How Weather Patterns Influence Bird Movements

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How Weather Patterns Influence Bird Movements

• Bryan GuarenteUniversity of Illinois at
  Urbana-ChampaignAtmospheric Sciences
  DepartmentCOS Presentation
• Monday March 21, 2005

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Outline

• Bird Navigation
• How To Read Weather Maps
• Two Caveats
• Case Studies
• Helpful Resources

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Bird Navigation

• How do birds migrate?
• Using landmarks (Point Peleé)
• Staying within the lines
• Highways (I-95)
• Ridges (Blue Ridge Hawk Mountain)
• Coastlines (Atlantic Coast, Lake Michigan)
• Magnetism of the earth
• Sun, Stars, Moon
• Believing their instincts
• Avoiding weather or go with weather

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Bird Navigation (cont)

• Most important thing
• Which family of birds?
• What habitat is needed?
• What time of year?
• Circlers (Soaring)
• Falconiformes
• Gruiformes
• Direct Flights (short and long distance)
• Anseriformes
• Charadriiformes
• Passeriformes

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Bird Navigation (cont)

• Circlers
• Thermals pockets of warm rising air
• Thermals enhance a good migration day for
  circlers
• Strong upper level winds also make for a good
  circler migration day
• Thermals are not required but circlers will limit
  distances on days without thermals

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Bird Navigation (cont)

• Short Distance vs. Long Distance Migrants
• Long migration is not effected greatly by weather
  patterns
• More dependant on season or amount of sunlight
• Examples Arctic Tern, Sandpipers, and Barnacle
  Goose
• Short migration is effected greatly by weather
  patterns
• Less dependant on season or amount of sunlight
• Examples Most Passerines and Waterfowl

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Problems encountered

• What would you do if you were flying and you
  encountered
• Significant Cloud Coverage?
• Frozen Precipitation?
• Strong Winds opposing your motion?

• Land!
• Birds experience these conditions and are
  forced to land all the time.

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Hows the weather up there?

• Upper atmosphere makes all the difference
• BIRDS DO NOT MIGRATE AT SURFACE
• Surface winds seldom important
• Between 1km and 5km AGL winds are the biggest
  weather factor
• 850mb (1km) to 500mb (5km) most important levels
  for winds
• However, surface weather systems effect upper
  atmosphere
• Surface cannot be ignored

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How to read weather maps

• Birds prefer to follow winds (cross country
  flight example)
• Most maps show winds
• wind barbs ?
• All directions are the same as a compass
• Plotted as the direction the wind is FROM

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How to read weather maps

• Rotation of highs and lows visible on surface obs

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How to read weather maps

• Convergence and divergence will show areas of
  preferential movement to and from a location
• Multiple kinds of convergence and divergence
  (directional and speed)

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How to read weather maps

• Areas of convergence and divergence visible

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How to read weather maps

• Streamlines
• Shows direction a bird would travel without
  outside forcing
• Can see where migrants will come from or end up
• Easiest way to see convergence at any level
• Fronts become obvious (lines of convergence)
• Fronts make some birds stop migration (strong
  pressure decline, assume bad weather)
• Uncommonly plotted especially for forecasts

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How to read weather maps
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How to read weather maps

• 850 mb (1km up)
• BEST place to look for strong winds that will
  promote movements
• Strong winds from preferential direction GOOD
  MOVEMENTS
• Season dependant
• Stronger winds at this level are called
  low-level jet
• The end of a low-level jet has speed convergence
  (great place to look for migrants)

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How to read weather maps
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How to read weather maps

• 700mb (2-2.5km up)
• Good place to look for strong winds for migrants
• Not as good as 850mb, but still important
• Low-level jet also present at this level
• Stacked strong winds (700mb strong winds above
  850mb strong winds) GOOD MOVEMENT

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How to read weather maps
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How to read weather maps

• 500mb (5-6km) and 250mb (10-12km)
• Winds at these levels only effect high altitude
  fliers
• Hard to track these birds
• Track vertical motions
• Upward vertical motion may lead to movement
• Barring cloud cover (which accompanies rising
  motion)
• Unproven, but feasible

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How to read weather maps
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How to read weather maps
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How to read weather maps

• Jetstreaks and vertical motions
• Jetstreaks areas of fastest moving winds in
  jetstream
• Dynamical effects cause divergence

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How to read weather maps

• Jetstream convergence and divergence

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How to read weather maps
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How to read weather maps
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How to read weather maps

• Infrared (IR) Satellite Imagery
• Low pressure systems look like commas
• High clouds versus low clouds
• Figure out low level winds from low clouds (if
  present)
• Sometimes see areas of preferred heating of the
  ground (areas good for circlers)
• Nighttime cloud cover

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How to read weather maps

• Visible Satellite Imagery
• Low pressure systems look like commas
• Cloud levels not clear in some cases
• Visible satellite not available at night

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How to read weather maps
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How to read weather maps

• Water Vapor (WV) Satellite Imagery
• Low pressure systems sometimes look like commas
• Rotations can be seen very clearly
• Rotations are usually associated with vertical
  motion and bad weather (can ground birds)
• Jetstream pattern is often clearly visible
• Can infer streamlines
• Images available at night
• Cannot see below 700mb

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How to read weather maps

• Radars
• Radar Reflectivity
• Two different modes used (for small particles and
  large particles)
• Clear air mode
• Precipitation mode
• Clear air mode
• Easy to pick up fronts and smaller particles
  (clutter issues)
• Precipitation cannot be present
• Precipitation Mode
• Hard to pick up fronts and smaller particles
• Precipitation will be present
• May be hard to distinguish birds from
  precipitation

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How to read weather maps
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Two Caveats?!

• Good weather patterns do not always equal good
  migration
• All weather forecasts are model produced
• Models differ
• Models are made using our current understanding
  of the atmosphere
• Weather forecasts beyond three days are
  pipedreams
• Because of this models are NEVER correct!
• BUT, we need to look for guidance somewhere

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Experience is the key

• As it is with birds
• The more you look, the more you understand
• This may not come easy for some of you
• Every day forecasts change
• Look often and be flexible
• Are you ready for your first try?

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What happened on this day?

• Black-legged Kittiwake (Rissa tridactyla) showed
  up near Chicago (reported by Eric Walters)
• Refer to emails on IBET (8077, 8078, 8082, 8087,
  8091) for discussion of patterns
• For sightings refer to IBET (8094 BLKI, 8096
  BLKI, 8100 FEHA, 8101 SACR)

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What happened on this day?

• Sandhill Cranes (Grus canadensis) clouded the
  Chicago area skies (1,269 reported by Matt
  Karabestos 400 reported by Leslie Cummings)
• First real push of Sandhill Cranes (G.
  canadensis) all season
• IBET posts (9514 9518, 9521, 9526, 9528)

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Summary

• Upper-level winds are the most important factor
  (weather-wise)
• The longer time scale the better
• Areas of convergence runways
• Surface fronts play a role but can be avoided by
  larger birds if they are weak fronts
• Clouds, precipitation, and strong winds opposing
  motion will make a bird land

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Useful Resources

• http//www.atmos.uiuc.edu/bguaren2/
  birdweather/index.html
• http//www.rap.ucar.edu/weather
• http//weather.cod.edu/
• http//vortex.plymouth.edu/
• http//www.crh.noaa.gov/

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Other helpful sources

• Severe and Hazardous Weather 2nd edition
• Rauber, Charlevoix, and Walsh
• Excellent introductory weather book
• Written with non-science students in mind
• Figures from todays presentation from book

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Thank you!

• COS
• IBET
• COS member Tom Kelly
• Bruce D. Lee and Catherine Finley
• Albert Guarente (my dad)