BREEDING EUROPEAN HONEY-BUZZARDS IN BRITAIN S. J. ROBERTS,J.M.S.LEWIS AND I. T.WILLIAMS European Honey-buzzards Pernis apivorus (S. J. Roberts) ABSTRACT The European Honey-buzzard Pernis apivorus has been one of the least-studied of Britain’s breeding birds, 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 Europe and eastwards and (c) upland coniferous plantations. The into boreal Asia (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). British Birds 92: 326–345, July 1999 327 BREEDING EUROPEAN HONEY-BUZZARDS IN BRITAIN 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 Wasp 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 wasps’ 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 insect 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. 328 British Birds 92: 326–345, July 1999 BREEDING EUROPEAN HONEY-BUZZARDS IN BRITAIN 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-bees, 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.