St. Croix River watershed wildlife: Rich in natural spaces and rare species

There were more than 24,000 observations logged on iNaturalist in the region this year, including many imperiled species.




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Red-shouldered hawk, Scandia, Minn. (Photo by Greg Seitz, St. Croix 360)

It was a busy year on iNaturalist, the website where anyone can document observations of plants, animals, and other living things. This was also true in the 8,000 square miles of Minnesota and Wisconsin in the St. Croix River watershed.

The 24,000 observations logged here this year was twice as many as 2019. In fact, with a total of about 50,000 observations, this year comprised nearly half of all observations so far.

For this year’s round-up of iNaturalist activity, St. Croix 360 is focusing on the rare, threatened, endangered and otherwise imperiled species. The river, its tributaries, and the surrounding region are rich in biological diversity, and offer opportunities to see creatures found few other places.

Top 10 species observed:

First, here are the most commonly observed species on iNaturalist for the St. Croix River watershed. To qualify as an observation, a photo or audio recording must be provided.

The list is pretty representative of the plants and animals that people are most likely to notice while exploring nature in the area. Two abundant non-native species (Great Mullein and Common Buckthorn) are also included.

Top 10 most observed threatened species:

All told, 55 species considered “threatened” in some way were documented in the watershed in 2020. Below are photos and a list of the 10 most observed species, with information from a variety of sources about the wildlife and what must be done to protect their survival.

Note: These species have been determined as “threatened” generally, not necessarily by state or federal governments. iNaturalist primarily uses the well-respected IUCN Red List and NatureServe for information about threatened species. A couple species on the list may be surprising as “threatened” to nature lovers around here: there are generally plenty of common grackles and dark-eyed juncos. Their inclusion considers their global status and overall population trend.

10. Karner Blue (Plebejus samuelis)

Observation and photo in northwest Wisconsin by Derek Anderson via iNaturalist

U.S. Fish and Wildlife Service: The Karner blue butterfly, an endangered species, is a small butterfly that lives in oak savannas and pine barren ecosystems from eastern Minnesota and eastward to the Atlantic seaboard. Historically, it was found in a continuous band throughout its range but today is found in portions of New Hampshire, New York, Michigan, Wisconsin, Ohio, Indiana, and Minnesota. The wild blue lupine (Lupinus perennis) is the only food plant for the Karner caterpillar.

St. Croix River Association: The Glacial lake Grantsburg Wildlife Management Complex consists of three wildlife properties encompassing nearly 54,000 acres. Within this area, Crex Meadows and Fish Lake wildlife areas have been chosen as federal recovery sites for the endangered Karner Blue Butterfly. The St. Croix River Association has partnered with the U.S. Fish and Wildlife Service to accelerate the restoration and management of oak savanna and grassland, which the Karner Blue Butterflies require to increase in abundance. Through a combination of mechanical and chemical brush control, and restoration of grassland habitat, this project will provide the necessary habitat for the Karner Blue Butterfly to thrive.

Wikipedia: This subspecies of Plebejus melissa was first identified and described by novelist Vladimir Nabokov. The name originates from Karner, New York (located half-way between Albany and Schenectady) in the Albany Pine Bush, where it was first discovered. In the novel Pnin, Nabokov describes a score of Karner blues without naming them.

9. Rattlesnake Master (Eryngium yuccifolium)

Photo and observation by Jessica Turtle in Scandia, Minn.

Minnesota DNR: Eryngium yuccifolium (rattlesnake master) is a native component of mesic prairies in southern Minnesota. At one time, prairies were the dominant vegetation type on the landscape of that region, but since settlement they have been systematically plowed under and replaced with crop fields. This process of land conversion was so complete that by the end of the 20th century less than one percent of the original prairie remained PDF. Obviously, the plant species that occurred in those prairies suffered the same fate. This was especially serious for prairie obligates, such as E. yuccifolium, that are restricted to prairies (Havercamp and Whitney 1983).

Efforts have been made to identify and protect even tiny scraps of remaining prairie habitat, especially those that harbor sensitive or specialized species like E. yuccifolium. However, results have been mixed. Many of the remnants are so small they need constant attention to protect them from aggressive non-native plant species that can easily overwhelm the natives. The worst invaders are the sod-forming grasses like Bromus inermis (smooth brome) and Poa pratensis (Kentucky bluegrass), but there are a host of others. Encroaching brush is also a serious problem that requires ongoing management. Eryngium yuccifolium was listed as a special concern species in Minnesota in 1984.

8. Butterfly Mussel (Ellipsaria lineolata)

Photos and observation by driftlessnative via iNaturalist

Wisconsin DNR: Butterfly (Ellipsaria lineolata), listed as Endangered in Wisconsin, is found in large rivers in the western and southern parts of the state. It prefers a stable substrate containing rock, gravel and sand in swift current. The known host species include three common fish; drum, green sunfish, and sauger.

Habitat destruction and river pollution have resulted in mussel declines. Protection of habitat and improvements in water quality along with restriction of dredging, impoundments, sand and gravel mining, and navigational improvements would benefit this species. The development of fish runways to facilitate the movement of host species through or around dams could help to protect this species.

7. Red-shouldered Hawk (Buteo lineatus)

Photo and observation in Scandia, Minn. by Greg Seitz, St. Croix 360

Minnesota DNR: Red-shouldered hawks are most commonly found in large tracts of mature deciduous forest with scattered wetland openings. Suitable habitat typically occurs in uplands with diverse topography characterized by numerous small hills, ridges, and depressional wetlands or small lakes. Red-shouldered hawks also frequent mature floodplain forests. Researchers have found that nesting sites include high, thick canopies and trees with large diameters (McLeod and Andersen 1996). Bosakowski and Smith (1997) found that the number of red-shouldered hawks increased with increasing size of wilderness areas.

Habitat alteration and destruction and pesticide contamination are thought to be responsible for the red-shouldered hawk’s decline in the northern states. The large, contiguous forest tracts that the species depends upon are becoming smaller and fragmented, resulting in habitat that is more suitable to the open-country red-tailed hawk (Buteo jamaicensis). The red-shouldered hawk was designated a species of special concern in Minnesota in 1984.

6. Common Grackle (Quiscalus quiscula)

Photo and observation in Linwood Township, Minn. by safechrislaurie via iNaturalist

Minnesota Breeding Bird Atlas: Distributed across the eastern two-thirds of North America, the Common Grackle reaches its highest breeding densities in the northern Great Plains, including southwestern Minnesota, and across the Eastern Tallgrass Prairie, including the states of Illinois, Indiana, and Ohio (Figure 1).

Assigned a Continental Concern Score of 9/20 by Partners in Flight and designated a Common Bird in Steep Decline.

IUCN Red List: Following the large increase in numbers, possibly due to agricultural development, the Common Grackle is now one of the most abundant species in North America. They occur in large flocks and dense roosting aggregations in parks and agricultural areas, where they damage grains, seeds and fruits and are now regarded as an economically significant pest species. Moreover, its roosting sites can hold the fungus Histoplasma capsulatum, which can cause the lethal human respiratory disease histoplasmosis. Consequently, the species has been subject to extensive deterring and population control measures, which may include chemical repellents or lethal surfactants.

5. Dark-eyed Junco (Junco hyemalis)

Dark-eyed junco, May Township, Minn. by Greg Seitz, St. Croix 360

NatureServe: Large range in North America; very large population size; many occurrences; apparently slowly declining. No major threats have been identified. Causes of the slow, apparently ongoing decline are not known.

Breeding Bird Survey (BBS) data for 1966-2007 indicate a significant survey-wide decline of 1.3% per year; this amounts to a 42% decline over this time period. BBS abundance (average number of bird per route) declined from roughly 8-9 in the 1960s and 1970s to around 6 in 2000-2007. Overall, based on BBS data, the species appears to have undergone a slow but steady decline in abundance over the past several decades.

4. Blanding’s Turtle (Emydoidea blandingii)

Photograph and observation in east-central Minnesota by Matthew Thompson via iNaturalist

Wisconsin DNR: Blanding’s Turtle (Emydoidea blandingii) is a Special Concern species in Wisconsin. They utilize a wide variety of aquatic habitats including deep and shallow marshes, shallow bays of lakes and impoundments where areas of dense emergent and submergent vegetation exists, sluggish streams, oxbows and other backwaters of rivers, drainage ditches (usually where wetlands have been drained), and sedge meadows and wet meadows adjacent to these habitats. This species is semi-terrestrial and individuals may spend quite a bit of time on land. They often move between a variety of wetland habitats during the active season, which can extend from early March to mid-November. They overwinter in standing water that is typically more than 3 feet deep and with a deep organic substrate but will also use both warm and cold-water streams and rivers where they can avoid freezing. Blanding’s turtles generally breed in spring, late summer or fall. Nesting occurs from about mid-May through early July depending on spring temperatures. They strongly prefer to nest in sandy soils and may travel up to 300m (984 ft) from a wetland or waterbody to find suitable nesting sites. This species appears to display nest site fidelity, returning to its natal site and then nesting in a similar location annually. Hatching occurs from early August through mid-October. This species takes 17 to 20 years or more to reach maturity.

Minnesota DNR: Although formerly more widespread in the eastern and central portion of the United States, the Blanding’s turtle is now restricted to a small number of states and provinces in the Upper Midwest, New England, and southeastern Canada. Minnesota lies on the northwestern periphery of its range and the species is relatively widespread in the state. The Blanding’s turtle is a late maturing, long-lived species unable to recover quickly from catastrophic events that reduce the population. Their relatively low mobility, high juvenile mortality rate, and low reproductive potential are also limiting factors for population growth. Loss and degradation of upland and wetland habitats, and mortality on roads are great threats to the species. The Blanding’s turtle was classified as a threatened species in Minnesota in 1984.

3. Plain Pocketbook (Lampsilis cardium)

Observation and photos in St. Croix River, Washington County, Minn. by Mark Hove via iNaturalist

This species is not really considered threatened in most places, but all mussels are imperiled by forces like too much sediment, water pollution, changes in river flows, and loss of fish species they require to reproduce. Friend of St. Croix 360 and mussel researcher at the University of Minnesota Mark Hove also had some great photos on iNaturalist, so we kept it on the list!

Mark Hove: Wanted to photograph some interesting interesting variation in Lampsilis cardium periostracum color. Specimens collected by Ian Cameron, Isabella del Furia, and Mark Hove while feeling around for mussels in St. Croix River along MN shoreline with hands in ≤4 ft depth. Quite a bit of Vallisneria in area and mostly sand substrate with patches of gravel and cobble.

2. Rusty-patched Bumble Bee (Bombus affinis)

Photo and observation in Minnesota by goeltlb via iNaturalist

Minnesota Secretary of State: The rusty patched bumblebee, Bombus affinis, became Minnesota’s state bee in 2019.

U of MN Bee Lab: The rusty-patched bumble bee (Bombus affinis) was once commonly found across the northern part of eastern North America, extending south along the Appalachian mountains. It is now listed as an endangered species in the US and Canada, currently found in low numbers in a very small part of its former range. Scientists and conservationists need your help finding the remaining populations of this bee. Please take photos and share on

IUCN Red List: The primary threats attributed to the severe decline of Bombus affinis include pathogen spill-over from commercial to wild bees; habitat loss due to agriculture and development; pesticide use; and climate change. Reduced genetic diversity, which can be a result of declining, isolated subpopulations caused by any of the aforementioned factors, likely also threatens this species.

U.S. Fish and Wildlife Service: Rusty patched bumble bees once occupied grasslands and tallgrass prairies of the Upper Midwest and Northeast, but most grasslands and prairies have been lost, degraded, or fragmented by conversion to other uses. The rusty patched emerges early in spring and is one of the last species to go into hibernation. It needs a constant supply and diversity of flowers blooming throughout the colony’s long life, April through September.

Center for Biological Diversity, Dec. 16, 2020: Lawsuit Launched to Protect Habitat for Critically Endangered Rusty Patched Bumblebee

1. Bald Eagle (Haliaeetus leucocephalus)

Photo and observation along St. Croix River near Osceola, Wis. by Greg Seitz, St. Croix 360

NatureServe: Widespread distribution in North America; large numbers of occurrences, many of high quality, particularly in Alaska and British Columbia, but suffered great decline in southern and eastern part of range earlier this century; still susceptible to a number of threats, particularly environmental contaminants and excessive disturbance by humans; recent rangewide improvement in numbers and the protection offered by governments prevent it from being ranked any higher.

U.S. Fish and Wildlife Service: Bald Eagles are no longer an endangered species, but bald and golden eagles are still protected by multiple federal laws, such as the Eagle Act, the Migratory Bird Treaty Act, the Lacey Act, and other state and municipal protections. Eagles, their feathers and parts, nests, nest trees, and winter/nighttime roosts are all protected by federal laws.

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2 responses to “St. Croix River watershed wildlife: Rich in natural spaces and rare species”

  1. PHIL SYLLA Avatar

    Very interesting article. Greg, how did you access the local information from iNaturalist? I would like to gather similar information for the Yellow River, one of the major Wisconsin tributaries to the St. Croix