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Darn Gophers…

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People who live in the country tend to view “gophers” in much the same way city people view rats. Suffice it to say, neither animal is particularly popular.

Much of the time, when farmers, gardeners, or groundskeepers are complaining about “gophers”, the animal in question is actually a ground squirrel – and around here it’s usually a thirteen-lined ground squirrel. Although they are beautiful little animals, thirteen-lined ground squirrels have run afowl of humans because their preferred natural habitat of short-cropped grassland is very similar to that found in many yards, baseball diamonds, gardens, and crop fields. When ground squirrels move into those human-built habitats, their burrowing and feeding behavior tends to get them in trouble.

 

Thirteen-lined ground squirrels are very attractive animals - unless they're eating your garden plants or digging holes in your landscaping.

Thirteen-lined ground squirrels are very attractive animals – unless they’re eating your garden plants or digging holes in your landscaping. There are actually two ground squirrels in this photo – can you find the second one? Click on the photo to see a larger and sharper version of it.

Thirteen-lined ground squirrels (Ictidomys tridecemlineatus – formerly Spermophilus tridecemlineatus) are found throughout much of central North America. They are 5-7 inches in length, not counting their 4-6 inch tail. Their name comes from the combination of light and dark stripes that run lengthwise along their body. The lines of spots within the darker stripes are particularly striking.

Thirteen-liners have a high-pitched call – among others – that sounds much like a bird. In fact, it took me several years to figure that out. I know my grassland bird calls very well, but couldn’t for the life of me figure out what bird species kept calling but never flushing as I moved in to investigate. I finally realized it wasn’t a bird at all, which made me feel both embarrassed for being so badly wrong and satisfied that I wasn’t woefully ignorant of some common bird call.

There are several kinds of burrows made by thirteen-lined ground squirrels, each with its own purpose. Nesting burrows can be 15-20 feet long, with multiple entrances. Hiding burrows are usually scattered around nearby to provide a quick escape, but those burrows are typically very short and have only one entrance. During the winter, the ground squirrels hibernate in burrows that extend below the frost line and the entrance is plugged up until the ground thaws enough in the spring that the hungry inhabitant can burrow back out again. In all cases, thirteen-lined ground squirrels disguise the entrances of their burrows by scattering the excavated soil away from the hole itself.

Ground squirrels are themselves well camouflaged, and help disguise their burrows as well, by spreading soil out away from entrances.

Ground squirrels are themselves well camouflaged, and help disguise their burrows as well, by spreading soil out away from entrances.

Thirteen-lined ground squirrels eat seeds throughout the year, but favor them most in the fall as they prepare for hibernation. During the spring and summer, they consume green leaves, fruits, and flowers from many plants, but are also fairly significant predators, feeding on worms and insects (especially caterpillars, beetle larvae, and grasshoppers) as well as small vertebrates. In fact, grassland bird studies have shown thirteen-lined ground squirrels to be a very significant predator of both eggs and young birds in some prairie landscapes.

In my part of the world (east-central Nebraska), there are two species of ground squirrels, which are differentiated by both habitat preference and coloration. While thirteen-lined ground squirrels have distinctive striping and prefer to live in very short vegetation, Franklin’s ground squirrels are found in tall grass and are unstriped.  Franklin’s ground squirrels are rarely seen, but we spot enough of them in our Platte River Prairies to assume they must be fairly common here. I’d like to know much more about their habits and needs because they are a species of conservation concern – especially in more eastern tallgrass prairie regions.

While Franklin’s ground squirrels are fairly uncommon in many places and difficult to find when they do occur, thirteen-lined ground squirrels are very common and abundant – much to the chagrin of those people who find themselves at odds with them. Thirteen-liners enjoy the more intensively grazed portions of our prairies, and seem able to find new patches of grazed prairie as we change the location of that habitat type through time.  I’ve often wondered whether an individual ground squirrel actually relocates each year to keep up with those shifting patches of short-cropped prairie, or if populations just increase (and/or become more visible!) where our grazing is most intensive each year.

Ground squirrels are important prey for many of the larger predators in our prairies, including hawks, coyotes, snakes, and badgers. In fact, their popularity as badger food can compound the hassles associated with having thirteen-lined ground squirrels living in cultivated or landscaped places. In our own prairie seed nursery, ground squirrels enjoy living and running around in the plots and mowed trails between them – and we can (mostly) live with whatever damage they cause. However, the giant holes created by badgers digging ground squirrels out of their little burrows are a lot harder to ignore.

Darn gophers…

Watching a Wetland Breathe

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It’s amazing what you can see when you compress time.

Back in October, I posted some early results from a timelapse photography project at our Niobrara Valley Preserve.  That project is helping document the recovery of the property from a wildfire and to see other changes that our eyes would otherwise miss.  We’re hoping to learn just as much from a similar, though smaller, timelapse project along a restored wetland/stream complex in the Platte River Prairies. Last week, I got my hands on the images from that project and have been looking through them to see what we can learn.

So far, one of the most fascinating things I’ve seen comes from a series of images from July 2012 – right after the camera was installed.  As I scanned through the photos, I realized that one little wetland pool kept changing size.  Its water level (exposed groundwater) was going up and down, making the pool bigger and smaller.  Looking more closely, I realized that it was happening in a regular daily pattern.  I’ve put a selection of images from a three day timeframe into a slideshow below.  If you let your cursor hover over the slideshow window, you can click the arrows to move through the images more quickly.  Watch the water level in the pool in the center of the photo – it starts out full in the morning, empties as the day goes along, and then is full again the next morning.  This same pattern repeated itself over and over throughout the summer.

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I shared what I was seeing with John Heaston, The Nature Conservancy’s Platte River Program Director (in Cozad, Nebraska), who said the pattern is a great illustration of the effects of evapotranspiration – the process through which water moves from the surface of the earth to the atmosphere.  Evapotranspiration is a combination of direct evaporation of exposed water and plant transpiration – the movement of water out of a plant’s stomata (pores in their leaves).

Plants try to regulate how much water they lose through their stomata by opening and closing those pores, but transpiration is also strongly affected by light, heat, humidity, and wind.  During hot, dry and windy days, plants pull a lot of water in through their roots and then lose it into the atmosphere as they try to cool themselves.  In dry soils,  plants may shut their stomata altogether during the hottest part of the day in order to conserve moisture.  In wetlands, however, plants have abundant water, so they can continue transpiration through the heat of the afternoon.  Add that high rate of transpiration to the evaporation of standing water during those same sunny afternoons, and you have evapotranspiration in high gear.

What’s exciting to me about these timelapse images is the opportunity to watch evapotranspiration happen.  The plants in the wetland are pulling so much water from the ground during the day, the local level of groundwater drops by at least a few inches.  During the night, transpiration slows dramatically, and that groundwater level recovers.  Interestingly, the stream to the left of the little pool doesn’t appear to change during the day.  While it doesn’t appear to have a strong flow, there is presumably enough water coming from upstream to negate any losses from plant transpiration, so the level of water stays stable through the day.

Watching the repeating pattern of dropping and rising water levels in a wetland is fascinating.  It’s as if we’re watching the earth breathe – which, in some ways, we are.  It’s also a great example of the power of timelapse photography.  By condensing time, we can see patterns we would otherwise miss.

To see more examples of timelapse photography, check out the Platte Basin Timelapse Project’s website.  They have one of their cameras on this same wetland (separate from the one that produced the images shown above) and you can see a couple years’ worth of images in a few minutes.

The other interesting aspect of both sets of timelapse imagery from this wetland is that 2012 was the driest year on record for this area.  Most streams, rivers, and wetlands went dry last summer, including most of the stream that runs through our property.  However, throughout the entire summer, the wetlands and stream in the stretch shown by these cameras maintained a fairly steady water level.  It’s one of the reasons we’ve spent so much effort trying to restore the site – we feel like we need to take full advantage of the unique resource there.  We’re not sure why the groundwater is so strong in that particular place, but in dry years, the fish, birds, invertebrates, and plants sure appreciate it.  So do we.

Thanks to John Heaston and Tala Awada for technical help with this post.  Any errors are mine, not theirs.  In addition, thanks to Michael Forsberg and Jeff Dale of Moonshell Media for partnering with us on the set-up of the timelapse project(s), and to Steven Speicher for his help and advice.