The loss of natural habitats such as hedgerows and hay meadows has led to far fewer nest sites being available and greater competition.
Dr Andrew Higginson from the University of Exeter found that species which nest late – in April or May rather than February or March – are declining more than other species, with the larger birds and bumblebees worst affected.
“The effects of habitat destruction are complicated, but we must understand them if we are going to save threatened species,” said Dr Andrew Higginson of the University of Exeter.
The study, published in the journal Behavioural Ecology and Sociobiology, combines mathematical modelling with an analysis of population changes in 221 bird and 43 bumblebee species worldwide.
The model shows that if animals are still doing what they did before habitat damage caused by decades of agricultural intensification, then large, early-nesting species such as great tits will be fine, but late-nesting species such as tree sparrows will decline.
“So far, conservationists have focussed on providing enough food for animals such as birds and bees, such as the important bee-friendly flowers in gardens,” Dr Higginson said. “These results suggest that to save rare species we need more focus on making sure that they have enough places to nest.”
He added: “To save bumblebees, people could let part of their garden grow wild between early spring and late summer.”
Haith’s comment: The general consensus is that January is a good time to put up a nest box and February 14th is National Nest Box Week which some have previously thought may be too late. This latest research suggests that it could be a good idea to put up a nest box later in the year, during March, April or even May.