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Monarch fueling up on Joe-pye Weed nectar. Kent McFarland

Field Guide to September 2022

It can happen almost anywhere. On a cool, foggy morning, for example, when fall warblers drop from their nocturnal migratory flights into your backyard. Or along a big river some evening when you notice a Common Nighthawk moving south — then another, and another. Or when the Monarchs gliding past you under a cool blue sky convince you that summer is indeed over. Here is your field guide to life slowing down and on the move in September.

By Vermont Center for Ecostudies September 2, 2022
2674, , Blackpoll Warbler, Blackpoll Warbler with a band. / © Jeff Nadler, , image/jpeg,, 1024, 805, Array, Array © Jeff Nadler
Male Blackpoll Warbler with a band. © Jeff Nadler
5735, , Ruby-throated Hummingbird by Russ Wigh, Ruby-throated Hummingbird in flight. PHoto by Russ Wigh, , image/jpeg,, 1600, 1280, Array, Array Russ Wigh
Male Ruby-Throated Hummingbird in flight. Russ Wigh

Tiny Birds Crossing Big Oceans

By Kent McFarland, conservation biologist

Hold two nickels and a dime in your hand. That is about how much a Blackpoll Warbler weighs while raising its young each summer. This black-capped songbird nests from the mountain forests of New England across the north woods to Alaska. This is a bird that only knows one season – summer. With frost nipping their toes, Blackpolls move to the eastern seaboard. Those from Alaska will have already flown over 3,000 miles. But, the migration doesn’t end here. This is just a place to check in for rest and relaxation.

Gorging on insects and berries, they double their weight. “They actually feel soft and pudgy in your hand, ” says Trevor Lloyd-Evans, a Manomet Center for Conservation Sciences biologist who has studied bird migration for over 30 years along the Massachusetts coast. Fat bulges from throat to tail. And then a cold front arrives from the north.

With favorable tailwinds, the birds depart into the darkening southeast sky and sail over the vast Atlantic Ocean. Radar data show migrating songbirds fly at an altitude of up to 2,600 feet within four hours after sunset in New England and rise to 6,500 feet by the time they reach Bermuda. As they approach the Tropic of Cancer, the winds shift to the northeast, allowing for drift toward the Lesser Antilles and South America. Over the Lesser Antilles, flight above 13,000 feet results in lower wind speeds and less headwind than at lower altitudes. They have been recorded as high as 20,000 feet over Antigua. As they approach South America over Tobago, their altitude drops to just 2,500 feet. The entire non-stop flight lasts 80 to 90 hours with an average speed of 25 miles per hour.

To track the flights, VCE and our colleagues captured warblers here in Vermont and Nova Scotia and fitted them with miniature devices called “light-level geolocators,” which resemble songbird backpacks. The warblers migrated south in the fall, spent a winter in the tropics, then returned to North American breeding sites in spring, where we recaptured five birds, removed their geolocators, and downloaded their flight itineraries.

Four warblers, including two from Vermont, departed between September 25th and October 21st from points between western Nova Scotia and western Long Island or New Jersey and flew day and night over the Atlantic Ocean until landing in either Hispaniola or Puerto Rico. Their flight times ranged from 49 to 73 hours.

A fifth bird, which we had also first captured in Vermont, likely took a shorter trans-oceanic trip. It departed the mainland on November 4th from Cape Hatteras and flew nearly 1,000 miles non-stop for 18 hours to land in Turks and Caicos before continuing to South America.

Blackpoll Warbler migration tracked with geolocators.
Blackpoll Warbler migration tracked with geolocators.


This tiny songbird is fueled entirely by stored fat. Scientists have calculated that a Blackpoll Warbler has to weigh more than seven-tenths of a gram to complete the trans-Atlantic flight. For us, “the metabolic equivalent would be to run four-minute miles for 80 hours,” note ornithologists Tim and Janet Williams. “If a Blackpoll Warbler were burning gasoline instead of its body fat reserves, it could boast of getting 720,000 miles to the gallon!” A Boeing 747 needs about 10 gallons of fuel to fly one mile, and a small Cessna travels just 10 miles per gallon.

Perhaps the Blackpoll Warbler hasn’t impressed you. Try removing the two nickels leaving just a dime in your hand. You now hold a Ruby-throated Hummingbird. Despite their tiny size, these birds fly non-stop across the Gulf of Mexico each spring and fall in 24 hours. Large numbers have been observed flying low over the waves trying to make landfall in the spring. And like the Blackpoll, they pack on fat to fuel the journey, easily doubling their weight. Just add another dime.

Frequency of Ruby-throated Hummingbirds reported on Vermont eBird checklists. Click on the chart to see the results so far this year on Vermont eBird.
Frequency of Ruby-throated Hummingbirds reported on Vermont eBird checklists. Click on the chart to see the results so far this year on Vermont eBird.

When the flowers stop blooming and insects stop flying, Ruby-throated Hummingbirds head south. Some adult males start migrating south as early as mid-July, but southward migration peaks in August and early September. By October, they’re all gone.

Most, if not all, of the hummingbirds at your feeders in September are migrants and not the same individuals you’ve watched all summer. Since they all look alike, it’s difficult to know for sure, but banding studies have shown the turnover. It’s not necessary to take down feeders to force hummingbirds to leave, and in the fall, all the birds at your feeder are already migrating anyway. Keep them up as long as you can; maybe a wayward rare species will find them.

Where do they all go? There is some evidence that more of them travel around the Gulf of Mexico in fall migration rather than cross it as they do in spring. They’ll spend the winter in Mexico and Central America. Weighing a mere two-tenths of an ounce, they’ll make the round trip back in April and delight us once again with their bright colors and active flights after our long, white winter.

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Roberval Miner (Andrena robervalensis) Lisa Cass -
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Roberval Miner (Andrena robervalensis) Lisa Cass -

Bee of the Month: Roberval Miner

By Spencer Hardy, Vermont Bee Survey biologist

With shortening days and falling temperatures, September marks the beginning of the end of the bee-watching season. But despite the fading flowers, a few species complete nearly their entire adult lives this month. One of these late fall species is the Roberval Miner (Andrena robervalensis), named for Roberval, Quebec, where the type specimen was collected. Well, at least that’s what we are calling it right now. These September-active, dark-haired lovers of asters are distinctive among the Vermont fauna, but there is considerable taxonomic uncertainty in this group of mining bees. Some authorities consider Andrena runcinatae and Andrena robervalensis the same species, with the name A. runcinatae having precedent since it was described first.

Regardless of what it is called, this is a species worth watching. Prior to last fall, it was entirely overlooked in Vermont (and poorly known in the region). But thanks to contributors to our iNaturalist project, we now know it is relatively widespread in the state. As for identification, phenology can be a good clue since the similar Cloudy-winged Miner (Andrena nubecula) tends to be active slightly earlier in the year. The features needed to clinch the ID include the dark hairs inside the facial fovea and abundant dark hairs on the scutum (top of the thorax).

For a look back in time, check out our blog post from last fall about this species and its “discovery” process in Vermont.

12799, , common-green-darner-1800x700_580x400_acf_cropped, , , image/jpeg,, 580, 400, Array, Array © Bryan Pfieffer
Common Green Darner in flight. © Bryan Pfieffer
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American Kestrel captures and eats a dragonfly in the air. © Kerry Ross -

Ready for take-off: Common Green Darners are headed south

By Michael T. Hallworth, conservation biologist

Right now, many Common Green Darners (Anax junius) are stretching their wings for the first time and are about to make the most important flight of their lives. Some lucky nymphs developed quickly this summer, but many have spent over a year in the cool waters of northern New England. As the temperatures dropped last fall, many nymphs entered diapause, a state of suspended development under the ice, and waited for their time to shine. Any day now, they will start a flight that could take several weeks to complete.

Each September, droves of Common Green Darners embark on a migratory journey south and start the transition into the next phase of their annual cycle, which requires at least three generations to complete. Common Green Darners aggregate along coastlines and rivers while they migrate. It’s spectacular to see. If you see adults on the move, upload your observations to or OdonataCentral to help us track their movements. The cooler temperatures signal it’s time for them to head south. It’s likely not an easy journey. Their migration coincides with two avid predators—the American Kestrel (Falco sparverius) and the Merlin (Falco columbarius)—that both frequently hunt and eat dragonflies while aloft. If and when the darners arrive in the southern reaches of the United States, or possibly even the Caribbean, they will lay eggs, starting a new generation that will not migrate. In early March and April, the entire cycle begins anew when the first generation of the year will migrate north and dazzle us once again when they arrive in May.

Champlain Beachgrass NY Natural Heritage
Champlain Beachgrass NY Natural Heritage

Vermont Beach Plants

By Ryan Rebozo, Director of Conservation Science

As summer comes to an end, we want to spend a little more time thinking about beaches. For a state famously known for its green mountains, beach plants don’t readily come to mind when most think about the diverse vegetation that Vermont supports. While there is no coastline, sandy beaches, and even dunes can be found in Vermont and are home to an interesting suite of disturbance-adapted plants.

Beaches and dunes are dynamic habitats that remain open through natural disturbances, a combination of ice scour, wind energy, and wave action. Most of our smaller lakes and ponds don’t have any natural beaches—instead, the forest reaches right up to the water’s edge. As you may imagine, these open beach habitats, subject to wind and wave energy with dry sandy soils, are difficult places for plants to survive. As a result, beach plants have evolved various strategies to help them persist in these environments. These strategies include prostrate growth forms (low, creeping plants) that keep them out of the wind, hairy or succulent leaves to limit desiccation from wind, long-term seed banking to wait for optimal conditions to germinate, and floating seeds to utilize the nearby water in aiding dispersal.

These habitats are rare in the state, with sand dunes (S2) being limited to Lake Champlain and lake sand beach habitats (S1) found primarily along Lake Champlain and in parts of only a handful of other large lakes in the state. Not surprisingly, with such limited habitat around, many of the plant species that require open beaches to persist are rare. A few examples are Champlain Beach Grass (Ammophila breviligulata ssp. champlainensis; S1 E), Beach Wormwood (Artemisia campestris ssp. caudata; S1), Wright’s Spikerush (Eleocharis diandra; S2), Beach Heather (Hudsonia tomentosa; S1), Beach Pea (Lathyrus japonicus var. maritimus; S2), Beach Pineweed (Lechea maritima var. maritima; S1) and Seabeach Dock (Rumex pallidus; SH), which is only known from historical records.

The state endangered Lake Champlain Beach Grass can only be found along the shores of Lake Champlain, Lake Ontario, and the St. Lawrence River. It is an earlier blooming subspecies with smaller inflorescences than the widespread Beach Grass (Ammophila breviligulata ssp. breviligulata). Our local subspecies is the result of breviligulata expanding west along the ancient Champlain Sea before being cut off from other populations when land rebounded and separated Lake Champlain from the Atlantic Ocean.

Next time you visit beach habitat on one of our larger lakes, take a minute to observe some of the plants in the sand and consider the strategies they need to grow, reproduce, and disperse seeds in these difficult conditions.

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Indigo Milk Cap underneath. Meg Madden
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Indigo Milk Cap Meg Madden

The Jewel Of September: Indigo Milk Cap

By Meg Madden

As with many other organisms, September in Vermont represents a transitional time in the world of fungi. Some summer species will take a break until next season, while fall species will begin fruiting in rhythm with the shorter days and cooler temperatures. One mushroom that really comes into its glory this time of year is the Indigo Milk Cap (Lactarius indigo). If sapphire is the gemstone for September, the brilliant blue Indigo Milk Cap should definitely be the mushroom of the month.

Very easy to identify, Indigo Milk Caps display a range of true blue shades not often found in nature. The cap of this medium-large (up to 15 cm across) mushroom is lovely, pale silvery-blue, sometimes with concentric rings of alternating light and dark shades, and can be quite sticky when fresh. A peek at the underside of the cap reveals gorgeous cobalt blue gills which run partway down the stem, a feature known as “decurrent” in mycology. The thick stem is often decorated with small pits and potholes called scrobiculi. When cut or damaged, all parts of the mushroom weep a deep indigo blue sticky “latex.” This liquid is characteristic of Lactarius, a large genus of fungi commonly known as milk caps (or milky caps), which contains over 500 known species worldwide. The latex acts as a deterrent, gumming up the mouthparts of hungry creatures such as slugs and snails, which would otherwise try to make a meal of them.

Beginning in July in Vermont, Indigo Milk Caps can be found pushing their way through the needle duff under Eastern White Pine trees (Pinus strobus), with which they form symbiotic relationships called mycorrhiza. With their peak in late September to early October, these stunning mushrooms can usually be found until the first hard freeze.

Meadow Jumping Mouse mellohrer -
Meadow Jumping Mouse mellohrer -

Hopping into Hibernation: Meadow Jumping Mouse

By Latrice Hodges, summer intern

The Meadow Jumping Mouse (Zapus hudsonius) is found throughout northern North America in fields, frequently in dense vegetation near wetlands, and in herbaceous openings in woody areas. Hibernation nests are typically found in underground tunnels between 0.3 to 0.9 meters deep and are built of grass and leaves. Meadow Jumping Mice begin to hibernate around mid-September to early October, lasting until mid to late spring. Adults usually start hibernating earlier than juveniles. These mice depend more on environmental factors than other species like ground squirrels and marmots, which have strong circannual cycles determining hibernation. For example, day length seems to have a significant role in determining when Meadow Jumping Mice hibernate. As days get shorter, Meadow Jumping Mice spend about two weeks building fat reserves before hibernating until spring.

Eastern Milksnake  Joanne Russo
Eastern Milksnake Joanne Russo

Autumn Herp Migration and Hibernation

By Madison Sayers, summer intern

The beginning of fall marks the start of migration and hibernation season for many amphibians and reptiles (herpetofauna). Most commonly, they move from lowland nesting and breeding sites to upland woodland/forested habitats with better drainage. Often, roads intersect their habitat and, unfortunately, they can be hit and killed. If you see any herpetofauna crossing the road this fall and can safely do so, I encourage you to help them safely cross in the direction they’re headed. Though Eastern Timber Rattlesnakes (Crotalus horridus) are exceedingly rare, if you see a snake with a triangular head, black tail, and a rattle, especially in their known location of Rutland County, keep your distance and don’t pick it up.

American Toads (Anaxyrus americanus) will back into burrows that they dig in loose soil with their hind legs. The soil then falls back on top of them. This occurs between September and October, and they re-emerge in spring after the frost passes. Like many other herpetofauna, they often repurpose old mammal passages and head deep underground to avoid freezing.
Aquatic frogs generally hibernate underwater between mud and ice. For example, Green Frogs (Lithobates clamitans) overwinter in streams, breathing through their skin in this highly oxygenated water, and rarely freeze. Spring Peepers (Pseudacris crucifer), Wood Frogs (Lithobates sylvaticus), and Gray Tree Frogs (Lithobates sylvaticus) hibernate in cracks under rocks, logs, and leaf litter. Even if they freeze, they can preserve their organ function and regain it in the spring.

Snakes, such as Dekay’s brownsnake (Storeria dekayi), Garter snakes (Genus Thamnophis), and Red-bellied Snakes (Storeria occipitomaculata) will wait until a warm day after the first frost to move upland to a denning location; ideally below the frost line, so they do not freeze throughout the winter. These denning locations are known as hibernacula. Bigger snakes like Timber Rattlesnakes, Eastern Ratsnakes (Pantherophis alleghaniensis), and North American Racers (Coluber constrictor) may travel upwards of two miles to get to their winter hibernaculum.

Eastern Red-backed Salamanders (Plethodon cinereus), Four-toed Salamanders (Hemidactylium scutatum), and Blue-spotted Salamanders (Ambystoma laterale) also move upland to overwinter in crevices or burrows. Eastern Red-backed Salamanders will do so overnight on a rainy fall evening, so their skin does not dry out. Spotted Salamanders (Ambystoma maculatum), Jefferson Salamanders (Ambystoma jeffersonianum), and Wood Frogs gradually travel uphill after breeding a few hundred feet to over a quarter mile to hibernate. They hibernate in forests until the ground is thawed and air temperatures are above 40 degrees Fahrenheit. They then return to wetlands to breed in the spring.

Eastern Newts (Notophthalmus viridescens) overwinter under logs and rocks, compost, paving slabs, or muddy banks of ponds near their breeding sites in their terrestrial ‘eft’ stage. They tend to come out to forage in milder weather, thereby being dormant more so than fully hibernating.

As introduced last month, turtle hatchlings may continue to emerge throughout the fall and travel towards the nearest wetland. Larger turtles may move to hibernacula with flowing water that won’t ice over and will help ensure a well-oxygenated environment all winter.

If you spot herpetofauna this fall and beyond, sightings can be reported to the Vermont Atlas of Life on iNaturalist and become part of the Vermont Reptile and Amphibian Atlas.

Common Nighthawk in flight.  Bryce Bradford -
Common Nighthawk in flight. Bryce Bradford -

Nighthawks obstruct investigation…again

By Jason Loomis, Vermont Atlas of Life Software Engineer

Keep an eye out in the evening during late August and early September for migrating Common Nighthawks. There are some easy ways to spot them. One is their distinctive flight pattern—dipping and darting side-to-side—due to their insect foraging practice. Another is the distinctive markings on their wings.

In the coming days, these aerial insectivores can be seen at dawn and dusk near open waterways foraging for food. Nighthawks survive on a diet of flying ants, moths, bugs, and other large flying insects that concentrate in these areas at either end of the day.

You’ll easily confirm a nighthawk sighting by the characteristic white band on their wings, which can seem to glow in the low-angle light of morning and evening. Nighthawks tend to migrate in sizable groups, another way to be alerted to their presence.

Not hawks at all; nighthawks are named for their hawk-like foraging behavior and are members of the nightjar family, which includes the Eastern Whip-poor-will. Nighthawks don’t breed here anymore, but they do dip into our food supplies on flyovers as they ingest food energy for a long journey. They migrate from their breeding grounds in Canada’s Yukon and Labrador to South America, a seven to eight thousand miles trip. They are observed along river corridors in Vermont as they traverse the continental US from North to South. Observers also note East-West movement during migration. This is not well understood, but the findings of a recent study of migratory connectivity in this species by the Smithsonian Migratory Bird Center (SMBC) could be explained.

To investigate why nighthawk populations are in decline, the SMBC, in collaboration with biologists at the University of Alberta, measured their migratory connectivity using GPS tracking backpacks. Migratory connectivity tracking adds critical data to investigations because separate populations of a species can be segregated by rates of decline, breeding habitat, migration path, and overwintering habitat. When there is high migratory connectivity, investigators may be able to distinguish the temporal and spatial environmental conditions that influence population-specific vital rates, allowing them to make associations between decline and the circumstances in each category and location.

However, according to Elly Knight, lead author and doctoral student in the Department of Biological Sciences at the University of Alberta, in a recent article:

“All breeding populations fly east or west to congregate in the midwestern United States along what we call the Mississippi migration flyway. From there, they all mix together and take a common route South across the Gulf of Mexico, down through the northern Andes and onto their wintering grounds, mostly in Brazil. That common route means that there’s little migratory connectivity for common nighthawks outside the breeding season.”

This gathering behavior in the Mississippi flyway could explain local observations of East-West movement.

It was already difficult to study nighthawks because they’re nocturnal and migrate long distances. Lacking migratory connectivity compounds those challenges.

Since nighthawks naturally obstruct our ability to understand them because of the long migration and low migratory connectivity, they leave us with the usual hypotheses for avian decline at the species level: loss/disruption of breeding habitat, diminishing and altered food supplies, and exposure to environmental toxins. Perhaps their migration timing is getting out of sync with insect hatches as climate change alters the landscape.

Despite the research challenges, these investigators are gathering testable hypotheses to explain nighthawks’ decline. Given what we know, answering additional questions might lead to better hypotheses. What triggers nighthawks’ migration? Is migration mortality significant? Can we measure the timing of insect hatches and combine those with nighthawk tracking data?

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