Biology Reference
In-Depth Information
to the normal arrival dates, and now seem to have a poorer chance of capitalizing on the
greatest insect abundance while raising their hungry young.
Goldfinches move south in winter following a pattern that seems to coincide with re-
gions where the minimum January temperature is no colder than 0°F on average.
A BIRD'S GOTTA FLY WHEN A BIRD'S GOTTA FLY
Researchers study migratory urges
by putting birds in an orientation cage, called
an Emlen cage after the scientist who designed it. It is a funnel shape in which birds can
stand upright. Birds that are in a migratory state try to escape from the cage by moving
from the bottom area up the sloping walls. Early models had an ink pad on the bottom,
and birds would leave footprints on the funnel walls as they tried to fly up. Newer ver-
sions may be lined with typewriter correction paper or another material so that the birds
leave scratches as they move about.
These marks are distributed fairly randomly by non-migratory birds or birds not in a
migratorystate,butshowstrongdirectionalityinmigratorybirdsundergoing
Zugunruhe.
Some modern cages also have perches fitted with microswitches that register a signal
wheneverabirdalights.Thesecagesindicatehowbirdsundergoing
Zugunruhe
aremuch
moreactivethanothers,andalsoshowpreferreddirectionsandlengthoftimespenttrav-
eling.
Q How do migrating birds know where to go and how to get there?
A
Somespecies,suchascranesandgeese,learntheirmigratoryroutesfromtheirparents.
They follow their parents on their first flight south, and sometimes for part of the return
