The end is near. Image credit: Mark Lenarz. (excerpted from slide show)
I recently was chided a bit for suggesting (without having provided a link to supporting scientific evidence) that the behavior of a central-Wisconsin black bear emerging from its den in early February might well be attributed to climate change. (See Black Bear, Bummed Out By Climate Change, Falls Asleep In Backyard ….)
Today I feel lucky, having stumbled onto some related science. The population density of northern Minnesota moose has been falling for years and bull moose are decreasing in proportion to cow moose. No, it’s definitely not a poaching problem; nor is it a human hunting or wolf-predation caused fall off (see below for some data). There is, however, a potential correlation of the long term Minnesota moose population collapse with climate change.
- Moose have an upper critical temperature of 14º C in the summer and -5 º C in the winter (Renecker and Hudson 1986).
- Moose increase their metabolic rate when these thresholds are exceeded in an attempt to maintain core body temperature.
- Non-hunting mortality was correlated with temperature indices, both seasonally and annually and these temperature indices have been increasing over the last 50 years.
- If increasing temperatures are the cause for the decreases in survival, the decline of the northeastern population will take place even more rapidly.
From the same presentation, here are summations of mortality causation and population trend.
Note: I am not personally suggesting that Minnesota moose are dying off mainly because they’re too hot, although, not being an expert, I can’t exclude the direct significance of heat stress, nor can I weigh the impacts on moose of changed seasons. The best thing to do if you are interested in understanding this is to dive into the full presentation and give it some consideration before you comment.
What I am saying, in general – regarding surrogate indicators of climate change – is that a bear crawling out of its den after a two-day Wisconsin February warm up is not a behavior that I’ve ever heard of before. There’s no evolutionary advantage for the bear to then fall asleep in the snow where he is vulnerable to predators. Sure…it happens in March or April; but, a February den emergence signals a change in nature.
Back to Bullwinkle.
Moose evolved to live in a boreal-like forest characterized, in part, by their fitness inside a certain band of seasonal temperatures. When these thermal optima shift upward, individual animals may migrate north and/or the overall moose population will decline. It is the nature of living things. Otherwise we’d have tapirs in Oklahoma and alligators in Maine.
So, I’m sticking with my intuition on this subject. What’s good for the Tea Party is good enough for me. Bears should be in their Wisconsin dens in February and Moose should flourish across northern Minnesota, assuming human-caused habitat changes and disease are shown not to be likely causes of the crash, for example.
All there is left to debate is whether and to what extent we humans are causing the climate to change.
If I lived in Minnesota and liked to hunt I would want to get to the bottom of this and would offer what ever support I could to the researchers studying the population crash. Same if I were a company making a rifle capable of downing a bull moose.