Although signs of the fall season are usually evident enough from changes in
the weather, there are many clues from nature that a seismic shift in the
seasons is occurring. Even if you did not have a calendar, you should be able
to predict the month if you study the many signs that nature provides.
During a recent walk on our farm I picked up a handful of nuts from the forest
floor. Can you identify the acorns, shagbark hickory nuts, black walnut,
buckeye, hazelnut, and chinquapin? These provide a bountiful crop for wildlife
to harvest and hide away for the future. Many such nuts are never recovered by
rodents and germinate.
There are many soft fruits in the forest including this nannyberry. It is
Viburnum lentago and is one of many viburnums which produce "haw" fruit which
are prized by animals of all kinds. The variation in fruit color is interesting
since it illustrates how plants communicate the ripeness of their fruits to
frugivores. It would be disadvantageous for the fruits to be eaten before they
are ripe, since the seeds are not mature, so unripe fruits are often
unpalatable or even poisonous. The change in color from green to red, yellow or
black that signals ripeness is easily recognized and is so familiar to us that
we often fail to understand the evolutionary meaning.
Grasses are also producing seeds and I here illustrate this with one of my
favorites, Indiangrass. Grasses do not have pretty flowers and they are wind
pollinated so we do not always consider them to be beneficial to animals. But
the seeds are eaten by a wide variety of birds and over an extended period. So
it is important to allow grasses to flower and mature seeds in the fall and
leave them in the fields during the fall and winter as wildlife food. Grasses
can also be quite beautiful at this stage of growth.
One distinct sign of fall around our ponds is the rapid decline in insect
activity and a change in the species present. For example the large common
green darner migrates south and is replaced by the similarly sized shadow
darner. The autumn or yellow legged meadowhawk is the last dragonfly to emerge
in the north and likely the last one seen before winter. The male shown here is
a beautiful red color to advertise its virility. The appearance of odonate
species that specialize in cooler conditions seems to be a classic case of
avoidance of competition by a temporal shift in activity.
Eastern tiger swallowtails are a common butterfly in our area but we almost
never find the caterpillars which feed on black cherry and tulip poplar. This
caterpillar found its way to our porch and has changed from green to brown as
it approaches the time for pupation. It has two false eye spots which may
confuse avian predators into thinking it is a scary snake. In addition when
disturbed it protrudes an osmeterium which looks very much like the tongue of a
snake. These mechanisms to avoid predation illustrate how intense the efforts
of birds are to find and eat caterpillars, and how gullible birds can be when
confronted by these elaborate ruses.
When I see large golden garden spiders on their webs I know it is fall. These
spiders over-winter as eggs or young spiders and gradually grow to an adult
size over the summer. The large female builds a characteristic orb web with
distinctive zig-zag patterns called stabilimenta that strengthen the web, and
may attract insects and warn birds not to fly into the web.
The migration of hawks is a characteristic fall phenomenon and I recently
noticed this juvenile red shouldered hawk in a tree on our farm. The juvenile
plumage pattern seems to be good camouflage and signals a lack of maturity to
adult hawks. We do not see red shouldered hawks during the breeding season so
this must be a bird that is migrating south. They make use of rising currents
of warm air or thermals to minimize their energetic cost of long distance
flight.
Although the arrival of fall signals the end of the growing season for most
animals and plants, it is a time of many changes in the world of natural
history that are of great interest. So get out and enjoy the beauties of fall
and observe how a few species wax while most others wane in abundance.
Bill Dunson
Galax, VA and Englewood, FL
http://lemonbayconservancy.org/news-blog/nature-notes-by-bill-dunson/
http://pieenvironmental.blogspot.com/
http://www.galaxgazette.com/blogs
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Nuts from farm hickory nuts, acorns, black walnut, buckeye, hazelnut, chinquapin 9.18.15 Bill Dunson IMG_9073 aa.jpg
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Ginseng at farm 9.17.15 Bill Dunson IMG_9048 aa.jpg
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Nanny berry viburnum fruit at farm 8.30.15 Bill Dunson IMG_8780 aa.jpg
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Iindian grass at farm 9.17.15 Bill Dunson IMG_9067 aa.jpg
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Shadow darner at farm 9.7.15 Bill Dunson IMG_8916 aa.jpg
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Meadowhawk autumn or yellow legged at pond eight farm 9.7.15 Bill Dunson IMG_8908 aa.jpg
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Tiger swallowtail cat near pupation at farm 9.1.15 Bill Dunson IMG_8787 aa.jpg
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Golden garden spider at farm 9.15.15 Bill Dunson IMG_9016 aa.jpg
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Red shouldered hawk at farm 9.17.15 Bill Dunson IMG_9042 bb.jpg
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