1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 Superpilots 8 9 9 10 10 11 migration in Africa 11 12 Jane K. Turpie 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 Each year, thousands of 28 29 29 30 millions of African undertake 30 31 31 32 seasonal movements, ranging 32 33 33 34 from a few hundred kilometres to 34 35 35 36 epic trans-continental journeys of 36 37 37 38 more than 10 000 kilometres. 38 39 39 40 Of the approximately 1 800 bird 40 41 41 42 species found in sub-Saharan 42 43 43 44 Africa, nearly 200 species migrate 44 45 seasonally between the Palearctic 45 46 46 47 (Europe and Asia) and Afrotropical 47 48 48 49 (sub-Saharan Africa) regions. 49 50 50 51 A further 50 or so migrate between 51 52 52 53 Africa and the New World, 53 54 54 55 Antarctica and oceanic islands. 55 56 56 57 In addition to these, more 57 58 58 59 This intra-African migrant, the Diederik , will have than 580 species are known to 59 60 tackled the journey from southern Africa to its tropical 60 61 non-breeding grounds and back without ever having had undertake seasonal migrations 61 contact with its parents. 62 nigel j dennis/abpl 62 within the continent. 63 1 here is no common thread linking habitats which undergo marked seasonal 1 2 the migratory bird species of changes in environmental conditions how do migrant birds 2 find their way? 3 T Africa. They are almost as diverse are more likely to be migratory. Species 3 4 as the resident species, representing nearly which have ‘opted’ for a migratory way 4 uch of migratory behaviour is 5 all of the 21 Orders of birds found on the 5 of life generally take advantage of the Minherited genetically. Although the 6 continent. Migrants are as different from relatively high summer productivity in majority of newly fledged juveniles set off 6 7 one another as from , waders strongly seasonal habits, either just for on migration in family parties or in flocks 7 8 from raptors and from warblers, to breeding or, in the case of trans-equatorial with adults, the juveniles of many species, 8 9 name a few. There is nothing that makes migrants, for both the breeding and particularly those breeding in the 9 regions, depart without (usually later than) 10 migratory species stand out from their non-breeding seasons. Migration allows carmine bee-eater 10 their parents. The youngsters will have 11 non-migratory counterparts: they gener- them to occupy high-quality breeding Breeding (March – Aug) 11 inherited a complex programme which 12 ally do not show any morphological ABDIM’S 12 habitats that would not be able to sustain guides them through their first migration Non-breeding 13 adaptations for migration in comparison them adequately (if at all) during the rest Breeding (May – Sept) Southern Breeding 13 experience, during which they develop and carmine bee-eater

14 to closely related resident species. Even of the year. expand their ‘familiar area’. Non-breeding Breeding (Oct – Feb) Non-breeding 14 15 body size appears to form no barrier: Afri- Experimental evidence suggests that, 15 The extreme mobility of birds in Africa Non-breeding 16 can migrants range in size from the nine raises questions about the seasonal on the programmed date, birds set off on 16 17 kilogram Dalmation Pelican Pelecanus changes in community composition, migration, travelling in a programmed Trans-equatorial migrants, such as Abdim’s Storks, may breed in the northern hemisphere and in the south, or vice versa. Other spe- 17 direction for a programmed length of time. 18 crispus to warblers less than one thou- cies, such as Carmine and Southern Carmine Bee-eaters, breed in more seasonal environments and spend the non-breeding season closer to 18 particularly with regard to competition The timing of migration is triggered with 19 sandth of that size. for resources between mig­rants and the aid of the bird’s ‘circannual clock’, and the tropics. Diederik capitalize on good breeding conditions in both northerly and southerly areas before moving to the tropics. 19 20 residents, and amongst the migrants is probably also linked to changing day 20 21 Why migrate? themselves. Although very little research length and in some cases, climatic cues. This surplus provides a niche for Patterns of migration among altitudinal migrants from sum- 21 22 has assessed competition between resi- Once the time is right, other factors (such migrant visitors. In equatorial forest mer high-altitude breeding grounds to 22 23 The high proportion of species and the dents and migrants, a simple explanation as the size of the gathering , wind areas where rainfall and food supply are Although several broad patterns of migra- winter quarters in lower lying areas. 23 speed and time of day) then determine the 24 sheer numbers of birds that migrate may be presented as follows. The number more constant, this surplus is likely to tion can be recognized among African Several species, such as the Stonechat 24 moment of departure. 25 annually bear testimony to the success of bird species, such as the well-known 25 of resident birds that any seasonal habi- Although gradually progressing along be negligible, which would explain why Saxicola torquata, can be tracked making 26 migration as a life history ‘strategy’ for tat can support will be determined by the their programmed path, juvenile birds relatively few migrants visit these habi- Palearctic–Afrotropical ‘flyways’, there is these movements between the Natal 26 27 birds. Seasonal migrants benefit by mov- conditions during the worst part of the actually make a lot of exploratory move- tats. In addition to this ‘surplus niche’, almost as much variation within these Drakensberg and the mid- and lowlands. 27 28 ing between environments where breed- year. Some of the increased food produc- ments en route, rather than sticking to a many non-breeding migrants occupy patterns as there are migrant species. Higher altitudes are effectively more sea- 28 29 ing is successful and environments where tion during the breeding season (when narrow, uni-directional path. To maintain marginal habitats which cannot support Regular seasonal movements by birds sonal (or extreme) than lower altitudes 29 30 survival during the non-breeding season conditions are best) will be required to their programmed general direction, the resident birds thoughout the year. have almost certainly occurred for as at the same latitude, thus providing pro- 30 young birds are innately able to orientate 31 is relatively easy. Species which occupy satisfy the increased food demand of Although there is undoubtedly competi- long as birds have been mobile, but ductive breeding habitats in early sum- 31 (as opposed to navigate). Birds have been environmentally stable habitats, such as many of the patterns we see today are 32 birds during this period, but the more shown to be able to orientate using several tion between­ migrant species them- mer, but harsh conditions force the birds 32 33 equatorial rainforests, tend to be seden- seasonal the habitat, the more likely that different compasses, including the sun, selves, there are areas in which this is probably fairly recent: migratory patterns to lower altitudes in winter. 33 34 tary because of a fairly constant year- there will be a surplus of food even stars, and the earth’s . somewhat alleviated by different species are continuously evolving and adapting Broader scale intra-African migration 34 35 round supply of food. Those occupying beyond these requirements.  Even polarized light is used to ascertain occupying the same areas at different to changing climates and circumstances. patterns are largely governed by the wet 35 36 nigel j. dennis/ABPl the sun’s position in cloudy conditions. By times of year. The shortest movements, typically, are and dry periods associated with the  36 orienting according to its genetic map, the 37 richard du toit/Abpl 37 juvenile migrant will arrive in the general 38 38 area of its non-breeding grounds, and may 39 then have to search for an appropriate site 39 40 to spend the winter. 40 41 During their first migratory journey, the 41 42 juvenile birds integrate the topographical, 42 43 celestial, meteorological and magnetic cues 43 44 perceived along the way to form a complex 44 spatial memory of their familiar area. Thus, 45 45 once a bird has completed its first round 46 trip, it will have learned enough to be able 46 47 to navigate (rather than simply orientate), 47 48 to and from the non-breeding grounds in 48 49 subsequent years. 49 50 50 51 51 52 Left Abdim’s Stork is one of the more 52 53 common intra-African migrants. The 53 54 (right), however, is a 54 55 trans-continental migrant and, like many 55 56 other migratory species which share 56 57 its plight, is dependent for its survival 57 58 on the implementation of effective 58 59 conservation measures which can only 59 60 come about through improved knowledge 60 61 of their ecology and movements and 61 62 through international co-operation. 62 63

62 africa – birds & birding june/july 1996 superpilots ~ bird migration in africa 63 1 again. As a result, most of Africa experi- oos, bee-eaters, , nightjars, 1 2 ences a summer rainy season, with the flycatchers, warblers and follow 2 3 exception of East Africa, which experi- the rains northwards from the tropics to 3 4 ences two wet seasons every year as the the Sahara or , some migrating there 4 5 (Sept – Dec) ITCZ passes to the north and south, and to breed, and others to spend the non- 5 6 the winter-rainfall regions of the south- breeding season. Many species which 6 7 western Cape and parts of North Africa. breed in southern Africa during summer, 7 8 Most intra-African migration systems includ­ing cuckoos, bee-eaters, swifts, 8 9 are closely related to the alternation of flycatchers and , migrate north- 9 10 rainy and dry seasons which results in wards during autumn. Wahlberg’s 10 11 sudden and far more dramatic changes of Aquila wahlbergi, on the other hand, 11 12 weather than, for example, the gradual breeds in southern Africa during the 12 13 transition of winter to spring in more winter dry season and moves northwards 13 14 (Dec – March) temperate latitudes. The onset of the during the wet season. Some species, like 14 15 European 15 rainy season is often highly predictable one of our better known harbingers of 16 and usually quite dramatic, resulting in a spring, the Redchested Cuckoo Cuculus 16 Breeding 17 proliferation of plant and animal life. solitarius, breed in both northern and blacktailed godwit 17 Non-breeding Breeding 18 Insects are most abundant early in the southern Africa and converge­ to spend the Non-breeding 18 19 Several species, such as the European rains, which also see the emergence of non-breeding season in the tropics. bartailed godwit 19 Breeding NIGEL J. DENNIS/ABPL 20 Marsh Warbler, track broadscale shifts in magnificent termite swarms. Although In many cases where a species’ breed- Non-breeding Resident waders, such as this Kittlitz’s Plover, 20 21 feeding conditions in what is known as most migrants take advantage of the ing range extends from the tropics to are ousted from their preferred feeding areas during 21 22 ‘step migration’. increased productivity of the wet seasons, the temperate areas, those individuals Map showing ‘leap-frog’ migration of the Bartailed Godwit. summer when the Palearctic migrants dominate. 22 23 there are a number of species, notably which breed away from the tropics 23 24 seasonal movements of the Inter-tropical raptors, that prefer drier conditions and migrate to the tropics and those breed- grounds in the areas of the far Superimposed on the above patterns breed from north-temperate to high 24 25 Convergence Zone (ITCZ). In July, the migrate away when the rains come. ing closer to the tropics are resident north and eastern Eurasia. Here, the of intra-African and intercontinental Arctic latitudes and winter over a range 25 26 ITCZ, essentially a low-pressure belt, lies A large number of intra-African mig­ there. In other words, individuals that breeding season is concentrated into a migration is the phenomenon of ‘leap- from low north-temperate to south-tem- 26 27 in a fairly straight line along the north- rants cross the equator to take advantage occupy breeding grounds which are short spring and summer when there is a frog migration’. This is particularly well perate latitudes, effectively leap-frogging 27 28 ern Tropic of Cancer. By January the ITCZ of seasonal rains and food abundance closer to benign non-breeding areas tend proliferation of life, insects in particular, illustrated among some of the longer dis- the short-distance migrant species. 28 29 lies in a more uneven configuration from during both their breeding and non- to be less migratory, resulting in the and breeding conditions are ideal. There tance migrants, in which birds breeding Many insectivorous species undertake 29 30 the equator in the west, dipping south- breeding seasons. These trans-equatorial phenomenon of ‘partial migration’. is no loafing around however, as these in Arctic regions overfly the breeding and what is known as ‘step migration’, stop- 30 31 wards to Zimbabwe in the south and migrants include northerly breeders such Probably the most impressive and well conditions are short-lived: the advancing non-breeding grounds of their counter­­­ ping in North or West Africa for two to 31 32 turning northwards again to Tanzania. as Abdim’s Storks abdimii and documented of the migratory pathways cold weather and impending food short- parts that breed further south. In fact, three months to take advantage of the 32 33 The oscillation of the ITCZ between these southerly breeders such as Lesser Striped are those which converge from the ages soon compel birds to head south. among African migratory shorebirds, rainy season until about November, 33 34 two extreme positions results in a corre- Swallows Hirundo abyssinica. Palearctic regions into Africa along a Palearctic–African migrants follow a two distinct groups of species can be rec- before moving on to the southern hemi- 34 35 sponding movement of rainy weather, Many more species migrate between the handful of narrow passages across the variety of migratory routes, but their ognized: short-distance migrants which sphere summer. Other species simply 35 36 from the northern hemisphere in the northern or southern parts of the Mediterranean, crossing formidable diversity decreases steadily towards the breed in mid- to low north-temperate stop at sites for as long as it takes to rest 36 37 northern summer to the southern hemi- continent­ and equatorial regions. Hordes tracts of sea and desert. Many African south with about half the number of latitudes and winter north of the equa- and regain the energy required to com- 37 38 sphere in the southern summer and back of tropical migrants such as , cuck- bird species migrate to breeding  species reaching South Africa. tor, and broad-ranging migrants which plete the next stage of the journey.  38 39 39 40 Weighing only 100 grams, are known to accomplish fantastic distances on migration. 40 41 ANTHONY BANNISTER/ABPL 41 42 42 43 43 44 44 45 45 46 46 47 47 48 48 49 49 50 50 51 51 52 52 53 53 54 54 55 55 56 56 57 57 58 58 59 59 60 60 61 61 62 62 63

64 africa – birds & birding june/july 1996 superpilots ~ bird migration in africa 65  1 Accomplishing the journey 1 2 Conservation of migrants 2 3 Migrants may traverse the continent in 3 ne of the greatest threats to migrants 4 Oworldwide is habitat loss. Isolated wet- short ‘hops’, longer ‘skips’, or impressive, 4 5 land habitats, upon which millions of shore- long-distance ‘jumps’. Although it is the 5 6 birds and wildfowl rely, are succumbing in latter movements that really capture the 6 7 rapid succession to development projects, imagination, most African migrants prob- 7 8 and savanna and grassland habitats are ably opt for relatively short-distance 8 9 increasingly over-grazed and transformed. movements. This is because a great many 9 The conservation of migrant species is 10 species are able to stop and feed en route. 10 much more complex than that of sedentary 11 species. Migrant populations must be con- These birds replenish their energy 11 12 served on both their breeding and non- T. SALATHE/BirdLife International reserves on a daily basis, and may migrate 12 13 breeding grounds, as well as at important Netting birds in North Sinai for only a few hours, covering less than 13 14 staging sites, by means of carefully designed 200–300 kilometres each day. This strate- 14 15 reserve networks. Apart from the necessary lobby is more powerful than the gy is also shared by some larger birds, 15 16 international co-operation, achieving this conservation lobby in several countries, this such as Steppe Buzzards Buteo buteo, 16 ideal requires a detailed understanding of 17 directive is frequently ignored. which stop regularly to hunt for prey. In 17 the movements of bird populations. There are a surprising number of organiza- 18 18 The survival of many migrant species is tions and political agreements dealing some cases the lengths of flights are 19 further threatened by hunting. Of the five restricted for other practical reasons – 19 with the problems of migrants and their ROBERT C. NUNNINGTON/ABPL HEIN VON HORSTEN/ABPL 20 billion migrants that cross the Mediterranean conservation, particularly in Europe, yet the large birds such as storks, which rely on 20 21 on their way to and from Africa, it is estimat- future of many migrant species appears to be warm thermals to glide, may only be able Above Most insect-eating migrate at night. The Lesser Striped , however, is an exception 21 ed that somewhere in the order of a fifth – 22 bleak. Existing programmes are mostly insuffi- to fly for a few hours during the day. and travels during the day. Above right The Stonechat (female shown) is an altitudinal migrant. 22 some one billion birds – are killed annually 23 cient, because they lack co-ordination, and Species which migrate long distances 23 by hunters, for food and, increasingly, for because countries that have not become 24 between stopovers tend to be those for ries and mates. nearly all cases it is the sex which estab- 24 sport. Almost all types of migrants fall prey to contracting parties have led to gaps in was ringed, had travelled 25 shotguns, nets and traps in the countries conservation projects. Conservation efforts which feeding en route is more difficult. 3 650 kilometres, while another, recov- Migrating long distances between lishes the breeding territory that 25 26 bordering the Mediterranean. Increased in the Palearctic regions are fruitless without The long nocturnal flights of shore- ered 14 days after being ringed, had breeding and non-breeding grounds has closest to the breeding grounds, and in 26 27 awareness of dwindling bird populations in the co-operation of developing countries in birds, for example, may be necessitated covered some 7 000 kilometres. interesting repercussions on the migra- species which lack strong sexual domi- 27 28 Europe led to the Directive on Conservation Africa to protect vital parts of migrants’ rang- largely by a scarcity of suitable The distances of their non-stop flights tory strategies of young birds. The juve- nance there is less tendency for spatial 28 of Wild Birds being passed in 1979, which 29 es, but burgeoning population growth habitats. Shorebirds have been known are reflected in how different long-dis- niles of many of the longer distance separation of the sexes on the non-breed- 29 requires member states to protect species in these countries gives rise to a different 30 to accomplish some fantastic distances tance migrants prepare for migration. The migrants often do not return to the ing grounds. Even so, some would argue 30 during migration. However, because the set of priorities. 31 in short periods: one ­ Arenaria majority of migrants, which usually travel breeding grounds in their first, and that the longest distance migrants within 31 32 interpres, captured four days after it  short distances between stopping to feed, sometimes second year. This delay is homogenous groups are subordinate 32 33 do little in the way of physiological prep- probably an adaptive response to a low birds which are forced to migrate further 33 34 Wahlberg’s Eagle migrates to summer breeding quarters, which extend from southern to East Africa. The exact aration for their journeys. Steppe Buzzards probability of breeding successfully, cou- due to competition for non-breeding sites 34 35 whereabouts of its non-breeding grounds are only now being discovered by means of radio-tracking. increase their weight by only about 10 pled with the fact that the risks of mak- closer to the breeding grounds. 35 36 BRENDAN RYAN/ABPL per cent prior to migration. However, ing a long-distance journey exceed the The most likely explanation lies in a 36 37 many of these species are capable of benefits of staying behind. This is fur- trade-off between the risk of dying on the 37 38 increasing their weight significantly, and ther exacerbated by the fact that the risk non-breeding grounds and the risk of 38 39 do so by up to 30 or 40 per cent immedi- of getting lost or dying on migration is dying on migration. Grey Plovers Pluvialis 39 40 ately before crossing the Sahara. In south- higher for young birds than for adults. squatarola which migrate from their 40 41 ern Africa, Palearctic shorebirds spend at Most of the ‘vagrant’ birds that are Siberian breeding grounds to western 41 42 least a month fattening up found at great distances from their usual Europe may suffer low mortality during 42 43 on their non-breeding grounds before migratory ranges are juveniles, and the their relatively short flight, but frequently 43 44 migration. Small bird species are capable probability of a juvenile long-distance encounter harsh weather conditions on 44 45 of doubling their body weight, but larger migrant surviving its first year is thought these non-breeding areas when the risk of 45 46 species must compromise between the to be as low as 30 per cent. The juveniles starvation becomes high. Those which 46 47 size of their fuel reserves and their body- of shorter distance migrants,­ even within survive the long and risky migration to 47 48 mass to wing-area ratio and cannot lay the same species, are more inclined to the tropics and southern hemisphere, on 48 49 down proportionally such large reserves. develop breeding and migrate the other hand, encounter comparatively 49 50 Most of the largest migratory birds are to the breeding grounds than those stable climatic conditions. Those that 50 51 thus heavily reliant on using energy-sav- which have travelled to more distant travel the furthest to the south-temperate 51 52 ing gliding flight. The extra weight is in non-breeding grounds. regions are further advantaged by the fact 52 53 the form of both increased muscle mass that their stay coincides with the summer 53 54 and fat used for fuel. The consequences of migrating season of high productivity of their inver- 54 55 The journey back to the breeding different distances tebrate prey. Evidence suggests that the 55 56 grounds, which commonly follows a risk of predation by raptors also decreases 56 57 quite different route from the outward Even in the context of all the patterns towards the south. The different distance 57 58 migration, is usually far more rapid than described above it is still noteworthy that migrants are probably equally well-off in 58 59 the outgoing migration; making a speedy some individuals of the same species the long run, merely differing as to 59 60 return is necessary to ensure timeous migrate thousands of kilometres further whether they risk their lives on the more 60 61 arrival on their breeding grounds, where than others. In many species one sex northerly non-breeding grounds or dur- 61 62 they must compete for breeding territo- migrates further south than the other. In ing migration.  62 63

66 africa – birds & birding june/july 1996 superpilots ~ bird migration in africa 67