For example, a comparison of maps of snow-covered areas in January and February 1999 with maps showing the reports of robins during the Great Backyard Bird Count of Feb. 19-22, 1999, clearly showed a sharp decrease in reports in areas where there was snow cover.
A similar comparison for the western Great Lakes region found only three reports of robins in Wisconsin, Minnesota and Michigan where snow cover exceeded 5 inches, while some areas with less cover had many more robins, even flocks of up to 1,200.
Interestingly, in metropolitan areas like Minneapolis-St. Paul and Detroit, many robins did overwinter that year, because ornamental fruit trees like hawthorns and mountain ash provided a generous food supply.
Does being colder mean growing older?
A large study published in 2011 in The Journals of Gerontology compared the ages and body temperatures of 18,630 people, ages 20 to 98, who had oral temperature readings as part of a standardized health appraisal at a health maintenance organization.
Mean temperature decreased with age, with a difference of 0.3 degrees Fahrenheit between the oldest and youngest groups, even after controlling for sex, body mass index and white-blood-cell count.
“The results are consistent with low body temperature as a biomarker for longevity,” the researchers concluded. As for possible reasons for such results, they suggested identifying genetic influences on body temperature and examining the effect of body temperature on multiple cellular processes.