BREEDING EUROPEAN HONEY-BUZZARDS IN BRITAIN

S. J. ROBERTS,J.M.S.LEWIS AND I. T.WILLIAMS

European Honey-buzzards apivorus (S. J. Roberts)

ABSTRACT The European Honey-buzzard Pernis apivorus has been one of the least-studied of Britain’s breeding , because of its limited range, its scarcity and its reputed susceptibility to disturbance. This paper shows, however, that it is far more widespread, considerably less rare and much less affected by human intrusion (if carried out with circumspection) than was previously thought. The authors hope to encourage a more-open attitude and to further responsible research into the species’ status and conservation requirements in Britain.

326 British Birds 92: 326–345, July 1999 BREEDING EUROPEAN HONEY-BUZZARDS IN BRITAIN

he European Honey-buzzard METHODS Pernis apivorus (hereafter referred Research during 1989-97 identified three Tto as the Honey-buzzard) is one of distinct breeding habitats: (a) lowland the most widespread raptors in the World, southern woodlands, (b) central hill breeding throughout the temperate and country with mixed farmland/woodland boreal regions of and eastwards and (c) upland coniferous plantations. The into boreal (Cramp & Simmons 1980). definitions of these habitat types are, It has always been regarded as a rare indeed, very broad, and we accept that summer visitor to Britain (Hollom 1957; identifying regions or counties would Parslow 1973; Holloway 1996), but, in certainly prove more enlightening to recent years, breeding has been recorded various aspects of the paper. Some of those more frequently away from the traditional who have contributed important data to the stronghold of the New Forest (Gibbons et al. paper have done so, however, only with the 1993; Lovegrove et al. 1994). Despite this, it provision that we would not identify remained a poorly studied species in this regions or counties. Sixteen nesting areas country, with only limited published data (an ‘area’ containing all the known nest (e.g. one or two pairs in Nottinghamshire sites of a pair: Newton 1979) were during 1971-79: Irons 1980). attributed to one of these habitat types, During 1988–1991, The New Atlas of eight in the lowlands, three in the central Breeding Birds in Britain and Ireland (Gibbons hills and five in the uplands. et al. 1993) recorded evidence of breeding in Individual nesting trees have been ten tetrads in Britain, with individuals termed ‘nest sites’. Data were compared present in a further 17 tetrads. Recent between the different habitat types. investigation has shown that this species is Breeding Honey-buzzards were located by more widespread than previously recorded protracted watches at key periods in the in Britain, but, owing to its attraction for cycle and, where possible, individual birds egg-collectors, most sites are kept were identified by plumage or moult confidential. Although several people patterns. Males and females were identified monitor the numbers and distribution of by these methods, as were intruders. breeding Honey-buzzards, we are not Distinctive egg types have been laid in aware of any scientific research being three nesting areas, aiding identification of undertaken at present. Partly as a result of the individual female. These egg types have this paucity of records, we and several co- been monitored for up to four years workers began in the late 1980s to study the (currently). This may be the case in other species’ breeding ecology. nesting areas, but annual visits during This paper is based on information gathered incubation have not always been possible. at 52 nests in 16 nesting areas in upland, central A sudden change in egg type at one site and lowland Britain during 1989-97, and alerted the authors to the presence of a new includes information received from other female. fieldworkers. As the Honey-buzzard is a Nest-site altitudes and the area of Schedule 1 species, all nest visits were made woodland within 25 km2 around the under licence from the relevant licensing nesting areas were measured from 1:50,000 authority. These nests and nesting areas are Ordnance Survey Landranger maps. Clear- located widely across England and Wales, from felled areas of forestry were included as the north of England to the southern counties, woodland since these could not be and include widely scattered individual nests distinguished on OS maps. Nest sites were and small discrete populations; no information located in mature conifer, mature broadleaf was received from Scotland. Because of the or mixed woodland (intimate confidential nature of the information, some of conifer/broadleaf mix, as well as blocks of our co-workers wish to remain anonymous. broadleaf and conifer in close proximity).

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Various parameters of the nest site were Despite an apparent historical association recorded, such as tree species, tree height, with lowland woodlands, Honey-buzzard nest height, distance of nest tree from rides nests were found across a wide range of or clearings, and topographical position. altitudes, with the lowest virtually at sea The minimum distances between active level and the highest at almost 500 m above nests were measured from 1:50,000 OS sea level. The median height of 50 nests was Landranger maps. between 90 m and100 m a.s.l. Detailed measurements of known-age Although generally associated with chicks were taken, and the ages of other large woodland tracts in Britain, the unknown-age chicks were estimated from amount of woodland in a sample of 14 nest their wing lengths. First-egg dates were areas across the range of habitats varied calculated by working back from the age considerably. Within 25 km2 around the of the oldest chick and allowing 35 days nest area, the woodland cover averaged for incubation. 45.8%. (The maximum was 81% and the Breeding success was estimated from a minimum 31%.) Only four nest areas total of 47 active nests found; it was also contained more than 50% woodland cover estimated for 15 of those that were located within the 25 km2. More-restricted at the egg stage. Chicks were weighed to measurements in the German Rhineland determine their rate of development. The revealed that 94% of nest-sites contained behaviour of adults and young at the nest 50-60% of woodland within 600 m of the was assessed during extended watches nest (Kostrzewa in press). from hides. Faecal samples were collected from CLIMATE active (and recently vacated) nests and It has been suggested that climate is a analysed at University College, Cardiff. crucial factor in the nesting success of species were identified by their jaws breeding Honey-buzzards (Kostrzewa 1989; (larval stage) or their head capsules (pupal Batten et al. 1990), either suppressing the stage). Partly destroyed ’ nests were reproductive drive or resulting in nest examined for possible ‘farming’ by Honey- failure through food shortage or adverse buzzards. All other prey items were weather conditions. The south of England, casually recorded, whether at nests or being and particularly the New Forest, has long carried by adult Honey-buzzards. been regarded as the Honey-buzzard's stronghold in Britain, its mild climate being BROAD HABITAT REQUIREMENTS expected to favour a large raptor with a The Honey-buzzard has traditionally been mainly insectivorous diet. regarded as being largely confined to the If this were true, Honey-buzzards in southern counties of England and, in upland Britain, nesting at higher altitudes particular, the New Forest in Hampshire and with colder, wetter weather, should (Brown 1976). In these areas, broadleaf have poorer breeding success. This has woodlands had appeared to be the not been the case in our study, where preferred habitat, particularly Beech Fagus pairs breeding farther west and north sylvatica (Brown 1976; Sharrock 1976) on have enjoyed exceptional breeding success light or sandy soils (Batten et al. 1990) compared with ‘southern’ birds, despite where sufficient food is available nest sites often being subjected to cloud and (Martin 1992). rain for long periods. Of the 19 recorded The 52 nests located in the study nesting attempts in the uplands since 1991, related to 16 nesting areas. A total of 32 15 successfully fledged two young each, different nest sites was used, eight in the with an average of 1.58 young per nesting uplands, four in the central hills and 20 in attempt. There were no failures caused by the lowlands. inclement weather or food shortages.

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Compared with the published accounts end of the range given for Europe when from Nottinghamshire (Irons 1980), this is breeding success was affected (Kostrzewa an exceptionally high level of breeding 1989). Unfortunately, too few nests are success. During the period when chicks in adequately monitored throughout much of the uplands were thriving on wasps and the species’ British range to gain a thorough bumble-, nests were known to fail in understanding of the effects of weather Devon and the south of England, with the on productivity. cause given as adverse weather resulting in failure to lay or poor food supply to the AERIAL ACTIVITY nestlings (R. Khan verbally) Génsbøl (1986) The Honey-buzzard has a distinctive and stated that ‘In cold wet springs there are diagnostic display flight, named variously few wasps and this evidently reduces the as ‘wing-clapping’, ‘butterfly flight’ and birds’ reproductive drive’, but, in his ‘sky-dancing’. It has been described by study of British wasps, Spradbery (1973) several authors (see Cramp & Simmons concluded that ‘weather conditions may 1980), with peak activity recorded between influence mortality of queens and hinder mid May and mid June, and again from establishment of colonies, but do not play a mid July onwards. dominant role in population control.’ Our study indicates that this form If breeding Honey-buzzards can thrive of display flight, although regularly in cold, wet weather, reasons for failure described as courtship between male and elsewhere should be examined more female, can be erratic and often little in closely in order to establish the causes. evidence. Indeed, protracted watches at Kostrzewa (in press) states that breeding established nesting areas often produce success depends upon many inter-related little evidence of wing-clapping display. At factors, including quality of territory, many established areas where pairs quickly experience and quality of breeding adults, settled, the commonest form of aerial and timing, and reports that some activity was found to be single or mutual researchers considered only food and circling over the nest site and surrounding ignored other factors. It is known, however, area. Synchronised soaring or gliding – from other species (e.g. Common Buzzards flying closely and mirroring each other’s buteo and Common Kestrels Falco flight pattern – has been observed several tinnunculus), that density and breeding times and proved to be between the success can be affected by very different resident male and an intruding female. factors in different years (Kostrzewa in Performed over a wide area, but not press). Rob Bijlsma (in litt.) stated that it is a directly over the nest, this can often be common mistake to think that adverse misinterpreted as a breeding pair or, weather results in declining availability of importantly, as failed breeders or wasps and thus may be responsible for non-breeders, particularly during the poor breeding success; he also stated that incubation period. there is no correlation between adverse More often, protracted wing-clapping is weather and breeding success in the used as territorial advertising, particularly Netherlands unless conditions are extreme. if single birds, or two males, are involved. His extensive studies of wasp activity and Protracted wing-clapping has also been radio-tagged Honey-buzzards have observed from intruding males over nest revealed that heavy rain had no real impact sites whilst the resident male was upon wasp foraging, and that Honey- incubating eggs. On other occasions, buzzards were perfectly able to trace intruding males have been seen to wing- wasps’ nests in poor weather. The highest clap vigorously at perched resident males May/June rainfall figures in the uplands or females. This can result in a similar during our study were only at the lower response from the resident male, but it is

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not unusual for established pairs with Once the presence of a pair on its nests to remain unobtrusive and to show territory has been established, instances of little wing-clapping. Females have also been a Honey-buzzard circling up from a wood observed wing-clapping for short periods. and moving off in a long, purposeful glide, Non-breeders have been observed wing- or gliding into a wood from a considerable clapping for 20 minutes or more, sometimes distance in a straight line, is regarded as carrying food (usually wasp comb) in a good indication of breeding. Some their talons, or sometimes pigeon carcases individuals also return high over nesting and even sticks. woods and plunge, with wings folded, Breeding pairs appear unusually towards the nest site. tolerant of intruders. In August, gatherings of five or six individuals have sometimes NEST SITES been observed in various forms of aerial The perceived preference for broadleaf activity in the vicinity of resident breeding woodland, particularly Beech (Brown 1976; pairs. This study has not revealed any Sharrock 1976), as the typical woodland for evidence that they may be young of the nest sites of Honey-buzzards in Britain has previous year. This view was supported by not been borne out by our study. Of 32 nest Forsman & Shirihai (1997), who stated that sites, 14 were in conifer woodlands, ten were ‘the vast majority of juveniles appear to in mixed woodlands and only eight were in spend the first summer in the wintering broad-leaf woodlands (table 1). areas’. They were unaware of any photo- An examination of the nesting trees graphically documented record of a further highlights the fact that conifers are second-calendar-year individual in the commonly used, despite the prevalence of Western Palearctic. nests in the lowlands (table 2). Of 52 nests Table 1. Woodland type used as nest sites by Honey-buzzards Pernis apivorus in three regions of Britain (n=32).

Conifer Mixed Broadleaf

Uplands 6 2 0 Central hills 2 0 2 Lowlands 6 8 6 Total 14 10 8

Table 2. Tree species used by nesting Honey-buzzards Pernis apivorus in three regions of Britain (n=52).

Uplands Central hills Lowlands

Beech Fagus sylvatica 00 3 Sweet Chestnut Castanea sativa 02 3 Oak Quercus 11 7 Total broadleaf 1 3 13

Sitka Spruce Picea sitchensis 70 0 Scots Pine Pinus sylvestris 04 4 Douglas Fir Pseudotsuga menziesii 0110 Western Hemlock-spruce Tsuga heterophylla 70 0 Larch Larix 20 0 Total conifer 16 5 14

Broad-leaf:conifer ratio 1:16 1:2 1:1

330 British Birds 92: 326–345, July 1999 BREEDING EUROPEAN HONEY-BUZZARDS IN BRITAIN found, only 17 were located in broad-leaf to have failed as a direct result of human trees, whereas 35 were in conifers. disturbance. In the lowlands, over half of the nests Many nest sites consisted of mature trees, found have been in conifers. Conifers are often past their commercial rotation. Large, chosen when native broad-leaf trees are well-spaced trees, whether coniferous or readily available close by, and, in some broad-leaf, were often chosen as a nest site. instances, an isolated conifer amongst Particularly in the upland and central hill broadleaf trees has been chosen. regions, there were, however, a few cases of Conversely, in the uplands, an isolated pairs nesting in smaller trees, the nests broadleaf tree amongst dense conifers has about 9 m up in 13-m trees. Another nest, also been used. in a stunted oak amongst dense The range of tree species shows Rhododendron Rhododendron ponticum, was considerable variation across all three also atypical. All these sites were, however, regions, with Beech one of the least-used, in prominent topographical positions, and and oak the most commonly used broadleaf this may be an important factor in tree. Four of the five most commonly used nest-site selection. trees were conifers, with Douglas Fir Pseudotsuga menziesii being the most NESTS frequently used. Kostrzewa (in press) As noted already, nest heights ranged from showed, however, that, even where conifers 8 m to 26 m, with most nests above 15 m were the most abundant trees (>60%), (n=37). In coniferous trees, nests were deciduous trees were preferred. usually placed against the trunk, in the live Tree height and nest height varied crown, making them difficult to see from considerably, with the highest and below. In broadleaf trees, however, nests lowest nests both found in the uplands. were usually in a fork near the trunk, but, The highest nest was 26 m above ground particularly in oak, often amongst Ivy level in a 30-m Western Hemlock-spruce helix. This, together with summer Tsuga heterophylla; the lowest was 8 m in a leaf cover, added to the difficulty in 12-m oak. The mean height for 37 nests was detecting nests. Some nests in conifers were 16 m. Most nests were found close to rides built along a limb and not against the trunk. or clearings, and these access routes One such nest collapsed when the young through the forest were found to be well were three weeks old; a fortuitous visit used by Honey-buzzards, particularly enabled the nest to be repaired and when approaching or leaving nests under repositioned in a different part of the tree, the forest canopy. Lengthy observation which the adults took to immediately. from trees high above the forest canopy has Contrary to some published accounts revealed that Honey-buzzards approach (e.g. Brown 1976), most nests are large, their nests with food along paths or rides some bigger than those of Common for hundreds of metres and leave by Buzzard. Only one nest was considered similar routes, rising above the canopy small (approximately 35 cm x 30 cm), only when some considerable distance although this increased in size through the from the nest. season with the addition of green material. Of 48 nesting attempts, 24 (50%) were in So far as could be determined, many trees adjacent to rides, paths or clearings, nests were built on the foundation of an old and a total of 37 (77%) was within 20 m. The nest or drey, though some pairs regularly farthest nest tree was 150 m from such an built a new nest from scratch. Old nests access route, but the trees were mature and of Carrion Crow Corvus corone corone, well spaced, affording easy access through or the woodland. Of 12 nests immediately Accipiter gentilis and Grey Squirrel Sciurus adjacent to used paths, only one is believed carolinensis dreys were known to be used as

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foundations. Where the history of practice of removing nests and supporting occupation was not fully known, the limbs during the winter. This may also foundation could originally have been a remove the focus for returning pairs. previous Honey-buzzard nest. Where nests Although Honey-buzzards in the New had been monitored for several years, the Forest will rebuild in crotches where dilapidated foundations were known to be previous nests and supporting limbs have Honey-buzzard nests from several years been removed, the new nests may be less before. It is possible, therefore, that this stable. Pairs may also have alternative sites, may have been the case in other instances. and the large distances between sites may Some nests are reused in the following also be attributed to the practice of nest year, with one nest used for four years in removal. Two pairs that normally moved succession and seven others used for two over 1 km from year to year reused the successive years. Four nests not reused in same nests when they were left in place. An the following year were, however, reused in artificial nest, erected in dense conifers subsequent years; in common with many surrounded by mature mixed broadleaf/ other raptors, Honey-buzzards have conifer woodland, also attracted a pair to several nests that are used in rotation nest, further suggesting that old structures (Brown 1976; Tubbs 1974). Personal may be important to the returning migrant observations in France have shown that birds. The justification for nest removal is pairs readily reuse nests in consecutive that it makes nest sites difficult for would- years. There are, however, instances of pairs be egg thieves to relocate the following which have never been known to reuse a year. During Irons’ study (1980) in nest over periods of up to 17 years (R. Khan Nottingham, nests were dismantled during verbally). In Germany, new nests were built the winter, but there is no published in 74% of all cases (Kostrzewa in press). information for that area on distances pairs Honey-buzzards invariably return to the moved between years. same nesting areas every year, and old Although nests are invariably cons- nests appear to have importance as a tructed from the same material as the nest focus for returning pairs, with some tree, linings are extremely varied, with refurbishment taking place even when a greenery from many tree species used. new nest is built nearby. During breeding, Some nests are copiously lined and the old nests continue to be a focus for some greenery obvious from below, whilst others pairs, with moulted feathers and wasp show no greenery, even though, upon comb being found at these nests. In one inspection, the cup is well lined, and others area, an old nest (200 m from a nest contain little greenery (plates 114 & 115). containing two young) had more moulted Seven nests with fresh eggs were found to feathers and droppings close by than there contain empty wasp comb. It is not known were at the occupied nest. The male at this if this was food taken to a nest with eggs site carried comb to the vicinity of the old (unusual for a raptor) or if it was taken back nest, presumably prior to taking it to the by an off-nest as decoration. occupied nest. This study found eight During this study, the minimum instances of nests being refurbished, with distance between the active nests of the pair subsequently laying in another different pairs of Honey-buzzards was 6 nest, usually within a few hundred metres, km (two instances), with two further but two instances in the New Forest of pairs instances of pairs nesting 8 km apart. In 1 moving 2 km and 1 ⁄2 km respectively. the past, however, pairs have nested more The New Forest population is unusual in closely than that (R. Clements verbally). A that pairs often move considerable pair was found to have built a ‘summer’ distances from one year to the next. This nest in August some 4 km from another unusual behaviour may be attributed to the pair with young. Kostrzewa (in press) gave

332 British Birds 92: 326–345, July 1999 BREEDING EUROPEAN HONEY-BUZZARDS IN BRITAIN nearest-neighbour distances of 3,000 m. We EGGS recorded three instances of ‘summer nests’ Honey-buzzard eggs are noted for their built in July or August, two of which were beauty and variety of colour and pattern, used in the following year. with a considerably greater range than that From 18 nesting attempts, the average illustrated in BWP (Cramp & Simmons distance for pairs to move between years in 1980). Some eggs are heavily marked, 1 the New Forest was 2 km, with 4 ⁄2 km the appearing a deep blood-red, whilst others maximum recorded distance. The average are blotched like those of Eurasian distance for pairs to move in the other Sparrowhawk Accipiter nisus. This study regions during this study was 250 m, with has shown that variation in clutches can the maximum being 750 m. After failure, one assist in the identification of individual pair in the uplands renested 500 m away. females, which often lay eggs with Nest-building takes place in the early characteristic markings (plates 114 & 115). morning, with one nest under observation Continuity of females at three sites was from first light at 03.30 GMT not attended suspected from characteristic egg type, by the pair (which arrived together) until confirmed by subsequent views of the 05.30. Nest-building can be very rapid. In a female. At one of these sites, after three protracted period of wet weather, a male years, we were alerted to the presence of a was seen to glide into a known nesting area new female by a change in egg type. on 26th May. Both old nests in the wood This study revealed that clutch size was were dilapidated and barely recognisable almost invariably two eggs, with only a as nests. On 29th May, still in very wet single recorded clutch of three eggs. conditions, one of the old nests was Historical records reveal one clutch of completely built up, and contained much four eggs in the nineteenth century in greenery on the rim. This nest held two Northamptonshire (Lilford 1895) and eggs on 15th June (with a first-egg date, records of three-egg clutches from the New calculated back from the age of the chicks, Forest in 1862 (Farren 1862) and Newent of 1st June). Woods, Herefordshire in 1869 (Walker &

114. Nest of Honey-buzzard Pernis apivorus, copiously lined with greenery, containing boldly marked eggs. Site in Douglas Fir Pseudotsuga menziesii; southern lowland mixed woodland; June 1997 (S. J. Roberts)

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115. Nest of Honey-buzzard Pernis apivorus, sparsely lined, containing ‘reddish’ eggs. Site in Sitka Spruce Picea sitchensis; upland conifer plantation; June 1997 (S. J. Roberts)

Smith 1975). There are also records of three 1976; Irons 1980). Irons (1980) gave the young fledging, in Norfolk in 1974 earliest nest-building date in Notting- (Sharrock et al. 1975) and 1977 (Batten et al. hamshire as 1st June and the average date 1979). The clutch of three eggs recorded for completed nests as 14th June. Recent during our study was at a regularly information from the same site proved that successful site, two eggs having previously a full clutch had been laid well before the been the norm there. All three eggs, laid end of May. Jourdain considered 10th June very late in July, were incubated well past a date when full clutches may be found full term, but failed to hatch. The clutch was (Bannerman & Lodge 1956). also unusual in that each egg was marked For 23 clutches during our study, first- differently. egg dates ranged from 21st May to 8th June, In Bannerman & Lodge (1956), with a median of 29th May (see table 3 for a Bannerman quoted egg sizes of 1.9-2.22 in. breakdown by region). First-egg dates for x 1.5-1.7 in., and F. C. R. Jourdain gave an all regions are earlier than those in most average for 25 British eggs as 50.22 mm previously published accounts, and, x 41.39 mm and an average for 100 surprisingly, are close to the earlier dates Continental eggs as 50.82 mm x 41.09 mm. given for the species on the Continent Measurements of 28 eggs (from 14 clutches) (Cramp & Simmons 1980). during our study gave a mean of 50.34±1.72 Replacement clutches are considered mm x 41.14±1.54 mm (range of 46.8 to 54.0 rare, with Cramp & Simmons (1980) noting mm length, and 38.3 to 43.6 mm width). only three records. One instance was Laying dates proved earlier than those recorded in our study: a pair in the uplands previously published for Britain (Brown which failed on eggs after 17th June, relaid

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Table 3. First-egg dates for Honey-buzzards Pernis apivorus for different regions of Britain.

Range Median

Uplands (n = 7) 27th May to 5th June 30th May

Central hills (n = 4) 21st May to 27th May 23rd May

Lowlands (n = 12) 24th May to 8th June 29th May and produced at least one fledged chick. Any notion that Honey-buzzards are The replacement nest was 500 m from the particularly sensitive to disturbance original. The same pair failed, and may also through nest visits by human beings is not have renested, in 1997. supported by our own experiences; no incidences of desertion or predation were INCUBATION found. During incubation, Honey-buzzards are extremely secretive, with protracted observ- YOUNG ations over nesting woods often revealing no Our findings concur with other published activity. Incubation has been observed on information on care for the young and their two occasions at the end of May (earliest development. Both adults have been 26th). The latest date on which a bird was observed feeding young bill to bill at the 1 1 incubating was 15th August, on a clutch ages of 1 ⁄2 to two weeks old and two to 2 ⁄2 which eventually proved to be infertile. weeks old. Young were still present on the Males take a large share of incubation nest when 35 days old (but were about to and are found incubating very early in the ‘branch’), and at another nest they were cycle (30th May and 1st June recorded). flying at 41 days. Nest relief is silent and, during this Cramp & Simmons (1980) gave the study, no calling has been heard during breeding success of 16 nests near Berlin as nest relief or whilst provisioning young 1.6 young per successful nest and 1.0 young with food. After fledging, the birds become per breeding attempt; and of 11 nests in more vocal. Belgium as 1.3 young per breeding attempt. Incubating Honey-buzzards are very Our study located 15 nests where the clutch confiding, most sitting closely. If disturbed, size was known and, of 31 eggs laid, 25 adults (both male and female) have on resulted in fledged young, giving a several occasions mantled eggs, with head breeding success of 1.66 young per lowered. When adults do leave, they often breeding attempt. One clutch of three eggs sit in a neighbouring tree. Occasionally, failed to hatch and one egg from a clutch of adults will threaten, with a posture of two failed to hatch; all were found to be wings held upright, stretched above the infertile. One egg from a clutch of two was body, both on the nest and on nearby soft-shelled, and the other egg was later boughs. Silent, close-flying ‘attacks’ are also found crushed in the nest with the pair still recorded. Some, however, away through in attendance. Additionally, one nest failed the woods, and are not seen until all for unknown reasons, although the female disturbance at the nest has ceased. subsequently relaid and reared at least one Alarm-calling varies with the individual: young. some pairs remain silent, whilst others call Only five out of a total of 47 active nests to varying degrees. The adults return that have been found are known to have quickly to nests, however, and it is failed. Three nests fledged single young, five pertinent to note that, during this study, no nests had at least one young, and 34 nests egg or chick predation has been recorded. fledged two young, giving a minimum

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300

250

200

150

100

Wing length (mm) Wing 50

0 1.5 (3) 2 (3) 2.5 (7) 3 (6) 3.5 (9) 4 (4) 4.5 (4) 5 (3)

Age in weeks (sample size)

Figure 1. Wing lengths of nestling Honey-buzzards Pernis apivorus in Britain, showing the rate of development. breeding success of 1.61. Since 32 of the Fig. 1 shows the mean and range of wing nests were not found until the chick stage, lengths for different-age chicks, and their however, this figure is biased towards weights are shown in fig. 2 (because of the successful nests. Our figures for breeding limited data, those in figs. 1 and 2 have been 1 success indicate that nest visits at the egg grouped to the nearest ⁄2-week interval). stage have no effect upon productivity. These weights are generally comparable Development of the young is similar to with those recorded for the Netherlands that of other raptors of comparable size, the (Bijlsma 1998). A number of chicks have primary quills sprouting at 14 to 16 days been weighed on more than one occasion: (own data and Bijlsma 1998) and this event 12 (six broods) have been weighed twice, has been used as the basis of ageing many four (two broods) three times and a single chicks (plates 116, 117, 118 and 119). chick four times. Generally, these multiple

1200

1000

800

600

Weight (g) Weight 400

200

0 0.5 1 (3) 1.5 2 (3) 2.5 3 (9) 3.5 4 (5) 4.5 5 (3) (2) (4) (7) (9) (5) Age in weeks (sample size)

Figure 2. Weights of nestling Honey-buzzards Pernis apivorus in Britain, showing the rate of development.

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1 weighings have taken place between 1 ⁄2 and 18 days (central hills, 1995). four weeks of age. The greatest average The lowest average weight increases were: 1 weight increases were: • 18.3 g/day for a 2 ⁄2-week-old chick over 1 • 47.1 g/day for a 1 ⁄2-week-old chick over nine days (upland, 1996) 1 seven days (upland, 1997) • 17.5 g/day for a 1 ⁄2-week-old chick over • 39.4 g/day for a two-week-old chick 13 days (upland, 1995) over nine days (upland, 1996) • 13.5 g/day for a three-week-old chick 1 • 36.9 g/day for a 1 ⁄2-week-old chick over over ten days (lowland, 1997).

1 116. Honey-buzzard Pernis apivorus chicks, ⁄2 & 1 week old. Site in Scots Pine Pinus sylvestris; central hill conifer plantation; July 1996 (S. J. Roberts)

1 117. Honey-buzzard Pernis apivorus chicks 2 ⁄2 weeks old. Site in Sitka Spruce Picea sitchensis; upland conifer plantation; July 1996 (S. J. Roberts)

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1 118. Honey-buzzard Pernis apivorus chicks, 3 ⁄2 weeks old. Site in oak Quercus; upland mixed woodland; July 1996 (S. J. Roberts)

1 119. Honey-buzzard Pernis apivorus chicks, 4 ⁄2 weeks old. Site in Sitka Spruce Picea sitchensis; upland conifer plantation; showing copious amounts of comb; August 1995 (S. J. Roberts)

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Weight gains for Continental chicks are leaving while the watch changed), and at given as: first ten days, 20 g/day; 11-20 11.30–14.10 (for 2 hours 40 minutes). The days, 30 g/day; and 21-40 days, 10 g/day male attended the nest from 08.10–09.20 (1 (Kostrzewa in press). The greatest weight hour 10 minutes), 10.20–10.32 (12 minutes), increases for British chicks are considerably 11.15–11.25 (10 minutes), 11.28–11.33 (5 higher than those given for Continental minutes) and 12.45–12.46 (1 minute). The chicks, and fig. 2 shows that total weight male brought food four times, feeding the gains are comparable. chicks twice; the female fed herself and the In most broods (13 out of 22), the chicks on two other occasions. Whilst the two young appeared to be of comparable female was off the nest, she could usually ages, and this was confirmed when be seen perched nearby. measurements were taken. This suggests During another extended watch (06.30– that proper incubation does not commence 15.40GMT) at a nest with two 12-day old with the first egg. In seven broods, chicks, the female stayed on the nest when however, an age difference of approx- the watch started and left only once, at imately three or four days was evident, 07.53, for a period of 2 hours 19 minutes. which is what one would expect if true She then remained on the nest for the next 1 incubation started with the first egg. 5 ⁄2 hours and was still there when the In one brood, an age difference of watch ended. The male brooded for nearly approximately one week was evident: at two hours whilst the female was off and 1 1 age 1 ⁄2 and 2 ⁄2 weeks for respective provided food on four occasions for either siblings, the respective wing lengths were the young or the female or both. The 60 mm and 120 mm, and weights were 213 g quickest return with food was after 1 hour and 390 g respectively. The relative weight 28 minutes. At both extended watches, the differences were still apparent two weeks female was never seen to supply food. At later (440 g and 814 g). The younger sibling another nest, the provision of food was was very small for its age. Another nest shared equally by both adults, with the 1 contained two young of three weeks and 3 ⁄2 female feeding the young (G. Hinchon weeks of age, which weighed 475 g and 900 g verbally). respectively. The smaller chick was Both parents proved extremely undernourished and blind in one eye, attentive, and adults were unusually whereas the larger chick was by far the tolerant of each other at the nest. The heaviest of all those weighed in that age female would stand over the male whilst group. The two lightweight chicks and the he brooded the chicks, and in hot sun she heavy chick account for the large weight would spread her wings fully in order to ranges shown in fig. 2 for the respective shade the young. Both adults fed the age groups. It is worth noting that no young bill to bill, one wasp at a time, aggression or sibling rivalry was evident, in each other’s presence. Extracting a contrasting with Continental video footage single wasp grub at a time without to the contrary. damaging the comb or larva may be During extended watches at the nests of achieved by virtue of the strange tongue of one pair over three years, the male the Honey-buzzard (plate 120). Unlike that provisioned the young and the female with of other raptors, it is fatter and tubular, and all the food. He also took a large share of we speculate that it may be pushed into the the brooding during some periods (plate comb chambers and drawn back, lifting the 121). At one watch (with young 14 days larvae slightly by suction, thus enabling old), between 07.25 and 14.10 GMT, the easy withdrawal with the bill tip. female left the nest at our arrival and then After the young have fledged, they attended the nest at 09.25 (for one minute), return to the nest to be fed. The male at 09.52–11.06 (for 1 hour 14 minutes, heralds his arrival with food by uttering a

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melancholy, trisyllabic whistle. This causes wasps’ nest had been completely rebuilt, the fledged young to return immediately to and was subsequently raided by the the nest, calling in response. By imitating Honey-buzzard. this call, one nest was found in a suspected Within the forested areas in the uplands nest area. and central hills, the thick, soft needle layer, Little information has been obtained which becomes friable when dry, must once the young leave the nest, but at least facilitate the excavation of wasps’ nests. two chicks have been found soon after This type of habitat may play an important fledging. One was killed by a predator role in the success of pairs in these two when grounded and another was found areas. A study in France (Yeatman 1976) weak and wet and was taken into care. A indicated that, although high wasp third chick (ringed) was recovered in its populations are to be found in the first autumn (1995), but the recovery data Mediterranean area, Honey-buzzards breed are not available. in very low numbers because excavation of nests is too difficult in the arid conditions. DIET This has also been suggested as a reason for Wasp larvae were the staple food provided failure in Devon during hot, dry summers for young Honey-buzzards at all nests (R. Khan verbally), although this needs inspected, although a variety of other further investigation as chicks thrived invertebrate and vertebrate prey was elsewhere under similar conditions. recorded. During incubation, it is likely that Adult males travel considerable dist- off-duty males spend some time locating ances, often as much as 7-8 km, to search for developing wasps’ nests in the feeding the nests of wasps or bees. One Honey- territory for future use. If males could not buzzard was closely observed raiding readily relocate wasps’ nests, then it is a wasps’ nest and then carrying the comb difficult to imagine how chicks could thrive 5 km to its nest (A. Page verbally). Adults during some of the inclement weather have been seen foraging on open moorland experienced in the uplands. With heavy and are often seen returning to their and prolonged rainfall, locating wasps’ nests carrying comb from moorland nests without prior knowledge seems and heathland several kilometres away. difficult by the methods described (i.e. Females are not often identified making following worker wasps back to the colony: these long-distance flights, and it is Brown 1976). During periods of poor presumed that they feed closer to their weather in the uplands, nestlings were nests and travel under the woodland provided with copious amounts of wasp canopy. Indeed, one female was seen comb and two chicks were invariably returning to her nest along woodland rides raised (plate 119). from a wasps’ nest which she had raided Once found, large wasps’ nests are about 400 m away. There is evidence from revisited over several days, providing food the Continent of differences between male whatever the weather. Honey-buzzards and female foraging distances, with have been observed raiding the same nest breeding males having a home range of 500 over a period of two or three days until ha and females only 250 ha (Kostrzewa in little is left. At one site, seven wasps’ nests press). Anita Gamauf also found smaller were found preyed upon within 150 m of a home ranges for females than males in nest containing two one-week-old Honey- Austria (Rob Bijlsma in litt.). At one nest in buzzards. Some of the wasps’ nests were our study, however, the female often only partly damaged, and the wasps were travelled long distances to collect food (G. still active. All debris and comb fragments Hinchon verbally). Wasps’ nests close to were removed from the damaged nests and Honey-buzzard nests (within 400 m) have the site revisited ten days later. At least one been preyed upon during incubation, and

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Table 4. Vertebrate prey recorded at nests of Honey-buzzards Pernis apivorus in Britain.

Prey Number of occasions Common Frog Rana temporaria 6 Common Lizard Lacerta vivipara 5 Wood Pigeon Columba palumbus 3 Meadow Pipit Anthus pratensis 2 Snake 2 Common Mole Talpa europaea 1 Rabbit Oryctolagus cuniculus 1 Brown Hare Lepus europaeus 1 Grey Squirrel Sciurus carolinensis 1 this is thought to be the work of the reflect selection on the part of the Honey- females. Observations in France revealed buzzard related to the peak activity for the wasps’ nests dug out close to Honey- respective species. Common Wasps were buzzard nests containing recently fledged represented by high numbers in most nests, young. are widespread throughout Britain, and Analysis of faecal samples collected nest underground. Norwegian Wasps were during our nest visits confirms that wasps found to be more prevalent in the upland dominate the diet (Lucy Parnell, in litt., samples, with relatively few in the lowland analysed 13 samples from nine nests samples (Parnell found the percentage collected in 1995 & 1996; Caroline frequency of Common or Red Wasps in the Saunders, in litt., analysed 12 samples from uplands, central hills and lowlands to be 16, five nests collected in 1997). Only insect 33 and 51; the corresponding figures for remains were found and these comprised Norwegian Wasp being 71, 10 and 19. mainly Common Wasp vulgaris and Saunders looked at the proportions of Red Wasp V. rufa, with Norwegian Wasp different wasp species per sample and Dolichovespula norvegica well represented in found 14-20% Norwegian in the uplands, the uplands. Three other species were but none in the lowland sample.) This found in very low numbers: Cuckoo Wasp species is more common in the west of V. austriaca, Tree Wasp D. sylvestris and Britain and nests mainly in trees; it may, Hornet Vespa crabro. No remains of German therefore, be the most abundant and Wasp were found, despite accessible species to breeding Honey- its being widespread and numerous. buzzards in many areas. Norwegian Wasp Parnell also found the remains of one non- availability may have an influence on the vespid insect, but, although present in all success of upland nests. her samples, it could not be identified. In addition to wasp comb, nests of One should be wary of drawing bumble-bees Bombus were often found at conclusions from the small number of Honey-buzzard nests in the uplands. samples, but analysis indicated that there Bumble-bees are often active despite bad may be variation in prey–species weather and are common on the heather composition throughout the season and moors which Honey-buzzards frequent. across regions. A larger proportion of These species may play an important role in Norwegian Wasps was found in July the nesting success of Honey-buzzards in samples and larger proportions of the wetter, upland regions within its range Common or Red in August samples in Britain. (Parnell found 91% of Norwegian Wasps in In addition to invertebrate prey, July samples and 59% of Common or Red vertebrate prey was recorded at nests Wasps in August samples). This could across the range of habitat types, and was

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taken even when wasp comb was same nest. Both squabs had been skinned abundant. Vertebrate prey in May is rather than plucked. At another nest, a considered important to adults in restoring female Honey-buzzard was observed body-fat levels to breeding condition after tearing flesh from a fledged Wood Pigeon the long spring migration. Favourable and feeding it to chicks about three weeks weather in May, enabling good foraging by old. Nests in France have contained females, is important to breeding success skinned Turtle Dove Streptopelia turtur (Kostrzewa in press), probably more so squabs as prey. than its effect upon wasp availability for the young in July and August. Indeed, Rob POPULATION Bijlsma (in litt.) says that, in many years in Recent population estimates of the number which wasps were poorly represented as of Honey-buzzards in Britain have prey items, Honey-buzzards enjoyed increased from ‘probably less than ten pairs’ excellent breeding success, possibly by (Brown 1976) to ‘possibly twenty or more preying on frogs and nestling birds (mainly breeding pairs in 1988’ (Spencer et al. 1990), pigeon squabs Columba and thrushes to ‘up to thirty pairs summering but not Turdus) (table 4). necessarily breeding’ (Batten et al. 1990) and An adult hare is a very unusual prey between 14 and 34 pairs breeding in 1996 item, but the carcase consisted of the head, (Ogilvie et al. 1999). Undoubtedly, this pelt and back legs, which was probably reflects a real increase in numbers over the picked up as carrion. A Grey Squirrel tail past 30 years. In our view, the most found on another nest involving the same important factor has been the colonisation pair may possibly have been used merely of upland forests in western and northern as decoration. Britain. Importantly, the present success One nest with two chicks had a large rate for Honey-buzzards breeding in wasps’ nest and a Wood Pigeon Columba managed plantations may be due to the palumbus squab, followed by another squab recent fundamental change in forest two days later, presumably raided from the structure now that plantations have entered

120. Adult female Honey-buzzard Pernis apivorus, found at roadside, stunned but uninjured, showing tubular tongue; June 1993 (R. A. Frost)

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121. Male Honey-buzzard Pernis apivorus about to brood small young at site in Scots Pine Pinus sylvestris; central hill conifer plantation; July 1996 (S. J. Roberts) a second rotation. Extensive clear-felling DISCUSSION and the presence of variable-age timber This study has proved to pose more have created a whole new habitat for the questions than it has answered. If anything, species. it has shown how little is known about the If all the upland forests in Britain were Honey-buzzard in Britain. Analyses of occupied at the density which we have faecal samples hint at differences in vespid encountered, there would be a population food between upland and lowland, but of over 200 pairs. We have no evidence that there is a desperate need for more samples. such a population exists and, in our Excellent breeding success, apparently experience, large areas of seemingly against all the climatic odds, confound suitable woodland are at present devoid of perceived wisdom regarding the suitability Honey-buzzards. of this country’s climate; but, again, many Upland forests are often remote and more nests need to be examined to gather difficult to monitor for such a secretive hard data on productivity. Supposition and species and, in areas where public hearsay regarding this species’ sensitivity to recreation is encouraged, disturbance may disturbance have proved, in every instance, render some woods unsuitable. ill-founded. Testimony to this is the Colonisation may be at a very early stage continued high breeding success, year after and evidence of an increase in the numbers year, of pairs visited during this study. This of those ‘summering’ suggests that this is a misconception that Honey-buzzards are prelude to future colonisation. particularly vulnerable to disturbance has The current British population is, in our been a major factor in the difficulties faced view, 50-60 breeding pairs and, at the by the authors in gathering data for this current rate of expansion, it does not seem publication. Tubbs (1993) supported a unduly optimistic to predict that a pop- policy of no disturbance by referring to two ulation of 100 pairs will be reached in the woodlands at Nijmegen in the Netherlands, not too distant future. one of which was heavily disturbed through recreational use, housing and major roads,

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whereas the other received little disturbance. and editing of this paper, providing time, The latter held six breeding pairs of Honey- information, advice and encouragement. buzzards, and the former only one. This Without them this paper would have example could illustrate that, not proved impossible to produce. Some, in surprisingly, Honey-buzzards are deterred order to protect the confidentiality of from nesting by high levels of continuous breeding sites, wish to remain anonymous. disturbance. This cannot, however, be These include various Forest Enterprise equated to disturbance caused by district rangers and personnel, private infrequent collection of data for scientific landowners, gamekeepers and agents. purposes carried out effectively by Their help and support have been essential. experienced ornithologists. More importantly, In addition, we should like to thank: however, the data do not even support Gordon Allan, Simon Aspinall, Bill Ayers, Tubbs’ conclusion, as Paul Opdam (the Rob Bijlsma, Linda Birch, Dave Burges, source of the data) censused these areas Nick Christian, Peter Clement, Rob only for Northern Goshawk and Eurasian Clements, Mike Coleman, Steve Cooper, Sparrowhawk, so statements on numbers Jane Corbishley, Malcolm Cowlard, Charles and densities of Honey-buzzards are Critchley, A. V. Cross, Fred Currie, Ian speculative (Rob Bijlsma in litt.). Moreover, Dawson, P. J. Everitt, Dr Peter Ferns, Roy Rob Bijlsma, who is familiar with these Frost, G. J. Hinchon, John Holmes, Richard woodlands, states that the large differences Jacobs, Robin Khan, D. R. King, Simon in habitat quality and food supply between Lester, Patrick Lindley, Kevin May, Dr the areas would be the more likely cause of Malcolm Ogilvie, Andy Page, Lucy Parnell, different densities. In his opinion, based on Steve Parr, Wayne Percy, John Roberts, visits to hundreds of nests, Honey-buzzards Caroline Saunders, Mike Shrubb, Rik are much more tolerant of human activities Smith, Cliff Smout, Ian Spence, Dick than is any other raptor species. Misleading Squires, J. Stacey, Adrienne Stratford, interpretations have caused an unwilling- Vaughn Thomas, Mike Thornley, Reg ness to record any but the most basic Thorpe, Jon Westlake, Gwyn Williams and information, exacerbated, in some areas, by Vanessa Williams. an unwillingness to share information. Those with concerns regarding the tolerance REFERENCES of Honey-buzzards to disturbance would Bannerman, D. A., & Lodge, G. E. 1956. The Birds of the British Isles. vol. 5. Edinburgh. certainly broaden their views upon reading Batten, L. A., Bibby, C. J., Clement, P., Elliott, the chapter on Honey-buzzards in Sporting G. D., & Porter, R. F. 1990. Red Data Birds in Interludes at Geneva (Buxton 1932). Britain. London. —, Dennis, R. H., Prestt, I., & the Rare Breeding We hope that this paper will help to Birds Panel. 1979. Rare breeding birds in the foster more-enlightened attitudes, so that United Kingdom 1977. Brit. Birds 72: 368. information can be shared and made Bijlsma, R. G. 1998. Handleiding veldonerzoek Roofvogels. available in the future to assist in the Brown, L. 1976. British Birds of Prey. London. understanding and consequent conservation Buxton, A. 1932. Sporting Interludes at Geneva. of the Honey-buzzard in Britain. In London. Cramp, S., & Simmons, K. E. L. (eds.) 1980. The Europe, great strides are already being Birds of the Western Palearctic. vol. 2. Oxford. taken by Fridtjof Ziesemer and Nils Kjellén Farren, W. 1862. Note on the breeding of the to increase our knowledge of Honey- Honey Buzzard in the New Forest. Zoologist buzzards, by means of radio-tagging and 20: 8159. Forsman, D., & Shirihai, H. 1997. Identification, satellite transmitters. ageing & sexing of Honey Buzzard. Dutch Birding. 19: 1-7. ACKNOWLEDGMENTS Génsbøl, B. 1986. Collins Guide to Birds of Prey in Britain and Europe, North and the Middle Many people have given considerable help East. London. with the fieldwork, research, compilation Gibbons, D. W., Reid, J. B., & Chapman, R. A.

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1993. The New Atlas of Breeding Birds in Britain in Britain and Ireland. Tring. and Ireland: 1988-1991. London. — & the Rare Breeding Birds Panel. 1975. Rare Hollom, P. A. D. 1957. The rarer birds of prey: breeding birds in the United Kingdom 1974. their present status in the British Isles. Honey Brit. Birds 68: 493. Buzzard. Brit. Birds 50: 141-142. Spencer, R., & the Rare Breeding Birds Panel. Holloway, S. 1996. The Historical Atlas of Breeding 1990. Rare breeding birds in the United Birds in Britain and Ireland: 1875-1900. London. Kingdom in 1988. Brit. Birds 83: 353. Irons, A. 1980. Breeding of the Honey Buzzard in Spradbery, J. P. 1973. Wasps. London. Nottinghamshire. Derby. Tubbs, C. R. 1974. The Buzzard. Newton Abbot. Kostrzewa, A. 1989. The effect of weather on — 1993. In Gibbons, D. W. et al. The New Atlas of density and reproduction success in Honey Breeding Birds in Britain and Ireland: 1988-1991. Buzzards Pernis apivorus. In Meyburg, B. U., & London. Chancellor, R. D. (eds.), Raptors in the Modern Walker, C. W., & Smith, A. J. 1975. Herefordshire World. Berlin, London & Paris. Birds. Hereford. — In press. Honey Buzzard. BWP Update. Yeatman, L. 1976. Atlas des Oiseaux Nicheurs de Lilford, Lord. 1895. Notes on the Birds of France. Paris. Northamptonshire and Neighbourhood. London. Lovegrove, R., Williams, G. A., & Williams, I. 1994. Birds in Wales. London. Martin, P. 1992. Birds of Prey of the British Isles. AUTHORS Newton Abbot. S. J. Roberts, Ty-Canol, Church Lane, Llanfair- Newton, I. 1979. The Population Ecology of Raptors. Kilgeddin, Abergavenny, Monmouthshire Calton. Ogilvie, M. A., & the Rare Breeding Birds Panel. NP7 9BE 1999. Rare breeding birds in the United J. M. S. Lewis, Y Bwthyn Gwyn, Coldbrook, Kingdom 1996. Brit. Birds 92: 131. Abergavenny, Monmouthshire NP7 9TD Parslow, J. L. F. 1973. Breeding Birds of Britain and Ireland. Berkhamsted. I. T. Williams, Bronallt, Y-Fron, Caernarfon, Sharrock, J. T. R. 1976. The Atlas of Breeding Birds Gwynedd LL54 7BD

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