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Winter phenology at Sax-Zim Bog

A Northern Hawk Owl flies over a snowy field with a vole held in its beak at the Sax-Zim Bog.
Lorie Shaull
A Northern Hawk Owl flies over a snowy field with a vole held in its beak at the Sax-Zim Bog on Jan. 9, 2024.

Clinton Dexter-Nienhaus is the naturalist at Sax-Zim Bog in northeastern Minnesota. The bog spans 300 square miles from Zim in the north to Floodwood in the south. Photographers and birders flock from all over the world to see the bird species and other wildlife in the black spruce and tamarack bog.

A sign welcomes visitors to the Sax-Zim Bog in Meadowlands, MN.
Special to KAXE
The Sax-Zim Bog is a magnet for birders from around the world, located in Meadowlands, Minn.

MEADOWLANDS – If you want an example of a man in his element, head to the Sax-Zim Bog near Meadowlands, Minnesota. There, crouched down in sphagnum-moss bogs or gazing up through the branches of a nearby pine tree, you’ll find Clinton Dexter-Nienhaus*. For the last nine years, Clinton has been the head naturalist for the Friends of Sax-Zim bog, a non-profit organization that originated in 2010 with a mission to preserve and protect this biodiversity hotspot.

Clinton has an enviable (to some) job - “I get to do education and outreach, and I also get to do traditional naturalist things: going out and looking at stuff to document, finding it and showing it to everybody. It’s a really cool thing. The Sax-Zim Bog is a really amazing ecosystem and set of ecosystems, so I don’t get bored. Whether it’s the winter or the summer bug season, there’s a lot going on,” he said during a recent interview with KAXE Morning Show co-hosts Heidi Holtan and John Latimer.

His work has already paid dividends. In addition to performing countless hours of education and outreach (including some phenomenal YouTube videos), Clinton and the Friends of the Sax-Zim Bog have also done impressive scientific work, documenting just short of 3,600 species in the area.

The place

The Sax-Zim Bog is known as one of the most famous birding areas in North America. Thousands of birders, naturalists and photographers flock to the bog each year, located 40 miles northwest of Duluth in St. Louis County. The bog covers 300 square miles and diverse habitats that attract Great Gray Owls, Black-backed Woodpeckers, Pine Grosbeaks, Northern Shrike and many others.

A boreal chickadee sits on a branch in winter at the Sax-Zim bog.
Lorie Shaull
Special to KAXE
Winter scene from the Sax-Zim Bog in Meadowlans, Minn. of a Boreal Chickadee.

For non-birders, the area also hosts charismatic species like American martens, porcupines, wolves, moose, otters, and more than a few frogs.

The Sax-Zim Bog and surrounding areas were formed by the glaciers. The tamarack and black spruce bogs that cover much of Saint Louis County, Itasca County, and Aitkin County were formed from the basins of Glacial Lakes Upham and Aitkin.

”If you look at the entire ecosystem that we consider...we've documented just shy at 3600 species now.”
Sax-Zim naturalist Clinton Dexter-Nienhaus

In addition to the bogs themselves, the glaciers left behind other ecosystems: glacial rivers formed long, winding ridges of deposited sediment called eskers. Over time, these ridges became covered in coniferous forests hosting jack pines, white pines, and red pines.

Human-modified landscapes provide yet another ecosystem: local hayfields and pastures provide habitat for prairie plants (and birds) to flourish.

Even the roadside ditches at Sax-Zim Bog are busy. During seasons of heavy snow, they act as a highway for wildlife, providing for easy movement for wolves, deer, otters, and more. The pools of water that form in ditches also host dragonflies and the much-maligned mosquitoes. (Many of these mosquitoes are not pests to humans and are important pollinators and vital members of the bog ecosystem. However, it must be said that a remarkable number of them are voracious blood-sucking nuisances.)

Mix of land ownership

The land itself is cared for by a wide variety of people and organizations. The Friends of Sax-Zim Bog own about 4,200 acres of the 500,000 total acres that comprise the Sax-Zim Bog. The rest is owned by a mosaic of county, state and privately-owned lands.

For a relatively rural area, the influx of 5,000-6,000 visitors in the span of a few months can be overwhelming for locals. The Friends of Sax-Zim Bog website – as well as a KAXE listener from the area – recommends following good birding etiquette, including pulling over before stopping, allowing faster cars to pass, and not pointing binoculars in the direction of people’s homes.

“Just remember, there’s people here: this is not just a state park or national park or something like that. These are their roads, and people drive them to go to work just like you and I do,” Clinton stated.

Clinton is particularly excited to see locals at his workshops. “It’s really exciting because they’ve been there: they grew up in the bog, they grew up in these places. But maybe they don’t know about the weird little orchids that are there, or the cool flies that are zipping around the goldenrods,” Clinton enthused.

Indigenous communities and winter phenology

Unsurprisingly, staff phenologist John Latimer lost little time before inquiring about winter phenology at Sax-Zim Bog. (John had recently traveled to Sax-Zim Bog to attend a winter phenology workshop with Clinton, but was foiled at the last minute when Clinton was waylaid by car troubles.)

“If you’re just getting into it, it might not seem like anything’s happening in the winter, but there’s so much. There’s so much that we can look at,” Clinton enthused.

“My big hope [for the winter phenology class] was to acknowledge that Indigenous communities have been doing this forever,” Clinton continued. “Moons are their calendar,” he said, “Oftentimes those moons have names that are directly related to phenology.”

He explained that Indigenous people have naturally been phenologists for thousands of years, because of its deep importance to daily life. “I grew up on Dakota lands, I’m on Ojibwe lands now, which means I get two very different perspectives on phenology, especially winter phenology,” Clinton explained. “So, growing up on the edge of the plains versus being up in the woods, different things are happening.”

A Rough-legged Hawk perches at the top of a dead birch tree near Finland, MN on Oct. 17, 2023.
iNaturalist user l_woodsy
A Rough-legged Hawk perches at the top of a dead birch tree near Finland, MN on Oct. 17, 2023.

For example, in both Ojibwe and Dakota languages, the winter moons relate to weather and the snow crust, an important seasonal marker. The thickness of the snow crust may not be obvious or relevant to most of us in our day-to-day life, but Clinton says snow crust has a large impact on birds and other wildlife such as Barred Owls.

During February and March, typically nocturnal Barred Owls are often spotted during the day. This is due to the thick, hard crust on the snow at night: the warmth of the midday sun loosens up the crust and allows the Barred Owls to punch through to capture prey.

Rough-legged Hawks and other arctic-breeding species are another seasonal indicator. Rough-legged Hawks descend from the arctic to the Sax-Zim Bog area in October but decrease in numbers in November. By January, they’ve vanished, only to return again in February and March.

The January nesting season (?!?)

Right now, Great Horned Owls, are already busy with mating and reproduction. They begin preparing for their new brood as early as December. "If you get outside in mid- to late December, typically Great Horned Owls are calling,” Clinton explained. “That’s territorial mating calling. That’s not just, ‘Oh, I’m a young bird and I’m just hootin’ around.’ No, that’s business. Business is happening in December.”

A Great Horned Owl sits on the branch of a flowering maple tree in May, 2023.
USFWS Midwest Region via Flickr
A Great Horned Owl sits on the branch of a flowering maple tree in May, 2023.

These businesslike birds lay eggs in January and welcome their newly hatched chicks in February.

It may seem like an odd time of year for nesting. However, starting early is necessary to successfully raise such large birds of prey. “You’re getting a head start,” said Clinton. “Especially large birds of prey take a long time to mature. It could be said of Bald Eagles, it could be said for Great Horned Owls, it could be said for Harpy Eagles if you want to go to South America.

In addition to the Great Horned Owls, crossbills – songbirds with curiously curved beaks well adapted to prying apart pinecones - routinely nest in the wintertime, especially if there’s an abundant cone crop.

“They’re going to set up shop, they’re going to nest, they’re going to fledge chicks, and they’re going to keep moving,” Clinton explained. “There are a lot of nomadic species in the boreal forest, whether they’re wintering – birds that are migrating from further north down to us – or birds that are sticking around for the winter and hanging out, birds like chickadees that don’t really go anywhere.”

Excitement is everywhere

Even in town, you can spot signs of the breeding season. After the Great Horned Owls, the next birds to nest will be Common Ravens and Canada Jays.

For ravens, the “best thing to do is go out and look at them right now, because I bet you’re going to see two ravens. I don’t think you’re going to see individuals, you’re going to see pair bonding going on right now,” Clinton suggested.

Look for pair bonding activities such as paired flights, barrel rolls, and collecting nesting materials. Those interested in crow and raven behaviors might enjoy the Corvid Ecology Field Trip at the Sax-Zam Bog on February 11.

If you have a birdfeeder, keep an eye on the chickadees and woodpeckers! They will begin practicing territorial displays before the breeding season, which starts in mid to late February. Listen for drumming and watch for bill-waving threat displays between rivals.

Hungry for more

With so many fascinating topics to cover, the interview with Clinton flew by quickly. John Latimer had many unanswered questions, so we can all look forward to a second interview sometime soon!

"Listen to the full KAXE interview above"

From virtual bog-ventures to in-person events like February’s Skull Study course, the public is welcome to explore the wonders of the bog.

Clinton was a wealth of information: listen to the full interview for more nuggets of nature wisdom.

*Author’s note: I (Charlie) first met Clinton at an Intro to Mosses workshop he taught at the Sax-Zim Bog. In the space of four short hours, I watched in growing glee as he unloaded several textbooks-worth of information, spotted microscopic sundew plants from several meters away, and chased an out-of-season butterfly across a boot-hungry bog in order to Properly Document it.

For more phenology, subscribe to our Season Watch Newsletter or join the KAXE - KBXE Season Watch Facebook group.

Funding for this project was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR).

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