The descent of the “polar vortex” into the upper midwest during December and January resulted in a long drought in deer observation in the backyard. The previous high of 19 deer in the backyard herd has declined substantially over the past few years to 7 last year, and now to 3 this year. But two days ago, when the temperature hovered right at freezing (warm front!), a lone deer appeared in the backyard to forage in the wildflower garden.
I have written earlier posts on strategies deer use to survive the long, cold winters of the upper midwest — click here to read more about that. Basically, their strategy is believed to consist of fattening up in the fall, reducing winter metabolism and activity, and coasting on reserves until spring with occasional bouts of foraging when weather permits.
However, careful monitoring of deer activity by telemetry in the winter has revealed that deer are more active (both metabolically and physically) than previously believed. Deer actually get more active when temperatures drop below about 8 F (-13 C), but then settle down to wait for better weather when temperatures drop below -8 F (-22 C).* So the intense cold we experienced in Dec-Jan probably explains the lack of deer sightings, as they temporarily ceased their ramblings through the backyard.
Most of the does are pregnant with singleton or twin fawns during the winter, and this means an increased metabolic expenditure for them throughout the period of coldest weather. First-year offspring are still growing (albeit slowly) to reach adult size all winter, so they too experience higher metabolic costs associated with growth.
It all translates to finding enough to eat — and there isn’t much out there. But they just keep trying anyway.
* Schmitz, OJ. 1991. Holarctic Ecology 14: 104-111.