interestiINTERESTING BEAR STUDY

[T.R. Michels]

The bears I am studying in Arkansas are actually descendants of bears that came from here in MInnesota, and it appears their yearly clock is still kind of tuned in to seasonal changes here in Minnesota, because my Arkansas bears are doing the saame things Dr. Lynn Rogers bears ( your know - HOPE) are doing in Ely, MN. And i know that because we are in contact at least once a week.

It is interesting to compare notes about bear behavior, in two widely separated States - because we learn that what happens at one latitude, may not happen at another latitude, just lke with whitetails.

Interesing Notes:

No one was sure how long a sow might stay in estrus, but they did know that a sow may breed with more than one male , because DNA studies show the cubs may have different fathers. I had one sow with the same boar for 10 days - long estrus period.

Many of us here in the Upper Midwest, thought that bears go nocturnal in the fall (not just as a result of hunting pressure but) as a result of their putting on a lot of fat, and growing long back fur - which makes for a pretty heavy winter coat in the summer and fall.

BUT - in Arkansas, I've got boars over 400 pounds, and bears of all ages, actively feeding at temperatures over 90 degrees - and there is no hunting pressure. on the 3000 acre preserve, but theris around it - so these bears are hunted. HIght temps so not bother black bears.

Right now they are active from about 8 AM to 5 PM, with peaks at around 10 AM and 4-5 PM - with basically no activity at night.

But, that pattern will change in late summer, because of their biological needs, which leads to different yearly phases.

Yearly Black Bear Activity Phases
Phase l; Winter
Bears do not really hibernate, they go through what is termed as torpor. In this state they go through continuous dormancy, with distinct decreases in heart and metabolic rate. They may use up to 4,000 kilocarories per day, which is mainly body fat. But they do not eat, drink, urinate, or defecate during this dormancy. They can reduce their oxygen consumption and metabolic rate by half, and they breathe only once every 45 seconds. Their heart rate can drop periodically to 8-21 beats per minute, and blood flow to skeletal muscle, particularly the legs, can be reduced by 45% or more, making some bears slow to arouse and run away in winter. Blood perfusion rates of peripheral tissues can fall below levels needed for aerobic metabolism in humans. (In Arkansas bears have been seen after hibernating, as early as Mach 23.)

Stage 2; Early Spring
Walking hibernation is the 2-3 weeks following emergence from the den, when metabolic processes adjust to normal summer levels. During walking hibernation, bears voluntarily eat and drink less than they will later during normal activity. They also excrete less urine, nitrogen, calcium, phosphorus, and magnesium.

Stage 3; Summer
Normal activity typically lasts from green-up in spring to the onset of hyperphagia in midsummer or fall, depending upon region. During this stage, bears with unlimited food eat 5,000 to 8,000 kcal per day. If they are denied water and food during this stage, they cannot duplicate hibernation responses. Instead, they become dehydrated, utilize muscle for energy, and accumulate nitrogenous wastes in the blood, which can be fatal.

Stage 4; Late Summer / Early Fall
Hyperphagia is a period of excessive eating and drinking to fatten for hibernation. Black bears with unlimited food and water ate 15,000 to 20,000 kcal per day and drank several gallons. Large amounts of water are needed to process the large amounts of food and rid the body of nitrogenous waste. Daily urine volumes for two bears were 2-4 gallons (8-16 liters). Nitrogen losses were 2.4 to 3.7 ounces (69-104 grams) (Nelson et al. 1983). They usually become nocturnal at this time.

Stage 5; Late Fall
Fall transition is a period after hyperphagia when metabolic processes change in preparation for hibernation. Bears voluntarily eat less but continue to drink to purge body wastes. They become increasingly lethargic, resting 22 or more hours per day, often near water. Active heart rates fall from 80-100 per minute to 50-60 per minute, and sleeping heart rates fall from 66-80 per minute to less than 22 per minute.(Arkansas bears start searching for dens in early October, and most have denned by late December.)