Benign But Persecuted Even
the most cursory examination of the lifestyle of a vulture, reveals it to be a
benign and useful creature, but countless individuals have been shot, trapped
or poisoned by people over the last hundred years or so. The not infrequent
sight of a group of griffons feeding on the carcass of a sheep or a calf, has
repeatedly led to the conclusion that these birds are predators, when in fact
they are dedicated scavengers performing the vital function of removing
(recycling) rotting carcasses. Unlike eagles and hawks - which have sharp
talons - vultures are not adapted to kill for themselves although there are
rare instances of desperate or hungry birds taking small or weak animals.
It is western man who is to blame for the "bad
press" and demise of vulture populations, for these useful birds are revered in
many other religions and cultures. The Hindu regard vultures as carriers of the
human spirit, while the ancient Egyptians depicted them in their hieroglyphics
and totems. The introduction of livestock and "ownership" of wild animals
(which then became "game") thrust vultures into conflict with farmers and
settlers in Europe, North America and Africa, where several species have become
endangered.
Icons of Africa Vultures are as much a
part of the African wilderness as giraffe or zebra, and it is always a thrill
to see them soaring in the sky above, or jostling with one another at a
carcass. Although their somewhat reptilian facial features (not to mention
their mostly "messy" feeding habits) eliminates them from any "beautiful bird"
line-up, they are majestic on the wing when their power and grace is evident.
Contrary to popular opinion, vultures are not
reliant on the left-overs of predator kills, although they will frequently
visit the site of a kill and will certainly take food if it is available. Lion
and spotted hyena usually hunt and feed after dark and if they do make a kill
by day, they are invariably too imposing for the vultures. In reality, the bulk
of vulture food comes from mortalites such as old age, diseased or broken
limbed-animals and still-born young. When one realises that up to 100 000
wildebeest must die each year in the Serengeti-Mara (for a population of one
million to be maintained among an animal that lives for a maximum of ten years)
it is plain to see that vultures would survive well enough without lions. In
Southern Africa - with its denser woodlands and lower biomass - it may be that
vultures gain a greater proportion of their meals from predator leftovers
although this has yet to be studied in any detail.
Interestingly, the eight species of vulture in
African savannahs are not only able to co-exist, but may actually benefit one
another through their different foraging techniques and feeding habits. When
vultures are feeding together at a carcass, co-operation is perhaps the last
word that might come to mind, as they hiss and stomp on each other to try a get
a mouthful of flesh, but closer examination raises this interesting prospect.
First Come, First Served The
White-headed Vulture is the most-lightweight (in relation to its wingspan) of
the African vultures and is therefore the most mobile and agile species.
Because it is up and about early in the day, it is frequently the first to
locate a carcass and often enjoys the first choice soft parts but it seemingly
prefers sinew and hide, and cannot reach this until a large flock of griffon
vultures have dismembered the body. Interestingly, the White-headed Vulture has
striking black and white plumage and its decent to a carcass will be easily
noticed by a griffon soaring at a higher altitude (ravens and crows - with
their white collars - do likewise in mountainous landscapes).
Guzzling Griffons Three species conform
to the typical image of a vulture - sinuous neck and bald head - and are
collectively known as "griffons". Most common is the White-backed Vulture, a
tree-nesting species which lives in loose colonies in tall trees along drainage
lines or rivers. Several hundred White-backed Vultures may gather at the
carcass of an elephant or giraffe, and they usually outnumber all other species
by at least three to one.
In East Africa, the impressive Rüppell's
Griffon occupies the open savannahs, with the largest population in the
Serengeti-Mara. Here, the natural die-off from the enormous migratory
wildebeest population provides them with ready sustenance. These heavy birds
breed on rock faces in the Gol Mountains and may traverse 200km and back when
the wildebeest herds have moved to Kenya's Masai Mara. It has been suggested
that the colonial lifestyle of the griffons is similar to that of gannets and
other cliff-nesting seabirds, in that it serves as a communication network:
birds arriving back at their nests with a full crop let others know that their
foraging has been a success and the direction from which they came will be
noted. In this way, foraging time for the others is reduced and the chances of
finding a meal increased (in Southern Africa the Cape Griffon occupies an
equivalent niche to the Rüppell's but is now endangered as it is now
largely restricted to agricultural landscapes.)
Many Eyes, Many Mouths In order to
locate carrion, scavenging vultures must employ various tactics. First, they
need to be able to soar at heights which afford them great visibility. Second,
they need to either fly at an altitude which allows them to detect a stationery
object (the carcass) or activity on the ground (other scavengers), or at a
higher altitude which allows them to monitor the movements of other vultures
and scavengers, and then follow them down to the food. This latter approach
widens the net, so to speak, and is used by the griffons which are so heavy
that they must anyway make use of the rising thermal currents to stay aloft
(they cannot maintain flapping flight). Being gregarious, there is invariably
more than one set of griffon eyes scanning the sky below and once one bird
drops to investigate, it will be rapidly followed by others.
This is where the trade-off takes place, for once
on the ground the griffons challenge and jostle with each other as they compete
vigorously for food. The griffons are red meat feeders, thrusting deep inside
the carcass with the long featherless necks to feed on soft flesh, in
preference to hide, sinew and bone. Depending upon the size of the carcass,
most will usually get something to eat (the most aggressive vultures get slower
as they fill up!) and it is presumably worth the fight to forage in a group
with many eyes.
The King The Lappet-faced Vulture is the
largest of the African vultures with a wingspan of over three metres. It
typically arrives at a carcass once the griffons have begun feeding, but is
able to dominate the proceeding by lunging out with its enormous bill and
outstretched wings - even forcing a couple of dozen griffons to retreat.
Interestingly, this is the only vulture with a bill strong enough to open the
tough hide of a buffalo or giraffe and proper access for the griffons can only
be gained once the Lappet-faced Vulture has dined.
On the Fringe The Hooded Vulture and
Egyptian Vulture are very similar anatomically, with feathered heads and long
thin bills. They are too small to compete with the larger vultures, but do well
for themselves by keeping to the fringes, snapping up morsels and retrieving
marrow from shattered bones. The Hooded Vulture is typical of wetter climates -
even occurring in the edge of tropical rainforest - while the Egyptian Vulture
prefers arid scrublands.
Winged Specialists The magnificent
Bearded Vulture (Lammergeyer to some) and fish-eagle-like Palmnut Vulture are
oddities in terms of habitat and feeding requirements, and only rarely interact
with other vulture species. The Bearded Vulture lives in the high mountains
where it feeds mostly on marrow and bones, while the Palmnut Vulture is
primarily vegetarian and seldom strays far from the Oil Palms from which it
gets its favoured diet of palm nuts.
Till Death Do Us Part Vultures - like
many other large, long-lived birds - pair up for life, which, in the case of a
Rüppell's Griffon, may be forty or fifty years. Just a single egg is laid
each year and the youngster is only just gaining independence when the next
breeding cycle begins. In Southern Africa, vultures time their breeding such
that their developing young are being raised at the end of the dry season when
visibility is greatest due to low vegetation cover, and natural herbivore
mortality is highest. The East African vultures may be more flexible in their
timing, as the two rainy seasons (the so-called "long rains" and "short rains")
in this region have an effect on herbivore breeding and movements.
African "Big Five"
