Grosbeak Migration Can Be Seen on Mackinac Island
Nature Notes
By Patricia Martin

Last Sunday at church, a friend mentioned to me that quite a number of Rose-breasted Grosbeaks had descended on their bird feeder. The birds apparently stayed around a few days, and then were off. She wondered where the birds summered, and where they migrated to in the winter.

For those of you not familiar with the Rose-breasted Grosbeak, they have a pale conical bill similar to their relative, the Northern Cardinal, and are of a similar size. Both the male and female have dark wings with small white patches and a dark tail. The male, however, really stands out with a black "hood," a bright red breast and inner underwings, and white underparts and rump. The female is less showy, with brown upper parts and buff underparts with brown streaking. Above her eye is a bold whitish "eyebrow" and she has a thin crown stripe. The song of this bird is a long, melodious series of whistled notes, up to two dozen, much like a fast version of a robin's song, which is interspersed with call notes. Their call is a distinctive squeak, sort of an "eek." The males often sing from their nest during incubation or brooding, during courtship, and occasionally at night. The female occasionally sings more softly, with a shorter song than the male.

Grosbeak

Mackinac Island is certainly in the summer range of this Grosbeak. They breed from Cape Breton Island in the east to central Ontario and central Manitoba all the way north to south central Mackenzie, south to central New Jersey, central Ohio, and central Kansas. I haven't seen the Rose-breasted Grosbeak nest on the Island. If anyone has, I'd like to hear from you. We have the requirements here for a good nesting site. They usually nest in deciduous forest, woodland, or second growth, often near water. They build their nests five to 15 feet off the ground in shrubs or small trees. The nest is made of twigs and coarse plant material, lined with finer material and hair. Their diet consists of insects, buds, seeds, fruits, and flowers. All in all, you might think to find them nesting here.

These birds winter in southern Mexico, south to Venezuela and Ecuador, though they are more common in the northern part of this range, particularly in the highlands. It is interesting that we often think of migratory birds like the Grosbeaks as "our birds," who merely go to Central and South America for the winter, while it would be probably just as correct to think of them as southern birds that make a relatively brief foray north to breed. It is quite amazing that hundreds of species make their long migrations, year after year, spring and fall. This seasonal movement enables birds to avoid the physiological stresses of unfavorable climates and to exploit food supplies that are available only at limited times of the year. It probably helps the reproductive rate. It permits exploitation of areas that either are more productive or provide less competition than the wintering grounds. In addition, the daylight periods in spring and summer are longer at higher latitudes, resulting in more hours per day in which birds can gather food.

In preparing for migration, birds experience both behavioral changes and physiological ones. Migration seems to be triggered by changes in temperature and change in day length, which trigger hormonal changes in the birds. They often accumulate more fat to

provide fuel for the journey. Some birds lose one-quarter to one-half of their body weight in migration. Behaviorally, they often become more nocturnal, altering their activity to the night time, as many of the smaller birds who migrate long distances fly at night and rest and forage during the daylight hours. When flying over water or unsuitable habitat, birds that normally stop may fly without a break for longer periods. Birds with shorter distances to travel often fly during the day, and some of those that are aerial foragers just pick up insects along the way and fly non-stop.

There are four main migration routes in North America: Pacific, Central, Mississippi, and Atlantic. In our area, we see birds that migrate on the Mississippi and Atlantic pathways. The main reason that we see so many migratory birds passing through the Straits of Mackinac is the geography of Michigan. Many birds do not like to fly over the cold waters of the Great Lakes, and so fly over land. This causes those who fly north into lower Michigan to be funneled to the "Tip of the Mitt" along the southern coast of the Straits of Mackinac. When they reach the shore, they have to fly over water, either directly across the Straits to the Upper Peninsula or to island hop, and then it only has to fly short distances over water to continue north. This is why we see so many hawks and eagles in April and warblers and other songbirds in May. Agreat-uncle of mine one spring recorded 16 different warblers passing through or nesting on Mackinac. We've also already seen a number of water birds passing through this spring.

Many birds have a strong tendency to return to the same breeding and nesting grounds year after year, and the same with the wintering grounds. They seem to have a great sense of attachment to a location if they've been successful in raising a brood there. If the environment has been disturbed, or they've had trouble raising young in a particular area, some birds are likely to go elsewhere. Take, for example, the Bank Swallows colonial nesters, who used to nest in the sandbank near the center of the Island. Quite a few years ago, the bank was bulldozed and the sand was used to fill in holes. The Swallows have never returned.

All in all, migration is a rather risky business if you think about it. The birds have to travel hundreds or thousands of miles, during which many things can happen, from perdition to weather problems. They have to have the right type of environment on both ends, their winter home as well as their summer one. This makes them particularly vulnerable to environmental disruptions, from deforestation to pollution, in at least two locations. Sometimes it seems that the risks may not be worth the benefits. How all these birds find their way is a subject for another column.

Now, not all birds migrate long distance, though most birds do some migration. Even the Blue Jays and the Northern Cardinals who are seen yeararound in our area do some migrating. Those which we see in the summer go a bit south for the winter and those that we see in the winter travel further north in the summer.

Over the next month or so, keep an eye out for our feathered friends who are summering with us and those that are just passing through. If you're interested, the state park has a "Birds of Mackinac" checklist for sale at a minimal price.

Trish Martin is a yeararound resident of Mackinac Island, has earned a master's degree in botany from Central Michigan University, and owns Bogan Lane Inn.