Birds of Seabrook Island

COAST BIRDS
  Contents
  Index
WORLD BIRDS
  Contents
  Index

ANECDOTES

  Radar sweep
 
 

BACK - NEXT
 

Species Acct.
Loons
Grebes
Procellarids
Pelicans
Herons
Ibises
Storks
Vultures
Flamingos
Waterfowl
Raptors
Turkeys
Quail
Rails
Limpkin
Cranes
Shorebirds
Gulls
Terns
Auks
Doves
Parrots
Cuckoos
Owls
Goatsuckers
Swifts
Hummers
Kingfishers
Woodpckrs
Flycatchers
Shrikes
Vireos
Crows/Jays
Larks
Swallows
Tits
Nuthatches
Creepers
Wrens
Kinglets
Gnatcatchers
Thrushes
Mimids
Starlings
Pipits
Waxwings
NW Warblers
Tanagers
NWSparrows
Cardinalines
Icterids
Finches
OWSparrows

TOP

 
Migration
 
Skip to:   
       
Annual Cycles Breeding Migration Migration in Captive birds
  Activity Cages
  Operations Recorder (Activity)
  Actual Count Data
  Zugunruhe
Energetics and the Annual Cycle
Estimates
A Model for Control
References
 
 

Migration

  The most obvious way to study migration is to observe the mass movements of birds that occur seasonally. Some birds (corvids, some thrushes, etc.) fly during the day and can be observed directly, especially when concentrated along shores or other leading lines. These migrants often fly below 1,000 feet and can be seen. (In the fall, movements of Fish Crows are particularly evident inland from Seabrook.)
   Many of our smaller birds fly at night, preserving the day for feeding and replenishment of energy reserves. Most nocturnal migrants appear to fly alone, but many utter flight calls as they fly. This may reinforce their desire to fly and could give some orientation information (if enough "vote" on the right direction, all may head that way). Some observers have specialized on flight calls and there are guides to their identification - thrushes are particularly evident at night.
   In contrast to small song birds, many shorebirds fly high (~20K feet or more) and at any time of the day or night. They often maintain tight flocks at fairly rapid air speeds - 20 knots of so, often with added tail winds helping them along. They can be observed only by using remote sensing such as radar.
   

Radar

    Right - Two progressive scans of an early radar (ARSR-I) stationed at South Truro, MA. The outline of Cape Cod can be seen on the screen. Time information is GMT (ZULU) and the frames are numbered. Masses of migrants can be seen aloft but only the general flow of migration can be followed in this older radar.
   In more modern weather and Doppler radars, it is possible to determine altitudes and even separate certain types of migrants. Shorebirds can be seen flying at higher elevations (15-20K feet) and speeds up to 45 mph while smaller birds fly lower (below) and slower (15-20 mph).
     
  Volume Altitude
  Using a weather radar, it can be seen that the volume of nocturnal migrants increases for about three hours after sunset and then declines progressively during the night. An average migrant might fly 100 miles or so during each flight over land... Compare this picture of migration with subsequent images of activity in caged birds. These images are from the work of S. A. Gauthreaux, Jr.


It is also possible to determine altitude of nocturnal migrants. It appears that the average altitude increases for the first three or four hours and then declines. The highest birds may reach 9K feet but the greatest majority are below 5,000 feet - actually most fly within 1,000 of the ground and may have problems with the guy wires of tall towers or lighted buildings... Also from S. A. Gauthreaux, Jr.
   Note that some shorebird flocks may fly at 15-20K feet for sustained periods.
   
  It is also possible to observe migrants directly.
  Landing migrants
Ceilometer

Birds may also be visualized at night crossing the disk of the moon during the night (Lowery). This method of observation is tedious and requires a full moon (and lots of math). It is known as moon watching.
  
An alternative is to look up the bright beam of a ceilometer beam and make observations on birds crossing through the light at night.

   

Patterns of coastal arrival during day light hours in Louisiana (Gauthreaux). Birds crossing the Gulf may continue to fly inland. If stopping they descend precipitously and land in coastal vegetation (recovering and feeding before moving on)...

       
    Banner - radar sweep off New England coast showing large groups of migrants (above).