Huge declines in woodland birds in the UK

Matt Walker, BBC News 30 Jun 09;

The nightingale has effectively vanished from woodlands across the UK.

A 30-year survey of British woodland birds has found that its population has fallen by more than 95%.

Seventeen other bird species have also declined significantly, many of which overwinter in tropical west Africa where their habitat is being destroyed.

Numbers of starling, linnet, bullfinch and willow warbler all crashed, while 12 species, including the blackcap, magpie and collared dove, increased.

These startling trends in the populations of some of the UK's best known woodland birds comes from the British Trust for Ornithology's (BTO) Common Bird Census, which gathered data on 49 species between 1967 and 1999.

The results of the survey have not been reported before.

Although the survey ended in 1999, the data provides the longest and most up-to-date trends anywhere in the UK or Europe for how the composition of woodland bird species has changed in modern times.

Of the species studied, the populations of 17 species significantly decreased since 1967, while the populations of 12 have significantly increased.

The greatest disappearing act has been that of the nightingale, whose numbers fell by 95% over the study period.

Numbers of starling fell by 91%, linnet by 89%, lesser redpoll by 85%, and spotted flycatcher by 83%.

Of the birds whose status in woodlands improved, numbers of the collared dove increased by 1052%, and the stock dove and wood pigeon by 359% and 344% respectively.

"Using these longer term datasets can provide really important additional insights over the more recent ones," says Chris Hewson of the BTO, who along with colleague David Noble has published the latest trends in the journal Ibis.

"For instance, much ado was [recently] made over the Red Listing of the Cuckoo. But an equally iconic species that missed out by the skin of its teeth was the nightingale, which actually declined in woodlands by 95% over the period examined, more than any other species studied and greatly in excess of the 63% decline shown by the cuckoo."

Hewson says that had these longer term trends been taken into account, then the nightingale would have been Red Listed too.

The causes of the varying fates of British woodland birds are many and varied.

"Some scarce resident species such as the lesser spotted woodpecker, redpoll, willow tit and hawfinch have declined and we're still not absolutely sure why," says Hewson. "But in some cases at least, less sympathetic woodland management looks a likely cause, along with possibly the impacts of browsing by an exploding deer population in some parts of the country."

The availability of food explains other trends. For example, numbers of collared and stock doves and wood pigeons have exploded due to the increased planting of winter crops, which provides a valuable source of food for these birds over the winter months. In contrast, linnets and turtle doves have suffered due to a lack of seeds in the summer.

However, changes in habitat outside of the UK are also having a major impact, particularly on migrant woodland species that spend part of the year in Africa.

"Our results illustrate that a whole suite of migrants are declining, but that over the 32 year period we studied the species of migrant in decline changed," says Chris Hewson.

During the beginning of the survey period, during the late 1960s and early 1970s, it was species such as whitethroat and redstart that spend the winter in the arid Sahel just south of the Sahara that were suffering due to drought conditions in that region.

"Now, though, these species are doing ok as rainfall levels have recovered," says Hewson. "But by the end of the period we looked at it was the species that winter further south in the humid tropics of west Africa that were suffering."

More recent data from the British Bird Survey, which replaced the Common Bird Census in 2000, shows that all the woodland species that migrate from west Africa continue to decline.

"That leads us to believe they are suffering from changes occurring in west Africa, possibly due to the intensification of agriculture and other land use changes leading to habitat degradation," says Hewson.

The BTO has now started a major research programme to study these migrant birds, backed by an appeal called Out of Africa recently launched in an attempt to fund the work.

That will involve starting a field project in Ghana and Burkina Faso this October with the Royal Society for the Protection of Birds.

The BTO is also collaborating on a pan-European project to track the migrations of nightingales using GPS tags, to find out more about where British nightingales spend the winter.

"This research will hopefully enable us to identify what the changes happening in Africa are that are causing these declines and ultimately, we hope, to enable us to come up with suggestions for solutions that would benefit not just the birds but also the people who live there," says Hewson.