Autumn Snow on Mount Mansfield, Vermont
© K.P. McFarland
October is a month of change. The forested hills fade from green to a kaleidoscope of red and gold that dazzles the eyes. Here’s your field guide to some moments that you might not otherwise notice during these few precious weeks that feature colored hills beneath a deep blue sky, with the calls of migrating geese high overhead and the last Monarchs gliding silently southward.
The yellow streaming blooms of Witchhazel (Hamamelis virginiana) can be found in the understory in October when most leaves have fallen to the ground. The long, bright-yellow petals, sweet smell of nectar with pollen loaded stamens near the source, suggest that insects are the mode of pollination. But with the cool temperatures, most insects are finished for the season. Who visits this late bloom?
No one really knew until University of Vermont biologist and naturalist Bernd Heinrich discovered that a group of Owlet moths feed at the flowers on late evenings in October and likely are the main pollinators. Because it is often cool (or downright cold) on October nights, moths need sugars to fuel the high body temperatures (~86° F) that are necessary for flight. These sugars mostly come from tree sap at this time of year, but nectar, if present, would suffice too.
When the moths are at rest, their body temperature falls to the air temperature around them and they enter a state of torpor. During daytime when temperatures fall below freezing, they hide under insulating leaves on the forest floor. But when night falls, they have to fly to find food and mates, which requires raising their body temperature—maybe by as much as 50° F—to activate their flight muscles. To do this, they shiver. On long flights they will sometimes repeatedly stop and shiver to warm up again. All of this is powered by the sugars they consume.
In a 1987 Scientific American article Heinrich wrote, “Adult winter moths generally feed on the sap of injured trees, although on late-fall nights a few years ago I saw many of them feast on the blossoms of witch hazel, Vermont’s latest-blooming plant. Until that time no one knew just how the plant was pollinated.”
The moths that pollinate Witchhazel are several species of Owlet moths (Family Noctuidae), including (click to learn more at iNaturalist):
Add your observations to the Vermont Atlas of Life on iNaturalist and help us track Witchhazel flower phenology and some of the insects you might find visiting the flowers.
With shorter days and colder nights, bee activity is slowing down – but it’s not done yet! Five species of bumble bees (Bombus) have been found in October and shared on the Vermont Atlas of Life at iNaturalist. On warm days, especially early in the month, the Common Eastern Bumble Bee (B. impatiens) can be found in decent numbers feeding on the last flowers of autumn, like New England Aster. But unlike spring and summer, the majority of bumble bees flying now are males who won’t return to the colony once they’ve left. These drones spend nights tucked under flowers waiting for warm days and the chance to find a newly emerged queen to court. After a few hard frosts, the remaining drones and workers will be dead and the new queens will be curled up underground waiting for spring. For the next 7 to 8 months there will not be any male or worker bumble bees alive. The remaining queens hold the future of the entire species, while waiting for spring.
Drone bumble bees don’t sting, so if you know the difference or are daring, males can be gently handled without consequence. Be sure to snap a photo of the bumble bees you are finding and share them with the Vermont Atlas of Life on iNaturalist and help us record their fall phenology.
In the spring Spotted and Jefferson’s salamanders crawl to vernal pools — temporary woodland ponds that fill with water but then dry out later in the summer, providing a fishless environment for larval salamanders, where they mate and lay eggs. But for 90% of the year these salamanders are elsewhere in the forest. Sometimes you can find them by flipping over a large stone or rolling a rotting log, but for the most part, they are tough to find.
Technology allowed VCE biologist Steve Faccio to easily spy on a salamander using miniature tags that emit a radio signal. With a radio receiver and small antenna, Steve could then monitor the salamander’s movements and locations.
Standing on a forest path near the site, Steve turned on the radio receiver and tuned to a salamander’s frequency. A faint, but audible “ping” sounded from the headphones. A few minutes later Steve was in the general area of the animal. The signal was strong, but he couldn’t quite pinpoint it. The salamander was underground.
After an hour on hands and knees, Steve found the exact spot. A series of narrow, branching tunnels under the leaf litter and rotting logs held the prize. Steve was able to move just a few leaves and there it was peering out from a tunnel opening.
These salamanders can’t dig. They use shrew, mice and chipmunk tunnels for refuge. In fact, the tunnels are so important to them that Steve could predict areas in the forest that would be used by the salamanders just by the density of mammal tunnels. Without small mammals, there were no salamanders to be found.
After tracking them to these surface tunnels all summer long, suddenly, with the chill of fall, the salamanders changed behavior. They entered more vertical tunnels that led deeper underground. By November nearly all of them were deep under the earth. The radio signal only traveled about two or three feet, so eventually the signals were lost. They had gone deep enough to escape the ground penetrating frost and spying by radio from above.
There are four basic colors in fall leaves and a different pigment produces each. Xanothophylls is responsible for yellow, carotenoids for orange, tannin for brown, and anthocyanids create red and purple tones.
During the growing season green chlorophyll in tree leaves is broken down by sunlight and constantly replenished. As day length decreases the abscission cells, a special layer at the leaf-stem junction, divide rapidly and slowly block transport of materials. As abscission begins, chlorophyll production wanes and eventually stops. As the green chlorophyll breaks down without replacement we begin to see the underlying orange carotenoids and yellow xanthophylls. These pigments help capture light energy during the growing season. But unlike yellow and orange pigments, red anthocyanins are made during fall leaf senescence. It is manufactured from sugars found in the leaf. They produce greater amounts during cooler nights and sunny days. When a hard freeze comes along, production ends.
Why would a tree use energy to make a pigment in a leaf that is about to die and fall off? In 2003 William Hoch, a biologist at Montana State University, found that if he genetically blocked anthocyanin production, the leaves were much more vulnerable to fall sunlight damage, and so sent less nutrients to the plant roots for winter storage before the leaf fell. The tree was not able to recuperate as much energy back from the leaves it grew earlier in the year.
A few years later, University of North Carolina at Charlotte graduate student Emily Habinck found that in places where the soil was lower in nitrogen and other important elements, red maple trees produced more anthocyanin in the leaves. Apparently trees growing in more stressful environments invest in more anthocyanin, which allows them to recover more nutrients that are stored in the leaves before they fall. Bright red leaves under a clear blue sky are spectacular to see. But what is beauty to us may be survival to a tree.
A few years ago on Outdoor Radio, we met Joshua Halman, a Forest Health Specialist with the Vermont Department of Forest, Parks and Recreation at Underhill State Park where the department has monitored these trees for over 25 years, recording color change and leaf drop here and at other places around the state.
Halman told us that this work has documented the impacts of climate change. “Seen over this time, the peak color and the main time for leaf drop has actually become later,” Halman explains. “What we’re seeing since we started recording our fall phenology data is that, on average, foliage is peaking about eight days later over that 25-year period.”
Keep an eye out for claw marks on American Beech tree trunks left by American Black Bear climbing into the treetop in search of nuts. When a bear finds a tree with a good quantity of nuts, it climbs up the trunk, parks itself in the canopy, and pulls nut-laden branches to its mouth. The bear often leaving a tangled ‘nest’ of bent and broken branches in the canopy where it has been feeding.
Black bears depend on body fat for the energy needed during hibernation. With protein content equivalent to corn (~11% dry mass) and fat content (~17% dry mass) that is more than 5 times that of corn, beechnuts are an important part of their fall diet. But the trees don’t produce lots of nuts every year. Beech trees normally have low yields, usually during odd-numbered years, followed by bountiful nut production (called masting) in even-numbered years.
If you find signs of bear or areas with good beechnut production, be sure to snap some photos and submit your discoveries to the Vermont Atlas of Life on iNaturalist to help track these feeding areas and the crops the bears depend on.
Excellent blog! Thanks!
“Even-“ and “odd-numbered years”?! Probably simply every other year!
Wonderful! Thank you.
Well done, Kent!