When David Livingstone arrived on the island of Zanzibar in 1866, he was so appalled at the filth and the stench that he called it “Stinkibar.”

Visitors sailing in could smell the island even before they caught sight of it. Epidemics were common – thousands died of cholera, bilharzia and chickenpox.

In an attempt to clean up the island, the colonial governor of the time, who had served in India prior to his posting to Zanzibar, introduced the Indian house crow to clean up the filth, little knowing the havoc it would wreak in Zanzibar and beyond. That was in 1891.

“He had seen Indian house crows eating rubbish in India, so he thought it would be a good way to clean up the island,” says Colin Jackson, conservation and science director at A Rocha, an international Christian organisation engaged in research, environmental education and conservation. He is also a research associate with the National Museums of Kenya.

“By 1917, the house crows were officially declared a pest in Zanzibar and a bounty put on their head,” Jackson says.

By then the bird had also hopped across to mainland Dar es Salaam and spread along the coast from Djibouti in the Horn of Africa to Cape Town in South Africa. But its rapid spread in the past two decades into the interior of Africa has been even more worrying.

Cringing from the Crow

There are 51 species and subspecies of crow, but the Indian house crow has been called the world’s most destructive crow. This aggressive monster is unafraid of humans and almost anything else, is a bully and very intelligent.

In comparison, Kenya’s indigenous pied crow is a welcome bird, and was even once the title of a local children’s environmental magazine.

“House crows work in teams. While one crow distracts, the others in the flock steal,” Jackson says. They compete for resources with other birds, prey on their eggs and chicks, and have been seen chasing gulls and terns 200 metres from shore. They regularly raid poultry, destroying farmers’ profits.

They are known to gouge out the eyes of infant cows, sheep and goats and are host to eight different human parasites. Research reveals they spread diseases by carrying and spreading bacteria like salmonella and E-coli, are carriers of cholera and typhoid, and may contaminate food and drinking water with their faeces.

It is difficult to bait the house crow because it can recognise human faces.

“If you shoot at them, they will remember you and spot you a mile off. It’s the same if you set traps for them. They will avoid them. The same thing with poison; they won’t come near it.

“In large flocks they are a major pest and you don’t want them spreading inland, otherwise they will be like the water hyacinth – difficult to get rid of,” warns Jackson.

In the past two years, house crows have been seen in Voi and Mtito Andei, having crossed the Taru Desert through Tsavo. Thriving on human waste, they are at home wherever there is lots of rubbish.

The only thing known to repulse house crows is the avicide Starlicide, manufactured in America to get rid of the European starling, hence the name. It breaks down after 10 to 12 hours, leaving no secondary or tertiary effects, unlike the agro-pesticide Furadan that is used to lace bait and, once ingested, inflicts a painful death on animals like vultures and lions.

“The big advantage is that the bait can be set at night,” Jackson explains. “They will eat it in the morning but die 12 hours later at the roost. The other crows don’t identify the bait.”

It worked well until the infamous 9/11 terror attacks, when the poison was banned for export by Americans for fear it could be used for other purposes. Since then, the house crow populations along the Kenyan coastal towns of Watamu and Malindi, according to A Rocha, have grown exponentially.

In 2005, 30 house crows were reported in Malindi and six in Watamu. By October 2012, there were 5,000 in both towns.

Kenyan authorities have taken no initiative to fight the menace. But Tanzanian is killing one million birds a month. The Tanzanian authorities are worried that the birds will fly across the border from Kenya.

Jackson says that, at this rate, in about 10 years, the house crow to be all over the country, and as with the water hyacinth and other invasive species threatening biodiversity and food production, we will be forced to carry the burden of fighting the pest.