November 2020 Natural Mystery

posted Nov 16, 2020, 9:52 AM by Jonathan Poppele   [ updated Nov 16, 2020, 9:53 AM ]

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October 2020 Natural Mystery Answered

posted Nov 16, 2020, 9:29 AM by Jonathan Poppele   [ updated Nov 16, 2020, 9:39 AM ]

We received a range of answers to our October natural mystery implicating a wide range of animals from birds and mammals to freshwater sponges. Congratulations to our generous Patreon supporter Mike Holtz and one anonymous contributor who successfully identified this common but rarely seen sign.

This is beaver scat. Mike Holtz gets us started with this pithy and useful description:

“Sawdust meatballs! Found in water, contents look like mostly woody fiber, size looks good at around an inch to an inch and a half.”

Our anonymous contributor goes into some additional depth and analysis:

"I notice the pellets appear to contain woodchip pieces. The size matches the range of 1"-1.25" in length for beaver pellets and 0.75" in diameter. The yellow coloring is interesting-- perhaps from the water that they were floating in? Or the type of tree? When I look at photos of fresh beaver chew sign on conifer trees (trees popular in BWCA), I see instances of yellow or red color to the cambium. Perhaps this is retained in the scat. Beaver would be likely inhabitants of the BWCA lake so also a reasonable candidate for scat. Owl pellets have a similar elliptical shape but would contain fur and bones rather than wood. Owl pellet size covers this range, but if they were in water, I'd expect to see the swollen appearance of wet fur."

Beaver usually deposit scat in the water, so we rarely find it even where it is quite abundant. We are most likely to find beaver scat after water levels drop, exposing previously submerged ground. Our tracking club has found beaver scat at Ft Snelling State Park on just four occasions, despite the dense population of beaver there.

Congratulations again to Mike and our anonymous contributor!

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Fall 2020 Wildlife Survey Story-of-the-Day

posted Oct 9, 2020, 10:46 AM by Jonathan Poppele   [ updated Oct 9, 2020, 10:46 AM ]

Our Fall Wildlife Tracking Survey took place this past October 3 at the Carlos Avery Wildlife Management Area. Eight members of the Minnesota Wildlife Tracking Project gathered to survey the sandy roads or Carlos Avery, just a few miles from our regular survey location at Cedar Creek Ecosystem Science Reserve. While we only found clear tracks of a few species of mammals, they included footprints we had never seen in the filed. We also may have verified a species we had never confirmed at Carlos Avery before. Here is our story of the day.

Our group divided into two tracking teams for the day. One team walked a loop around Pools 6 & 8, focusing attention on an old sand pit just off Wyoming Rd. dubbed “Peaceful Canyon” by our friend Blake Southard. The other team followed South Rd into the southern extension of the WMA, just across Co Rd 18 from the DNR headquarters.

The dirt roads through Carlos Avery provide a mix of substrate ranging from hard, gravely soil to soft sand. There are natural track traps along most roads, but many of these areas get regular traffic. With duck hunting season in full swing, there were few clear tracks along the roads. Digging sign from fossorial mammals along the edges of the roads, however, abounded.

Both of the teams noted large, fresh pocket gopher mounds and mole runways. The greater Twin Cities Metro Area is home to only one species of Pocket Gopher—the Plains Pocket Gopher (Geomys bursarius)—so we can identify these mounds with confidence. Two species of moles are found in the area. The Eastern Mole (Scalopus aquaticus) and the Starnosed Mole (Condylura cristata). Starnosed Moles are weaker diggers than Eastern Moles, are most common along the edges of waterways, and rarely push up the kinds of prominent runs we were finding. We can safely identify most of these runs, many of which were extremely large, as having been made by Eastern Moles.

Many of the pocket gopher mounds we found had tunnel openings in them. Some of the mole runs we found showed openings in them as well. Pocket gophers typically plug their tunnel entrances to maintain consistent humidity and deter predators. Most times of the year, it is rare to see open tunnels in pocket gopher mounds. On this occasion, however, they were quite common. Do pocket gophers have a different set of needs at this time of year? Are these open tunnels related to dispersal? Are they the work of other species, such as voles, making use of the gophers tunnels?

The open mole tunnels were their own mystery, and also offered a rare treat. On the two-track road leading into Peaceful Canyon, one team found a mole runway so shallow that it was an open trench rather than a tunnel. And on the floor of the runway were the clear tracks of an Eastern Mole. Unlike species such as the Hairy-Tailed Mole (Parascalops breweri) which regularly come to the surface to forage in leaf litter, Eastern Moles are almost completely fossorial and may spend their entire lives underground. Eastern Mole tracks are quite rare, and none of our trackers had ever seen them in the field before. As far as we know, these are the only photographs of Eastern Mole tracks on iNaturalist, or anywhere in the tracking literature. 

And these weren’t the only surprising tracks our teams found at Carlos Avery. One team returned with a photo of a single large canine print from a sandy roadside. It was an isolated tracks. The rest of the trail had been covered over by human traffic. But it was tantalizing. The print measured 3 3/8” long and 2 1/2” wide, with a star-shaped negative space. It is always difficult to identify a large canine to species based on a single track. Carlos Avery is a popular spot for dog walkers, and canine tracks in the WMA are generally best considered “domestic dog until proven otherwise.” In this case, we had something to compare the track to—field drawings of the hind track of the wolf our team had been tracking at Cedar Creek for the past few years, prior to the pandemic. Not only is the size of this track an exact match, but specific shape of the palm pad is as well. While it is possible, at least in principle, that there is a domestic dog with a rear palm pad that has the exact proportions of the wolf we have tracked at Cedar Creek, it is highly improbably. If we found this track at Cedar Creek, I think none of us wold have any doubt that it was from our local wolf. Cedar Creek is only about 10 miles away from where this observation was made, and is connected by nearly unbroken stretches of woods and wetlands. So this shouldn’t be a huge surprise. But this is the first time we have gotten a strong indication that the wolf is ranging into Carlos Avery. It also appears to be the first track from this animal we have recorded since last winter.

There were other sightings throughout the day as well. We identified some animal remains, such as this meadow vole and this red-bellied snake who were unfortunate victims of cars. Our teams also found the tracks of three species of squirrels and were able to take a deep dive into the sometimes subtle differences between the tracks of chipmunks, red squirrels and gray squirrels. Some of these observations also offered a reminder to us in the value of multi-factor analysis. One of the chipmunk trails we found measured 3 3/16” wide, which is wider than any of the published ranges for chipmunk trails. Elbroch lists 2 7/8” as the upper limit. But the track size and foot morphology were distinct. Apparently they grow ‘em big in Carlos Avery.

You can see all of our observations from the day here on iNaturalist.

Our Fall Survey is the last wildlife survey for 2020. We are holding off on scheduling or 2021 dates until we have a better understanding of when normal operations will resume at Cedar Creek. Stay tuned for future announcements and keep an eye on the calendar. We hope you can join us for a future survey.

October 2020 Natural Mystery

posted Oct 9, 2020, 10:22 AM by Jonathan Poppele   [ updated Oct 9, 2020, 10:22 AM ]

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September 2020 Natural Mystery Answered

posted Oct 9, 2020, 8:53 AM by Jonathan Poppele   [ updated Oct 9, 2020, 8:54 AM ]

Our September Natural Mystery was an entomology puzzle more than a tracking question—and the answers showcased the broad and deep knowledge of the naturalists in our community. Congratulations to Bill Kass, Catherine Zimmer, Eric Vehe, Kirsten Welge, and Mike Holz who correctly identified this species, and carefully distinguished it from its closest look-alike.

This is a Brown Belted Bumble Bee, Bombus griseocollis.

To explain, I’ll let Bill Kass start us off:

"The first thing to note is that the thorax is mostly yellow with a black spot in the middle. This eliminates several species that have a lot of black between their wings. The abdomen is mostly black except for the 2nd abdominal band which is not even yellow all the way around. If it was all the way around the abdomen and with the black spot on the middle of its back, this would most likely be a Common Eastern Bumble Bee,… but it’s not."

Mike Holtz points out similar features, and also guides us to a useful resource:

"Looking at the Guide to Minnesota Bumble Bees, the bee in the picture appears to have a black spot in the center of the thorax. That, in combination with the rusty brown color directly above the black of the abdomen point to Bombus griseocollis, the Brown-belted bumble bee."

The closest look-alike to the Brown Belted Bumble Bee is the Rusty Patch Bumble Bee, Bombus affinis. As Eric Vehe explains:

"Bombus affinis (Rusty-patched Bumble Bee) has a prominent rusty patch with multiple black segments in the lower abdomen, but it also has yellow between the rusty patch and the lower black segments, which does not appear in this photo. While the angle makes it slightly hard to see detail of it, it also has a central black spot on the back of the thorax that appears relatively round. Bombus affinis has a wider patch that tapers and extends both laterally and down to the base of the thorax."

Kirsten Welge explains the difference this way:

"Rusty patched bumble bees are most commonly confused with brown-belted bumble bees. The rusty patch on Bobbus affinis, which is an area of rust-colored hairs, is on the front of the second abdominal segment with yellow hairs on the sides and towards the back of the segment. The second abdominal segment of the brown belted bumble bee, Bombus griseocollus, has brown hairs towards the front and black hairs on the sides and back."

And Catherine Zimmer notes even more succinctly: "Not the Rusty-patch bumble bee because the brownish patch is not surrounded by yellow."

Eric Vehe also rules out two other native bumblebees that have reddish brown on their abdomens:

"While Bombus ternarius (Tricolored Bumble Bee) and Bombus rufocinctus (Red-belted Bumble Bee) also have distinct rusty abdominal segments, they both have two abdominal segments with that color rather than one and also have significantly less black abdominal segments in the lower abdomen."

Finally, Kirsten Welge points out: "The slender, black hind leg appearance points to no pollen basket on hind leg - indicating this is likely a male."

I haven’t verified this yet, but I plan to go back and have a look!

Congratulations again to Bill, Catherine, Eric, Kirsten, and Mike. Thank you for sharing your knowledge and your process with all of us!

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September 2020 Natural Mystery

posted Sep 14, 2020, 9:31 AM by Jonathan Poppele   [ updated Sep 14, 2020, 9:32 AM ]

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August 2020 Natural Mystery Answered

posted Sep 7, 2020, 12:04 PM by Jonathan Poppele   [ updated Sep 14, 2020, 8:42 AM ]

We received a range of guesses for our August natural mystery including muskrat, beaver, otter and raccoon—all of which are common on the muddy banks of the Minnesota River in Ft. Snelling Sate Park. Congratulations to Bren White and our generous patron Mike Holtz who correctly identified the species and which foot of four left this particular track.

This is the right front track of a river otter, This is the right front track of a river otter, Lontra canadensis.

As Mike shares:
"At first glance it looks like raccoon, but I think the carpal pad registering at the bottom of the track is helping tip it towards otter. The size is right, and the location certainly fits for otter."

Mike is exactly right here. And as he points out, the carpal pad is a key clue. Let's go through some of the other possibilities and see how we can distinguish this track from each:

Raccoon palm pads are more fully fused than mustelid palm pads and show less definition. The leading edge of the palm usually forms a smooth arc, rather than showing distinct lobes. In this track we can see several distinct, round palm pads. Raccoons do not have a separate carpal (heel) pad, seen in this track. Raccoon toes tend to register more uniformly along their length, and rarely show a bulbous tip.

Beaver have five toes on their front feet, but their toes taper from the palm to the tip, rather than appearing bulbous at the end. Their nails are more stout (they are a burrowing animal), and they have a different arrangement of pads. As in other rodents, beaver front feet have two heel pads. One of these is a carpal pad, and the other is the metacarpal pad at the base of toe 1. These two pads register roughly side-by-side and have a similar size and appearance. In this track, the metacarpal pad at the base of toe 1 is fused with the palm pads and the carpal pad registers as a separate heel. Finally, while toe 1 on beavers is more developed than in many rodents and has a claw, it is still much less developed than the other toes.

Muskrat hind feet are smaller, lack well developed palm pads, and don't have any pads on their heel. Their toes are lack a bulbous tip and are more slender. Though the fringe of hair can make them appear wide, they typically appear widest at the base.

Most often, otter tracks do not show the length of the toe this clearly—but while uncommon, this presentation isn't exceptionally rare. In this track, the structure of the palm pad and the distinct heel pad are some of our clearest clues that we are looking at a mustelid track. The size, habitat, location, and crisp tracks showing no signs of fur on the foot leave us with otter as our best candidate.

Congratulations again to Bren & Mike, and thanks to everyone who sent in guesses!

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August 2020 Natural Mystery

posted Aug 10, 2020, 10:34 AM by Jonathan Poppele   [ updated Aug 10, 2020, 10:34 AM ]

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July 2020 Natural Mystery Answered

posted Aug 10, 2020, 10:25 AM by Jonathan Poppele   [ updated Aug 10, 2020, 12:06 PM ]

A few years ago, I ran across a large collection of barred owl pellets in Ft. Snelling State Park. In dissecting them, I found nearly 20 small mammal skulls. Eighty percent of those skulls were from this species. By some combination of them being so common, their habitat being so exposed, and perhaps them being so tasty, they appear to be an extremely common prey animal for barred owls. Congratulations to Mike Holtz and one anonymous contributor for correctly identifying these common, tiny skulls to species. And an honorable mention to Joe Conrad who identified the genus based on this species' analog in the UK.

These are the skulls of meadow voles, Microtus pennsylvanicus.

Joe Conrad and Mike Holtz gets us started with our analysis. Joe began by thinking about the context--that these skulls came from an owl pellet:

"Field Voles [ed: Microtus agrestis, a Eurasian species] are abundant and common prey for owls. I presume that there is a similar vole in North America. So I searched for vole skulls. The features look quite similar to the Field Vole. Kind of striking lower jaw shape."

Mike began by comparing measurements, then looking at teeth and mandible shape:

"I started with a chipmunk, just to pick a random starting point. The sizes for chipmunk skulls and mandibles seemed higher than what's in the picture. Dropping down in size from there, the teeth on the mandible don't match for shrews. Looking at mice vs voles, the sizes matched pretty close for both, but the shape of the mandible and the teeth seemed to line up nicely with meadow vole."

Now let's talk about those teeth. Our ridiculously knowledgeable anonymous naturalist explains:

"Voles are herbivores, so they have miniature cow's teeth built to withstand all of the coarse plant material they grind up. Like a cow, the maxilla (upper jaw) is wider than the mandible (lower jaw), allowing the animal to chew with a significant amount of lateral movement. (It's better to grind your fibrous food than pound it.) You can see zig-zag ridges of dentin showing on the occlusal surfaces, pointing almost perfectly at right angles to the midline of the skull (allowing upper and lower molars to slide sideways over each other during chewing). The sides of the teeth are also deeply and regularly corrugated, and an individual molar appears block-shaped from gumline to chewing surface. These are characteristics of teeth that continue to erupt over the animal's lifetime. The continual growth enables the animal's upper and lower teeth to maintain contact even as they wear away over time.

Contrast this against Mus spp. [ed: Old World mice, such as the common house mouse], which have molars that resemble a human's. More discrete molars (when viewed from the side), often with a visible 'neck' at the bone-tooth interface, and more irregular "mountains" on the chewing surface. They are seed eaters more than plant eaters, so they do not have a diet that requires constantly-erupting molars.

It isn't a member of the shrew family either; these tiny little predators have molars that resemble tiny dog or cat molars, with sharp shearing peaks."

So it's a vole skull. But how can we distinguish which species of vole? There are four species of voles and lemmings found in east-central Minnesota: the Meadow Vole (Microtus pennsylvanicus), the Prairie Vole (Microtus ochrogaster), the Southern Red-Backed Vole (Myodes gapperi, formerly classified as Clethrionomys gapperi), and the Southern Bog Lemming (Synaptomys cooperi).

As our anonymous naturalist notes: "Based on range distribution, a vole in the Twin Cities area is most likely to be M. pennsylvanicus, the meadow vole." And since we are looking at a minimum of three skulls that all came from a single owl pellet, this is likely an extremely abundant species. The Meadow Vole is the most common and abundant vole in this part of the state. But there are some details on the skulls that can help us confirm this guess.

Myodes species such as the Southern Red-Backed Vole have narrower and more rounded zygomatic arches (cheek bones) than Microtus species. Also, the angular process (the lower-most rearward extension on the lower jaw) is shorter and more blunt. Synaptomys species such as the Southern Bog Lemming have more robust zygomatic arches that extend much wider than the brain case. Their angular process is also shorter and more blunt than in Microtus. The differences between Meadow Vole and Prairie Vole skulls are subtle. Perhaps the most distinguishing feature is the structure of the cheek teeth. According to Elizabeth & Charles Schwartz in The Wild Mammals of Missouri, Meadow Voles have five "islands of dentine" surrounded by enamel on the second molar of their upper jaw, while Prairie Voles show four.

Congratulations again to Mike, Joe and our anonymous contributor.

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July 2020 Natural Mystery

posted Jul 21, 2020, 11:20 AM by Jonathan Poppele   [ updated Jul 21, 2020, 11:23 AM ]

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