Field Guide to October 2021

A Prickly Courtship

By Julia Pupko

As you walk through the woods this October, you may hear screaming in the treetops. Look closer and you may just see a North American Porcupine (Erethizon dorsatum) or two. In October, North American Porcupines are in the middle of their mating season, which lasts from late summer through December. Courtship and copulation often occur high in trees, along with a lot of screaming.

Porcupines have several challenges when it comes to mating. The first is that females are only fertile for one eight to 12 hour period a year, meaning that mating has to happen quickly. When a female is almost ready to mate, she begins spreading a mixture of vaginal mucus and urine across her roughly 20 acre territory, which attracts males. When her suitors arrive, they will begin to violently fight each other for hours, biting and quilling each other until one male comes out victorious. These battles can lead to serious injury and even death, along with a lot of lost quills. If you come across a lot of quills scattered around in one area, you may have found a recent battle ground.

Once a male has fought off the other prospective males, he must navigate the second challenge of being a Porcupine during mating season – the roughly 30,000 deadly quills that also cover female Porcupines. For many species in the animal kingdom, victorious males do not always wait for a female’s consent before mating with her. Female Porcupines have no issue with this – if a male approaches too soon, he will receive a facefull of quills, or at minimum, more screaming. The male must wait, sometimes for days, until the female has entered her window of fertility and becomes receptive to mating (a lot of screaming and squawking occurs while he waits). When the female is ready, the male approaches on his hind legs and tail, grunting at her. He then sprays her with urine. The female will lift her tail and curve it over her back, allowing the male to proceed without becoming impaled on her quills.

When a female is done, she will walk away from the male, turn around, and scream at him yet again. In spite of the 12 hour maximum period of fertility and all the screaming, females have a 90 percent reproductive success rate. Porcupines can live for up to 30 years, and the average female will have a single porcupette (the endearing name of a baby porcupine) for each year of her life, from the time she is sexually mature to the time she reaches menopause. This means she is pregnant or lactating for 11 months of each year.

Keep your ears out for screaming prickle rodents this October. Remember, you can upload audio recordings to iNaturalist!

Changing Leaves

By Julia Pupko

My absolute favorite activity in the fall is hiking to the top of one of Vermont’s many peaks, perching myself on the best vantage point, and looking at the changing leaves. I watch as wind rushes through the trees, causing a swirl of yellow, orange, red, and brown.

For leaves that turn yellow, orange, and brown, trees either do not produce any new color pigments, or just produce a small amount of new pigment. As the days grow shorter and colder, these deciduous trees slow then stop their production of chlorophyll. The beautiful colors that appear have been in the leaves the entire time, masked by the large amounts of green pigment. Under optimal conditions, the trees can break down chlorophyll and reabsorb the compounds used to create it.

Trees whose leaves turn red follow a slightly different pattern. Anthocyanins (the compound that turns leaves red, purple, or crimson) are synthesized just before the leaves fall off the tree. The prevalent theory to explain anthocyanins production is that they are used as a form of sunscreen and allow trees to recover nutrients in the leaves before they fall. Temperature, sunlight, nutrient availability, and amount of rainfall in the summer and fall affect the level of anthocyanin production each year. When autumn is drier with abundant sun, anthocyanin production is higher than a fall with more overcast, rainy days. Additionally, other stressors such as limited nutrient availability seem to increase the amount of anthocyanin synthesized.

Temperature and rainfall levels also influence the overall timing of leaf color change. As climate change has progressed, many areas have experienced shifts in the timing of leaf color. This has ecological impacts for more species than the trees. A study by Ellwood et al. (2015) found that delayed leaf change correlated with delayed migration of several bird species, suggesting that some bird species may use leaf phenology as one of the cues to migrate. This finding is complicated by the multiple complex interactions occurring in the fall, influencing both migration and leaf senescence. Further research is necessary to better understand the wider implications of changing fall phenology.

The Aeronautics Behind V-shaped Flight Patterns

By Julia Pupko

A familiar autumn sight in Vermont is that of Canada and Snow Geese (among many other species) migrating in a classic V-shaped flight formation. The V- or J-shaped flight pattern utilized by many migrating birds conserves group energy, allowing flocks to migrate faster than individual birds could. The aerodynamics behind this energy saving mechanism are fascinating.

Bird wings are slightly curved; they look like a slightly cupped hand with the palm facing towards the ground. Based on the properties of air and the shape of the bird’s wing, air moves faster over the top of the wing than it does over the bottom of the bottom of the wing during flight. When the bird flaps, the fast-moving air over the top of the wing is sucked backwards and under the wing, giving the bird lift. However, the air at the wing tips moves slightly differently—it forms a vortex that is bent behind the bird, forming a “tube” that is perpendicular to the tip of the wing.

As the bird moves forward, the wake from the bird’s body creates a downward draft, but the wake from the wing tip vortex tubes creates an upward draft, or an upwash vortex field. A bird flying behind another bird can position themselves with one wing in the updraft vortex zone at a slightly lower elevation than the bird in front of them. This allows them to utilize the upwards draft from the bird in front of them, pushing them into the air with less energetic output. To use this upwards draft, a bird has to time their flaps just right and stay out of the downwards draft that is created directly behind the bird in front of them (which explains why they form a V-shape). It is estimated that flying in formation results in energy savings between 11.4 and 14 percent.

The bird flying at the point of the V does not receive any lift since they are leading the flock. As a result, the birds switch positions in coordinated manners, allowing individual birds to rest and benefit from the updraft of others before switching to the front and allowing the previous leaders to rest. The timing, method, and frequency with which these changes occur remains a mystery for now.

Darting Dragonflies Prepare for Winter

By Julia Pupko

Dragonflies are fascinating little insects, but they weren’t always so little. Dragonflies were one of the first winged insects to evolve (around 300 million years ago), and some dragonfly fossils have wingspans of roughly two feet! As October rolls in and brings colder weather, Vermont’s dragonflies have to prepare for winter. Different species have different reactions to the coming cold.

The Overwintering Egg or Larvae
Many dragonfly species overwinter as eggs or larvae. The final adult generation of dragonflies lays eggs in ponds, streams, or on vegetation or logs near water. For dragonflies who hatch before winter comes, larvae live at the bottom of surface waters below the ice. They enter diapause, slowing down their biological functions to make it through the winter. Come spring, they resume growth, and for many species, will emerge as adults in the coming months. Some species remain in their larval state for several years. Overwintered eggs will hatch when warm weather returns. Some species overwinter in both the egg and larval phase.

Adults
Not all dragonfly species lay a final batch of eggs and then die. For some species, such as the Common Green Darner (Anax junius), adults migrate from the northern parts of their range to the southern United States, Mexico, Caribbean, and Central America. Once these adults have reached their destination, they lay their eggs and usually die, giving rise to another generation that will make the journey northwards again in the spring. While some individuals migrate over the course of the summer, peak migration for many species is between September and October. However, with many species of migratory dragonfly, migration is not obligatory–northern populations consist for both residents (who overwinter as larvae or eggs) and migrants. For the Common Green Darner, residents and migrants have vastly different annual phenologies, which limits breeding between the two populations.

Dragonfly migration is still poorly understood. Make sure you report observations to iNaturalist or Odonata Central to contribute valuable data on these fascinating insects.

Fall Flowering Gentians

By Ryan Rebozo

When we think of fall flowering plants, some of our 18 species of asters or 22 species of goldenrods often come to mind.  While these two genera are diverse in themselves and support an even greater diversity of insects, there are other species of plants that wait until late summer and early fall to bloom. A good example are the three species of Gentian that are native to Vermont, Bottle Gentian (Gentiana clausa), Closed Gentian (G. andrewsii), and Narrowleaf Gentian (G. linearis). Gentiana is a diverse genus with 361 species worldwide occurring in Asia, Europe, North and South America and to a limited extent, in Africa and Australia.  Species in this genus have evolved to exist in a wide range of extreme environments including alpine zones, nutrient poor and acidic soils and fire adapted systems.

Vermont’s three Gentiana species are often called “bottle” gentians because their petals do not spread, and instead conceal the plants reproductive parts. This floral trait suggests a pollination syndrome (co-evolution strategy where the floral traits of a plant are used to attract a specific group of animals as pollinators) with insect visitors that are big enough to push through the petals to reach the plant’s nectaries, carrying and exchanging pollen along the way.

Here in Vermont we often find bumble bees pushing through these closed flowers to feed on nectar and to pollinate, though some enterprising individuals can be seen “nectar robbing” by chewing through the base of the flower to reach the nectar without providing any pollination services.  Gentiana andrewsii and G. linearis are both rare in the state, but G. clausa is common and can be found along trails in both dry and moist sites. Keep an eye out for these blueish/purple flowering plants as they begin to set seed on your next early fall hike, though your closest access to Gentiana may be at your bar, as the bitters used in many mixed drinks comes from the roots of gentians!

View images and reports of Gentian at the Vermont Atlas of Life on iNaturalist, and add your observations too!

Long Live the Queen!

By Kent McFarland

Each year in the bumble bee kingdom, only a queen will carry the colony’s torch through winter to produce the next generation. Everyone else – workers, drones, and the old queen – dies with the onset of fall frost.

Not so with the honeybee, with which more people are familiar. In the dead of winter, I have often visited the honeybee observation hive at the Montshire Museum of Science, which is made with a pane of glass on each side of a thin box. The workers are all gathered around the queen in one spot. If you put your hand on the glass away from them, the glass is frigid, but the back of my hand on the glass right in the center of the cluster is incredibly warm. Eating stored honey keeps their metabolisms high enough to produce excess heat and keep the cluster alive.

Bumble bees take a completely different approach. They do not put all of their energy into food storage for the winter but hedge their bet on the survival of a few queens. During the waning days of late summer and early fall, larvae begin to develop into virgin queens and males rather than the workers that have been hatching all summer. Colonies may produce up to one hundred reproductive bumble bees, hoping that at least one or two queens will survive to re-establish a colony the next spring.

When male bumble bees emerge from the cocoon, they may spend several days in the hive and drink some of the stored honey. (Bumble bees do produce some honey, just not the great quantities of their honeybee brethren.) Then the males leave the nest to forage and live on their own, often finding shelter under plant leaves and flowers during inclement weather and at night. I have seen them in the cool morning air sitting on goldenrod flower heads barely able to move. The male bumble bees have one charge in life: stay alive long enough to mate. Each male leaves a chemical attractant along a regular flight path in its territory.

New queens emerge from the hive a week after the males. Unlike the males, they will leave the nest to forage by day and return for shelter at night. And unlike their sisters, the workers, they do not add any provisions to the nest.

As the days grow shorter, a fertilized queen visits flower after flower, drinking lots of nectar to build body fat and fill her honey stomach. The honey stomach is a small sack that can hold between five-hundredths and two-tenths of a milliliter (A teaspoon holds about five milliliters). Each flower may yield only one thousandth of a milliliter of nectar, causing the queen to visit up to 200 flowers to get her fill.

Not all flowers are alike. Fall flowers like goldenrod and aster, for example, generally yield far less food than jewelweed blossoms. Bumble bees must sustain thoracic temperature at 86 to 95 degrees F. to be able to fly. So when the morning temperatures are cool, it does not pay for them to visit flowers of poor quality, because they burn as much fuel as they gain from foraging. Queens won’t emerge to forage in the cool mornings until the air temperature is around 50 degrees.

While the young queens are buzzing around foraging, they are also picking up any perfume left by a male. If the scent is to their liking, they may land and wait for the male. Mating can last up to an hour and a half, but sperm transfer generally occurs in the first two minutes. Why the long encounter? Males want to make sure the future colony belongs to them. When he is done mating he exudes a gummy substance onto the queen that blocks any other males from mating with her.

When the queen has mated, she searches for a good place to burrow into the soil for the long winter wait. Once under ground, usually one to six inches down, the queen somehow knows to avoid the false start of the January thaw and wait until late April or early May, when the warmth of the spring sun penetrates her underground home and she emerges to forage and start a new colony. The queen lives!

Fall Frogs

By Julia Pupko

October is crunch time for many species—late migrants are trying to put on enough fat to start their journey, and residents are also bulking up for the coming winter months. Adult frogs are preparing to nearly freeze solid; their adaptation for surviving the winter includes producing high levels of glucose, which acts as an antifreeze in the frog’s organs. But what about tadpoles?

Some frogs, such as the Green Frog (Lithobates clamitans), a common species in Vermont, will continue to reproduce for the entire summer, right up to fall, depending on the weather. As a result, some of their young do not have time to mature into adults before the weather gets too cold. These individuals will delay metamorphosis until the coming spring or beyond, depending on resource availability.

Tadpoles get a cue to metamorphose based on their thyroid hormones, which are affected by different conditions including water temperature. As the temperatures drop through October, tadpoles still in tadpole form are cued to remain as tadpoles, rather than emerge as tiny frogs only to freeze. Tadpoles slow down and enter dormancy to await the spring. Additionally, tadpoles have an advantage over aquatic frogs overwintering in the water—tadpoles have a higher surface area to volume ratio, and can more effectively respire through their skin in oxygen-limited conditions, such as those created when ponds freeze over. How environmental conditions interact with thyroid responses is still not entirely understood.