Lecture 8 – Migration & Navigation
Migration Timing• Highly precise due to “biological clock”• Phenology of Minnesota Birds
– Winter (November –February)– Early Spring (March-April)– Late Spring (May)– Summer (June – July)– Late Summer (August)– Fall (September – October)
• Specifics (Jim Gilbert) (S. Stensaas)– March 12th – Woodducks - Feb 19th – G.H.Owls– April 2nd – Tree Sparrows - March 13th – Gulls– May 5th – Red-eyed Vireo - April 1st – Tundra Swans– May 16th-23rd – Warblers - May 1st – Winter Wrens
North American Flyways
Fat Deposition
• Completion of fat deposition in small passerines can be accomplished in 4-10 days
• Most species can rapidly restore depleted reserves during migration– stopover habitats
• Amount of fat deposited is related to distances to be covered– fat deposits may constitute 30 - 50 % of
live weight
Stopover Ecology
• Refuel• Examples
– Woodlands in agricultural areas– Riparian areas in the desert– Coastal Areas
• Habitat loss = loss of essential stopovers– Coastal stopovers heavily impacted
Navigation• Topographic – diurnal migrants –
coastlines, river valleys, mountain ridges; “Lead lines”
• Solar orientation – evidence of orientation with the sun
• Stellar orientation – evidence of orientation with different night skies, continuously recalibrated
Navigation continued
• Geomagnetism – use of the Earth’s magnetic field for orientation, continuously recalibrated
• Olfactory – use of smell, evidence in some seabirds
“thrushes set their courseusing a magnetic compass,which they calibrate to thesetting sun before takeoff each evening.”
“use stars, sun, geomagnetic field and polarized light for orientation”
Navigation Continued
• Twilight Cues– Polarized setting sun rays align N-S– Define departure after dark
• Learning– Young birds often get lost– Learn stopovers from experience– Ex: Whopping Cranes
Migration ‘Help’Whooping Crane Recovery Programs
Songbirds Fly Three Times Faster Than ExpectedScienceDaily (Feb. 16, 2009)
The study found that songbirds' overall migration rate was two to six times more rapid in spring than in fall. "We were flabbergasted by the birds' spring return times. To have a bird leave Brazil on April 12 and be home by the end of the month was just astounding. We always assumed they left sometime in March," she said.
Fig. 1. Interpolated geolocation tracks of individual purple martins (A and B) and wood thrushes (C and D) that bred in northern Pennsylvania, USA (42°N, 80°W). Blue, fall migration; yellow, winter range movements; and red, spring migration.
Studying Migration
Why?How:• Observing• Trapping• Tracking• Radar
Migration Trends• Case Study early 1960s• Hawk Mountain migration counts show numbers of
Peregrine Falcons and Bald Eagles in rapid decline• Rachel Carson sites declines due to DDT in Silent Spring• DDT banned in 1972
Observing and Counting
Passerine Banding
Trapping – the Blind
Trapping - Nets
Mist-net trap of a Sharp-shinned Hawk
Tracking
www.hawkwatch.org
Swainson’s Hawks
Radar Ornithology
http://virtual.clemson.edu/groups/birdrad/COMMENT.ht
WSR-88D (NEXRAD) weather surveillance radar
• Near complete coverage of U.S.• Transmits microwave signals into the
atmosphere and measures returning energy– “reflectivity”
• Reflectivity estimates density of targets
• Doppler radar at Duluth airport
Migration on the North Shore
Hawk Ridge, Duluth
• Averages 94,000 raptors
• Over 180,000 non-raptors– Many are Passerines– Corvids
Conservation Issues
• Impacts with structures – towers, guy wires, buildings, houses, windows
• Wind-turbine development• Stopover habitat Loss• Climate change
Birdsafe and Lights Out
•Minnesota Audubon•Migrating birds attracted to lighted structures•Results in exhaustion or collisions
A study of North Shore bird migration in the
context of potential wind turbines
Anna Peterson Jerry Niemi, Heidi Seeland, Annie Bracey,
Hawk Ridge Bird ObservatoryNatural Resources Research Institute
University of Minnesota Duluth
Wind Potential along North Shore
The Conflict…
http://www.ckwag.org/issues.html
http://www.aweo.org/
(320 feet tall)
Diurnal Migration Study
Study Sites
Percent of migratory birds at each flight height category
0102030405060708090
100
Mig
rant
s (P
erce
nt o
f To
tal)
100m to 500m
Canopy to 100m
Below Canopy
North Shore Stopover Study
Important Bird Areas- MN Audubon
• Identify, monitor and conserve important sites for birds
• MN’s first IBA: Hawk Ridge– Stopover habitat