Birds in the Urban and
Garden Environment

Introduction

Birds are the most frequent of urban wildlife encountered by most people, yet despite their popularity (conservative estimates suggest at least 75% of households provide food for birds), relatively little is known about the ecology of birds in cities and suburbs of the UK compared to other habitats. This is despite the fact that gardens and parks hold significant proportions of the English national population for several species, most notably for the declining Song Thrush and House Sparrow. BTO research into urban habitats is a growing area and includes analysis of monitoring data, research into urban parks and several collaborative projects involving intensive field studies.

Monitoring

Several BTO schemes include urban/suburban habitats and indeed urban-specific trends from BBS data are currently being analysed for certain species. There are two schemes that specifically monitor birds in gardens: Garden BirdWatch (GBW) and the Garden Bird Feeder Survey. More details of these schemes can be found at (WEBLINK). GBW and GBFS research considers three main issues:

(i) Garden bird recording could prove to be a useful tool in monitoring biodiversity in built environments, which are typically not well covered under other schemes. Are these surveys good monitors of wider populations of birds, or do they simply measure garden (and therefore usually garden feeder) use? Certainly for the declining House Sparrow and Starling, both GBW and GBFS trends closely match those from other schemes in the wider environment. Similarly, strongly increasing species such as Collared Dove appear to be well-monitored. Furthermore, garden bird trends do appear to respond to sometimes quite subtle changes in the surrounding environment. For example, several woodland species are significantly less likely to occur in gardens in winters of high beechmast abundance.

(ii) Interactions between garden birds and habitat will influence the garden (and therefore the wider urban/suburban) bird community. But is the garden habitat important, or is it the wider landscape outside the garden that determines the bird community? Current BTO research suggests that the wider landscape is the more important for most species. The lack of associations with garden habitat is perhaps surprising, but this seems to arise because: (i) gardens in BTO schemes are likely to be bird-friendly, hence there is not enough variation to detect effects of garden ‘quality’; (ii) the provision of bird food is a key determinant of bird occurrence in gardens and its effects are likely to overshadow any additional effects of garden management. These issues are the subject of further research.

(iii) Both GBFS and GBW collect data at weekly intervals, allowing analysis of some very detailed annual and seasonal patterns of garden use. The BTO is using these data to study species’ interactions in gardens, i.e. does the presence of one species alter the occurrence of another species. Currently GBFS data are being analysed to assess whether Sparrowhawk re-colonisation since the early 1970s has had any impact on use of garden feeders by passerines. This analysis may be extended in the future to consider other inter-specific interactions.

Urban Green Space

Studying habitat associations may be key to advancing our knowledge of urban bird ecology. The BTO’s recent London Bird Project, a survey of over 200 parks and other public green spaces within the capitol, identified bushes and areas of rough grass and nettles as important habitats for birds, probably due to the invertebrate and plant food sources that these habitats provide. It would seem likely that these habitats are of similar importance in private gardens, but there are several unknown issues here. For example, we don’t know what are the relative roles of native versus non-native plants, nor do we know how the configuration of habitats (e.g. bushes as understorey compared to bushes only, connectivity with semi-natural habitats) may affect their use by birds. It is hoped that similar surveys can be carried out in the green spaces of other large cities in the UK to address these and other issues.

Collaborative Projects

The BTO is involved in several collaborative research projects with an urban theme.

(i) Andrew Cannon recently completed a PhD thesis ‘Wild Birds in Urban Gardens: Opportunity or Constraint?’ at the University of Sheffield under the Supervision of Prof. Kevin Gaston, funded under a NERC CASE studentship and supported by BTO and CJ Wildbird Food Ltd. This was a multi-faceted study centred on an intensively researched 1-km square in urban Sheffield. The thesis includes a description of urban communities, cat and feeders surveys, ringing recovery data, dietary analysis and analyses involving BTO datasets (GBW, BBS, Breeding Atlas). This impressive work provides an invaluable baseline for any urban bird research.

(ii) How does the food we provide at bird tables and feeders affect the bird community? This issue is being addressed by Gillian Robb at Queen’s University Belfast under the supervision of Dr Stuart Bearhop, funded under a DEL studentship with support from BTO and Gardman Ltd. The research takes an experimental approach, using non-urban woods provided with food in winter to mimic garden feeding and monitoring the effects. The density and reproductive performance in tits is then compared between these woods and unfed control sites. Another aspect is to determine any knock-on effects of increased competition with migrant warblers. Furthermore, state-of-the art technology is being used to precisely identify which individual birds in a population are making use of artificial feeders (e.g. is dominance or bird condition involved; how far will birds travel to exploit feeders) via stable isotope analysis. Broad-scale influences of urban settlements are being considered using BTO monitoring data.

(iii) A further PhD project, taking a similar approach to the above, is considering how provision of food in the breeding season affects reproductive performance and foraging by tits. Tim Harrison at the University of Birmingham is undertaking this research under the supervision of Dr Jim Reynolds. This is a NERC CASE studentship, supported by BTO and CJ Wildbird Foods Ltd. A key aspect will be how parents provisioning young make use of the food, including a comparison of nuts/seed only vs live food (mealworms). BTO Nest Record Scheme data will be analysed in order to compare reproductive performance of urban vs rural populations. The Belfast and Birmingham PhD students are working closely together in order to determine year-round effects of food provision on birds.

(iv) The House Sparrow is probably the bird species of most conservation concern in the urban environment. The ecology of urban House Sparrows is being investigated by Lorna Shaw from the University of Exeter in Cornwall, under the supervision of Dr Matthew Evans. This is a NERC CASE studentship, supported by BTO and CJ Wildbird Foods Ltd. The study is taking place in urban Bristol, with support of Richard Bland and John Tully, who have done some excellent work on House Sparrows there. The research focuses especially on the ecology of House Sparrows in gardens. In addition, broad-scale analyses of House Sparrow distributions in urban conurbations will be carried out using GBW data.

The Future

Urban expansion is clearly an increasing issue, with the government planning to build thousands of new homes in south-east England alone in the next few years. It should be a high priority for new homes to be built in a way that is not detrimental to biodiversity. The BTO is in a unique position to use existing datasets to inform the planning process for such developments. It is likely that research in this area will increase substantially in the coming few years. With our growing expertise in urban ecology, the BTO hopes to be at the forefront of this research.

Key References

• Chamberlain, D.E., A.G. Gosler & D.E. Glue (in press). The effects of winter beechmast crop on bird occurrence in British gardens. Bird Study.
• Chamberlain, D.E., S. Gough, H. Vaughan, J.A. Vickery & G.F. Appleton (in press). Determinants of bird species richness in public green spaces. Bird Study.
• Cannon, A.R., D.E. Chamberlain, M.P. Toms, B.J. Hatchwell & K.J. Gaston (2005). Trends in the use of private gardens by wild birds 1995-2002. Journal of Applied Ecology 42: 659-671.
• Chamberlain, D.E., J.A. Vickery, D.E. Glue, R.A. Robinson, G.J. Conway, R.J.W. Woodburn & A.R. Cannon (2005). Annual and seasonal trends in the use of garden feeders by birds in winter. Ibis 147: 563-575.
• Chamberlain, D.E., S. Gough, H. Vaughan, G. Appleton, S.N. Freeman, M. Toms, J.A. Vickery & D.I. Noble (2005). The London Bird Project. BTO Research Report no. 342. British Trust for Ornithology, Thetford.
• Chamberlain, D.E., A.R. Cannon & M.P. Toms (2004). Associations of garden birds with gradients in garden habitat and local habitat. Ecography 27: 598-600.