Backyard Biology

Nature stories from my backyard and beyond

Nature Stories

Sounds of Nature

Friday, October 9, 2009

Ah, how I love the sounds of the woods. There is as much to hear in nature as there is to see. Often more. Try sitting in the woods with eyes closed and listen. Many creatures will become visible to your ears that are hidden from sight. You can track the passing seasons as easily by the sounds you hear as by the temperature of the air or the position of the sun.
Over the years, I have come to associate certain sounds with each season.

Winter is the time of quiet. The wind whispering in the pines or a family of chickadees keeping in touch might be the only sounds I hear until the peepers and wood frogs announce the coming of warmer weather.
Next are the birds, ushering in the spring with their love songs. As the summer heats up, the birds give way to the cicadas. Their loud buzzing high in the trees is a sure sign of a hot day approaching.
Fall is for the night insects. With a background chorus of crickets, the katydids fill the night with their song. Ka-ty,Ka-ty-did, clunk, Ka-ty,Ka-ty, Ka-ty-did, clunk.

Wait a minute. What was that sound. The one I didn’t recognize. That “clunk” sound. Sounds like someone throwing a rock against a tree.

Not a rock, but an acorn. Acorns are falling in record numbers. Must be a mast year.

Mast is defined as, “the nuts of the oak or beech tree, or any other forest tree”. A mast year is any year that these trees produce large numbers of nuts. For the oak trees, this happens every two to five years. In the in-between years, very few, if any nuts are produced. Scientists have noticed that many trees synchronize their mast years. This includes many species of trees over large geographical regions, like all of New England and into Canada. How the trees coordinate this and why is up for debate.

There appear to be two schools of thought as to how trees mast in the same year. The first is climate. Trees will produce large amounts of nuts only when the weather is favorable. This of course can affect trees over a wide area. The second is genetics. There is a genetic clock in the DNA of trees telling them when to mast.
Which ever it is, and I suspect it’s some of both, what advantage do the trees gain from masting? Of course there is a favorite theory. One that seems perfectly obvious and therefore must be true. But while there is much evidence for this favorite theory, there is also some evidence against it. Be that as it may, can you guess the favorite theory? What possible advantage could trees gain by masting?

Nuts are the seeds of many trees. For the species to survive, at least a few of the nuts must grow into trees. But nuts are in high demand as food by many animals. These include turkeys, blue jays, mice, squirrels, deer and many others. The population of these animals is limited by the food available. If the trees produce few nuts for a number of years, the animal populations will be small. If, however, after 5 years of few nuts, the trees were to produce an overabundance of nuts, the predators would not be able to eat them all and there would be a better chance of some surviving to grow into trees. Of course, the population of animals would rise that year because of the large food supply, but with a poor crop the next year, their numbers would die back again.
The problem with masting is that for it to be effective, many species of trees must mast at the same time. If they mast in different years, there will always be some food available for the predators, thereby conferring no advantage to the trees from masting.

Any event in nature has far reaching, and sometimes quite unexpected consequences. And so it is that the mast year affects us humans in many ways. It has been shown that the mast year has an indirect effect on gypsy moths and lyme disease – two large concerns of humans.
In a mast year, with an abundance of food available for young mice, the mouse population soars. Since mice are one of the major predators of gypsy moths – feeding on the moth pupa- gypsy moth infestations are smaller during a mast year. In fact, some scientists think that this is the main cause of gypsy moth population crashes.
Deer ticks spread lyme disease. Adult deer ticks feed primarily on deer. During an oak mast year, deer will migrate into oak forests in the fall to feed. After the ticks have fed, they fall to the floor of the oak forest, and lay their eggs the next spring. The eggs hatch in the late summer and the larvae feed on mice. If these mice have the bacteria for Lyme disease, then the larval ticks become infected when they feed. Once they have fed, the larvae overwinter and in the late spring molt into juvenile ticks. This is the stage that mostly infects people. Therefore, two years after a mast year, an oak forest is likely to have a greater abundance of the juvenile deer ticks, the most infective stage for Lyme disease.
The clunking of acorns is the sound of a mast year. It is also the sound of gypsy moths being eaten and deer ticks on the prowl. Who knows what else it is the sound of?

Ah, how I love the sounds of the woods. There is as much to hear in nature as there is to see. Often more.

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