If you are struggling to get any mobile phone reception tonight, it may be the fault of the peregrine falcon. Vodafone said three pairs of the world's fastest bird were spotted nesting in and around masts across London and could be slowing down networks. Engineers involved in a £200million 4G upgrading project in the capital found nests on a church, hospital and office block in the last few days. Vodafone engineers discovered the bird of prey nesting in and around masts across London (stock image) Under the Wildlife and Countryside Act of 1981 it is illegal to disturb the birds while they are nesting . Peregrine falcons became almost extinct in the 1960s after a population crash caused by pesticides. They have been a protected species since 1981. Legislation controlling use of pesticides meant their numbers slowly recovered. Its long, pointed wings and short tail allow it to be fast and agile while flying for prey. They eat medium sized birds, small ducks and pigeons. The Royal Society for the Protection of Birds estimates there are 1,402 breeding pairs in the UK. They nest in areas they consider resemble a cliff-face, such as tower blocks and church towers. Phone masts are a popular nesting site for the bird of prey and the company will be unable to remove the nests until the chicks are hatched and leave, which could take up to three months. It is a criminal offence under the Wildlife and Countryside Act of 1981 to disturb the birds while they are nesting. If prosecuted, offenders face six months’ imprisonment and a fine of up to £5,000. Vodafone says this will cause delays to service upgrades and and customers could face disruption to the current network as they reroute mobile traffic from the affected sites to other masts. Simon Gordon, of Vodafone, told MailOnline: 'There are three nests in London. They are in Shadwell, Lewisham and Hammersmith and there is a pair in a small place in Hampshire. 'We have to call in the experts to work out exactly where the nest is and we can then upgrade the network or leave them alone for two to three months.' He added: 'We apologise to any customers who experience a dip in service, but we have to respect the environment and the law. 'This is the first time to my knowledge we've had this in London, so for us it's unprecedented. They can sometimes nest on the mast itself which is like a big metal climbing frame or use the box underneath where the computer stuff sits. There are believed to be around 30 nesting pairs in Greater London, and six more birds have moved in to nest in Hammersmith, Shadwell and Lewisham (stock image) Peregrine falcons - which can reach speeds of 240mph - have enjoyed a revival in the UK in the past few decades after their existence was threatened by pesticides in the 1960s. Stuart Harrington, from the London Peregrine Partnership, told the Evening Standard: 'There are more peregrine falcons in London than there are in the more picturesque areas up north. 'London probably has the highest density of peregrine falcons in the UK, with many flying up from the south coast and settling here.'
Peregrine falcon spotted nesting in and around masts across London . Workers in £200m upgrade saw nests on church, hospital and office block . Vodafone - company affected - says this will cause delays to upgrades . But criminal offence to disturb the birds under Wildlife and Countryside Act .