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Fall's Journey South Update: October 6, 2000

Today's Report Includes:


Have You Seen Any Orioles?
Baltimore Oriole
(Click to Enlarge)
Every spring when leaves are first emerging, orioles surge conspicuously through North America, visiting orange and nectar feeders and brightening early spring. In autumn, when twice as many orioles are racing south, you'd think orioles would be twice as obvious, but they're not. Some of them visit feeders, but in this season of abundance they get plenty of their natural food, from insects to fruit, so many people don't notice the fall migration at all.

So how do you see migrating orioles? During dry weather, many are attracted to birdbaths or sprinklers. Some orioles do come to nectar feeders or bowls of grape jelly, and a very few come to oranges, although they usually lose interest in oranges after spring migration. People with grape vines have an excellent chance of seeing orioles feeding on the grapes. The people who see the most orioles in autumn are usually the people who check out every movement in trees and shrubs. When birders do this, they see so many interesting birds that they're satisfied even if they don't find a single oriole!

The Baltimore Oriole and the Bullock's Oriole are the bright orange orioles that have the biggest ranges in the US and Canada. One difference between them is where they live. Get out a field guide and see if you can answer:

Challenge Question #5
"East or West? Which species--Baltimore or Bullock's--is found in the West, and which species is found in the East?"

(To respond to this question, please follow the instructions below.)

Two Species, Two Molts
Besides their range, there's another difference between Baltimore and Bullock's Orioles. One of these species molts into fresh new feathers before migrating to the tropics and the winter feeding grounds. But the other oriole species does not molt until it arrives on its wintering grounds. (Molt means to drop old, worn feathers and grow new, strong ones in their place.)

Molting requires a lot of a bird's energy. That energy comes from the bird's food supplies, so a good food supply is important when it's time to molt. Areas that normally have plenty of moisture, such as areas in the East, can produce abundant insects and fruit--the foods that orioles eat. Areas that are dry or receive less rainfall will not have abundant insects and fruits. These are clues that can help you figure out the answer to our next challenge question:

Challenge Question #6
"Molting Matters! Which oriole (Baltimore or Bullock's) do you think molts on its summer breeding grounds? Which oriole probably molts on its winter feeding grounds?"

(To respond to this question, please follow the instructions below.)

When 1 + 1 = 3
In the Great Plains in the center of the continent, Bullock's and Baltimore Orioles meet and mingle. Sometimes they mate. The babies of the two different kinds of oriole parents are called "hybrids." Hybrids are different from either parent, so here's when 1 + 1 adds up to a third type of bird.

Because Baltimore and Bullock's Orioles could successfully interbreed, ornithologists used to think that the two orioles were not different species, but simply different races. Then Ornithologists learned more about the molt (see Challenge Question #6 above). This information helped them figure out why the hybrid offspring of a Baltimore and a Bullock's does not survive as well as a bird whose parents are both the same species. Imagine having one parent that molts before migrating and another that waits until arriving on the wintering grounds before molting! The hybrids of such parents usually molt BOTH on their breeding grounds and on their wintering grounds. This is an enormous waste of energy. It lowers the number of eggs hybrid females can produce, and it lowers the life expectancy of both males and females.

Oriole Clues to Watch For
Oriole Nest in the fall
(click to enlarge)
The orioles are heading south and winter is coming to your backyard, but you can still learn about the presence of orioles in your neighborhood. How? Go out and look for their nests hanging in the leafless trees. Oriole nests are strong and last at least a year. If you find an oriole nest in a leafless three this fall or winter, you'll know your area is a favorite nesting place. You can help make sure that tree and others like it remain in place for orioles. Next spring you can start a neighborhood watch for orioles, and you can join with others across the continent in unpaving the way for orioles! See:

Morning, Noon, or Night Flight: Response to CQ #4
Last time we asked, "Why might hummingbirds migrate more at midday than morning or later afternoon and evening?"

Students from Temple St. Academy in Tampa Florida sent a response that is true for migrating species such as hawks, eagles, and some cranes: They migrate more at midday because the warming effect of the sun creates thermals that help them stay aloft with less energy. However, our bird expert Laura Erickson reminds us of something about hummingbirds that no responses mentioned:

"Hummingbirds are so tiny that they lose a lot of heat and body weight during the night when they can't feed. When they wake up in the morning, hummers must spend a lot of time feeding to replenish the energy they lost during the previous night. During the late afternoon and evening, they rest and feed to store up energy for surviving the following night."

How to Respond to Today's Challenge Questions:

1. Address an e-mail message to: jn-challenge-fall@learner.org

2. In the Subject Line of your message write: Challenge Question #5 (or #6).

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


The Next Journey South Update Will Be Posted on October 20, 2000.

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