The populations of roe, fallow, red and muntjac deer have all increased over the past 18 years, according to the British Trust for Ornithology’s (BTO) Breeding Bird Survey, which also looked at nine species of mammal.

The BTO claims the rising deer population is a conservation concern, because browsing in woodland reduces the understorey.

The data, which was collected by volunteers, also shows that rabbit numbers have declined by 48 per cent over the same period, while hare populations are down 50 per cent in northwest England and up 70 per cent in the east Midlands. It also shows that grey squirrel numbers in north-west England are increasing, which is worrying for the red squirrel population largely confined to Scotland.

The results have been published in a paper. Lead author Lucy Wright said: “This study highlights the value of the BTO’s network of volunteers when it comes to monitoring groups other than birds. This group of species are an interesting mix of rapidly spreading invasives and species which are of conservation concern. There are many conservation questions that could be investigated using this data, so look out for more about mammals from the BTO in the future.”