Fall's Journey South Update: September 18, 1998

Today's Report Includes:

Living Off the Fat of the Land
Imagine if your teacher suddenly, in a matter of weeks, doubled his or her weight! What effects would this have on her or his skin? Legs? Heart? Would you be able to notice a difference?

What if YOU suddenly doubled your weight? It would take a long time for you to adjust to the new size, and the extra weight would slow you down. You'd get out of breath a lot faster when running or going up a hill or staircase.

Blackpoll Warbler in Fall Plumage
Photo by Jeff Spendelow

Small songbirds called Blackpoll Warblers double their weights twice a year, in preparation for the flight of their life. The added weight is all fat, but it doesn't clog their arteries and veins and doesn't slow them down. The amount of fat on their bodies will determine whether they live or die, but it's virtually impossible to notice any difference in their appearance without holding them in your hand! Their feathers cover them up, and air sacs keep them looking plump even when they're starving.

Even though it's migrating for the first time in its life, the young Blackpoll Warbler pictured to the left will fly farther than almost any other songbird.

Fueling Up
Every fall, Blackpoll Warblers pig out on insects and spiders as if their lives depended on it. As their bodies become fat enough, they take off on their own personal marathons.

But before striking out over the Atlantic, they wait for a low pressure system. Trace the blackpoll's flight path on a map and you'll see why: The wind blows from the northwest after a low pressure system. These winds carrying the blackpolls southeast, toward the Bermuda Islands. Once they reach that area of the ocean, they meet air currents called "trade winds". These winds push them southwest toward the coast of South America.

Use the map's scale to calculate how many miles a Blackpoll would fly if :

Loose Weight in Only 80 Hours

Spring Plumage of a Male Blackpoll Warbler
Photo by Jim Stastz

We've seen ads promising rapid weight loss, but for blackpolls it's true. Imagine running three four-minute miles. Now imagine running 1,200 four-minute miles, keeping up that high speed the whole way, for 80 hours. That's how one ornithologist calculated the exertion involved in a Blackpoll Warbler's migration. If all goes well, the blackpoll is back to its pre-migration weight by the end of the trip.

Where They Are Now
Right now many Blackpolls are still in Canada and Alaska, but a lot have been trickling south. American Birding Association secretary Blake Maybank, an active birder in Nova Scotia who leads birding tours, says 7,000 - 8,000 pairs of Blackpolls breed in Nova Scotia every year, and that there are a LOT more in Newfoundland--too many to census. He told Journey North that Gros Morne National Park (49.5N -57.5 S) has half a million breeding pairs!

Blake told us that in Nova Scotia, local birds start moving as early as late July, and by early September it's not hard for someone to see several in a day. But by late September and early October you can find 100 in a single day.

Fascinating Facts

Which leads us to this week's--

Challenge Question # 3
Using a map, figure out the minimum distance between North America and the British Isles. How many degrees off course would a Blackpoll Warbler have flown if it ended up there rather than the Bermuda Islands? Can you name three possible reasons why a warbler might fly so far off course?

How to Respond to Today's Challenge Question
1. Address an e-mail message to: jn-challenge-fall@learner.org

2. In the Subject Line of your message write: Challenge Question # 3

3. In the body of the message, answer the Challenge Question.

Discussion of Last Week's Challenge Question #2:
What evidence could you give to show that dragonflies and kestrels migrate together? Frank Nicoletti's graph shows the numbers of kestrels and dragonflies every day in September. Every day with a bug number of dragonflies has a big number of kestrels, and every day with a low number of dragonflies has a low number of kestrels. It's easy to see that the graph's peaks and valleys for both species happen on the same days. Scientists say these numbers are correlated.

The Next Journey South Update Will Be Posted on September 25, 1998

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