The Autumn Show

Autumn is finally settling in the St. Louis area; the overnight chill lingers a little longer in the morning, the hours of daylight are decreasing, and the leaves are finally turning colors.

Have you ever wondered what causes the leaves to turn those brilliant shades of red, orange and yellow, and why it seems that the autumn foliage is more colorful some years than others?

Let’s begin with the leaf.

The carotenoids, the pigment responsible for the fall colors, is already present with in the leaf but is concealed by the green color of chlorophyll, the component essential for photosynthesis. The base of each leaf contains a special layer of cells, known as the separation layer, where the exchange of water and food between the leaf and tree takes place.

The leaves are responsible for providing food for the tree and it performs this duty through photosynthesis. In photosynthesis, the leaves use water and carbon dioxide to produce carbohydrates for the tree and oxygen is the by-product of this process. On any given day, the average tree will take in 1-1/2 pounds of carbon dioxide and release about a pound of oxygen into the atmosphere. The leaves also produce more food than is needed and the tree will convert the excess sugar into starch to consume during the winter months.

The shorter hours of daylight and cooler temperatures trigger a reaction that allows the leaves to reveal their autumn colors. During this time, the cells within the separation layer form a cork-like material that cuts the exchange of water and glucose from the leaf. The chlorophyll within the leaf disappears when the water supply is cut off, revealing the hidden oranges, reds or yellows.

The orange leaves are produced from carotene pigments,

yellow leaves are a result of xanthophyll pigments

and anthocyanin create the red and purple leaves.

Interestingly enough, not all trees produce anthocyanin and this pigment is only made during the fall months.

Contrary to popular belief, rainfall is not the only factor responsible for the colors of autumn. Sunlight, cloud cover, temperature and soil acidity also determine the intensity and duration of fall’s colorful show. For example, bright light produces anthocyanin. The brighter the sunlight, the more vivid the red and purple leaves. A warm wet spring followed by a summer that is neither too hot nor too dry that leads into a fall with warm sunny days and cool nights will produce a dazzling leaf display.

Now that you know the work the leaves put into their visual displays, I hope you get a chance to go outside and enjoy Autumn’s show.

Mist Netting 101

I have been mist netting for about 13  years now and when I talk about it, I'm often asked "How do you catch the birds?" or "What is mist netting?" and "Why do you do it?"

I find the process of mist netting difficult to explain without photographs. Of course it's best to demonstrate it in person, but that's usually not possible. So, without further ado...here is your crash course in mist netting.

"Mist nets" are nylon or polyester nets that vary in length. The net mesh also varies in width and length. Depending on location, the nets can be fairly easy to see, as in this picture.

Or, nearly invisible.

A bird will fly into the net

Red-eyed Vireo

Author removing a bird.

Extracting a bird.

Once the bird is removed from the net, a lightweight band made of aluminum or stainless steel is placed on its leg, wing and tail measurements are taken, the overall health of the bird is assessed, and  the age and sex of the bird is determined if it's possible.

Banding a Winter Wren.

Yellow-billed Cuckoo. Note the band in the lower center of the picture.

Processing a Veery with the aid of a technical book.

Examining the wing coverts of a Swamp Sparrow.

Banding is essential for field ornithologists in tracking migrating raptors and songbirds,

population growth or decline and reproduction success. Bird banding is done worldwide, but specifically here in the United States, all banders order their bands from the Dept of the Interior and report their data to the Patuxent Bird Banding Lab. If a banded bird is captured in a different location, the person who caught the bird will submit their findings to the Bird Lab who in turn, notifies both parties, thus tracking the migration habit of that particular bird.

Gray-cheeked Thrush. Because of banding, we know these birds migrate through St. Louis in the spring and fall.

On a local level, bird banding is especially helpful in monitoring the birds that return to the same site each year.

This Indigo Bunting was banded in 2008 and later recaptured at the same site in 2012

Over 63,000,000 birds have been banded since the beginning of the program in 1902 and 3,500,000 have been recovered and reported to the banding offices. As I stated earlier, banding birds is also a good way to keep track of the nesting success and the longevity of our avian friends. The Bird Banding Lab has compiled a list of the longest lived birds based on submitted band information. Here is the link.
Mist netting is a wonderful opportunity to examine the variety of colors and textures in the feathers of the birds. A bird that looks drab from afar may have several shades of brown and minute stripes and speckles not seen through a pair of binoculars. Often I have discovered tiny bristles around a beak, a shade of yellow hidden under the wings or beautiful chestnut colored eyes on a bird in my hand. Things I may not ordinarily see on that bird while it is hopping around in a sycamore tree or miss because the lighting washed out the colors.

Mist netting and handling the birds has also helped improve my bird watching skills because in constant handling of the birds, you notice the overall shape of the bird, proportion of wing and tail length and yes, those feather colors and arrangement of colors. And more importantly, mist netting has enhanced my respect and admiration of these tiny creatures.