autumn raptor migration over Buskett, Malta

Transcription

1 Autumn raptor migration over Buskett, Malta and Edward Bonavia ABSTRACT The wooded area of Buskett, on the western side of Malta, is situated on an important flyway for many raptors in the autumn, yet there are few published data on the numbers migrating over the area each year. Here, we present the results of autumn counts during inclusive.these show that considerable numbers of raptors migrate through the site, and many use it for roosting purposes. Towards the end of August, when hot and humid summer weather is still at its best, the first grey cumulus clouds start to form in the sky. It might not rain at all, but it heralds the beginning of the autumn raptor migration The Maltese Archipelago consists of a small group of islands in the central Mediterranean, situated some 89 km south of Sicily and 334 km north of Libya. In spring, many of the birds heading north from the North African coast, and funnelling through Cap Bon, in Tunisia, choose the route with the shortest sea crossing this being towards the western coast of Sicily (146 km), from where most proceed farther north and east across the Strait of Messina. Situated well to the east of this direct route, the numbers of raptors migrating over Malta in spring are much lower than those observed at both the Strait of Messina and Cap Bon. In autumn, however, raptors converge over the eastern side of Sicily and fly along the east coast. Most of these will subsequently pass over Malta, since Malta is situated just to the west of a north-south line connecting Capo Passero, the southernmost point of Sicily, with the North African coast. Although the numbers of raptors crossing the central Mediterranean are not as large or impressive as those passing through the eastern and western parts of the Mediterranean, it is still an important migration flyway, especially for certain species. The Strait of Messina is the most important European migration flyway for Pallid Circus macrourus and Montagu s Harriers C. pygargus, Eleonora s Falcon Falco eleonorae and Longlegged Buzzard Buteo rufinus, while for three other species (Marsh Harrier C. aeruginosus, Common Kestrel F. tinnunculus and Hobby F. subbuteo), the site is the most heavily used flyway within the Western Palearctic (Corso 2001). In spring, raptors migrate over Malta on a broad front, generally from late February to mid May (sometimes into June), with peak passage between mid March and early May. Typically, the individual species peak at different times, and since the birds are often widely spread across the islands, it is extremely difficult to monitor migration from a single site. Autumn passage occurs from mid August to the end of October, with peak numbers between mid September (occasionally early September) and early October. Although still Gozo Comino Malta Buskett Fig. 1. Map showing location of the study site at Buskett, Malta. 318 British Birds 97 July

2 essentially a broad-front pattern passage in autumn is more concentrated than in spring, especially as raptors converge on the wooded area of Buskett where many attempt to roost. This pattern makes monitoring more feasible. Study area and methods Buskett comprises a small wooded area and a valley, surrounded by hills, in the western part of the largest island of the archipelago (fig. 1). At 220 m above sea level it provides a fine view over the northern and eastern half of the island. It is one of the few wooded areas in the islands and is thus attractive to raptors, combining an area of relatively high land (ideal for the formations of thermals) with a sheltered and reasonably safe roosting place. The highest numbers of raptors are observed towards late afternoon, concentrating over the wooded areas as they attempt to find a roost site. Weather conditions greatly affect observations. Light winds are best, southwest being the optimum direction. Northern-quarter winds tend to be stronger than those from other directions and result in fewer birds, although Short-toed Eagles Circaetus gallicus are usually seen in northerly winds. The data presented in table 1 were derived from systematic daily counts from mid August to late October during a five-year period, Observations were carried out between and hrs, and in all weather conditions. Raptors A total of 24 species and one distinctive subspecies (Common Buzzard B. buteo of the race vulpinus, hereafter referred to as Steppe Buzzard ) have been recorded at Buskett. Two of these are vagrants: Rough-legged Buzzard B. lagopus (a bird shot in 1956 is the only record of this species for Malta; de Lucca & de Lucca 1959) and Barbary Falcon F. pelegrinoides, of which one seen in 2002 will be the third record Table 1. Totals of each raptor species counted at Buskett, Malta, during autumn migration Totals Honey-buzzard Pernis apivorus 816 1,145 1, ,317 5,368 Black Kite Milvus migrans Red Kite Milvus milvus 1 1 Egyptian Vulture Neophron percnopterus 1 1 Short-toed Eagle Circaetus gallicus Marsh Harrier Circus aeruginosus 1,129 1,310 1,948 1,265 2,056 7,708 Hen Harrier Circus cyaneus Pallid Harrier Circus macrourus Montagu s Harrier Circus pygargus unidentified ringtail harrier Circus Eurasian Sparrowhawk Accipiter nisus Common Buzzard Buteo buteo Steppe Buzzard Buteo buteo vulpinus unidentified broadwing sp Lesser Spotted Eagle Aquila pomarina Booted Eagle Hieraaetus pennatus Osprey Pandion haliaetus Lesser Kestrel Falco naumanni Common Kestrel Falco tinnunculus Lesser/Common Kestrel Merlin Falco columbarius Hobby Falco subbuteo Eleonora s Falcon Falco eleonorae Saker Falcon Falco cherrug 3 3 Peregrine Falcon Falco peregrinus Barbary Falcon Falco pelegrinoides 1 1 unidentified falcon Falco TOTALS 2,289 2,881 3,986 2,463 3,905 15,524 British Birds 97 July

3 for Malta if accepted by the Maltese Rarities Committee. One other species, Lesser Spotted Eagle Aquila pomarina, is also extremely rare, although a group of four adults and a juvenile seen on 13th October 2001 is the largest flock of this species ever recorded in the central Mediterranean in autumn. The site is a major flyway for Honey-buzzards Pernis apivorus, Marsh Harriers, Common Kestrels and Hobbies. The most numerous species in autumn are Marsh Harrier (mean 1,542 individuals per autumn, range 1,129-2,056) and Honey-buzzard (mean 1,074, range 627-1,463); followed by Common Kestrel (mean 134, range ) and Hobby (mean 124, range ). Other species which are also recorded annually in relatively large numbers include Osprey Pandion haliaetus, Lesser Kestrel 187. Honey-buzzards Pernis apivorus, Buskett, Malta, May Verdala Castle, which dominates the skyline of Buskett, on the western side of Birkirkara, Malta, January British Birds 97 July

4 189. Honey-buzzard Pernis apivorus, Buskett, Malta, May F. naumanni and Eleonora s Falcon. Honey-buzzards, Marsh Harriers, Ospreys, Lesser Kestrels and Hobbies are seen throughout the whole autumn period, peaking on different dates from year to year. Adult Honey-buzzards migrate mainly in early September while juveniles (the majority of autumn migrants are juveniles) peak later in the month. Black Kites Milvus migrans, Montagu s Harriers and Eleonora s Falcons are seen mainly from the end of August to mid September, whereas Eurasian Sparrowhawks, Common Buzzards, Common Kestrels and the larger eagles are seen in mainly late September and October. Overall, the number of raptors observed at Buskett has been increasing during our study period. This is due mainly to the numbers of Marsh Harriers, which have increased steadily during the recent years and now overtaken Honey-buzzard as the most numerous raptor observed. For example, during , total counts of autumn Marsh Harriers varied between eight and 80 (Beaman & Galea 1974). On 13th September 2002, no fewer than 1,014 were recorded over Buskett, the highest daily count yet recorded. The increased frequency of certain species, such as Pallid Harrier and Steppe Buzzard, can be attributed, at least in part, to improved field-identification skills and knowledge, together with better optical aids. On the other hand, species recorded more frequently in the past, like Egyptian Vulture Neophron percnopterus, seem to have almost disappeared. This species breeding population has declined considerably (Levy 1996), in Italy by 40-60% with now only about breeding pairs left (Corso 2000). Most probably the ones British Birds 97 July recorded in Malta are from the Italian population. As stated above, Buskett is of particular importance in providing the only relatively safe roosting place on the islands, particularly for Honey-buzzards and Marsh Harriers. An unusual roosting behaviour observed regularly at Buskett involves the latter species roosting in trees: single birds were first noted in 1981 (Balzan & Fenech ), while flocks of treeroosting Marsh Harriers were first noted in 1991 (Mallia & Mangion 1991). On a few occasions in recent years, flocks of Marsh Harriers have roosted in trees at Buskett, chiefly in Aleppo Pines Pinus halepensis and cypress Cupressus trees. Owing to the numbers of other migrants present, particularly hirundines, the area is also frequently used as a hunting ground during migration. The key species are Eurasian Sparrowhawk, Common Kestrel, Hobby and Eleonora s Falcon. These species are frequently seen hunting small passerines and dragonflies (Odonata), while on one occasion, we observed an Eleonora s Falcon hunting pipistrelle bats Pipistrellus pipistrellus. Conclusion As the data in table 1 illustrate, Buskett is an important migration and roosting site for various raptor species during the autumn months. Unfortunately, owing to the lack of observers in our country, it is not possible to cover all potentially good sites for raptor migration, so the data in table 1 probably underestimate the true numbers of raptors passing through Malta in autumn. In addition, an unde- 321

5 190. Osprey Pandion haliaetus, Buskett, Malta, date unknown. termined number of raptors (sometimes relatively large numbers) migrate in the morning and are therefore not included in this paper. The raptors attract not only birders but also poachers, and for many years an unbelievable massacre of raptors and other birds took place at Buskett, notwithstanding the fact that it is a bird sanctuary and thus no hunting is permitted. Consequently, every year, birdwatchers have been going to Buskett not only to watch, count and identify birds but also to protect them by establishing a presence and reporting any illegal activities. In recent years, this has been aided by frequent police patrols and by foreign activists who attend a raptor camp and has resulted in the lowest-ever numbers of raptors being shot within Buskett. Sadly, many raptors continue to be shot in the immediate surroundings and rest of the islands. Acknowledgments We would like to thank all the local birdwatchers who assisted us in the field observations, especially David Attard, Norman Bonavia, Raymond Galea and Marvic Sammut. Special thanks go to Andrea Corso for his invaluable help and field identification discussions; and also to Carmela Cardelli, Gianluca Chiofalo, Anna Giordano and Deborah Ricciardi from the Strait of Messina. We also wish to thank David Attard, John Azzopardi, Jules Bos, Oliver Cardona, Bill Clark, Raymond Galea, Roberto Gildi, Cristoph Hein, Renzo Ientile, Ottavio Janni, Klaus Malling Olsen, Guido Premuda and Remo Probst for their assistance in preparing this paper. References Agostini, N., & Logozzo, D Autumn migration of Accipitriformes through Italy en route to Africa. Avocetta 21: & Malara, G Entità delle popolazioni di alcune specie di rapaci Accipitriformi migranti, in primavera, sul Mediterraneo centrale. Riv. Ital. Orn. 66 (2): Balzan, S., & Fenech, N Marsh Harriers roosting in trees. Il-Merill 22: Beaman, M., & Galea, C The visible migration of raptors over the Maltese Islands. Ibis 116: Corso, A La migrazione del Capovaccaio. Quaderni di birdwatching 4: Raptor migration across the Strait of Messina, southern Italy. Brit. Birds 94: Cramp, S., & Simmons, K. E. L The Birds of the Western Palearctic.Vol. 2. OUP, Oxford. de Lucca, C., & de Lucca,V Note sull ornitologia delle Isole Maltesi. Riv. Ital. Orn. 29 (2): Ferguson-Lees, J., & Christie, D. A Raptors of the World. Christopher Helm, London. Giordano, A The migration of birds of prey and storks in the Strait of Messina. Birds of Prey Bull.4: Gustin, M., & Pizzari,T Migratory pattern in the genus Circus: sex and age differential migration in Italy. Ornis Svecica 8: Hein, C., & Kissling, M Der Fruhjahrszug von Greifvogeln und Storchen auf der mittleren Zugschiene.Tunesien-Sizilien 1990/1991. DBV. & Der Fruhjahrszug von Greifvogeln und Storchen auf der mittleren Zugschiene.Tunesien-Sizilien DBV. Levy, N Present status, distribution and conservation trends of the Egyptian Vulture (Neophron percnopterus) in the Mediterranean countries and adjacent arid regions. In: Muntaner, J., & Mayol, J. (eds). Biologìa y Conservacìon de las Rapaces Mediterràneas, Monografìas, no. 4. SEO, Madrid. Mallia, M., & Mangion, J. M Marsh Harriers roosting in Aleppo Pines at Buskett. Il-Merill 27: 27. Sultana, J., & Gauci, C A new guide to the birds of Malta.The Ornithological Society.Valletta, Malta. Thiollay, J. M Migration de printemps au Cap Bon (Tunisie). Nos Oiseaux 33: Zalles, J. I., & Bildstein, K., L. (eds.) Raptor Watch: A global directory of raptor migration sites. BirdLife International, Cambridge., 11 Rigu Aley, Birkirkara, BKR 05, Malta Edward Bonavia, Rossignol, Spartans Street, Blata L-Bajda, Malta 322 British Birds 97 July