On The Vultures Of Africa

Transcription

1 110 On The Vultures Of Africa Peter J. Mundy Dept. National Parks, Box 2283, Bulawayo, Zimbabwe Abstract The Old World vultures comprise 15 species in Africa, Asia and Europe, of which 11 occur or occurred in Africa. They are to be seen as scavenging eagles, clearly related to other eagles in the family though having their own set of adaptations. However, the vultures are not all closely related to each other, but indicate three different lines of evolution (polyphyletic). Vultures are among the largest flying birds to be found today, with wingspans up to three metres and weights up to 11 kg. They are famous for their ability to ride high above ground level in thermals, perhaps on occasion up to 10,000 m a.s.l. and they may even take advantage of jet streams. At least one species has a unique form of haemoglobin which allows it to use the low oxygen levels at these heights, and all the species are well wrapped in downy feathers. When gliding across the African savannas, birds have been clocked at speeds up to 100 kph. So a flying griffon is a formidable object in the skies. In addition, as is very well known, vultures can gather in large numbers at a food source, whether it be 1000 birds at a dead elephant or 500 birds at an abattoir. Such congregations have also included thousands at airports in India. Indeed, vultures have been party to strikes with aeroplanes, including the tragic death of young Michael Grzimek over the Serengeti, as just one example. The birds actually like to fly in formation with gliders. Eurasian griffons and Egyptian vultures migrate into (and out of) Africa at three main points: Gibraltar, Suez/Red Sea, and Bab-al-Mandab. They then seem to disperse widely over the savannas and mountains south of the Sahara, and to date have been lost to us. This is one of the big unknowns of African vulture study. Résumé Il existe 15 espèces de vautours en Afrique, Asie et Europe dont 11 existent ou ont existé en Afrique. On doit les considérer comme des aigles charognards, visiblement proches des autres aigles bien qu ils aient leurs propres adaptations. Cependant, les vautours ne sont pas tous aussi proches les uns des autres. Il existe trois lignages évolutifs (polyphylétiques). Les vautours sont parmis les plus grands oiseaux volants actuels, avec des envergures atteignant 3 mètres et un poids allant jusqu à 11 kg. Ils sont réputés pour leur capacité à voler très haut grâce aux ascendances thermiques, probablement jusque 10,000 mètres au dessus du niveau de la mer et ils peuvent même utiliser des vents de haute altitude. Au moins une espèce possède un forme unique d hémoglobine qui lui permet d utiliser les faibles taux d oxygène à très haute altitude et toutes les espèces sont bien protégées par un duvet. Lorsqu ils plannent au dessus des savannes africaines, ces oiseaux peuvent atteindre la vitesse de 150 kilomètres par heure. Un vautour est donc un magnifique objet dans les airs.

2 111 De plus, il est bien connu que les vautours peuvent se rassembler en grand nombre là où il y a de la nourriture, que ce soit 1000 individus près d un éléphant mort ou 500 à un abattoir. De tels rassemblements ont compté plusieurs milliers de vautours dans des aéroports en Inde. En effet, les vautours ont été impliqués dans des collisions avec des avions, dont la mort tragique du jeune Michael Grzimek au dessus du Serengeti, pour ne citer qu un exemple. Les vautours aiment en fait voler de concert avec les planneurs. Les vautours fauves et les percnoptères d Egypte migrent vers (et depuis) l Afrique à trois endroits principaux: Gibraltar, Suez/la Mer Rouge et Bab-al-Mandab. Il semble qu ensuite ils se dispersent largement au dessus des savannes et montagnes du Sahara pour nous échapper totalement. Ceci constitue un des grands mystères pour l étude des vautours. Introduction Very much has been written about vultures over the years, as they are such conspicuous and (sometimes) awe-inspiring birds. They are also widely distributed on three continents in the Old World and on two in the New World, and a few species have even adopted quite an intimate relationship with humans. Whereas a detailed review of vultures in Africa has been published (Mundy et al 1992), such is unfortunately not yet comprehensively available for Asia or Europe, or for North and South America (but see Kiff 2000, Satheesan 2000, Schlee 2000). One could note in passing that it is now frequently accepted that the vultures of the Old World and those of the New World are not closely related. The former can be thought of as scavenging eagles (Accipitridae family in the Falconiformes) whereas the latter are perhaps scavenging storks (Cathartidae family in the Ciconiiformes?). Both groups have certain characteristics in common - for example a hooked bill, naked or downy head, food-holding crop - such that they illustrate very well the phenomenon of convergent evolution (Houston 2001). In addition, within the Old World vultures, commonly regarded as comprising 15 species, there are at least three different evolutionary lines (polyphyletic) (Seibold & Helbig 1995). Finally, it should be emphasised that within this group of birds there is a smaller group of five species of super -vultures, all of which should colloquially be called griffons. They exhibit a whole set of adaptations to a life scavenging on the carcasses of large (migratory) animals (Houston 1983). My purposes in this article are to bring together facts about vultures that are relevant to the bird-strike problem on aeroplanes, and to explore the vulturine connections in the Old World among the three continents of Africa, Asia and Europe. Vultures and bird strikes Some vultures are among the world s largest flying birds (Table 1), for example the cinereous vulture (scientific names are listed in Table 2) is said to weigh up to 12,5 kg, and the lappetfaced vulture has a wingspan up to 2,9 m. The adult cape griffon (Photo 1) would probably have a weight of about 9 kg and a wingspan of about 2,5 m and is a considerable flying

3 112 Weights Wingspans Flying heights Glide speed Haemoglobin Table 1: Some physical characteristics of Old World vultures 1,18-12,5 kg 1,50-2,90 m (?) m a.s.l. up to 96 kph 4 types in Rüppell s Griffon (unique) object. In addition, the griffons are renowned for flying together (Photo 2) at their colonies and in particular in thermals over open country. In the latter they would usually be outnumbered by the common white-backed vultures (av. weight about 5 kg). A thermal of around 100 circling vultures is an awesome sight - but not for an aeroplane pilot. When foraging, vultures would perhaps usually fly along at about 300 m a.g.l. and at gliding speeds of up to 96 kph. At times they will fly or soar at very much higher altitudes than 300 m, even up to m a.g.l., though they have rarely (if ever) been seen by pilots at these phenomenal altitudes. Here, the partial pressure of oxygen is very low, and the cold is very intense, but vultures - at least the Rüppell s griffon - can cope with these well, it seems. Among other adaptations, this griffon is so far unique in having four haemoglobins in its blood, with strong affinities for oxygen. Vultures are also renowned for congregating in numbers at a carcass. A dead elephant can attract 1000 birds at a time and for several days, and even a small impala can bring in up to 250 (though over a few hours only). Other well-known congregations occur at abattoirs; for example 500 Hooded Vultures at Kumasi, or up to 600 of three species west of Bulawayo. Nothing to my knowledge in Africa, however, compares with the astounding numbers that (used to) occur at airports and rubbish dumps in India - except at the Addis Ababa slaughterhouse where more than 5000 vultures and other birds of prey are present (Yohannes & Bekele 1998). All of these attributes - large size, soaring ability, congregating and ability to live in towns - make some vultures, and in particular the hooded and African white-backed vultures, formidable objects in the skies. These two species are also probably the most numerous in sub-saharan Africa. They have caused several fatal strikes on aeroplanes, including one with Michael Grzimek s light aircraft over the Serengeti. Indeed, vultures even try and fly in formation with gliders, in a behaviour which was exploited by Dick Reucassel over 40 years ago in his film Whispering Wings. That vultures have not been involved in more accidents is testament, I suppose, to their expertise and manoeuvrability in the air - they can drop out of the way, almost like a stone, in spite of their size. It should be easy to keep vultures away from airports, simply by cleaning up any likely food source. There should be no carcasses, no messy abattoirs, no bone dumps, nor even any rubbish dumps, within several kilometres of an airport.

4 113 Species Africa Europe Asia Eurasian griffon Rüppell s griffon Cape griffon Long-billed griffon Himalayan griffon African white-backed vulture Indian white-backed vulture Lappet-faced vulture Cinereous vulture White-headed vulture Pondicherry vulture Hooded vulture Bearded vulture Egyptian vulture Palm-nut vulture Gyps fulvus* G. rueppellii G. coprotheres G. indicus G. himalayensis Pseudogyps africanus P. bengalensis Torgos tracheliotos Aegypius monachus Trigonoceps occipitalis Sarcogyps calvus Necrosyrtes monachus Gypaetus barbatus Neophron percnopterus* Gypohierax angolensis *Strongly migratory +Extinct (1) In the Middle East only Table 2: The species of Old World vultures and their continents of distribution. + (1) Continental connections The distributions of each species of vulture in the Old World are shown in Table 2. Four species are/were recorded on all three continents, but of these only two - Eurasian griffon and Egyptian vulture - are strongly migratory. In the former, mostly the juveniles migrate to North Africa and Ethiopia, and even Kenya (Clark 2001), and presumably return in the following spring, while in the latter all ages migrate. As far as is known, all migratory routes are on a north-south axis (e.g. Yosef & Alon 1997), and there are three main gateways into and out of Africa, viz. Straits of Gibraltar, northern Red Sea (Eilat, Suez), and Bab-al-Mandab strait. Table 2 indicates that all the European vultures are also represented in Asia, and indeed into the Indian subcontinent. But it is not known whether there is any connection - or gene flow - between India and Europe in these species, and certainly no east-west (or

5 114 vice versa) movements or migrations have been discovered. In addition, the detailed distributions of vultures from western Pakistan through Afghanistan and Iran to Iraq and Saudi Arabia are not yet known (The atlas in Arabia is for breeding birds only). At the moment, and on the face of it, there is no known connection between European vultures and their conspecifics in the Indian subcontinent, unlike the well-known connection between Europe and Africa. Within this Palaearctic-African bird migration system, our assumption is that the vultures migrate to and from Africa from Europe, and do not stay in Africa to breed. If true, this clearly constrains any gene flow by these species, although of course they are presumed to mix - or socialise - with African vultures at carcasses (e.g. Clark 2001). In terms, then, of the Indian (or Asian) vulture crisis (Prakash 1999), and an infectious disease as the possible cause, there seems genuinely to be a very limited chance of the problem spreading westwards. Whether or not it does, I think that Israel and the Arabian peninsula are once again pivotal, and would act as an early-warning system for Africa. Within Africa itself, there is one further gateway or bottle-neck, and that is Kenya. African vultures are savanna birds, and start breeding at the end of the rainy season - about November north of the equator, and about May south of it. The great rain-belts cross over in Kenya which therefore has two rainy seasons. All vultures can breed only once per year, and must therefore choose which belt to be associated with. It seems to me that this will be a further barrier to gene flow between vulture populations north and south of Kenya, though of course the individual birds would presumably mix at carcasses. Acknowledgements I am grateful to Yossi Leshem for the invitation to attend the African seminar in Israel in May 2001, and to him and Keren Or for the impeccable arrangements. Air Zimbabwe provided my free return ticket to London. References Clark, W.S First record of European Griffon Gyps fulvus for Kenya. Bull. Afr. Bird Club 8 (1): Houston, D.C The adaptive radiation of the griffon vultures, pp In: Vulture biology and management, (eds.) Wilbur, S.R. & Jackson, J.A. University of California Press: Berkeley. Houston, D Vultures & Condors. Colin Baxter Photography: Grantown-on- Spey (Scotland). Kiff, L.F The current status of North American vultures, In: Raptors at risk, (eds.) Chancellor, R.D. & Meyburg, B.-U. World Working Group on Birds of Prey and Hancock House, Berlin and Surrey (Canada):

6 115 Mundy, P., D. Butchart, J. Ledger & S. Piper The vultures of Africa. Acorn Books and Russel Friedman Books: Randburg and Halfway House (South Africa). Prakash, V Status of vultures in Keoladeo National Park, Bharatpur, Rajasthan, with special reference to population crash in Gyps species. J. Bombay Nat. Hist. Soc. 96: Satheesan, S.M Vultures in Asia. In: Raptors at risk, eds. Chancellor, R.D. & Meyburg, B.-U. World Working Group on Birds of Prey and Hancock House, Berlin and Surrey (Canada): pp Schlee, M.A The status of vultures in Latin America,. In: Raptors at risk, eds Chancellor, R.D. & Meyburg, B.-U. World Working Group on Birds of Prey and Hancock House, Berlin and Surrey (Canada): pp Seibold, I. & A.J. Helbig Evolutionary history of New and Old World vultures inferred from nucleotide sequences of the mitochondrial cytochrome b gene. Phil. Trans. R. Soc. Lond. B 350 : Yohannes, E. & A. Bekele Behavioural responses of vultures to aircraft at Bole Airport in Addis Ababa, Ethiopia. Vulture News; Yosef, R. & D. Alon Do immature Palearctic Egyptian Vultures Neophron percnopterus remain in Africa during the northern summer? Vogelwelt: 118 :