Oriole Migration Update: April 23, 1998
Today's Report Includes:
Orioles Land by the Hundreds During 1st Fallout in Texas
At last, the first big wave of Baltimore Orioles was reported from Texas. On Saturday, ornithologists from Cornell University counted over 200 Orioles among thousands of birds that had just flown across the Gulf of Mexico:
"At about 2 pm we began a seawatch to determine whether or not migrants were coming in off the Gulf. Up to that point we had seen no definitive evidence that any trans-gulf migrants had been downed by the strong N winds or light precipitation.
"Another interesting observation comes from several friends who witnessed large numbers of birds crossing Laguna Madre in flight below 100ft above the water beginning at 1 pm and continuing for several hours. Apparently some transgulf migrants were strong enough to continue flying into a headwind and cross another body of water albeit not as substantial in any way as the Gulf of Mexico.
"There was a relative lack of dead birds. This could be a function of grackles, gulls or other animals scavenging the remains. We observed only three window kills at the South Padre Convention center (one bay-breasted warbler and two sora rails). While driving the road we found 10 road kills (4 Chipping, 3 Vesper, 2 Lincoln's and one Lark Sparrow). Also of note was the beginnings of what seemed a major wash up of bird remains on Sunday."
Andrew Farnsworth and Bill Evans
What Were the Weather Conditions?
Ornithologist David Aborn reports from Texas
The front that came through Texas last weekend was slow to move, so the Texas coast had a couple of days of rain. This was followed by north winds. As you should know by now, birds trying to migrate north cannot fly
with such strong headwinds, and must land.. On the Gulf coast, people reported a spectacular fallout on the 18th, with 53 species of migrants being seen! The most numerous birds were Nashville Warblers (100 seen),
Indigo Buntings (500 seen!!!), and Northern Orioles (200 seen!!!)."
"Have a good week, and good birding!"
All Around the Mulberry Bush
While waiting for orioles in Texas, recall Harlen Aschen's adage: "When the fruit on the mulberry trees is ripe there will be orioles and tanagers."
"No Orioles for us YET ...", he reported on Tuesday (04/22/98). "Have been checking out the mulberry trees every day for 13 straight days ... The tree that has the most ripe fruit has about 70% that are pink turning red and less than 1% that are dark red ... maybe by Friday. The other two trees are about 4 days behind."
Then this on Wednesday: "... saw our first oriole today near the mulberry tress ... a female orchard ... and the grosbeaks and tanagers were fantastic!"( firstname.lastname@example.org)
Let's see what happens next week....
Discussion of Challenge Question # 5
How do Birds Forecast the Weather?
"How do birds sense weather conditions, and know whether good or bad migration weather might be coming?" we asked last week.
Wisconsin students Jessi and Gale--who are still waiting to see their first oriole--knew: "We think Orioles detect changes in weather by sensing changes in air pressure," (Sandy_Roggow@mail.mhlt.k12.wi.us)
Like humans, birds feel warm and cold temperatures and wind, and they see as well as feel rain and snow. But unlike us, birds can also feel barometric pressure. They apparently have an inborn barometer that is extraordinarily sensitive: scientists have long noticed that birds feed intensely as air pressure falls.
An internal barometer is a handy adaptation for all birds, even non-migrants, because storms usually are associated with falling pressure, and birds have a hard time getting food during a storm. The sooner they can predict a storm before it hits, the more time they have to prepare.
Scientists also have known for a long time that migrating birds fly at different altitudes than non-migrating birds, and maintain this altitude even on moon-less nights when they can't see the ground at all. How do they maintain a particular altitude? Many scientists suspect that this is
also due to their ability to "feel" air pressure. Studies have proven that birds are extremely sensitive to small changes in air pressure, comparable to differences of only 5 to 10 meters in altitude.
Recognizing air pressure is also handy because birds often migrate along frontal systems, and changing air pressure is one of the first signs that a front is coming. High pressure systems often have clear skies, which make using celestial navigation easier, and flying on high pressure days may
even help "buoy" birds up a bit.
How do birds judge air pressure?
Scientists don't know!! They do have a couple of guesses. One is that birds may be able to detect it through their inner ear. We detect large changes in air pressure in our own inner ear when we make a fast change in altitude--that's when our ears "pop." Another guess is that the birds detect air pressure somehow though the huge air sacs that connect to their lungs and fill much of the space inside their bodies.
How would you design an experiment to test how a bird's internal barometer might work? There's no way for you to check your answer except to try it out--maybe one day you will be the scientist who learns the answer!
The Next Oriole Update Will be Posted on April 30, 1998.
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