Scottish Natural Heritage Commissioned Report 369 Whooper swan (Cygnus cygnus) distribution and habitat use in the Black Cart flood plain during winter 2008/2009 COMMISSIONED REPORT Commissioned Report No. 369 Whooper swan (Cygnus cygnus) distribution and habitat use in the Black Cart flood plain during winter 2008/2009 (Contract No. 266539) For further information on this report please contact: Dave Lang Scottish Natural Heritage Caspian House Mariner Court Clydebank Business Park CLYDEBANK G81 2NR Telephone: 0141 951 4488 E-mail: [email protected] This report should be quoted as: Harding, N. (2010). Whooper swan (Cygnus cygnus) distribution and habitat use in the Black Cart flood plain during winter 2008/2009. Scottish Natural Heritage Commissioned Report No. 369 (Contract No. 266539). This report, or any part of it, should not be reproduced without the permission of Scottish Natural Heritage. This permission will not be withheld unreasonably. The views expressed by the author(s) of this report should not be taken as the views and policies of Scottish Natural Heritage. © Scottish Natural Heritage 2010. COMMISSIONED REPORT Summary Whooper swan (Cygnus cygnus) distribution and habitat use in the Black Cart flood plain during winter 2008/2009 Commissioned Report No. 369 (Contract No. 266539) Contractor: Scottish Natural Heritage Year of publication: 2010 Background The purpose of this project is to determine the distribution, habitat use, abundance, and behaviour of whooper swans wintering on the Black Cart flood plain during the 2008/2009 winter. Whooper swans are listed for special conservation measures on Annex 1 of the EC Birds Directive and the core part of the whooper swan range at the Black Cart was notified as an SSSI in 1999 and a SPA in 2000. This study builds upon earlier work to improve understanding of long term patterns of behaviour and population trends. Such information is of vital importance to SNH in discharging its duties with regard to securing favourable conservation status for the swan population and in its role in ensuring the sustainability of future development in the area. Main findings Up to 183 whooper swans were recorded in the Black Cart study area during the winter. This is the greatest number of wintering birds recorded since 2001/2002, and contrasts with the steady decline in numbers of recent years. The percentage of juveniles in the flock was 26% which compares favourably with estimates of breeding success from other parts of Britain and from the most recent international whooper swan census. In November, the three most abundant habitats in the study area were improved pasture, stubble and winter cereal with 36%, 20% and 10% cover respectively. All other habitats had less than 5% cover. The area of improved pasture and winter cereal remained unchanged through the winter. However, the cover of stubble declined from 22% to 6% as it was ploughed. Up to the 29th January birds fed almost wholly on stubble and after this date they fed almost wholly on improved pasture. This switch occurred much later than during the 2007/2008 winter. The switch from stubble was not due to its physical loss, but was probably due to deterioration in its quality as feeding habitat. Birds roosted in five locations: the Black Cart and nearby fields, Linwood Pond, Newshot Wetland, Linwood Moss Pond and field 178A at Auchans. The peak counts were 163 for the Black Cart, 16 for Linwood Pond, 57 for Newshot Wetland, 72 for field 178A and 5 for Linwood Moss Pond. The Black Cart was regularly used as the main roost throughout the winter. The other roosts acted as satellites, and were used less regularly, by smaller numbers of birds, at particular times of year. In December 2008 birds were regularly feeding in the fields to the east of the airfield and flying directly over the main runway to the Black Cart. To prevent an incident proactive management must be employed to deter birds from feeding in these fields. From the previous winter there were major changes in population size, feeding distribution, roost usage, habitat use and flight lines. These changes were not predictable, indicating that in the short term at least annual monitoring may be required to provide the information necessary for SNH to respond effectively to the development pressures and agricultural changes which could potentially threaten the favourable conservation status of these birds, whilst ensuring air safety is not compromised. For further information on this project contact: Dave Lang, Scottish Natural Heritage, Caspian House, Mariner Court, Clydebank Business Park, Clydebank, G81 2NR Tel. 0141 951 4488 e-mail: [email protected] Acknowledgements Many thanks to all the farmers and landowners who provided access to their land. Table of Contents Page 1 INTRODUCTION ............................................................................................................. 9 2 METHODS .......................................................................................................................9 2.1 Overview ................................................................................................................. 9 2.2 Roost surveys........................................................................................................ 10 2.3 Feeding surveys .................................................................................................... 10 2.3.1 Overview............................................................................................................ 10 2.3.2 Survey routes and field numbering.................................................................... 10 2.3.3 Habitat recording ............................................................................................... 12 3 RESULTS ...................................................................................................................... 13 3.1 Data management and analysis environment ....................................................... 13 3.2 Population ............................................................................................................. 13 3.3 Feeding distribution ............................................................................................... 15 3.3.1 Data issues........................................................................................................ 15 3.3.2 Chronology ........................................................................................................ 15 3.3.3 Changes in feeding distribution between the 2007/2008 and 2008/2009 winters 18 3.3.4 Field usage........................................................................................................ 19 3.3.5 Habitat availability.............................................................................................. 20 3.3.6 Habitat use........................................................................................................ 20 3.4 Roost use.............................................................................................................. 22 3.4.1 Introduction........................................................................................................ 22 3.4.2 Black Cart.......................................................................................................... 23 3.4.3 Linwood Pond.................................................................................................... 24 3.4.4 Newshot Wetland.............................................................................................. 24 3.4.5 Linwood Moss Pond .......................................................................................... 25 3.4.6 Field 178a.......................................................................................................... 25 3.4.7 Auchans Pool.................................................................................................... 25 3.4.8 Field 52.............................................................................................................. 26 3.4.9 Other possible roosts......................................................................................... 26 3.4.10 Use of sub roosts within the Black Cart site .................................................. 26 3.5 Flight lines ............................................................................................................. 26 3.6 Colour ringed birds ................................................................................................ 27 3.7 Disturbance ........................................................................................................... 27 4 DISCUSSION................................................................................................................. 27 5 REFERENCES.....................................................................................................28 List of Figures Figure 1: Field numbering and feeding survey route for the 2007/2008 winter. Figure 2: Field numbering used in the 2008/2009 winter. Figure 3: Survey route followed from the 26 November 2009 till the 29 January 2010 inclusive Figure 4: Survey route followed from the 6 to the 19 February 2010 inclusive. Figure 5: Survey route followed from the 26 February till the 10 April 2010 inclusive. Figure 6: Best estimates of total numbers of whooper swans within the Black Cart study area on different dates within the 2008/2009 winter. Figure 7: Percentage of aged birds which were juveniles on each date Figure