Bird Migration in Africa 11 12 Jane K

1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 SUPERPILOTS 8 9 9 10 10 11 Bird 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 birds 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 Cuckoo, 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 seabirds from owls, waders strongly seasonal habits, either just for on migration in family parties or in flocks 7 8 from raptors and storks 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 Arctic 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 STORK DIEDERIK CUCKOO 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 winter 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 food resources between mig rants and the aid of the bird’s ‘circannual clock’, and the tropics. Diederik Cuckoos 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 flock, 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 magnetic field. 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 White Stork (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, kingfishers, nightjars, 1 2 ences a summer rainy season, with the flycatchers, warblers and sunbirds 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 Sahel, 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.

Load more