BTO Research Report No. 164 Relationships Between Grazing and Birds With Particular Reference to Sheep in the British Uplands Author Robert J. Fuller December 1996 A report by the British Trust for Ornithology to the Joint Nature Conservation Committee © British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU Registered Charity No. 216652 CONTENTS Page No. List of Tables & Figures .............................................................................................................. 5 EXECUTIVE SUMMARY.......................................................................................................... 7 1. INTRODUCTION........................................................................................................... 9 2. SHEEP STOCKING: PATTERNS IN TIME AND SPACE (with S.J. Gough)...... 13 2.1 Historical and Long-term Aspects............................................................................... 13 2.2 An Analysis of Sheep Numbers Since 1950................................................................. 14 2.3 Local Recent Changes in Sheep Numbers in the Uplands......................................... 16 2.4 Conclusions.................................................................................................................... 17 3. MECHANISMS BY WHICH GRAZING MAY AFFECT UPLAND BIRDS ........ 19 3.1 Population Changes of Upland Birds in Relation to Grazing................................... 19 3.2 Overview of Potential Mechanisms ............................................................................. 20 3.2.1 Modification of Vegetation.............................................................................. 21 3.2.2 Dung and Drugs ............................................................................................... 21 3.2.3 Carrion.............................................................................................................. 22 3.2.4 Predation by Sheep .......................................................................................... 23 3.2.5 Trampling of Nests and Chicks ...................................................................... 23 3.2.6 Disease............................................................................................................... 23 3.3 Vegetation Change - Alteration of Vegetation Succession and Structure................ 23 3.4 Vegetation Change - Loss of Heather.......................................................................... 24 3.5 Vegetation Change - Alteration of Mosaics ................................................................ 26 3.6 Vegetation Change - Alteration of Food Resources................................................... 28 3.6.1 Fruit ....................................................................................................................... 28 3.6.2 Invertebrates .................................................................................................... 28 3.6.3 Small Mammals................................................................................................ 30 3.7 A Link Between Grazing Pressure and Predation Rates?......................................... 30 3.8 Relationship Between Grazing and Other Habitat Changes .................................... 30 3.8.1 Burning ............................................................................................................. 31 3.8.2 Drainage and ‘Land Improvement’ ............................................................... 31 3.8.3 Forestry and Predator Control....................................................................... 31 3.8.4 Acidification and Air Pollution....................................................................... 32 3.9 Conclusions.................................................................................................................... 32 4. CHANGES IN GRAZING PRESSURE - A SPECIES PERSPECTIVE................. 35 4.1 Red-throated diver Gavia stellata ................................................................................ 35 4.2 Black-throated diver Gavia arctica.............................................................................. 35 4.3 Greylag goose Anser anser............................................................................................ 35 4.4 Wigeon Anas penelope .................................................................................................. 36 4.5 Teal Anas crecca............................................................................................................ 36 4.6 Mallard Anas platyrhynchos......................................................................................... 36 4.7 Common scoter Melanitta nigra................................................................................... 36 4.8 Red-breasted merganser Mergus serrator................................................................... 36 4.9 Goosander Mergus merganser...................................................................................... 36 4.10 Red kite Milvus milvus.................................................................................................. 36 4.11 Hen harrier Circus cyaneus.......................................................................................... 36 Page No. BTO Research Report No. 164 December 1996 1 4.12 Buzzard Buteo buteo ..................................................................................................... 37 4.13 Golden eagle Aquila chrysaetos.................................................................................... 37 4.14 Kestrel Falco tinnunculus............................................................................................. 38 4.15 Merlin Falco columbarius............................................................................................. 38 4.16 Peregrine Falco peregrinus........................................................................................... 38 4.17 Red grouse Lagopus lagopus ........................................................................................ 38 4.18 Ptarmigan Lagopus mutus............................................................................................ 39 4.19 Black grouse Tetrao tetrix............................................................................................. 39 4.20 Oystercatcher Haematopus ostralegus......................................................................... 39 4.21 Ringed plover Charadrius hiaticula............................................................................. 39 4.22 Dotterel Charadrius morinellus.................................................................................... 40 4.23 Golden plover Pluvialis apricaria................................................................................. 40 4.24 Lapwing Vanellus vanellus........................................................................................... 40 4.25 Temminck’s stint Calidris temminckii ......................................................................... 40 4.26 Purple sandpiper Calidris maritima............................................................................. 41 4.27 Dunlin Calidris alpina ................................................................................................... 41 4.28 Ruff Philomachus pugnax............................................................................................. 41 4.29 Snipe Gallinago gallinago............................................................................................. 41 4.30 Whimbrel Numenius phaeopus .................................................................................... 41 4.31 Curlew Numenius arquata............................................................................................ 41 4.32 Redshank Tringa totanus.............................................................................................. 42 4.33 Greenshank Tringa nebularia ...................................................................................... 42 4.34 Wood sandpiper Tringa glareola ................................................................................. 42 4.35 Common sandpiper Actitis hypoleucos........................................................................ 42 4.36 Red-necked phalarope Phalaropus lobatus................................................................. 42 4.37 Stock dove Columba oenas ........................................................................................... 42 4.38 Cuckoo Cuculus canorus .............................................................................................. 42 4.39 Snowy owl Nyctea scandiaca ........................................................................................ 42 4.40 Short-eared owl Asio flammeus.................................................................................... 43 4.41 Nightjar Caprimulgus europaeus ................................................................................. 43 4.42 Skylark Alauda arvensis ............................................................................................... 43 4.43 Shore lark Eremophila alpestris ................................................................................... 43 4.44 Meadow pipit Anthus pratensis.................................................................................... 43 4.45 Grey wagtail Motacilla cinerea .................................................................................... 44 4.46 Pied wagtail