Africa Invaded: Indian house crow

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As its name suggests, the native range of the Indian house crow, Corvus splendens, is centered in India, and extends from Iran in the west to Burma in the east. However, the bird was introduced to Africa in the 1890s, reportedly via Zanzibar, where it was brought to help keep the island free of rubbish. It subsequently spread along the coast of East Africa by hitching lifts on ships, and is now found right down to Cape Town at the southern tip of Africa. The crow also inhabits parts of the North African coast bordering the Suez Canal and Mediterranean Sea. It mainly occurs in urban and suburban environments, living in close association with humans.

A mean competitor

As an avian invader, the Indian house crow is undesirable for a host of reasons:

• It is an aggressive and opportunistic feeder, and has a  devastating impact on indigenous bird populations by eating eggs  and chicks, and mobbing other birds that might compete with it.
• It threatens the local wildlife by preying heavily on frogs,  lizards, small mammals, fish, crabs and insects.
• It affects agricultural productivity by stripping fruit trees in orchards and decimating grain crops, eating chicks of domestic poultry, and has even been known to peck out the eyes of sheep and pigs.
• It is unafraid of humans, and may enter houses to steal food, dive-bomb people walking past the nest, and frighten or even injure children by snatching food from their hands.
• In Cape Town many of the roosting areas are close to the airport,   representing a bird-strike hazard for air planes.
• Indian house crows have also been blamed for causing power cuts in some areas, as they often construct nests out of wire in  electric pylons.
• Furthermore, their droppings at roosts and feeding areas have been known to strip paint off walls and deface statues.

More seriously, however, the birds pose a threat to human health, because they are a vector for pathogens that cause cholera, typhoid, dysentery, and salmonella poisoning.
They scavenge for food in rubbish dumps, informal settlements, open-air abattoirs and markets, and may contaminate food and drinking water with their faeces. It is primarily because they represent a health hazard that efforts are made to control their populations.

Control

To date, the most effective control has been achieved using the poison Starlicide (3-chloro-p-toluidine hydrochloride). The poison is mixed with meat bait, ideally beef, which should be cut into small chunks and fed to the birds at a feeding site near their roost. However, before any poisoning takes place the birds should be accustomed to being fed by conducting pre-baiting for at least two weeks. A regular feeding routine should be established until the birds recognise the baiter and a large group gathers at the feeding site well before feeding. Pre-baiting also lessens the risk of ingestion by non-target species, as the crows will chase off any other birds approaching the feeding site.
Once the crows are habituated, they should be fed poisoned bait. Starlicide takes about 20 hours to take effect, but since it is metabolised during that period, the corpse will be free of poison and will not affect other animals that might scavenge on it. Dead crows around
the roost site should be collected by somebody other than the baiter to avoid arousing the birds’ suspicion.

Island innovation

An innovative ‘bounty system’ has proven highly successful in controlling the Indian house crow in the Seychelles. A cash reward is paid for each crow delivered to the authorities, which encourages community involvement in the control programme. In addition, a ‘green line’ has been set up, allowing members of the public to phone in and report sightings of the crow and other alien invaders. The initiative is part of an aggressive campaign to raise public awareness about the threats posed by invasive alien species to this island paradise.

DID YOU KNOW?

It is thought that the Indian house crow was introduced to Europe via Egypt as a stowaway on warships passing through the Suez Canal while returning from the Gulf War. The first European record was from Gibraltar in March 1991, and a small breeding colony has since become established in Holland.

The Indian house crow is known to stage gang attacks on domestic livestock, pets and even people in its native range. Records of the crow feeding on human corpses and killing young goats, calves, sheep and domestic cats are commonplace in India. It is not unusual to see the birds hitching rides on the backs of pigs, feeding on watermelon rinds and street garbage, flitting in and out of train stations or darting through open windows to snatch food.

Reference: Matthews S. & Brandt K.   Africa Invaded: The growing danger of invasive alien species  Global Invasive Species Programme 2004

   
 
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