Good heavens! The invasive house crow is spreading wings inland

Ms Ng’weno said they had no idea the birds had reached as far as Marigat, until they received the recent reports.

Marigat is 700km inland from Mombasa, the coastal city that has seen the worst of the house crow.

Of the world’s estimated 51 species and sub-species of crow, the house crow is infamously labelled the world’s most destructive.

“It is responsible for a 90 per cent loss of resident bird biodiversity along the Kenyan coast,” said Dr Francis Gakuya of the Kenya Wildlife Service, who chairs the crow eradication management committee.

Destroys nests

He added: “It pushes out resident birds and destroys nests, consumes chicks and eggs, using ‘mob’ tactics. Even birds of prey and vultures are not spared.”

Jennifer Oduori, one of Kenya’s top birders, said that she first became aware of the house crow when visiting friends in Mombasa around 1980.

“People had to close their house windows just to keep the house crow from flying in to steal food. Once in, it was very difficult to get them out,” she said.

To get rid of the birds, residents of Tudor estate in Mombasa began collecting and boiling the eggs of the house crow, keeping a vigil on which trees the birds nested, recalls Oduori. It worked as numbers reduced, but not before Oduori saw them raid the nest of a barn owl that had two chicks.

“They pushed the owl chicks out of the nest, and trampled on them before eating them. The adult owls were afraid of the crows because they came in such big flocks,” she said.

What really interested Oduori was that residents were so angry with the house crows for killing the owlets because, to them, owls are a bad omen and should be left alone.

The house crow was introduced on the east African coast in 1891 by a colonial governor serving in Zanzibar after a stint in India, where he had seen flocks eat rubbish. At the time, the famed Spice Island was nicknamed ‘Stinkibar’, a filthy port where thousands died of cholera, bilharzia and chickenpox.

Little did the governor realise the havoc he was to create in Africa in the coming centuries.

In 1917, the house crow was officially declared a pest in Zanzibar and a bounty put on its head. Soon it had spread along the coast from the Horn of Africa to Cape Town in South Africa.

“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,” Dr Colin Jackson warned in an earlier interview in 2013.

Dr Jackson, the deputy director of A Rocha Kenya, an international Christian organisation engaged in scientific research, environmental education and community-based conservation projects around the globe, said that at this rate, it will take five to 10 years for the house crow to spread to all parts of the country.

Water hyacinth

It’s come to pass, like the water hyacinth, parthenium and other invasive species that are on the rise in Kenya, threatening biodiversity and the food economy.

Concerned about the house crow seen inland in Makindu, Dr Titus Imboma, an ornithologist at the National Museums of Kenya, was commissioned to carry out a survey in 2013.

“We counted 11 house crows in Makindu,” said Dr Imboma. “It was easy to rid the town of the birds by destroying the nests before they spread further inland.”

But they are back.

It’s difficult to bait the house crow because it recognises human faces. The species remembers where the traps are set for them, and learns to avoid them. 

The avicide Starlicide is the only known substance that can kill the house crow and is safe to use. Starlicide was manufactured in the United States to get rid of the alien European starling, hence the name.

The poison only affects a few bird species and quickly loses toxicity. It was used in Watamu and Malindi by concerned residents. In 2005, only 30 house crows were reported in Malindi and six in Watamu.

But after terrorist attacks in the US, the poison was banned for export by the Americans (claiming that it could be used for purposes other than pests) – and imports to that country were allowed only with permission from the authorities.

With no enemy on the horizon, the house crow population ballooned in Kenya. Now they thrive in tens of thousands.

“KWS has identified the house crow as an alien invasive species and a pest of national concern,” Dr Gakuya said. As such, a five-year national eradication plan for the birds, spearheaded by KWS, has been endorsed by the Ministry of Tourism and Wildlife since Kenya is a top birding destination.

"The programme involves mapping areas where the house crow is, and (we are) importing Starlicide,” he said.

Inland areas

In the meantime, Dr Gakuya says there are "some stakeholders’ awareness programmes held mostly on the coast. More programmes will be rolled out in inland areas where the house crow has been seen, and we are asking the public to report any sighting to the closest KWS offices."

Dr Imbona said: “We must eradicate the house crow in Marigat as soon as possible. It may not be possible to eradicate it in Kenya, but we must be prepared to deal with any populations inland. The longer we wait, the further they will fly inland.”

Between 2010 and 2013, Tanzania received foreign funds to use poison to control the house crow. The programme killed 1.2 million crows, with a small population surviving. In 2015, it repeated the exercise, killing almost half of Zanzibar’s house crows.

But the house crow knows no boundaries. If persecuted in one area, it just flies somewhere safer. This time to neighbouring Kenya. The world’s most destructive crow is a regional problem.