New research suggests that deer may be affecting some bird species on a far scale than was previously thought.
A study just published in the British Ecological Society’s Journal of Applied Ecology, shows evidence that the populations of several woodland birds fare worse in areas with high numbers of deer.
Researchers, led by Dr Stuart Newson from the British Trust for Ornithology (BTO), applied new methods of analysis to large national bird and deer monitoring data, and focused on 11 woodland bird species in lowland England, including Marsh Tit, Bullfinch and Song Thrush, and their relationships with three deer species – Reeves’s Muntjac, Roe Deer and Fallow Deer.
All 11 species depend on low dense vegetation in woodland and scrub and are therefore potentially vulnerable to browsing by deer, which reduces such vegetation.
There was evidence that increases in deer have been associated with large-scale population declines for five of the 11 bird species, with the greatest impact on the Amber-listed Nightingale and the Red-listed Willow Tit, which have declined by 54% and 65% respectively over the last 10 years.
Dr Newson said: “Our results emphasise the importance of developing co-ordinated national strategies for minimising deer impacts. With numbers and ranges of deer predicted to expand even further, it is suggested that such strategies should be targeted on areas that continue to support concentrations of species that are especially vulnerable to over-browsing by deer.”
Other factors are potentially implicated in the species’ declines, but the study does confirm earlier experimental work carried out on Nightingales by the BTO that has showed that deer can reduce its habitat quality.
Evidence from other parts of the world suggests that increases in deer abundance may be depressing population levels of breeding woodland birds that are associated with dense understorey habitats.
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