Prairie Word of the Day – Habitat Heterogeneity

Do you know what time it is?  It’s time for another PRAIRIE WORD OF THE DAY!

Today’s Prairie Word of the Day (fine, it’s actually two words) is:

Habitat Heterogeneity

Heterogeneity is really just a longer word for Diversity, which is another way of saying “lots of different things”.  So why use the word “heterogeneity” instead of just saying “lots of different things”?  Well, for one thing, using big words makes a person sound smart, and when you’re a prairie ecologist and no one really understands what it is you do for a living, it’s good to at least sound smart.

More importantly, there’s a nice alliterative (another big word!) feel to the phrase Habitat Heterogeneity, which happens to be one of the most important phrases in prairie ecology.  In fact, I would argue that the foremost objective of any prairie manager should be to create habitat heterogeneity within the prairie(s) they manage.

Habitat heterogeneity simply means diversity or variety in habitat types.  Habitat homogeneity is the opposite – a lot of habitat that is all the same.

Every organism in a prairie has its own unique habitat requirements, so the number of different habitat types in a particular prairie is correlated with number of species that can live there.   Let’s use prairie birds as an example.  Birds such as upland sandpipers like to nest in large patches of relatively short-stature grassland.  Around here, a big hay meadow is great habitat for them, especially if it was cut fairly late in the previous year and is still short in stature when the subsequent breeding season starts.  On the other hand, Henslow’s sparrows want to nest in prairie habitats with relatively tall and dense vegetation.  It would be highly unusual to find Henslow’s sparrows and upland sandpipers nesting in the same patch of prairie because their habitat preferences are very different.  So, if you want both species in your prairie, you have to provide both short and tall/dense habitat.  Other birds have their own unique habitat requirements, including nearly bare ground (e.g., horned lark), relatively short, but with abundant thatch (grasshopper sparrow), tall with lots of tall/weedy wildflowers (dickcissels), tall and nearly impenetrably dense vegetation (sedge wrens), and many others.  Only if your prairie provides all those different habitat conditions will you attract all those different bird species.

Dickcissels prefer

Dickcissels prefer habitat with lots of tall wildflowers or weeds.  They often weave their nest into the stems of a tall clump of vegetation.

The same diversity of habitat preferences exists in other groups of prairie species as well.  Among small mammals, for example, voles tend to prefer habitats with abundant thatch, while pocket mice are more often found where bare ground is abundant – and there are many others.  Insects and other invertebrates have the same kind of diversity in habitat preferences

Scale is important.  While a bird, mammal, or insect might have a broad preference for a certain kind of habitat structure, it is likely to need some heterogeneity within that habitat too.  A mouse, for example, might prefer patches of prairie with fairly sparse vegetation, but it is likely to need a few clumps of vegetation dense enough to hide in when predators are near.  Insects and reptiles are ectothermic (cold blooded) and need to regulate temperature, so while a snake might like to hide in tall dense so it can bite your ankle as you walk by (I’M KIDDING!), it also needs some places to bask in the sun.  All of this means that habitat heterogeneity is important any many different scales.  Heterogeneity at a fairly large scale (acres) helps provide places for many different animals to live in a prairie, but heterogeneity within the home range or territory of each animal (square meters, or even centimeters) can be important too.

Some habitat heterogeneity occurs simply because soil texture, nutrients, and moisture, along with topography all vary across a landscape.  A prairie is likely to have areas of more productive soils where vegetation grows tall and thick, and less productive soils where vegetation is more sparse, for example.  In addition, water will pool in some areas of a prairie more than others because of topography, altering the habitat for both plants and animals.  However, despite this “naturally occurring” heterogeneity, it’s still important for prairie managers to look for ways to provide more.

This landscape at The Nature Conservancy's Broken Kettle Grasslands in northwest Iowa shows the kind of natural heterogeneity that occurs in many landscapes.

This landscape at The Nature Conservancy’s Broken Kettle Grasslands in northwest Iowa shows the kind of natural heterogeneity that occurs in many landscapes.  Topography, soil variability, and other factors create a diverse set of conditions for plant growth and habitat structure.  Land management can add to that heterogeneity and improve it even more.

Prescribed fire and haying/mowing do a great job of altering habitat structure at a fairly large scale (acres).  By applying those treatments in different parts of a large prairie each year (and varying the timing of each from year to year), a manager can create a shifting mosaic of habitat patches that supports a wide diversity of animals.  However, both fire and mowing are pretty non-selective – most or all of the vegetation within a burned or mowed area gets the same treatment.  Leaving unmowed patches of grass here and there and varying the height of the mower as it moves across the site can help leave more heterogeneity behind.  Designing prescribed fires so that not all vegetation burns (e.g., mowing around some patches ahead of time, burning on days with lower temperatures or higher humidity, etc.) can also help with habitat heterogeneity – though those kinds of fire might also be less effective at killing trees or accomplishing other objectives.

In prairies where livestock grazing (cattle or bison, for example) is feasible, it is much easier to create small scale heterogeneity because grazers pick and choose which plants, and how much of each plant, to eat at any one time.  By controlling grazing intensity, and varying it across both time and space, managers can create prairie patches that are ungrazed, almost completely grazed, and in various stages of partial grazing – with a mixture of tall vegetation and nearly bare ground.  The uneven application of “fertilizer” from the rear ends of grazers contributes even more to habitat heterogeneity by temporarily altering soil productivity in lots of little spots across the prairie.

These cattle at Konza Prairie in Kansas

These cattle at Konza Prairie in Kansas have created a nice example of small scale habitat heterogeneity by grazing many of the grasses short while leaving leadplant, purple prairie clover, and other wildflowers ungrazed.

Whether it’s fire, mowing, grazing, herbicides or various combinations of those, creating habitat heterogeneity may the most important job of a prairie manager.  We still have a lot to learn about how the scale and configuration of habitat patches affect wildlife and insect populations.  What we do know, however, is that the prairies thrive when they have a lot of different types of habitat.  …When they have habitat heterogeneity.

And that, folks, is your Prairie Word of the Day.

Posted in Prairie Management | Tagged , , , , , , , , , | 9 Comments

Photo of the Week – January 15, 2016

I was looking through a couple batches of winter photos from recent years and found some images I’d never posted here.  Since my camera hasn’t left its bag in the last week or so, I’ll post a few of those old photos today.

So – I hereby present:

“Miscellaneous photos I didn’t previously feel were worthy of posting but are better than nothing.”

Or maybe, “I bet you’ve never seen THESE photos before!”

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Stiff sunflower (Helianthus pauciflorus) buried in snow. Aurora, Nebraska.

Frozen stream/wetland. The Nature Conservancy's Platte River Prairies, Nebraska.

Frozen stream/wetland. The Nature Conservancy’s Platte River Prairies, Nebraska.

Sun and shadow contrast on snow drift.

Sun and shadow contrast on snow drift.

 

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Hubbard Fellowship Blog – LeConte’s Bonanza

This post was written by Evan Barrientos, one of our Hubbard Fellows.  Evan is a talented writer and photographer and I encourage you to check out his personal blog. If you would like to see more of his photographs, you can follow him on Facebook.

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LeConte’s Sparrows are one of the most secretive sparrows in North America. Until this October I had only caught glimpses of two before. But last fall it seemed that while migrating through Nebraska these birds drop their reclusive habits and adopt the friendliness of rural Nebraskans. Two hundred yards from my house is a wetland that was restored by The Nature Conservancy, and as I birded it last October I was stunned to repeatedly find multiple LeConte’s Sparrows feeding in the tall wetland vegetation. Not only were they numerous (up to 7 at a time!) but they were also curious and approached me! As far as I know, LeConte’s Sparrows are not known for doing that. I took many walks reveling in this rare bird bonanza and even was even able to record a few videos of this gorgeous wetland recluse. I always wondered why this species had an orange coloration, but after seeing them in dry, yellow cattails bathed in the golden light of sunset I finally understood.

LeConte’s Sparrows breed in wet meadows of central Canada and the northern edge of midwestern U.S. Their remote location and preference to remain under cover of dense vegetation make them a notoriously difficult species to observe. In fact, their nest wasn’t documented until 100 years after the bird was first seen by Europeans. Each fall they discreetly migrate south through the U.S., occasionally delighting birdwatchers by exposing themselves, until reaching southeastern U.S., where they spend the winter. I look forward to seeing if they’re as friendly on their return trip in spring!

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The restored wetland where I found several LeConte’s Sparrows last October.

Posted in Hubbard Fellowship, Prairie Animals | Tagged , | 1 Comment

An Aquatic Stick Insect

While my wife Kim and I were at the Niobrara Valley Preserve for several days in December, we spotted a small creature neither of us had seen before.  We were walking along the edge of the river (hoping to see more otters, of course) and stopped to look at a small school of minnows near a patch of ice along the riverbank.  As my eyes wandered away from the minnows, I was startled to see what looked like a walking stick insect swimming slowly through the water.  Kim and I watched it for a few minutes and even pulled it out of the water to examine it briefly.  It was swimming slowly, but steadily, and seemed very at home in the water.  Up close, we could see that it wasn’t actually a walking stick, but it sure did look similar.

Water stick insect (Ranatra). The Nature Conservancy's Niobrara Valley Preserve.

Water stick insect (Ranatra). The Nature Conservancy’s Niobrara Valley Preserve.

Later, a quick google search revealed that we’d seen a water stick-insect (genus Ranatra), also known as a water scorpion.  Water stick-insects are predatory insects that are apparently active throughout the winter.  What look like long mouth parts on the front of the insect are actually long strong front legs used for capturing and holding prey.  The long pipes extending from their tail are used for breathing.

Walking stick insect on silky prairie clover in the east bison pasture of the Niobrara Valley Preserve.

I photographed this walking stick insect about a mile from where we saw the water stick-insect.  This one is on silky prairie clover in the sandhills prairie portion of the Niobrara Valley Preserve.  Can you see how I thought the water stick might have been this instead?

While the water stick-insect does resemble the terrestrial walking stick insect in many ways, the two are not at all closely related.  They are both insects, of course, but that’s as close as they get, taxonomically.  They are not only in different insect families, but completely different insect orders as well.  In fact, they are more closely related to assassin bugs and ambush bugs, and use a similar strategy for subduing and eating their food.  All three pierce their prey with sharp beaks and inject saliva that both paralyzes and liquefies the inside of the hapless creature.  Water stick-insects feed on insects, but also tadpoles and small fish.

 

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Posted in Prairie Insects, Prairie Natural History, Prairie Photography | Tagged , , , , , , , | 2 Comments

Photo of the Week – January 7, 2016

Earlier this week, we had a foggy and frosty day.  When the clouds finally started to thin, I popped across town to Lincoln Creek Prairie to see if I could get some photographs of the frost.  Here are a few images I came back with.

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Frosty Lincoln Creek Prairie earlier this week.  Aurora, Nebraska.

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Frost on stiff sunflower (Helianthus pauciflorus).

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Tall thistle (Cirsium altissimum).

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Another stiff sunflower.  Sunflowers seem to display frost very attractively.

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See what I mean?  Maximilian sunflower this time (Helianthus maximiliani).

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Hubbard Fellowship Blog: Ant Swarm (and Lunch)

This post was written by Evan Barrientos, one of our Hubbard Fellows.  Evan is a talented writer and photographer and I encourage you to check out his personal blog. If you would like to see more of his photographs, you can follow him on Facebook.

Don’t worry, I didn’t eat a swarm of ants. But late last September while I was harvesting seeds I did notice enormous clouds of small flying insects swarming above the prairie. The swarms were constantly shifting shape but they were roughly the size of small cars slowly floating across the land. Intrigued, and slightly mesmerized, I walked directly beneath one.

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Closer up I could see that the mystery insects had very narrow waists, which suggested that they might be in the order Hymenoptera (ants, bees, and wasps). Their brown color made me think they might be flying ants.

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Then I began to notice several individuals crawling in the grass below the swarm. Some were caught in spider silk; not complete webs, but loose strands of silk. Looking around, I realized that there were dozens of silk strands scattered among the grasstops of the prairie. As I knelt to photograph one ensnared ant, I saw a small jumping spider stalking another. The spider crept up, grabbed the ant, and carried him away for lunch. Were these silk strands deliberate traps set by the jumping spiders or were they just remnants of ballooning juvenile spiders that happened to catch the ants? I still don’t know.

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Later, I sent the photo below to James Trager, an ant expert, and learned that these were in fact flying ants, Myrmica americana to be specific. It still AMAZES me that there are people who can identify insect species  from just one photo!  He explained that there are actually three different species that currently are all called M. americana because two have not been officially named yet. The unnamed species I encountered is very common, which shows how much we still have to learn about even the insects in our backyards.

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Not only did Trager know the species’ name, but also the explanation for their hypnotic swarming behavior. When it’s time for M. americana to reproduce,  winged males swarm together, forming what’s called a lek.  Reproductive females are drawn to the spectacle and watch from the leaves below. Males will periodically descend from the swarm to crawl around in search of females to mate with (or get snagged by spiders). If a male is lucky enough to avoid the predators below, he may find a female to copulate with. But the challenge doesn’t end there. Once a male begins copulating, dozens of other males will often swoop in and try to do the same, forming what’s called a “mating ball.” After the whole fiesta has ended, the female pulls out her wings (so that she can convert her wing muscle into food to feed her offspring via glandular secretions) and walks away in search of a place to start her own colony.

Finally, here’s a video of the lek, first at full speed, then in half-speed slow motion.

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My Long Irrational Nightmare is Over. Sort of. Nevermind.

Many of you are familiar with one of the great disappointments in my life.  I know you’re familiar with it because you take great delight from bringing it up in conversation when I see you in person.  I can’t count the number of times I’ve been introduced to someone at a conference or other event, and as I shake their hand, they smirk and ask, “Have you seen an otter yet?”

And I always answer “no.”

This is despite the fact that I have spent more than 20 years working along the Platte River, where there are very high populations of river otters – especially in the stretch of river where The Nature Conservancy owns most of our land.  I see tracks, scat, and other sign of otters often.  Other staff, researchers, volunteers, neighbors, and (I assume) people just driving past on the interstate have all seen otters.  But I have not.

Well, I have an update on that situation.  During the week of Christmas, my wife Kim and I spent several days up at the Conservancy’s Niobrara Valley Preserve.  It was a combination work trip/vacation.  One morning, Evan Suhr, the Preserve’s land steward took us out to look at the results of last year’s grazing and fire treatments.  During the trip, we took a brief break and walked down to the river to see where Hazel Creek dumps into it.

Evan Suhr. Niobrara river in winter. The Nature Conservancy's Niobrara Valley Preserve, Nebraska.

Evan Suhr along the bank of the Niobrara River.  The Nature Conservancy’s Niobrara Valley Preserve, Nebraska.

As we stood on the river bank admiring the view, I heard the sound of soft ice cracking, looked up, and stared right into the face of a river otter.  Yes, really.

I had my camera in hand, but had my wide angle lens on, which was worthless for photographing wildlife.  I called out to Evan and Kim to look at the otter and fumbled around in my camera bag for my longer lens.  Before I could get the lenses switched, the otter dipped back below the surface.  A few minutes later, however, we saw it reappear just upstream, and a second otter head popped up next to it.  Unfortunately, there was a dead cedar tree partially blocking my view of the otters.  I stepped slowly and carefully around the tree, but just as I did, both otters disappeared again.  Kim managed to see the two of them once more before we headed back to the truck, but I didn’t, and never managed to get a photo.

So, how am I to feel about this?  First, defensive.  YES, I saw an otter.  I have two witnesses to back me up, as well as a photo of the hole through which the first one popped its head.  I don’t care what you say – I saw an otter.  Two, in fact!

Ice hole where an otter was a few seconds earlier...

This is the hole in the ice through which an otter head popped up.  I have witnesses.

Second, it was really cool to see those two otters.  After waiting so long, and enduring so much grief, the experience was even more sweet than it would otherwise have been.  We didn’t get to see them for long, but they were fairly close, and it was exciting.  It was especially nice that Kim and I both got to see them.

Third.  Now that I’ve moved beyond the initial thrill of seeing those otters, I can’t help slipping a little back into the kind of bitterness I’ve expressed about otters before.  Yes, I saw otters, but I still haven’t seen them along the Platte, where I’ve spent many years waiting and looking for them.  I also didn’t manage to get even a bad photo of them, despite the fact that I saw them twice and HAD MY CAMERA IN MY HANDS at the time.  I can’t help thinking this may be part of the broad otter conspiracy against me.  It’s almost as if the otters were afraid I was giving up on ever seeing them and decided it’d be a lot more fun to throw me a crumb and make me want the rest of the cake even more.

I know, I know.  I’m being completely irrational and ungrateful.  I know I should just enjoy the experience of seeing them and not worry about the fact that it happened on a different river or that I didn’t get a photo taken.  I also acknowledge that it’s unlikely (but not impossible!) that the otters of Nebraska are in any way conspiring against me.  I know all of that.  But I can’t help it.

Kim Helzer. Niobrara river in winter. The Nature Conservancy's Niobrara Valley Preserve, Nebraska.

Kim, being a normal and well-adjusted human, was ecstatic to see the otters and harbors no hard feelings toward them.  That, or she’s in on the plot.  I’m not sure.

Until I see an otter along the Platte River, I’m just not going to be satisfied.  Sure, I’ll do my best to enjoy my life otherwise.  My wife and kids are wonderful, I have a great job, and life seems very good.  It’s just not quite complete.  But sooner or later, those otters are going to slip up.  One of them is going to fail to notice that I’m there and it’ll pop out of the water with a fish in its mouth and start tap dancing on the bank – as they do when I’m not around.  But THIS time I’m going to be there.  With my camera.  And we’ll see who’s laughing then, won’t we??

Yes we will.

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Photo of the Week – December 31, 2015

My wife and I have a tradition of spending part of our holiday break up at the Niobrara Valley Preserve.  It’s only a two year old tradition, but nevertheless…

This year, the weather was great for hiking, so we spent quite a bit of time exploring.  Here are a few photos from our trip.  Think of them as a Happy New Year gift from me.  (Sorry, it’s all you get.)

Happy New Year!

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Kim and I spent a long afternoon on the north side of the river, exploring the former pine woodland (now grassland).

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Evan Suhr (land manager) took us out to look at some of last year’s management results, and on the way back we came upon a couple big bison bulls.

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Rose hips provided some rare color in the winter landscape.

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While almost all the ponderosa pines on the north side of the river (on Preserve property, at least) were killed by the 2012 wildfire, there are still numerous pines alive elsewhere on the Preserve, including this one.

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A very light snow fell while we were at the Preserve, and it made for a very pretty Christmas Eve morning.

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This hoary vervain (Verbena stricta) leaf turned into a cup of snow.

waterfall

On Christmas Day, we found several small springs and followed the stream they created all the way to the Niobrara River.  There were several great waterfalls along the way.

moonrise

On Christmas Eve, a big full moon rose over the river not long after sunset.

 

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Hubbard Fellowship Blog – What Does the Fox Eat?

This post is written by Kim Tri, one of our two Hubbard Fellows for this year.  Kim is an excellent artist, as well as an ecologist, writer, and land steward.  As you can see, her drawings of animals are exceptional.

If you take a look at the official taxonomy of the red fox (Vulpes vulpes), and you follow it up the classification ladder to the Order level, you’ll see that it belongs to the order Carnivora.  The meat eaters.  It keeps company there with such formidable predators as mountain lions, wolves, and polar bears (oh my!).  But if you know much about foxes, you know that they’re real punks.  They don’t care what we’ve labelled them.

A drawing inspired by the indiscriminate dietary habits of foxes. Everything inside of the fox itself are things that they will eat if they can get them. Marker drawing by Kim Tri.

A drawing inspired by the indiscriminate dietary habits of foxes. Everything inside of the fox itself are things that they will eat if they can get them. Marker drawing by Kim Tri.

While they do eat meat, as much of it as they can, they are not obligate carnivores—creatures that subsist only on meat.  Felines are obligate carnivores.  Foxes, however, eat a diet quite similar to that of the poster child of omnivory, the raccoon.  Omnivores are real opportunists, eating whatever is available.  During the summer and fall, nearly 100% of a fox’s diet may consist of insects and plant matter such as fruit and seeds.  During these seasons, these represent the most abundant and least energy-intensive of food sources.  I imagine that during the summer on our prairies, a fox could subsist entirely on grasshoppers if it desired; it could just sit with its mouth open and let them hop right on in.  It is during the winter when foxes rely on what most people think of as more typical prey, such as small mammals and carrion.  If you want to kill some time and your boss isn’t looking, I recommend looking up videos of foxes hunting mice in the snow.  They’re quality entertainment.

To get a real good idea of what comprises any given animal’s diet, take a look at its dentition.  Below, I’ve included some quick sketches comparing the teeth of different native mammals.

The skull of a fox, with different types of teeth labelled with their intended purpose.

The skull of a fox, with different types of teeth labelled with their intended purpose.

First, the fox.  It does have the pronounced canines and big shearing carnassials of a carnivore, but in the back of its mouth also possesses flat molars for grinding plant matter.  You can see evidence of our species’ omnivory inside your own mouth—our canines aren’t just there to look pretty, after all.

raccoonteeth

Compare this with a raccoon.  Their array of teeth is quite similar, though a raccoon’s canines are more blunt and less finely developed, being more adapted to crunching crayfish than catching mice.

bobcatteeth

The bobcat, an obligate carnivore, as you can see only possesses the teeth developed for meat eating: canines, premolars, carnassials, incisors.  If you have a pet cat who permits such familiarities, you can take a look at these teeth for yourself.  Fun fact: according to the people who take it upon themselves to research such things, felines also cannot taste sweetness.  Since they don’t eat fruit or other plant matter, it does not make sense for them to be able to detect the ripeness of fruit, which is what the ability to taste sweetness is really all about.

deerteeth

The white-tailed deer has only flat grinding teeth, as well as a single set of lower incisors, which it uses for stripping bark to eat during lean times.  There are actually species of deer which possess formidable canines, but they are more omnivorous and definitely not native to this country.

And now back to foxes.  It is partially the red fox’s ability to eat anything that has allowed it to thrive in the face of human expansion.  Our overflowing trash cans, roadkill-covered roads, and unattended pet dishes are like a buffet.  The fox’s big cousin, the coyote, has experienced similar success.  A large part of this success is also due to human’s extermination of large predators such as wolves and cougars, as well as our introduction of the fox to new areas, but that is a different and more contentious subject.

On the flip side, there is another fox native to Nebraska, the swift fox (Vulpes velox), which has not done so well since settlement of the country.  This has much more to do with habitat than diet.  It is strongly tied to grassland habitat and used to range nearly statewide.  Since much of its original habitat has been converted or degraded, it is now only found in the sparsely populated grasslands of the panhandle and is a state-listed endangered species.  The red fox, being a habitat generalist, has taken advantage of the range vacated by its smaller cousin.

Unfortunately, I must admit that I’ve never actually seen a red fox on our prairies, though I feel safe in assuming that they are here.  After all, this is wonderful habitat for them, with lots of wooded edges, prey, and forage.  They are generally fairly elusive creatures—I’ve seen more wild wolves in my life than I have foxes.  Though with the arrival of winter, I’m excited to keep an eye out for little canine tracks in the snow.

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Favorite Photos of 2015

As has become an annual tradition, I’ve once again put together a collection of my favorite photos from the last year.  Most of these have appeared in 2015 blog posts, although I think at least one or two haven’t.  (I’m not telling you which ones.)

You can view the photos in one of two ways.  First, you can simply watch the slideshow below – and you can click on the arrows to control the speed of the slideshow if you wish.  If the slideshow doesn’t work on your particular device, you can also (hopefully) watch the same show on the YouTube video below the slideshow.

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Thank you, as always, for reading this blog.  Please help me spread interest and enthusiasm about prairies and conservation by passing along this or any other blog post you think others might enjoy (including the three minute video I put together earlier this year).  Together, we can fight the perception that prairies are just boring patches of grass!

Have a wonderful holiday season and enjoy the final week of 2015!

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