Population changes of some bird species in Scottish and Welsh Atlantic Oakwoods between the 1980s and 2003/4 using data from the repeat Woodland Bird Survey

This art icle was downloaded by: [ Universit y of Cape Town Libraries] On: 05 Oct ober 2011, At : 06: 01 Publisher: Taylor & Francis I nform a Lt d Regist ered in England and Wales Regist ered Num ber: 1072954 Regist ered office: Mort im er House, 37- 41 Mort im er St reet , London W1T 3JH, UK Botanical Journal of Scotland Publicat ion det ails, including inst ruct ions f or aut hors and subscript ion inf ormat ion: ht t p: / / www. t andf online. com/ loi/ t ped19 Population changes of some bird species in Scottish and Welsh Atlantic Oakwoods between the 1980s and 2003/ 4 using data from the repeat Woodland Bird Survey Arj un Amar a , Ken Smit h a & Jeremy Lindsell a a Royal Societ y f or t he Prot ect ion of Birds, The Lodge, Sandy, Bedf ordshire, SG19 2DL Available online: 22 Apr 2009 To cite this article: Arj un Amar, Ken Smit h & Jeremy Lindsell (2005): Populat ion changes of some bird species in Scot t ish and Welsh At lant ic Oakwoods bet ween t he 1980s and 2003/ 4 using dat a f rom t he repeat Woodland Bird Survey, Bot anical Journal of Scot land, 57: 1-2, 179-185 To link to this article: ht t p: / / dx. doi. org/ 10. 1080/ 03746600508685096 PLEASE SCROLL DOWN FOR ARTI CLE Full t erm s and condit ions of use: ht t p: / / www.t andfonline.com / page/ t erm s- and- condit ions This art icle m ay be used for research, t eaching, and privat e st udy purposes. 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We used data from 29 woods in Argyll in western Scotland surveyed in 1985~and from 27 woods in Gwynedd in northwest Wales surveyed in 1983 and compare them with data from repeat surveys carried out in 2003 and 2004. In this paper, we report the population changes for these species between these two periods and examine whether changes differed between Scottish and Welsh sites. Introduction In the UK, Western Atlantic Oakwoods are important habitats for several bird species, in particular wood warbler (Phytloscopus sibilatrix), redstart (Phoenicurus phoenicurus), tree pipit (Anthus trivialis) and pied flycatcher (Ficedula hypoleuca), which are all found widely within this habitat with limited distributions elsewhere. The first three species are included on the amber list of birds of conservation concern (Gregory et al., 2002) because of their moderate population declines in the last few decades. In addition, recent research suggests pied flycatcher populations have also declined since the late 1980s (Wright et at., 2004). All four species are long distant migrants wintering in Africa, south of the Sahara (Wernham et al., 2002). Recent work has suggested that for those species which breed within woodland, the long distant migrants are showing greater declines than many middle distant migrants or indeed residents (Amar et al., 2006). All four species are insectivores, feeding on insects obtained either through hawking, gleaning or through foraging on the ground (Snow & Pert'ins, 1998). The BTO national monitoring schemes, using data from the Breeding Bird Survey (BBS) and the Common Bird Census (CBC) suggest differing trends for these species. The wood warbler is amber listed based on moderate declines of between 25-49% over the last 25 years, although between 1994-2004 the BBS indicated a 52% decline. Redstart populations have fluctuated in the UK according to the national monitoring schemes, declining in the late 1960s and early 1970s. but increasing subsequently. The tree pipit declined by 82% according to the combined CBC/BBS data, although they remain amber rather than red listed because the surveyed sites are not thought to be representative of Bot. J. Scot. 57(1+2), 179-185 Downloaded by [University of Cape Town Libraries] at 06:01 05 October 2011 180 ARJUN AMAR, KEN SMITH & JEREMY LINDSELL the species distribution, since they are biased toward the south east, whereas the species has a predominately north-western distribution (Gibbons et al., 1993). The pied flycatcher has a similar distribution, and as such, there was insufficient CBC monitoring to estimate long-term population trends; however, the BBS data suggests declines of 35 % between 1994-2004. Thus, many of the species associated with Western Atlantic Oakwoods ale not well monitored by national schemes, with small sample sizes and with much of the data being collected from sites outside of the core range and key habitats, In this paper, we have used data derived from the Repeat Woodland Bird Survey (RWBS), a national re-survey of broadleaved and mixed woodland surveyed first in the 1980s and repeated in 2003-4 (Amar et al., 2006). We used counts of the four key species from broadleaved woodland sites located along the west of Wales and Scotland, to estimate the population changes between the 1980s and 2003/4 in this key habitat type. Methods The original bird surveys were undertaken by RSPB staff as part of a UK wide survey of woodlands conducted in Argyll, Scotland in 1985 (Averis & Martin, 1985) and in Gwynedd, Wales in 1983 (Martin & North, 1983). We used data from 29 sites in Argyll and 27 sites in Gwynedd (Fig. 1). Sites in Argyll extended from Loch Linnhe in the north to the Lochgilphead area some 80 km to the south. In Gwynedd sites extended from Conwy in the north to the southern shores of the Afon Mawddach. In Argyll, pied flycatcher were not recorded in any of the woods, but the other three species were recorded at least once at all sites. In Gwynedd, redstart was absent from a single site and tree pipits from two sites. These sites were re-surveyed in 2003/2004, with five sites in each region being surveyed in both these years. We hereafter refer to the 1980s as episode 1 and 2003/4 as episode 2. At each wood ten random points were selected, with each point being at least 100 m away from any other and at least 50 m from the woodland edge. In each year of survey, two survey visits were made to each wood, one earlier in the season (mid April to mid May), and one later (mid May to mid June). Counts of all birds heard or seen at each point were recorded, although in this paper we have restricted the analysis to just the data from the four key species. Counts at each point lasted five minutes after a five minute settling period. All bird surveys were started within one hour of dawn and completed by 11 am. To test whether there had been any change in the numbers of the four species within the woods in the two regions and as a whole, we ran separate generalised linear mixed models for each species, in SAS version 8.0 (SAS Institute, 1999). The models included visit, episode, region and interaction of episode*region (to examine whether population changes had been different in Scotland than in Wales) as fixed effects, with a Type III analysis. Because we had a number of records from the same site, from early and late visits in different years, in different episodes, we included site, visit*year and site*episode as random effects in the models. To calculate the percentage changes that had occurred in each region and overall, and to test for differences between the two episodes, we used the least squares means and their differences in the outputs in SAS. Downloaded by [University of Cape Town Libraries] at 06:01 05 October 2011 BIRD POPULATIONCHANGES IN ATLANTIC OAKWOODS 181 ~9 IP 8 / / Fig. 1. Map showing the locations of the sites in the two regions (Argyll and Gwynedd) used in this study. Results The percentage changes for each species are shown in Table 1. Wood warbler showed an overall significant decline in these regions of 34 %. The magnitude of the declines were very similar in Scotland (-35 %) and Wales (-32 %) with no interaction between episode and region (F~.H= 0.04, P = 0.85), although declines in Wales were marginally non-signficant (P = 0.06). Redstart showed an overall non-significant decline of 30 %, with a significant decline of 45% in Scotland, but a non-significant decline of only 10 % in Wales. The interaction between episode and region was not significant (F~.~= 2.79, P = 0.15). Pied flycatchers were only present in our Welsh sites and here the population showed a non-signficant decline of 9 %. Tree pipit showed a significant overall decline of 45 %. Sites in Wales showed a significant decline of 58 %, whereas sites in Scotland showed a non-significant decline of 28 % which gave rise to a near significant interaction between episode and region (F,: = 4.48, P = 0.07). This suggests the possibility that numbers of this species had changed differently between these areas. 182 ARJUN AMAR, KEN SMITH & JEREMY LINDSELL Downloaded by [University of Cape Town Libraries] at 06:01 05 October 2011 Discussion Although the national monitoring schemes generate population indices for these species they are based on all records and therefore include birds in habitats other than western Atlantic Oakwoods. Our study is the first to examine the population changes of the characteristic species of western Atlantic Oakwoods based on data collected solely within this specific habitat itself. Our results reveal some worrying declines in the populations of some of these species. Across all sites, wood warbler and tree pipit declined significantly and redstart showed large declines in the sites in Scotland. Of less concern were pied flycatchers and redstarts in Wales, which did not show such big declines (non-significant declines of around only 10%). The near significant interaction for tree pipit between population change in the two episodes and region, with the species declining more in Wales, suggests that the driving factors behind this decline may be operating at a higher level in Wales compared to Scotland. How do these declines compare with those in the wider UK countryside? Table 1 shows the population changes of these species estimated from three sources over a comparable time period to the present study. These data are taken from Amar et al. (2006): (i) The RWBS data comes from all the RSPB survey sites for the full Repeat Woodland Bird Survey (RWBS). The Argyll and Gwynedd results are a subset of these data. (ii) The CBC/BBS is the combined indexes of these two national schemes from 1984/85-2003/4. (iii) The wCBC percentage change is taken from the woodland only plots of the CBC monitoring scheme between 1984/85-1999 (the year this scheme ceased). The key species appear to have declined less in Western Altantic Oakwoods than in the overall RWBS sample (Table 1). For example, the declines documented by RWBS in sites throughout the UK were nearly twice those found within Atlantic Oakwood sites for tree pipit and wood warbler. Redstart declines in Scotland were more similar to the national levels. Redstarts and pied flycatchers generally appeared to be doing better in the Welsh Atlantic Oakwood sites than elsewhere in the UK. The CBC/BBS confirmed the larger widespread declines of tree pipits across the UK, but gave conflicting results for redstart, with no significant change and a suggestion of a small increase. Data were insufficient to look at wood warbler and pied flycatcher. The woodland CBC index between 1984/85-1999, again confirmed the very large declines of tree pipits nationally, suggested little change in pied flycatchers or redstart and showed a small non-significant decline in wood warblers. Taken together these results overall suggest that these species may be faring better in this important habitat that in the wider countryside, with the exception of redstart, where the decline in Scottish sites and in the national RWBS appear out of step with the other national monitoring schemes. What other messages can we take from this study? This work confirms the worrying trends that were suspected for the wood warbler and the tree pipit. Although declines had been documented previously, uncertainty remained over how geographically representative the data were. We now know that even within their key western habitats these species are showing worrying downward trends. What factors could be responsible for these declines? The population sizes BIRD POPULATION CHANGES IN ATLANTIC OAKWOODS Table 1. Percentage change between episode 1 and episode 2, by region and for both regions combined. Species Wood warbler Redstart Pied flycatcher Tree pipit Downloaded by [University of Cape Town Libraries] at 06:01 05 October 2011 183 Scotland Wales Overall RWBS CBC/BBS wCBC -35" --45* -32 ~:° ..... - 10 -9 -58** -34* -30 -55 -54 -20 -85 na 13 na -81 -29 1 17 -75 -28 --45* Significance values *<0.05: **<0.01. Also shown are figures for percentage change taken from Amar et al. (2006): RWBS data are taken from the RSPB portion of the national Repeat Woodland Bird Survey:CBC/BBS is changederived from the combinedindex between 1984/85 and 2003/4: and wCBC is taken from the woodland only CBC index between 1984/85 and 1999. Figures in bold are statistically significant. of migratory species can be influenced by conditions in more than one part of the world. Declines may be the result of changes in the breeding or wintering areas or both (Newton, 2004). Several studies have found that temporal changes in the breeding density of pied flycatchers have been linked to changes in summer conditions, i.e. with higher breeding densities in years following good productivity (Virolainen, 1984; Stenning et al., 1988). However, few studies have explored the factors affecting changes in breeding densities for the other species. Amar et al. (2006) examined population changes between the 1980s and 2003/4 and examined whether changes were related to factors operating within woods, such as habitat structure and pressure from deer, and factors operating outside the woods, such as local landscape composition and spring climate change. A range of factors was found to be important in influencing the population trend of each species within the UK, with few general factors influencing multiple species. Tree pipits declined in areas with higher trees and less grass, where there had been increases in foliage cover between 0.5-2 m and 2-4 m and in woods with more tracks. Wood warblers declined in sites with fewer dead limbs and at sites surrounded by more woodland and less grassland within a 1 km radius. Redstarts declined in sites with fewer dead limbs, at higher elevations, where there were fewer tracks and in areas that had undergone a reduction in foliage cover at 0.5-2 m. For Redstart, the first association may relate to their hole-nesting habit: the latter two associations contrast with tree pipit. Pied flycatchers declined at sites with higher canopy cover and at sites with less lichen and ivy cover. Furthermore, they were the one declining species that appeared to be negatively affected by climate change, with declines more likely at sites with greater increases in April rainfall. These relationships have not been explored for the Atlantic Oakwoods in particular so it is unclear whether they hold true there as well. With so many different factors apparently influencing population changes of the different species, it is difficult to generalise as to the underlying causes. It is important to note however that the study of Amar et al. (2006) study was purely correlative and further more, that just because correlations were found with population trends and habitat or conditions on the breeding grounds, this does not rule out that the driving forces of any declines could be taking place elsewhere, such as on the wintering grounds in Africa. Correlations between habitat 184 ARJUN AMAR, KEN SMITH & JEREMY LINDSELL conditions and population change could simply reflect the redistribution of the fewer returning birds into their favoured habitat types. Further research is needed to determine the factors influencing productivity, survival and return rates, both on the breeding grounds and on wintering and migratory sites if we are to fully understand the factors responsible for the declines of these species. What is clear, however, is that the key species of the Atlantic Oakwoods are not immune to the causes of population change that are affecting woodland birds right across the UK. Downloaded by [University of Cape Town Libraries] at 06:01 05 October 2011 Acknowledgements We are grateful to all the fieldworkers involved in 2003/4 surveys including Paul Daw, John Dyda, Chris Thaxter, Matt Harding, David Anning, Steve Coney, John Day, Graeme Lyons, Paul James and Robin Eddleston. We would like to thank Stijn Bierman from Biostatistics Scotland for all his helpful advice on the statistical analysis used in this study. Thanks also to Paul Britten, from RSPB's Data management unit for constructing the Map used in this paper. Lastly we are particularly grateful to all the land owners whose cooperation enabled this survey to happen. Refeences Amar, A., Hewson, C.M., Thewlis, R.M., Smith, K.W., Fuller, R.J., Lindsell, J,A., Conway, G., Butler, S. & MacDonald, M.A. (2006). What's happening to our woodland Birds? Long-term changes in the populations of woodland birds. RSPB research report: 19; BTO research report: 169. Averis, B. & Martin, J. (1985). 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