To: Journey North Students From: Ornithologist David Aborn University of Mississippi Hattiesburg, Mississippi Dear Students:
Last week I told you how to interpret some of the features on a weather map. Looking at a weather map this week, you should be able to make an educated prediction about migration along the Gulf coast.
Like last week, there is a cold front on Mississippi's back door. However, it looks like this front may not make it through the state. If that happens, then the winds will continue to blow from the south, which means that many birds will be able to migrate farther inland (rather than stop on the coast). As a consequence, banding operations and birdwatchers in the central and eastern Gulf coast area probably won't be seeing large numbers of migrants.
Last week I also asked you to think about why migrants usually do not take advantage of winds around a low pressure area. The answer is that low pressure areas generally bring bad weather (rain), poor for migration. High pressure areas bring clear skies, which are good for flying and navigating.
Now I would like to tell you about my own research. I am studying habitat selection and activity patterns during migration. Here's a question I'm asking,
"Do migrants use whatever habitat they land in after crossing the Gulf of Mexico, or do they explore the habitats and select the best one?"
CHALLENGE QUESTION: What do you think makes a good stopover habitat?
Send your answers to: jnorth@informns.k12.mn.us
To answer this question, I have been radiotracking Summer Tanagers on Horn Island, a barrier island of the Mississippi coast, for the past 3 springs. (See if you can find it on a map.) These are not the fancy satellite transmitters you may have learned about. These transmitters only have a range of 1/2 mile, and I have follow the birds on foot. It's definitely a challenge.
I have found that tanagers that have used most or all of their energy stores do explore the various habitats before settling, whereas fatter birds do not move very much. I also found that lean birds spend 3/4 of their time in scrub habitat, while fat birds spend most of their time in pine forest. I think that lean birds need to find the best habitat to fatten up and resume migration, and fat birds are resting and avoiding predation, since they already have fat and can migrate come nightfall.
Activity budgets were also different for fat and lean tanagers. Fatter birds spent much more time perched, and half as much time feeding as lean birds. The fatter birds also spent a lot of time preening and vocalizing. As you might expect, leaner tanagers spent a lot of their time feeding and moving around. They ate a variety of insects, including ants, beetles, dragonflies, and carpenter bees. One bird even ate a monarch butterfly without getting sick, and later tried to eat a small lizard! I also saw tanagers eating two types of fruit.
TRY THIS! As a project, you may want to look at activity patterns of a backyard migrant, such as robins. Make a list of behaviors you might see (perching, feeding, singing, etc.), and look at differences between males and females in how much time they spend doing different things. You might also look at differences in habitat use. What differences might you expect between males and females in activity and habitat use?
I hope you have learned that migration is not only an important part of a bird's life, but it is also very complex. There are many factors that are important if a bird is to survive and breed. The complex nature of migration also makes it exciting to study, because there is so much to learn. Understanding as much as we can about nature, from bacteria to blue whales, is extremely important to finding solutions to the environmental problems we face. I hope some of you will select a career in biology. Take care, good luck, and stay in touch!
David Aborn david_aborn@bull.cc.usm.edu
Journey North 125 North First Street Minneapolis, Minnesota 55401 Phone: (612)339-6959