http://news.bbc.co.uk/2/hi/science/nature/3260821.stm
Tuesday, 11 November, 2003, 15:02 GMT
Crows menace African bird life
Daniel Dickinson
BBC News in Tanzania
An "airborne black tide mark" is menacing the native bird life of East
Africa, according to ornithologists.
The common crow is using its natural cunning to squeeze indigenous
species off the centre stage. It stands accused of killing local birds
in Tanzania - such as the paradise flycatcher - causing their numbers
to nose-dive.
At last count there were an estimated 300,000 to 500,000 crows in
Tanzania's capital, Dar es Salaam, and efforts to control them have
been short-lived.
The crow arrived in East Africa in 1891, when the British governor of
Zanzibar ordered their import from India. He hoped to harness their
scavenging tendencies to combat the litter problem in Zanzibar's
streets.
Pandora's Box was opened and the crow population spread, grew and
flourished. Now their hunched Hitchcockian figures can be seen in their
thousands around East Africa's cities.
Pandora's box
"The crow is not just interested in food scraps," said Fiona Reid,
author of Birds of Dar es Salaam. "It also attacks and kills indigenous
birds to eat, or to get to, their eggs. They have even been known to
attack sick animals like goats or domestic pets."
Crows are amongst the most intelligent birds and their hunting skills
are finely tuned, according to Ms Reid. "Crows often work as a team.
One will chase a bird away from its nest by swooping aggressively at
it, leaving the way open for the second bird to steal the egg," she
said.
This entrepreneurial flare is taking its toll on the indigenous bird
life of East Africa, driving many species from their natural habitats.
"The effect on indigenous birds has been drastic," Fiona Reid told BBC
News Online. "Numerous species, such as the African paradise flycatcher
and many sunbirds, have virtually disappeared from Dar es Salaam
gardens."
The situation is worsening rapidly. Crows are working their way further
inland, feeding off the rubbish that East Africa's growing human
population is producing.
Baited traps
Sadly, the history of crow control is not as remarkable as the history
of crow expansion. In Tanzania there have been a number of small-scale
attempts to cut their numbers, but the initiatives have not been
maintained.
The Wildlife Conservation Society of Tanzania (WCST) is orchestrating
the anti-crow efforts. At the end of the 1990s, the society mounted a
concerted extermination campaign using traps.
The menace terrorises local birds
We had 80 traps across the city at hotels, restaurants, hospitals and
social clubs," said Annette Mwyakimi, of the WCST. "We were catching
and killing over 1,000 crows a week."
In 1998, the WCST managed to reduce the crow population in Dar es
Salaam by over 32,000.
"People from all walks of life told us they could see a big difference,
even though the actual crow population had only been cut by about 10%,"
said Annette Mwyakimi. "They told us they could hear other birds sing
for the first time."
Despite its early success, the trapping scheme has been neglected. Many
traps have fallen into disrepair and the crow population is beginning
to swell dangerously again.
"The crows are encroaching from all corners of Africa," said Ms Reid.
"They have been recorded in Cape Town and Durban in South Africa as
well as in cities along the north African coast."
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