Field Guide to March 2023

A Little Skunk Oil Goes a Long Way

By Kent McFarland

There is nothing like the fresh smell of a spring morning, unless, during the night, a skunk skulked about your neighborhood. The striped skunk is armed with just a teaspoon of odoriferous oil in its two anal glands, but a little bit goes a long way. These smelly yet charming mammals have recently been emerging from their winter burrows, and March marks the peak of the striped skunk breeding season. After surviving the winter cozied up in underground burrows in a state of torpor, skunks are on the hunt for a mate. Striped skunks are polygamous; males will mate with multiple females, while females will only mate with one male. With skunk activity picking up this time of year in Vermont, read on to learn more about these animals’ fascinating adaptations for deterring predators.

Skunk oil research has been going on for over a century as scientists have tried to determine what makes the stuff so potent that it can drive a bear away. Way back in 1896, Thomas Aldridge at Johns Hopkins University showed that humans could detect the smell at just 10 parts per billion, the equivalent to detecting just one drop of it diluted into a medium-sized backyard swimming pool. More recently, William Wood, a chemist from Humboldt State University, pointed out that a number of chemicals have been incorrectly attributed to skunk oil over the years, and his work has now given us a reasonably complete understanding of the chemical compounds and how to neutralize them.

The scent-gland secretion is a yellow oil composed primarily of volatile compounds known as thiols and their derivatives. (A thiol is a compound distinguished by its sulfur-hydrogen bond.) Most of us immediately recognize the smell of ethanethiol (also called ethyl mercaptan), a common thiol added to otherwise odorless propane gas so we can easily smell any leaks. Another thiol creates the “skunky” smell of beer after exposure to ultraviolet light. The thiol derivatives present in skunk oil are not particularly odoriferous, but they are easily converted to far more potent thiols when they react with water.

Skunks are reluctant to use the oils, though. With only enough for a half dozen sprays at most and a 10-day period to manufacture more, skunks will only spray if they absolutely have to. In an attempt to avoid spraying, skunks often give warnings. First, they show their striped white back to warn you. This is followed by threatening behaviors, like stomping with both front feet, sometimes charging forward and then edging backward, dragging their feet, and hissing. If all this fails, watch out.

Each spray gland has a nipple, and skunks can aim and direct the spray using highly coordinated muscles. A skunk can spray up to 25 feet and hit something fairly accurately up to 7 feet away. When there is a target, they can direct a fine stream right at the victim’s face. When being chased, a skunk will instead emit a foul cloud for the predator to run into.

There is one predator that remains undeterred by the odiferous oil, the great-horned owl. The small size of the olfactory lobes in their brains suggests that they have a very poor sense of smell. Some individual owls can downright stink of skunk, a common complaint among wildlife rehabilitation workers. Their nests can even smell of their musky meals. But larger-lobed mammals quickly learn to avoid the white stripe in the night.

Make sure to share your skunk sightings to the Vermont Atlas of Life on iNaturalist!

Bumble Bee ID

By Spencer Hardy

Despite the snow piling up, many of us are getting ready for warmer weather and the flush of life that comes with it. In many years, the end of March brings the first bees, including a few of the hardiest (or foolish) Bumble Bee queens. This charismatic genus is recognized and appreciated by many Vermonters, though a closer look reveals a fascinating diversity that easily entices the keen observer into the world of bee-watching. Unlike many of Vermont’s 38 other bee genera, many Bumble Bees can be identified to species with a good view and a little bit of practice. Check out our Bumble Bee page for a lesson in identifying live bumble bees and several field guides designed to be downloaded or printed for quick reference.

Early Blooms

By Kent McFarland

Silver Maple (Acer saccharinum) is North America’s first maple species to bloom. Flowers bloom long before leaves appear, and these delicate red blooms can appear as early as February in the southern part of the silver maple’s range and as late as May in the north. Early blooms mean that pollen is produced much earlier in spring than other trees, so this tree may be a critical pollen source for bees and other pollen-dependent insects. Most references describe silver maple as a primarily wind-pollinated species, but insect pollination may also play a role, as many bees have been seen visiting the flowers. Seeds develop quickly – within 24 hours of pollination – and shortly after they bloom, the flowers wither, and the ovaries begin to swell in preparation for seed production.

One of the first flowers to emerge is Coltsfoot (Tussilago farfara), a species introduced from Europe that can often be found along roadways where the snow first melts away. The name “tussilago” is derived from the Latin tussis, meaning cough, and ago, meaning to cast or to act on, and harkens back to its medicinal uses. But the discovery of toxic pyrrolizidine alkaloids in the plant has resulted in liver health concerns. One of the earliest native species to flower is Hepatica. Sharp-lobed Hepatica (Anemone acutiloba) is an attractive wildflower of the deciduous forest understory. It differs from the closely-related blunt-lobed hepatica (Anemone americana) in having more acutely pointed leaf lobes. Be sure to add your sightings to our database on iNaturalist. You can also add notes about plant phenology to iNaturalist observations, so be sure to make note of whether the plant is budding, flowering, or fruiting.

Snow Wanderers

By Nathaniel Sharp

If you happen to find yourself near a stream slowly emerging from the icy grip of winter, turning your eyes toward the slowly melting snow at your feet could reveal a unique treasure, the winter stonefly. Even to experts, many species of winter stoneflies are nearly indecipherable, but all are in the family Capniidae. Some are wingless, but most have long bodies, with darkly veined wings that lay folded across their back. As nymphs, winter stoneflies spend their lives huddled in the layer of silt and gravel beneath the stream bottom, only moving towards the surface of this layer when they are preparing to emerge as adults. Emergence occurs throughout the winter and into early spring, and adults are often seen wandering on top of the snow. Anglers might be familiar with stoneflies, as they are a popular food source for trout and often inspire very effective lures. Winter stoneflies are significantly smaller than their relatives, the Common Stoneflies, some barely measuring more than 5mm. Glycerol in their bodies, acting as antifreeze, prevents these hardy insects from freezing, but they tend to be easiest to find on sunny days in winter and early spring when temperatures are at or above freezing. Winter stoneflies, like their other stonefly relatives in the order Plecoptera, are frequently used as indicators of water quality and overall stream health. If you come across a Winter Stonefly this month, snap a photo and post to the Vermont Atlas of Life on iNaturalist, and know that somewhere nearby, there is a happy, healthy stream.

The Cold Hop

By Kevin Tolan

Wood Frogs (Lithobates sylvaticus), the only amphibian found above the arctic circle in North America, are regularly the first amphibians to appear from hibernation in Vermont. Even while there’s snow on the ground and ice on the water, throughout late March and early April, these unique creatures begin their annual migration to their chosen vernal pool. iNaturalist observations of Wood Frogs from March show that these early-appearing individuals are centered within the Champlain Valley, where phenology is ahead of the rest of the state.

There are a host of reasons that breeding early may be beneficial to a Wood Frog’s offspring. Wood Frogs form rafts with their egg masses while breeding, with numerous pairs laying eggs in large aggregations. The eggs toward the center of the raft receive better protection from predators than those on the outskirts. The earlier that a pair breeds, the closer to the center their eggs will be. Additionally, eggs toward the center of the raft absorb heat from the surrounding eggs, allowing them to develop faster. This accelerated development, coupled with being laid early, results in offspring metamorphizing earlier in the season than others. By adults laying their eggs before other individuals, they permit their offspring to leave the pools earlier, which increases a metamorph’s chance of survival should their vernal pool dry out.

Through the Vernal Pool Monitoring Project, we aim to understand the phenology of Wood Frog breeding in Vermont better. Utilizing automatic audio recorders, we can determine which date Wood Frogs begin calling, which signifies the beginning of their breeding season. Over an extended period, this data can be used to quantify differences in breeding phenology across different biophysical regions of Vermont and from year to year.

No Waiting for Warmth

By Emily Anderson

If you’ve spent time hiking in the high mountains of Vermont or New Hampshire, you’ve probably encountered a Canada Jay. Who knows, maybe one even tried to steal your snacks. If you happen to visit these same areas in the winter, you will likely still see these notoriously bold, curious birds. Canada Jays typically don’t migrate, choosing instead to brave freezing temperatures in their northern homes.

Canada Jays are certainly not alone in staying in Vermont all winter long. However, while many birds breed later in the spring, Canada Jays begin incubating their eggs in March and April. They primarily build their nests in mature conifers, situating them close to the tree’s trunk at the base of a branch. Most nests will contain anywhere from 2 to 5 eggs.

In some ways, nesting while temperatures still regularly hover just below freezing may seem crazy; however, starting early has some benefits. Nesting in March allows Canada Jay young more time to grow and get stronger before winter returns, in theory giving them a better chance of surviving. These birds are well-suited to frigid temperatures. Their soft, fluffy plumage provides excellent insulation, helping them stay warm. They will also often line their nests with moose hair and other insulating materials.

If you want to learn more about Canada Jays in March, check out this episode of Outdoor Radio. And make sure to record your sightings of these charismatic birds on VT eBird and the Vermont Atlas of Life on iNaturalist.