August 23, 2007
By Susan Benson,
CNHM Director of Education
While gardeners are busy harvesting green beans, sweet corn, zucchini, eggplants, tomatoes, and peppers, seasonal changes in nature are occurring all around. A bumper crop of acorns is falling right now, and squirrels can be seen in a frantic scurry to collect them. We can also find small piles of broken and chewed pine cone bracts as squirrels have eaten the pine seeds and left the remains behind.
Even more fascinating is what occurs in the bird world this time of year. During these late summer days, migratory birds have been feeding heavily, increasing their body weight sometimes by as much as 100 percent as they store fat and protein. They are able to eat more food because their digestive organs actually increase in size (those that do not feed during migration actually shrink.) The birds’ reproductive organs actually atrophy and shrink as hormone levels fall with decreasing daylight. Flight muscles, heart, and lungs also increase in size.
Flocks of birds, especially red-winged blackbirds, are flying about in extremely large groups. The first nighthawks have been spotted flying through the evening sky. Crows and blue jays can be seen migrating in flocks of up to 200 birds. Grackles and robins are moving through, flying fast and straight through the sky. Migrating birds of prey can be seen circling on thermals, large bubbles of warm air rising in the sky. Migrating flickers fly through in swooping flight and sun themselves on roadsides.
Adult loons begin flying south in late August and early September. Chicks stay on the nesting lakes, feeding and taking their first test flights, until nearly ice-over. One day, they start running across the water, take flight, and head south, where they will stay for the next three years. Most loon chicks will eventually return to their original nesting lake or find one nearby. Some loons do not establish their nesting territory until they are five years old.
We are beginning to see geese and some ducks flying in a regular V-shaped formation. One theory as to why they fly in this v-shape is that all birds except the one in the lead can gain lift from the wing-tip angles produced by the bird in front of them. According to scientists, the most efficient flight would include a one-fourth wingspan distance from the bird in front of it. However, motion pictures of flocks in flight show that Canada geese do not travel in these types of formations. Some scientists believe that the formations geese do use enable the birds to maintain visual contact and avoid possible mid-air collisions.
Become a phenologist! Keep your eyes open for migrating birds. Try counting them as they move through and track the date and numbers you observe. To get a good count, try counting as many as you can in a short time (before they are out of sight), and then estimate what fraction of the flock you have counted and multiply.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.