DOI: 10.5061/dryad.t76hdr871
title: Cranes soar on thermal updrafts behind cold fronts as they migrate across the sea

description: Thermal soaring conditions above the sea have long been assumed absent or
 too weak for terrestrial migrating birds, forcing large obligate soarers
 to take long detours and avoid sea crossing, and facultative soarers to
 cross exclusively by costly flapping flight. Thus, while atmospheric
 convection does develop at sea and is utilized by some seabirds, it has
 been largely ignored in avian migration research. Here we provide direct
 evidence for routine thermal soaring over open sea in the common crane,
 the heaviest facultative soarer known among terrestrial migrating birds.
 Using high-resolution biologging from 44 cranes tracked across their
 transcontinental migration over 4 years, we show that soaring
 characteristics and performance were no different over sea than over land
 in mid-latitudes. Sea-soaring occurred predominantly in autumn when large
 water-air temperature difference followed mid-latitude cyclones. Our
 findings challenge a fundamental paradigm in avian migration research and
 suggest that large soaring migrants avoid sea crossing not due to absence
 or weakness of thermals but due to their uncertainty and the costs of
 prolonged flapping. Marine cold air outbreaks, imperative to the global
 energy budget and climate system, may also be important for bird
 migration, calling for more multidisciplinary research across biological
 and atmospheric sciences.
description: # Cranes soar on thermal updrafts behind cold fronts as they migrate
 across the sea This
 dataset and accompanying R scripts pertain to the research study on crane
 migration above the sea. The focus of this study is to analyze the
 migratory patterns of cranes, particularly their utilization of thermal
 updrafts and soaring-gliding dynamics during sea crossing. The dataset
 includes high-resolution GPS and accelerometer data, annotated with
 environmental variables, and the R scripts are tailored for statistical
 analysis and visualization of these data. ## Description of the data and
 file structure The data folder contains the following files:
 **1HzGPS_and_ACC_annotated (multiple files):** * 1Hz data for individual
 cranes, annotated with environmental variables. * File names include
 individual crane IDs. **ThermalStats.csv:** * Summarizes 10-minute
 segments with and without thermal activity. * Used in
 `ThermalSections_analysis&plot.R` and `time_scales_analysis.R`.
 **SoarGlide.csv:** * Contains data on coupled soaring-gliding events. *
 Used in `soaring&gliding_plot&analyse.R`.
 **AnnotatedTimePointsMedSea.csv:** * Data for annotated time scale data
 for Mediterranean sea crossing. * Used in `time_scales_analysis.R`.
 **TimesOfMigrationFall.csv:** * Number of days crane stayed at the last
 stopover site before crossing the Mediterranean sea * Used in
 `time_scales_analysis.R`. ## Code/Software The code folder includes R
 scripts designed for the statistical analysis high-resolution datasets:
 **ThermalSections_analysis&plot.R:** * Performs statistical analysis
 of 10-minute thermal sections. * Generates Figure 2B.
 **soaring&gliding_plot&analyse.R:** * Analyzes coupled
 soaring-gliding events. * Generates Figure 3A. **time_scales_analysis.R:**
 * Conducts time-scale analysis. * Generates Figure 4A. ### Metadata
 Description ### (1) Data 1HzGPS\_and\_ACC\_annotated Tables: NAN indicates
 not available. 1. **Tag:** Identifier for the tracked animal 2.
 **TimeCont:** timestamps of observations (UTC). 3. **Latitude:**
 Geographic latitude where the observation was recorded. 4. **Longitude:**
 Geographic longitude where the observation was recorded. 5.
 **Altitude_m:** Altitude of the crane (m). 6. **Speed_km_h:** Speed of the
 crane (km/h). 7. **direction_deg:** Direction of crane movement (degrees
 clockwise from north). 8. **OverSeaOrLand:** Indicator of whether the
 crane is over the sea or land during observation (0=land, 1=Black sea,
 2=Mediterranean sea). 9. **mag_x, mag_y, mag_z:** Components of the
 magnetic field measurement in the x, y, and z directions. 10. **acc_x,
 acc_y, acc_z:** Accelerometer readings in the x, y, and z directions
 (m^2/sec). 11. **Interpolated_Lat:** Interpolated latitude values. 12.
 **Interpolated_Lon:** Interpolated longitude 13.
 **InterpolatedElevation:** Interpolated elevation values (m). 14.
 **running_Flap_rate:** estimated flap rate form 1Hz data based on a
 calibration dataset of 10Hz (flaps per second) 15. **AleAboveTerrain:**
 Altitude of the crane above the terrain (m). 16. **TerrainHeight:** Height
 of the terrain above sea level (m). 17. **quartile:** Statistical quartile
 information. 18. **Individual:** tag number used for environmental
 annotation. 19. **t2m:** Temperature at 2 meters above surface level (°C).
 20. **sst:** Sea surface in C temperature (°C). 21. **blh:** Boundary
 layer height (m). 22. **cbh:** Cloud base height (m). 23. **cape:**
 Convective available potential energy (J/kg). 24. **cin:** Convective
 inhibition (J/kg). 25. **msshf:** Mean sea sensible heat flux (W/m^2). 26.
 **tcc:** Total cloud cover (%). 27. **msl:** Mean sea level pressure (Pa).
 28. **u850, u925:** Zonal wind component at 850 hPa and 925 hPa pressure
 levels. 29. **v850, v925:** Meridional wind component at 850 hPa and 925
 hPa pressure levels. 30. **t850, t925:** Temperature at 850 hPa and 925
 hPa pressure levels. 31. **sstDiff:** Difference between sea and air
 temeperature (°C) 32. **windDirection850, windDirection925:** Wind
 direction at 850 hPa and 925 hPa pressure levels. 33. **windSpeed850,
 windSpeed925:** Wind speed at 850 hPa and 925 hPa pressure levels. ###
 **(2) ThermalStats:** NAN indicates not available. 1. **Individual**:
 Identifier for the tracked animal. 2. **UniqueSectionCounter**: Sequential
 counter for a distinct 1 Hz GPS burst (min10 min., but can be longer). 3.
 **Date**: Date and time of observation (DD-MMM-YYYY HH:MM:SS). 4.
 **lat_start**: Geographic latitude at the start of a 10 minutes segment
 (Degrees). 5. **lon_start**: Geographic longitude at the start of a 10
 minutes segment (Degrees). 6. **OverSea**: Flag indicating whether the
 segment is over the sea (0=land, 1=Black sea, 2=Mediterranean sea). 7.
 **day_time**: Flag indicating it during daytime or during nighttime
 (0=night, 1=day). 8. **time_since_sunrise_h**: Time since sunrise at the
 start of the segment (Hours). 9. **time_since_sunset_h**: Time since
 sunset at the start of the segment (Hours). 10. **time_of_part_min**:
 Duration of the observed segment (Minutes). 11. **TotalDistance**: Total
 distance covered in the segment (meters). 12. **vg**: Ground speed during
 the segment (m/sec). 13. **va**: Airspeed during the segment (m/sec). 14.
 **tw**: Tailwind component during the segment (m/sec). 15. **sw**:
 Sidewind component during the segment (m/sec). 16. **meanFlapRate**:
 Average flap rate of the individual during the segment (Flaps/sec). 17.
 **percent_time_in_thermals**: Percentage of the segment time spent in
 thermals (%). 18. **time_in_thermals_sec**: Total time spent in thermals
 during the segment (Seconds). 19. **mean_thermal_length_sec**: Average
 duration of thermal events during the segment (Seconds). 20.
 **mean_climb_rate**: Average climb rate during thermal events (m/s). 21.
 **mean_max_elevation_above_ground**: Average maximum elevation above
 ground level for each thermal during the segment (Meters). 22.
 **Mean_blh**: Mean boundary layer height during the segment (Meters). 23.
 **Mean_msl**: Mean sea level pressure during the segment (Pa). 24.
 **Mean_DeltaT**: Mean temperature difference during the segment (Degrees
 Celsius). 25. **wvel**: Wind velocity during the segment (m/s). 26.
 **wang**: Wind angle during the segment (Degrees). 27.
 **number_of_thermals**: Number of thermal events encountered during the
 segment. 28. **age**: Categorical age of the individual (1= Breeding
 adult, 2 = Adult with unknown breeding status, 3 = Subadult, 4 =
 Juvenile). 29. **age_w**: Age class of the individual. 30. **sex**: Sex of
 the individual (e.g., Male, Female, Unknown). ### **(3) SoarGlide:** NAN
 indicates not available. 1. **individual**: Identifier for the tracked
 animal. 2. **datetime_start**: Date and time when the soaring-gliding
 segment started (DD-MMM-YYYY HH:MM:SS). 3. **lon_start**: Geographic
 longitude at the start of the observation (Degrees). 4. **lat_start**:
 Geographic latitude at the start of the observation (Degrees). 5.
 **time_soaring_sec**: Total time spent soaring during soaring-gliding
 segment (Seconds). 6. **climb_rate_m_sec**: Average climb rate while
 soaring (m/s). 7. **falp_rate_climb**: Flap rate during the climb phase
 (Flaps/sec). 8. **falp_prop_climb**: Proportion of time flapping during
 the climb phase (%). 9. **type_thermal**: Type of thermal encountered (1 =
 classic soaring, 2 = spring-like soaring pattern). 10.
 **start_alt_above_terr**: Starting altitude above terrain at the beginning
 of the soaring phase (Meters). 11. **exit_alt_above_terr**: Exit altitude
 above terrain at the end of the soaring phase (Meters). 12.
 **time_gliding_sec**: Total time spent gliding during the soaring-gliding
 segment (Seconds). 13. **distance_gliding_m**: Total distance covered
 while gliding (Meters). 14. **sink_speed_m_sec**: Average sink speed while
 gliding (m/s). 15. **air_speed_m_sec**: Airspeed during the gliding phase
 (m/s). 16. **air_speed_calc_m_sec**: airspeed during the gliding phase
 based on tailwind estimated from thermal drift (m/s). 17. **tail_wind**:
 tailwind during the gliding phase (m/s). 18. **tail_wind_calc**: estimated
 tailwind using bird drift in thermals from the horizontal displacement of
 thermals (m/s). 19. **side_wind**: sidewind during the gliding phase
 (m/s). 20. **side_wind_calc**: estimated sidewind using bird drift in
 thermals from the horizontal displacement of thermals (m/s). 21.
 **falp_rate_glide**: Flap rate during the gliding phase (Flaps/sec). 22.
 **falp_prop_glide**: Proportion of time flapping during the gliding phase
 (%). 23. **mean_blh**: Mean boundary layer height during the observation
 period (Meters). 24. **sea_land**: Indicator of whether the
 soaring-gliding segment (0=land, 1=Black sea, 2=Mediterranean sea).. 25.
 **day_time**: Indicator of whether the soaring-gliding segment was during
 daytime or nighttime (0=night, 1=day). 26. **age**: Categorical age of the
 individual (1= Breeding adult, 2 = Adult with unknown breeding status, 3 =
 Subadult, 4 = Juvenile). 27. **age_w**: Age class of the individual. 28.
 **sex**: Sex of the individual (Male, Female, Unknown). 29. **Vopt**:
 Optimal flight speed which maximizes bird cross-country speed (m/s). 30.
 **RAFI**: Risk-Averse Flight Index. 31. **RAFIcalc**: Risk-Averse Flight
 Index calculated based on estimated tailwind. 32. **Date**: Date of the
 soaring-gliding segment (DD-MMM-YY). ### **(4)
 AnnotatedTimePointsMedSea:** NAN indicates not available. 1. **indev**:
 Identifier for the tracked animal. 2. **Date**: Date of the real sea
 crossing event (YYYY-MM-DD). 3. **fall**: Flag indicating whether the
 season of the sea crossing event (0 = spring, 1 = fall). 4.
 **thermap_presence**: Indicator of thermal presence during the observation
 (0 = no thermal soring during crossing, 1 = at lest 1 thermal soaring
 event). 5. **daysBack**: Number of timescales relative to the autumn real
 sea crossing event. 6. **lat**: Geographic latitude used for annotation
 (Degrees). 7. **lon**: Geographic longitude used for annotation (Degrees).
 8. **mig_ang**: Migration angle at the time of observation (Degrees). 9.
 **datetime_utc**: Date and time at the location (DD-MMM-YYYY HH:MM:SS).
 10. **datetime**: Date and time UTC used for annotation (DD-MMM-YYYY
 HH:MM:SS). 11. **t2m**: Temperature at 2 meters above the surface (Degrees
 Celsius). 12. **sst**: Sea surface temperature (Degrees Celsius). 13.
 **blh**: Boundary layer height (Meters). 14. **cbh**: Cloud base height
 (Meters). 15. **cape**: Convective Available Potential Energy (Joules per
 kilogram). 16. **cin**: Convective Inhibition (Joules per kilogram). 17.
 **msshf**: Mean Sea Surface Heat Flux (Watts per square meter). 18.
 **tcc**: Total Cloud Cover (fraction from 0 to 1). 19. **msl**: Mean Sea
 Level Pressure (Pascals). 20. **u850**: Zonal wind component at 850 hPa
 (Meters per second). 21. **u925**: Zonal wind component at 925 hPa (Meters
 per second). 22. **v850**: Meridional wind component at 850 hPa (Meters
 per second). 23. **v925**: Meridional wind component at 925 hPa (Meters
 per second). 24. **t850**: Temperature at 850 hPa (Degrees Celsius). 25.
 **t925**: Temperature at 925 hPa (Degrees Celsius). 26. **sstdiff**:
 Difference between sst and t2m (Degrees Celsius). 27. **windDir850**: Wind
 direction at 850 hPa (Degrees). 28. **windSpeed850**: Wind speed at 850
 hPa (Meters per second). 29. **windDir925**: Wind direction at 925 hPa
 (Degrees). 30. **windSpeed925**: Wind speed at 925 hPa (Meters per
 second). 31. **GPCC**: Precipitation (Millimeters). 32. **time_point**:
 location during the crossing used for annotation, "sea enter"
 was used for the analysis (1 = starting point, 2 = sea enter 3 =in sea).
 33. **tw**: Tailwind component (Meters per second). 34. **sw**: Sidewind
 component (Meters per second). ### **(5) TimesOfMigrationFall:** NAN
 indicates not available. 1. **indev**: Identifier for the tracked animal.
 2. **Date**: Date of the sea crossing event (YYYY-MM-DD). 3. **fall**:
 Flag indicating season (0 = spring, 1 = fall). 4. **Hz1_section_num**:
 number of 10 minutes 1Hz sections during the sea crossing event. 5.
 **mean_thermal_prop**: Mean proportion of time spent in thermals during
 the sea crossing event. 6. **prop_section_with_thermal**: Proportion of 10
 minutes sections containing thermal soaring during the sea crossing event.
 7. **thermals**: Number of thermal events encountered during the sea
 crossing event. 8. **lat_start_migration**: Geographic latitude at the
 start of the sea crossing event (Degrees). 9. **lon_start_migration**:
 Geographic longitude at the start of the sea crossing event (Degrees). 10.
 **datetime_start_migration_utc**: Date and time at the start of the sea
 crossing event in UTC (DD-MMM-YYYY HH:MM:SS). 11.
 **datetime_enter_sea_utc**: Date and time when the individual enters the
 sea area in UTC (DD-MMM-YYYY HH:MM:SS). 12. **datetime_exit_sea_utc**:
 Date and time when the individual exits the sea area in UTC (DD-MMM-YYYY
 HH:MM:SS). 13. **time_at_sea**: Total time spent at sea during the sea
 crossing event (Hours). 14. **Days_at_stopover**: Number of days spent at
 the last stopover site before the sea crossing event. 15. **ang**: Angle
 of movement at the beginning of the sea crossing event (Degrees).