COS 41-6: Changes in dates of emergence from hibernation by chipmunks, ground squirrels, and marmots at high altitude in the Colorado Rocky Mountains: An effect of climate change?
David W. Inouye, University of Maryland and Billy Barr, Rocky Mtn. Biological Laboratory.
Chipmunks (Tamius minimus), golden-mantled ground squirrels (Spermophilus lateralis), and yellow-bellied marmots (Marmota flaviventris) are common near the Rocky Mountain Biological Laboratory (2,886 m). All three hibernate for 6 – 8 months, during which there is usually significant snow cover. Since 1974 - 1976 Barr has recorded dates of first sighting of these species during daily spring observations. These dates have changed significantly during the study, but not similarly for all species. Marmot emerge about 28 days earlier now than they did in 1976 (typically before snow has melted from their burrows), and dates are now earlier for chipmunks (~10 days) and ground squirrel (~ 9 days) than in 1974. Marmot dates have changed progressively at about the same rate over years, while dates for the other two species trended toward later (3 weeks for ground squirrels, 10 days for chipmunks) for over two decades before rapidly reversing since about 1999. Dates for chipmunk and ground squirrel sightings are significantly correlated with each other, but not with marmot dates. Dates of chipmunk sightings are significantly correlated negatively with average April temperature and positively with the first date of bare ground at a permanent snow measurement station. Dates for ground squirrels show a similar pattern. Sightings of ground squirrels and chipmunks have been as much as 19-20 days earlier or later than each other, with a mean of 0. Marmots average 4-5 days earlier than the other species but with a tremendous range (23 days earlier to 47 days later), and over years the relationship has a significant non-linear trend. Changes by marmots may be related to global warming (April temperature); changes since 1999 in the other species might be related to regional climate change that has altered winter snowpack, or to an evolutionary change in behavior.