Citation
Ross, K.E., Burton, N.H.K., Balmer, D.E., Humphreys, E.M., Austin, G.A., Goddard, B., Schindler-Dite, H. & Rehfisch, M.M. 2016. Urban breeding gull surveys: a review of methods and options for survey design. BTO Research Report 680: British Trust for Ornithology, Thetford
Overview
This report was commissioned by Natural England to inform the design and implementation of future census efforts for breeding urban gulls, and to make recommendations for the most cost-effective survey strategy for delivering urban gull population estimates for the UK and Republic of Ireland, as well as any specified key sites.
In more detail
- This report has been commissioned by Natural England to inform the design and implementation of future census efforts for breeding urban gulls, and to make recommendations for the most cost-effective survey strategy for delivering urban gull population estimates for the UK and Republic of Ireland, as well as any specified key sites.
- Within this report we review existing and potential urban gull survey methods (section 2); review the existing knowledge of breeding gull distribution within the UK and Ireland (section 3); and develop a bespoke survey design to deliver an urban gull census (section 4).
- The review of existing methods covers land-based methods (section 2.2), including: counts from vantage points, sample quadrat counts; transect counts (and distance sampling) and flush-counts of adults; aerial methods (section 2.3), including: digital aerial survey (DAS), visual aerial survey, unmanned aerial vehicles (UAVs), microlight, cameras on kites, aerial thermal imagery and satellite; and survey methods for Kittiwake (section 2.4). The benefits and risks of each method are considered (including privacy issues for aerial survey methods and health and safety) as well as costs. Techniques to account for detectability (double observer, distance sampling) are also discussed.
- Generally, land-based methods create more disturbance to birds than aerial methods and are likely to be more labour- and time-intensive than aerial methods. However, land-based methods may better enable differentiation between species and between breeding and nonbreeding birds. The most suitable remote methods from a purely technological viewpoint are likely to be digital aerial stills, video and UAV. These methods also provide repeatability, permanent data record and adequate resolution for differentiating gull species. However, flight restrictions for UAVs may render their use impractical in urban settings for anything other than targeted surveys of some known colonies.
- In section 3 we provide a review of the current breeding distribution of gulls in relation to urban areas. Using data from Bird Atlas 2007-2011 (Balmer et al. 2013) and urban land cover data from Land Cover Map 2007 (Morton et al. 2011), we show that there is a clear association between breeding gull occurrence and urban areas at inland sites, but also that gulls may nest inland even at sites with very low urban cover. The ‘urban’ habitat in which gulls may nest (i.e. man-made structures, and particularly flat rooftops) occurs virtually everywhere in the UK and Ireland, both in areas of high urbanisation and in landscapes that would otherwise be defined as ’rural’ or not urban, by any habitat classification scheme. Given this, a truly complete census of urban gull populations in the UK and Ireland is unlikely to be feasible.
- As an alternative, in section 4 we thus propose a broader survey using a paired key site and stratified sampling approach, the latter covering the entire spectrum of urbanisation. The proposed stratification would be based on gull abundance, region, % urban cover, and whether the site is coastal or inland. We suggest, in the first instance that the survey would best be achieved by digital aerial survey, given the practicalities of using cherry pickers or vantage point surveys on a broad scale.
- Costs are thus provided separately for coverage by digital aerial survey of potential key sites and for covering any 10 km square within defined regions and at the country level. Nevertheless, it should be noted that the key sites identified in this report represent a potential suite of sites that might be selected, and it is likely that a final choice of key sites will depend on casework needs and statutory monitoring priorities. Once a final selection of key sites has been determined, consideration should be given as to whether it may be possible to save on survey costs at some of these sites by using alternative methods, such as visual aerial survey, cherry pickers or vantage point surveys, especially where these have proven successful before, utilising volunteer or public involvement where appropriate.
