BTO Research Report No. 666 How high do birds fly? A review of current datasets and an appraisal of current methodologies for collecting flight height data: Literature review Authors Chris B. Thaxter1, Viola H. Ross-Smith and Aonghais, S.C.P. Cook1 1 British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU, UK Report of work carried out by the British Trust for Ornithology1 on behalf of Natural England and the Crown Estate August 2015 British Trust for Ornithology The British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU Registered Charity No. 216652 2 CONTENTS Page No. List of Tables ........................................................................................................................................... 5 EXECUTIVE SUMMARY ........................................................................................................................... 7 1. INTRODUCTION ....................................................................................................................... 11 1.1 Background .............................................................................................................................. 11 1.2 Project aims and objectives .................................................................................................... 12 2. METHODS ................................................................................................................................ 13 2.1 Literature review ..................................................................................................................... 13 2.2 Collating flight height data...................................................................................................... 13 3. RESULTS ................................................................................................................................... 15 3.1 Visual Surveys and Boat-based Transect Surveys .................................................................. 15 3.1.1 Examples of use .......................................................................................................... 15 3.1.2 Calibration, testing and validation ............................................................................ 15 3.1.3 Advantages and disadvantages ................................................................................. 16 3.2 Digital Imagery Survey Methods ............................................................................................ 17 3.2.1 Examples of use .......................................................................................................... 17 3.2.2 Calibration, testing and validation ............................................................................ 17 3.2.3 Advantages and disadvantages ................................................................................. 18 3.3 Bird-borne telemetry ............................................................................................................. 18 3.3.1 Altimeters (pressure sensors) .................................................................................... 19 3.3.1.1 Examples of use ................................................................................................19 3.3.1.2 Calibration, testing and validation ..................................................................20 3.3.1.3 Advantages and disadvantages .......................................................................20 3.3.2 GPS and satellite telemetry ....................................................................................... 22 3.3.2.1 Examples of use ................................................................................................22 3.3.2.2 Calibration, testing and validation ..................................................................23 3.3.2.3 Advantages and disadvantages ....................................................................... 23 3.4 Radar ....................................................................................................................................... 28 3.4.1 Examples of use .......................................................................................................... 28 3.4.2 Calibration, testing and validation ............................................................................ 29 3.4.3 Advantages and disadvantages ................................................................................. 29 3.5 Laser rangefinder .................................................................................................................... 31 3.5.1 Examples of use .......................................................................................................... 31 3.5.2 Calibration, testing and validation ............................................................................ 31 3.5.3 Advantages and disadvantages ................................................................................. 32 3.6 Inclinometer .......................................................................................................................... 33 3.6.1 Examples of use .......................................................................................................... 33 3 3.6.2 Calibration, testing and validation ............................................................................ 34 3.6.3 Advantages and disadvantages ................................................................................. 34 3.7 Acoustic monitoring: audible microphones ........................................................................... 35 3.7.1 Examples of use .......................................................................................................... 35 3.7.2 Calibration, testing and validation ............................................................................ 35 3.7.3 Advantages and disadvantages ................................................................................. 35 3.8 Thermal and night vision infrared imaging ............................................................................ 36 3.8.1 Examples of use .......................................................................................................... 36 3.8.2 Calibration, testing and validation ............................................................................ 36 3.8.3 Advantages and disadvantages ................................................................................. 36 3.9 Ornithodolite .......................................................................................................................... 37 3.9.1 Examples of use .......................................................................................................... 37 3.9.2 Calibration, testing and validation ............................................................................ 37 3.9.3 Advantages and disadvantages ................................................................................. 37 3.10 Moon-watching, artificial light and ceilometers .................................................................... 38 4. DISCUSSION ............................................................................................................................. 43 4.1 Comparison of methods .......................................................................................................... 43 4.1.1 Visual estimation and high definition imagery ......................................................... 45 4.1.2 Telemetry ................................................................................................................... 45 4.1.3 Radar .......................................................................................................................... 47 4.1.4 Relative use of other “near-field” methods .............................................................. 47 4.2 Comparison of estimates produced from different survey methods .................................... 48 4.3 Conclusions ............................................................................................................................. 49 Acknowledgments ................................................................................................................................ 53 References ........................................................................................................................................... 55 4 LIST OF TABLES [top] Page No. Table 3.1 Summary of seabird tracking telemetry studies estimating at flight altitude ...... 27 Table 3.2 Summary of advantages and disadvantages of methods reviewed that have estimated flight heights of birds. ....................................................................................................... 39 Table 4.1 Summary ranking of relative suitability of all techniques as a primary method for estimating flight height distributions in the offshore environment; criteria for a primary method include: Expense and ease of use, error precision on measurements, species restriction - e.g. tags too heavy or attachment impractical, species-specific ID possible, full flight height distribution, general applicability to the marine environment, spatial scale covered, measurement through the 24-hour day, measurement through the year, influence of environmental conditions, sample size of birds of species, life-history status (e.g. breeding/non-breeding) of individuals determined ................................................ 44 Table 4.2