One of the changes that appears to be occuring in the North American climate, involves greater snow pack in the winters at high elevation, and warmer temperatures at low elevation. This could have two important effects. 1) Animals that are migratory may find that environmental cues from one area to another have changed (more on this below). 2) The "average" temperature may appear fairly constant despite great changes at either end of the altitudes studied. A report a few years back looked specifically at two species. One, a marmot, hibernates at low elevation and moves to higher elevations after coming out from hibernation. The second species, a robin, flies to higher elevations when certain environmental cues stimulates such behavior. Both species are migrating earlier and earlier, as low altitude climate warms. This creates a probelm, however, because the thicker snowpack prevents these species from finding food at the higher altitudes. Here is the abstract of the article: Calendar date of the beginning of the growing season at high altitude in the Colorado Rocky Mountains is variable but has not changed significantly over the past 25 years. This result differs from growing evidence from low altitudes that climate change is resulting in a longer growing season, earlier migrations, and earlier reproduction in a variety of taxa. At our study site, the beginning of the growing season is controlled by melting of the previous winter's snowpack. Despite a trend for warmer spring temperatures the average date of snowmelt has not changed, perhaps because of the trend for increased winter precipitation. This disjunction between phenology at low and high altitudes may create problems for species, such as many birds, that migrate over altitudinal gradients. We present data indicating that this already may be true for American robins, which are arriving 14 days earlier than they did in 1981; the interval between arrival date and the first date of bare ground has grown by 18 days. We also report evidence for an effect of climate change on hibernation behavior; yellow-bellied marmots are emerging 38 days earlier than 23 years ago, apparently in response to warmer spring air temperatures. Migrants and hibernators may experience problems as a consequence of these changes in phenology, which may be exacerbated if climate models are correct in their predictions of increased winter snowfall in our study area. The trends we report for earlier formation of permanent snowpack and for a longer period of snow cover also have implications for hibernating species. The reference is: PNAS Vol. 97, Issue 4, 1630-1633, February 15, 2000 Climate change is affecting altitudinal migrants and hibernating species David W. Inouye, Billy Barr, Kenneth B. Armitage, and Brian D. Inouye Note that these species are migrating weeks ahead of schedule. Note also that the increased snowpack has left the "melt date" largely unchanged at high altitudes, and note that this is particularly problematic for animals that have evolved with a certain synchronization of micro-environments.