Field Guide to October 2023

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 make a small amount of new pigment. As the days grow shorter and colder, these deciduous trees slow and then stop their chlorophyll production. 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. Trees synthesize anthocyanins (the compound that turns leaves red, purple, or crimson) just before the leaves fall. The prevalent theory to explain the function of anthocyanins is to act as 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; overcast, rainy days lower anthocyanin production. 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 progresses, many areas are experiencing shifts in leaf color timing. This shift has ecological impacts beyond the tree community. A study by Ellwood et al. (2015) found that delayed leaf change correlated with delayed migration of several bird species, suggesting that some 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 needed to better understand the broader implications of changing fall phenology.

The Flight of the Flycatcher

By Michael T. Hallworth

The Olive-sided Flycatcher (Contopus cooperi)—a bird species with a steeply declining population—migrates nearly 15,000 miles round-trip in just 95 days. Even more remarkable, they embark on this long journey after courting, nesting, and caring for fledglings on their breeding grounds. These flycatchers depart tropical forests each spring, bound for a summer in northern forested wetlands. By early August, they begin their return to wintering grounds in South America.

By now, most of them have arrived in countries like Brazil, Peru, Ecuador, and Colombia after refueling in specific regions of Central America. Several of these areas are important during both fall and spring migration. Scientists recently discovered these essential stopover regions using tracking technology and now hope these areas hold the answers to why Olive-sided Flycatchers are declining so rapidly.

VCE scientists are collaborating with researchers throughout this species’ range to identify potential threats at key stopover sites throughout Central America. To learn more about the spectacular journeys of the Olive-sided Flycatcher, see our recent paper published in Animal Migration.

The Return of the King (of Fish)

By Jason Hill

The water swirls, and a fin breaks the surface—suddenly, you are watching dozens of large fish impossibly launch themselves up a waterfall. That scene played out each fall on nearly every coastal New England river and its tributaries 150 years ago.

But unless you live along a few rivers in Maine, you’ve likely never seen an Atlantic Salmon (Salmo salar) returning to spawn in the Northeast. Over a century of dams, culverts, pollution, habitat degradation, and overfishing have robbed us of witnessing this annual autumn ritual as the Gulf of Maine’s distinct population segment is now listed under the Endangered Species Act.

Atlantic Salmon breed across the North Atlantic and are mostly anadromous—returning from the open sea to breed in their natal brooks during October and November. Other anadromous fish species in New England include American Shad, Blueback Herring, Sea Lamprey, and Alewife. There are, however, landlocked populations of Atlantic Salmon (the same species as sea-going Atlantic Salmon) stocked in Lakes Champlain and Memphremagog in Vermont, the Swift River in New Hampshire, and numerous other places.

In the summer and fall, the remaining sea-going Atlantic Salmon make their way from the Gulf of Maine into a handful of Maine rivers. Adults undergo impressive skeletal and color transformations during this time, especially males, whose lower jaw bends into a hook (called a kype) used to battle other males for reproductive access to females.

The eggs are deposited into redds (gravel depressions), where they will spend the winter before hatching in spring. Like most Pacific salmon species, Atlantic Salmon usually die after spawning, but perhaps as many as 10% of adults (mainly females) live to spawn again in subsequent years. Those adults that succumb to the rigors of their journey and mating provide an important autumn food source for our eagles, aquatic invertebrates, and plants. Young fish that eventually make it downstream to the Gulf of Maine travel thousands of kilometers up to the coasts of Greenland and the Labrador Sea before returning to their natal brook to breed in several years.

For more information about the biology of and threats to Atlantic Salmon, check out the State of the North Atlantic Salmon report, Inside Climate News’ story about Atlantic Salmon on the Connecticut River, and the hydropower page of the Connecticut River Conservancy.

The Bobolink’s Missing Link

By Kevin Tolan

In the middle of the night throughout September, while most people are sleeping, Bobolinks are busy flying over Vermont as they undergo one of the most incredible migrations of any species in the Western Hemisphere. These 30-gram, long-distance migrants begin molting into their winter plumage in August—a sign that it’s about time to begin their flight south. By mid-October, most stragglers leave the state. Their annual journey takes them on a 14,000-mile round trip, with most Bobolinks crossing the Caribbean while passing between North and South America. A perusal of eBird even shows a smattering of records of wayward birds in Europe and Africa.

Bobolinks’ nocturnal flight calls as they pass over Assateague Island, Maryland

One of the longstanding mysteries of their migratory movements is the annual passage of a small number of Bobolinks through the remote Galapagos Islands, located 650 miles off the coast of Ecuador. Longtime friends of VCE may even recall the 2015 expedition to the Galapagos Islands when VCE cofounder Roz Renfrew (now the Wildlife Diversity Program Manager at Vermont Fish and Wildlife Department) and University of New England’s Noah Perlut ventured into the countryside of San Cristóbal in search of the few, small Bobolink flocks that forage in highland pastures. Blood samples taken during this excursion also helped shed light on the potential transmission of avian malaria from the mainland to the Galapagos, an important discovery with grave implications for the islands’ native endemic birds.

Scientists have long hypothesized about the origin of the Bobolinks that pass through the archipelago. Are they coming from the midwestern population core, or are they random groups pushed west off their southward migration? Noah and Roz’s recently published research sheds light on the population ecology of Galapagos-faring Bobolinks. Genetic sequencing from across the continent shows that the most likely source for these island-hopping individuals is the eastern portion of the population, particularly those breeding in Ontario and surrounding areas. Since the Galapagos are due south from the mouth of the Mississippi River, small numbers of Ontarian Bobolinks following the Mississippi Flyway may continue along that line south until reaching the islands.

While more research is needed to understand the intricacies of Bobolink migration more deeply, new technologies are providing insight into the full lifecycle of these imperiled birds. Because scientists expect Bobolinks’ range to shift significantly northward in the coming decades due to climate change, improving our understanding of their population dynamics may help us maintain healthy genetic diversity and gene flow between regions.

If you want to support Bobolinks on your land and in your communities, check out VCE’s Grassland Ambassadors program.

Mazes and Mines

By Nathaniel Sharp

No, we’re not talking corn mazes here, though they may be a favorite activity during the harvest season in Vermont. Instead, I encourage you to take a closer look at the leaves around you before they fall this October; you may find the miraculous, maze-like patterns of leaf-mining insects.

The catch-all term “leafminers” encompasses four different orders of insects and several thousand species, with new species still being discovered and described. All these insects spend part of their lives as larvae feeding on the inner layers of leaves, sandwiched between the protective layers of the leaves of a vast array of plant species. As they feed, they leave behind diagnostic trails that twist and wind, or radiate from a central point, and are often dotted with tiny dark specks of excrement (frass). Since most leafminers feed on one species, genus, or family of plants, curious naturalists can often reliably identify leafminers by noting the host plant and shape of the mine!

More than 150 species of leaf-mining insects have been reported to the Vermont Atlas of Life on iNaturalist, and there are undoubtedly many more out there to be discovered. Some distinctive and commonly encountered mines to be on the lookout for this fall include the winding mines of Agromyza vockerothi found on blackberries, raspberries, and other brambles, the calligraphic wanderings of the Aspen Serpentine Leafminer Moth found on aspens, and the amorphous blobs of the Hazel Blotchminer found on the leaves of hazels.

To learn more about leafminers, there is no better place than Charley Eiseman’s blog, BugTracks, where you can find a wealth of information about these fascinatingly diverse insects. If you encounter winding insect trails while admiring the leaves of fall, snap some photos and upload them to the Vermont Atlas of Life on iNaturalist and the North American Leafminers project, where, if you make note of the plant that was hosting the leafminer, experts like Charley and others will help you figure out what species you have found. Perhaps it will be a new species for Vermont, and it’s even possible that you could discover a species of leafminer as yet unknown to science!

Going Deep

By Kent McFarland

In the spring, Spotted and Jefferson’s Salamanders crawl across the forest floor to vernal pools, where they mate and lay eggs. But for 90% of the year, these salamanders live 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 spy on a salamander easily 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. It turns out that 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, mouse, and chipmunk tunnels for refuge. In fact, the tunnels are so important to them that Steve could predict areas in the forest that salamanders would use 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, Steve found that the salamanders suddenly changed behavior with the chill of fall. They entered more vertical tunnels leading deeper underground. By November, nearly all of them were sheltered deep under the earth. The radio signal only traveled about two or three feet, so eventually, the signals were lost. The salamanders had gone deep enough to escape the ground-penetrating frost and radio spying from above.

Long Live the Queen!

By Kent McFarland

Most of the bumble bees you see flying right now are males (drones) looking for a mate or young queens preparing for winter. 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 more familiar honeybee. In the dead of winter, I have often visited the honey bee observation hive at the Montshire Museum of Science, made with a pane of glass on each side of a thin box. The workers all gather around the queen in one spot. If you put your hand on the glass away from them, it is frigid, but the glass right in the cluster’s center 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 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, increasing the odds that at least one or two queens will survive to re-establish a colony 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 produce some honey, but just not in the great quantities that honeybees do.) 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 sitting on goldenrod flower heads in the cool morning air, barely able to move. 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 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. For example, fall flowers like goldenrod and aster generally yield far less food than jewelweed blossoms. Bumble bees must sustain thoracic temperature of 86 to 95 ^oF 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? The male wants to make sure the future colony will consist of his offspring. When done mating, he exudes a gummy substance onto the queen that blocks 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 underground, 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. Long live the queen!