Microclimates II: How Do They Affect Animals?

Lon chatting with fellow environmentalists at Prairie Preview.

Wasn’t Prairie Preview great? Only two years at the Celebration Barn and we are already overcrowded. Bur Oak Land Trust’s executive director, Tammy Wright, mentioned that the search is already on for a larger space – with parking (and affordable).

Several folks mentioned that my latest microclimate blog was only about plants. What about the animals? Unfortunately, for many local animals, we just don’t have enough observation or published data, except for the birds. Fortunately, the Iowa Christmas Bird Count (CBC) has been happening for more than a century. For their 1996 book, Birds in Iowa, Tom Kent and Jim Dinsmore especially drew upon CBC info from 1960-1995. In Iowa, the largest and most dependably milder microclimates are narrow strips along our southern reaches of the two big rivers. If migratory birds are going to linger as winter comes on, it is going to be there. So I scanned Tom and Jim’s book and here is what I found regarding migrants seen during the annual Christmas Bird Count:

Pileated Woodpecker (p. 227) “…found on 94% of CBC’s along the Mississippi River and rarely on other counts.”

Blue Jay (p. 242) “…greatest number found on counts near Mississippi River.”

Black-Capped Chickadee (p. 251) “…greatest numbers found near Mississippi and Missouri Rivers.”

Tufted Titmouse (p. 252) “…greatest numbers near the Mississippi River.”

Brown Creeper (p. 255) “…most commonly found near the Mississippi and Missouri rivers.”

Winter Wren (p. 260) “…most commonly near the Mississippi River.”

Golden-crowned Kinglet (p. 263) “…most commonly found near the Mississippi and Missouri rivers.”

Eastern Bluebird (p. 266) “…most are found near the Mississippi and Missouri rivers.”

American Robin (p. 272) “By far, the most are found… near the Missouri River.”

Northern Mockingbird (p. 274) “…most consistently found along the Mississippi River and in southeastern Iowa.”

Northern Cardinal (p. 321) “Greatest numbers are along the Mississippi River.”

So yes, we do have evidence that at least some migratory birds do take advantage of milder local microclimates. It therefore also seems likely that they will be sensitive to cold air drainage microclimates and avoid those areas. Note that whole categories of birds are absent from the above list. One example is the group which migrates deep into the tropics, including the warblers, tanagers, orioles, and swifts, who are clearly not tempted by an upgrade in winter conditions. Also note that the CBC data is for early winter, and Kent and Dinsmore anticipate that as winter deepens into January and February, and food supplies start running low, some of those on the list may move further south. At a much more local scale, following cold air drainage nights, I can walk about my neighborhood above the drainage and see where deer have bedded down under dense, low-branched red cedar trees, which block their radiant heat loss to the night sky.

But for most of our critters, I still don’t have a clue how microclimates affect their lives. For example, do woodchucks preferentially hibernate beneath sunny, south facing slopes so their food supply greens up early in spring? Or does their hibernation favor a more constantly cold climate which doesn’t interrupt their sleep and maintains their metabolism during a moderate thaw and doesn’t produce meltwater leaking into their den?

What have you observed? Share it with us!