Q. I’ve noticed a lot more robins staying in my area during the winter in recent years. Why do some stay and some fly south?
A. Food availability is probably the major factor influencing the number of American robins that overwinter in an area, said Steve Kelling, a developer of BirdSource, a joint project of the Cornell Lab of Ornithology and the National Audubon Society. Heavy snow and ice also may play an important role, limiting the fruits and berries that the robins depend on during winter and early spring, said Kelling, director of information science at the lab.
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?
Q. Does a lower body temperature mean a longer life?
A. Some studies show a correlation between lower body temperatures and greater longevity, though there is no proof of a cause-and-effect relationship in humans.
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.