EPOW - Ecology Picture of the Week

Caribou on Snow

Caribou (Rangifer tarandus), Family Cervidae
Northwest Alaska, USA

Explanation:  Dots on white!  This is a massive migration of caribou in remote northwest Alaska, USA.  

It is mid-July here in the high arctic, and snow persists along some valley bottoms and streambeds (for now, anyhow).  And here gathers the massive numbers of the Western Arctic Herd of caribou, one of many named herds in this huge state.  We are in the extreme northwest corner of Alaska, not far from the coast, between the village of Kivalina and Point Hope (see map on this page).

But why do they gravitate to these residual snowfields?  Ever been in tundra country in the summer?  The density of mosquitoes and black flies and friends can be astounding.  The caribou seek the snow cover as a refuge and relief from being constantly pestered and bitten, as the insects typically do not occur there.  
  

Also, at this time of year, the Western Alaska Herd is using this area as a post-calving resting site, after having dropped calves on calving grounds further east.  
   

Difficult to see in these photos, above (but see below) are thousands of caribou trudging across the brown snowless tundra toward these snowy refuges.  They typically make hundreds of criss-crossed trails across tundra, slopes, ravines, and mountainsides, in their ceaseless annual migration circuit.  
  

In the photo above, you can see them spread out on the tundra in the foreground, foraging mostly on caribou lichen (well named, eh?).  

And that's another story.  Their primary foodstuff, especially in winter, is the ground-growing lichen, which the caribou reach by pawing through the snow.  But with climate change, wintertime is bringing greater instances of "rain-on-snow" events.  This causes the snow to freeze to ice, making it difficult to impossible for the caribou to reach the lichen beneath, causing malnutrition or starvation.  

Further, climate change in the Alaskan arctic is causing warming of the air, and ground with its permafrost, at about twice the rate of warming elsewhere on the globe.  This, in turn, is causing a "greening" of the arctic, with a northward expansion of shrubs and woodlands ... that is covering or replacing the barren-ground tundra environment and its critical supply of caribou lichen for these herds.  

And that's not all that a shifting climate is doing.  It is also causing far greater incidences of tundra fires (from lightening strikes, mostly), which changes the vegetation.  And a shifting climate is also changing the relationships and interactions between caribou and other species, principally with their main predator, wolves.  

  
And, in the above, final image, we are looking northeast across the rolling tundra to the De Long Mountains, the western part of the Brooks Range that borders the North Slope, beyond, fringing the Arctic Ocean.  
  

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This EPOW episode is being presented in mid-December, as we edge toward another seasonal holiday where caribou's cousin, the reindeer, plays a central role in song, festivities, and folklore.  

May the caribou and their cousins persist and thrive in the face of the major environmental and climate changes we are all facing (and ... creating).  
   
  

Information:
    Hansen, I. J., C. J. Johnson, and H. D. Cluff. 2013. Synchronicity of movement paths of barren-ground caribou and tundra wolves. Polar Biology 36(9):1363-1371.
    Joly, K., R. R. Jandt, and D. R. Klein. 2009. Decrease of lichens in Arctic ecosystems: the role of wildfire, caribou, reindeer, competition and climate in north-western Alaska. Polar Research 28:433-442.
    Joly, K., and D. R. Klein. 2011. Complexity of caribou population dynamics in a changing climate. Alaska Park Science 10(1):26-31.