How Weather Patterns Influence Bird Movements Bryan Guarente University of Illinois at...

How Weather Patterns Influence Bird Movements

Bryan GuarenteUniversity of Illinois at Urbana-Champaign

Atmospheric Sciences DepartmentCOS Presentation

Monday March 21, 2005

Outline

• Bird Navigation

• How To Read Weather Maps

• Two Caveats

• Case Studies

• Helpful Resources

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

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


• “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


• 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

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.

How’s 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

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


• Rotation of highs and lows visible on surface obs


• Convergence and divergence will show areas of preferential movement to and from a location

• Multiple kinds of convergence and divergence (directional and speed)


• Areas of convergence and divergence visible


• 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


• 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)


• 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


• 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


• Jetstreaks and vertical motions– Jetstreaks: areas of fastest moving winds in

jetstream– Dynamical effects cause divergence


• Jetstream convergence and divergence


• 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


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


• 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


• 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

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

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?

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)

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)

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

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/

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/

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 today’s presentation from

book

Thank you!

• COS

• IBET

• COS member: Tom Kelly

• Bruce D. Lee and Catherine Finley

• Albert Guarente (my dad)

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