of the habit of'decorating' nestless crag sites, as well as nests, with fresh greenery. The function of this behaviour, which seems to be to show territorial ownership, is discussed, and other evidence of ownership is outlined. Buzzard nests on crags vary considerably in structure, and may be no more than a lined hollow with a few token sticks added. The highest nest was at 2,100 feet (640 m). Tree nesters used a variety of broadleaved and coniferous tree species. Crag sites appear usually to be vacated after one year's use, whereas one tree site was occupied for nine or ten consecutive years. Among avian prey brought to the nest, naked or near-naked nestlings were found on five occasions. Nestlings of birds the size of Carrion Crows Corvus corone are sometimes taken.

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