Scottish passerines buck the trend

Thanks to the hard work of a range of BTO volunteers, and in particular those that undertook BBS squares, the latest indicators for terrestrial birds in Scotland have been released.

The newly published long-term trend for the terrestrial breeding bird index — from 1994 to 2009 — increased by 23%. Interestingly, farmland and woodland birds increased significantly (by 25% and 44% respectively), and upland birds showed no overall change.

Over the period of the current indicator, 1994-2009:

• 43 of the 65 bird species increased in abundance — the all-species (smoothed) index increased significantly by 23%;
• the smoothed woodland bird index increased significantly by 44%;
• the smoothed farmland bird index increased significantly by 25%;
• the smoothed upland bird index showed no overall change;
• the unsmoothed data show that the all species index decreased significantly by 7% between 2008 and 2009, with woodland birds decreasing significantly by 14%. Farmland and upland birds showed no significant inter-annual change.

The significant decrease in the unsmoothed index between 2008 and 2009, most significant for woodland birds, is largely attributed to the cold winter of 2008-09. Small-bodied residents such as Goldcrest, Treecreeper and Wren are known to be susceptible to cold winters and each declined by more than 25% that year; Goldcrests declining by 60%. Marked declines were also seen among Stonechat, Grey Wagtail, Kestrel, Starling, Cuckoo and Greenfinch. A contributing factor for Greenfinch may be the disease trichomoniasis.

European Stonechat, Cairn Gorm, Highland (Photo: Pauline Greenhalgh)

Among long-distance migrants, only Cuckoo declined markedly between 2008 and 2009. However, other long distance migrants such as Swift, Meadow Pipit and Common Sandpiper declined in abundance by more than 20% since 1994. Conversely, Chiffchaff, Whitethroat, Wheatear, Swallow and Willow Warbler increased. Spotted Flycatcher and Wood Warbler, which are known to have declined severely across the UK, are not included in the indicator because they occur in fewer than 30 Scottish BBS squares.

Cuckoo, Achinhoan, Argyll (Photo: Jimmay MacDonald)

Modest increases in woodland and farmland bird abundance since 1984 contrast with the declines observed between 1970 and 1990. Farmland birds declined in range in Scotland by 8%, woodland birds declined by 5%, and upland birds remained largely unchanged. Range declines were similar to those observed throughout the UK since 1970 and across Europe since 1980.