Moose lower body temperature and heart rate in winter
Using surgically implanted sensors, researchers have for the first time been able to measure precisely what happens in the body of the moose during the changing seasons. Their body temperature and pulse are at their lowest in early spring - when conditions are the toughest.
Wintertime in the north is challenging for many animals. While the bears go into hibernation and wait for better times, the moose are still out and about in the woods.
But how does this majestic beast adapt to the cold and lack of food?
A new Swedish-Norwegian study shows that the moose save energy simply by lowering their heart rate and body temperature.
One of the researchers behind the study is Wibeke Neumann. “It’s exciting to learn how the moose’s metabolic rate decreases when the food supply is less,” she says in a press release from the Swedish University of Agricultural Sciences.
The Swedish researchers are collaborating on the study with Norwegian researchers at Inland Norway University of Applied Sciences.
Functioning with minimal activity
The result isn’t surprising, says Olav Hjeljord, professor emeritus at NMBU, the Norwegian University of Life Sciences.
“During the winter, the moose function with minimal activity,” says the retired moose researcher.
Nevertheless, this is the first time researchers have been able to measure what happens in the body of the moose during the changing seasons with such precision.
The new information is that moose lower their body temperature, according to Hjeljord.
“It’s interesting that moose are a little bit like animals that go into hibernation and lower their metabolism and temperature,” he says.
Half a degree difference
The body temperature of the moose fell by an average of half a degree – from a peak in July to the lowest levels in March.
So we’re not talking a big change here.
By contrast, Norwegian researchers in 2016 found that a bear's body temperature drops from 37.5 to 31-34 degrees Celsius while hibernating. You can read more about this study at what was then called Hedmark University College.
According to the Store norske leksikon (Norwegian lexicon) the common hedgehog’s body temperature drops almost to the freezing point during its winter hibernation.
Surgical sensor implants
The heart rate measurements of the twelve female moose, on the other hand, showed a greater seasonal difference.
The heart rate topped out at an average 72 beats per minutes in July.
The lowest heart rate measurements were 41 beats per minute at the beginning of March.
The large drop in pulse rate is in line with the moose resting a lot during the winter, Hjeljord says.
To obtain the measurements, the researchers first had to anesthetize the twelve female moose.
Then they surgically implanted sensors to measure body temperature and heart rate and attached a GPS collar around the neck of each moose.
Tough going for moose in March
In the winter, food availability for moose is limited.
They have to survive on hard twigs and shoots – which are tough to digest and not very nutritious – and on their body’s fat reserves.
The cold doesn't make matters any easier.
However, the researchers observed that the very lowest heart rate and body temperature in the moose occurred in March.
This finding is very interesting, Hjeljord says .
“It’s precisely during this period that conditions are the hardest for these animals. This is when we see most of them dying, too. They’ve used up a lot of their body’s reserves and the browse has been depleted, so that’s the tough period. So it makes sense that they’re trying to save a little extra energy then,” says Hjeljord.
His research team focused on measuring the amount of droppings moose produce. They also found that the least moose scat was found in March and April, which is another sign of a low metabolic rate in the moose.
Like fresh shoots
Now, at the start of summer, the eating is good again for moose.
The large ruminants love the newly sprouted leaves, because they are nutritious and easy to digest for the moose. Rowan is a favourite species, according to Hjeljord.
The female moose need plenty of nourishment to provide their calves with enough milk. And all moose have to eat heartily throughout the summer and fall to put on enough weight to survive the next winter.
Fortunately, the moose are at least able to make those extra kilos last longer by slowing down their metabolism.
Translated by: Ingrid P. Nuse
Anne Randi Grysli et al.: Seasonal hypometabolism in female moose, Frontiers in Ecology and Evolution, 2020. https://doi.org/10.3389/fevo.2020.00107