Information and Advisory Note Number 141                        Back to menu

NATURAL HERITAGE TRENDS Forest and woodland: woodland birds

1. Geographical range

1.1 Between 1968-72 and 1988-91 the number of woodland bird species showing marked range size expansions (i.e. of at least 10%) almost equalled that showing marked contractions in Scotland (Figure 1).

1.2 Losses. The capercaillie showed the greatest contraction in range, being recorded in 64% fewer grid squares in c. 1990 than in c. 1970. Although, historically, the species' range has contracted as a result of habitat loss and fragmentation, more recent, rapid declines have been attributed to poor reproductive success and increased adult mortality, partly through collisions with deer fences (Moss et al, 2000). Scotland is at the edge of the capercaillie's range, as it is for the willow tit, whose 36% decline in range has no clear explanation. A similar reduction in the woodcock's range size may partly reflect a change in the methodology used during the 1988-91 survey, as well as a decline in the area of young plantation, much of which was established in the 1950-70s.

1.3 Gains. Between the 1950s-70s and the late 1980s the area of coniferous forests over 25 years old doubled, enabling several species to extend their range. The greatest apparent gains were made by the crossbills, whose combined ranges increased by 133%¹. The bulk of this increase was due to an expansion by the highly eruptive common crossbill. Maturation of coniferous plantations also lead to a 32% increase in geographic range of the siskin. Other species showing marked range expansions were the blackcap (39%) and garden warbler (30%).

1.4 Slightly more species showing range expansions were insectivores, most of which were (migratory) warblers, whose populations are strongly influenced by conditions on their wintering grounds. Overall, more migratory woodland birds made marked gains (six species) than losses (one species).



Figure 1. Woodland species showing geographic range-size changes of greater than 10% between c. 1970 and c.1990.

2. Abundance

2.1 During 1994-99, populations of 14 farmland bird species were assessed on 30 or more Breeding Bird Survey (BBS) sites in Scotland. One species showed a statistically significant decline, five increased, and the remainder showed no significant change. In all cases, significant increases occurring in Scotland exceeded those shown in the UK as a whole (Figure 2).

2.2 All five woodland species showing significant increases are primarily insectivorous. Four species are resident, and likely to have benefited from recent mild winters. These were: goldcrest (+87%), wren (+60%), great tit (+31%) and robin (+17%). Four other resident woodland birds (blackbird, song thrush, blue tit and dunnock) showed non-significant increases in Scotland, but significant increases within the UK as a whole.

2.3 One of the five insectivores showing a significant increase in Scotland was a summer visitor, the willow warbler, whose numbers rose by 43%. Tree pipits also showed a significant increase (of 86%), but were recorded on fewer than 30 sites.

2.4 The only woodland species showing a significant decline in Scotland was the pheasant, whose population is influenced by the number of birds released for shooting.

2.5 Of three Biodiversity Action Plan woodland bird species surveyed, none showed significant changes in Scotland. A (nonsignificant) increase in song thrush numbers in Scotland mirrored a significant increase (+6%) in the UK as a whole. The bullfinch showed a substantial, but non-significant increase in Scotland, contrasting with a significant decline (-28%) in the UK. Finally, the spotted flycatcher showed no significant change in the UK, but was recorded on too few sites in Scotland to provide meaningful results.

3. Sources

3.1 Range data were provided by the British Trust for Ornithology (BTO), drawn from the BTO breeding bird atlas projects of 1968-72 (Sharrock, 1976) and the BTO, Scottish Ornithologists' Club and Irish Wildbird Conservancy atlas project of 1988-91 (Gibbons etal., 1993). Abundance data were drawn from the BTO Common Birds Census, and the BTO/ Joint Nature Conservation Committee/ Royal Society for the Protection of Birds Breeding Birds Survey (BBS: Noble et ai, 2000). BBS data are presented only for species recorded on at least 30 Scottish sites.



Figure 2. Significant changes in the abundance of woodland bird species between 1994 and 1999. All were recorded on more than 30 survey sites in Scotland.
* Change also significant in the UK as a whole.

4. References

Gibbons, D.W., Reid, J.B. & Chapman, R.A. (1993). The New Atlas of Breeding Birds in Britain and Ireland: 1988-1991. London: T.&A.D. Poyser.

Moss, R., Picozzi, N., Summers, R.W. & Baines, D. (2000). Capercaillie Tetrao urogallus in Scotland - demography of a declining population. Ibis 142: 259-267.

Noble, D.G., Bashford, R.I. & Baillie, S.R. (2000). The Breeding Bird Survey 1999. BTO Research Report 247. Thetford: British Trust for Ornithology.

Sharrock, J.T.R (1976). The Atlas of Breeding Birds in Britain and Ireland. Berkhamsted: Poyser.

5. Further information

Further detailed information on Natural Heritage Trends: Forest and woodland can be found in Information & Advisory Note No. 137.

6. Contact

To obtain further information about any of the issues raised in this l&A Note, please contact

Dr Phil Shaw (Author) or Mr Ed Mackey
Environmental Audit Group
Chief Scientist's Unit
Scottish Natural Heritage
2 Anderson Place
EDINBURGH EH6 5NP
Tel: 0131-446 2464
Fax: 0131-446 2405
E-mail: phil.shaw@snh.gov.uk

Species mentioned in the text





Note
¹Survey data for common and Scottish crossbill were combined, due to difficulties in separating these species in the field. Note also that the true extent of their range in any one year may have been much less than that suggested by the (composite) four-year survey (1988-91).

Back to menu