Extended summers hurting southern moose populations

Posted 10/25/22

Shiras moose, the southernmost moose population on earth, are in decline, according to a new study by researchers at the University of Wyoming. 

While populations of moose stretch around the …

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Extended summers hurting southern moose populations


Shiras moose, the southernmost moose population on earth, are in decline, according to a new study by researchers at the University of Wyoming. 

While populations of moose stretch around the globe in northern climates — across the northern part of North America but also in Scandinavia, Europe, Russia and even into China — Shiras moose live in the Rocky Mountains reaching as far south as Utah and Colorado and occasionally wandering into places like Nebraska in search of habitat. 

Unfortunately, as the climate warms and summer continues to stretch deeper into fall, birth rates have been dropping. The study suggests a number of reasons, but the species’ need to regulate their internal body temperatures through behavior (they don’t have the ability to sweat) is cited as the most compelling evidence.

The condition is called thermoregulatory behavior. In other words, when moose get hot they are forced to seek water or shade. They also seek moist ground to bed down, which helps lower their internal temperature, or to move higher into the hills seeking lower temperatures without going too high where lunch isn’t readily available. 

Moose feed for about eight hours a day for most of the year. During summer, they consume 30-40 pounds of vegetation a day. 

The bigger the moose, the harder it is to deal with the heat. As summers grow more intense and the heat encroaches on fall, it affects breeding habits. 

University of Wyoming graduate student Rebecca Levine leads the Meeteetse Moose Project for the Monteith Shop at the university. For the past three years, she has been immersed in everything moose. She was invited to share her experiences at the Draper Natural History Museum’s Lunchtime Expedition speaker series earlier this month.

Levine isn’t a drive-by scientist. She puts in long days in the isolation of the Absaroka Range conducting her research. 

“Much like moose, Levine prefers to be in or around water whenever possible,” said Corey Anco, interim curator of the Draper.

Recently Levine wanted to observe a cow moose with her calf near the Jack Creek drainage. Instead of walking up the drainage with the possibility of disturbing them, she took the long way around. 

“I really didn’t want to disturb the pair. So instead, what we did is we hiked up Willow Creek and over Phelps mountain,” she said.

From 300-feet above, she was able to watch the pair without disturbing them. She told the fully engaged crowd at Coe Auditorium the time and effort paid off. 

“I think it’s one of my favorite things to get to watch them totally undisturbed and to see, like, how they are when no one’s watching.”

Her research is based in habitat near Meeteetse. An estimated 100 moose live in the region and 30 of those have been collared for the research. The collars aren’t your normal GPS data generators. When the researchers catch the moose (through immobilizing drugs), they do a field ultrasound to check for pregnancy. If the cow is pregnant, they fit them with a vaginal implant transmitter. 

The transmitter will trigger a camera on the collar to start recording so the team can capture the first six minutes after the birth event. For the rest of the summer, the camera takes 10-second videos every 60 minutes during daylight hours.

Collars on bulls are set to drop after three years, while collared females are recaptured every year so the team can download the data and do another ultrasound. The videos give researchers clues to their behavior, interactions with other moose including their calves, their dietary choices through the seasons and their habitat.

One significant observation they have documented is: The bigger the moose, the more sensitive they are to the changing climate. During the rut, which happens in mid-September through October, males travel long distances, fight with other males for dominance and rarely stop for a meal. When the season is warmer than normal, the largest bulls are at a disadvantage, more often needing to cool down than smaller bulls. 

The question Levine seeks to answer: Do higher temperatures and longer summers result in more successful breeding by smaller bulls and fewer dominant bull genes being passed on?

“Warmer falls could be impacting whether or not the best genetics get passed along into the population,” Levine said.

If the breeding starts to shift to later in the season, due to the restrictions of heat, it will adversely affect calves, she said.

“There are actually really big consequences for moose calves that are born too late in the summer,” she said. “Moose have to gestate for a certain amount of time, that’s not super flexible. And if the rut shifts later, that means moose calves are born later. And that means that they’re smaller and weaker when winter sets in.”

The team has found very few adult moose face predation, but a weak calf going into winter is a real target for large carnivores.

The study does not look at populations in the Bighorns. It’s not uncommon to see several moose in the mountains east of the Big Horn Basin, which may give the impression that the species is doing just fine. Yet, Levine points out that the population, which was introduced in 1948, don’t have to compete with large carnivores and were translocated to an area with lush vegetation.

“What we see is often when they’re introduced, there’s this huge spike like what we’re seeing in the Bighorns,” she said. “Then they might start to actually deplete that habitat and the population will start to crash. Right now they still have really wonderful habitat to use. Also, there are no wolves and grizzly bears there.” 

Moose are still hunted in the state, but the number of licenses available has been falling for quite some time. In the past decade, the number of permits has fallen from just under 500 to 369 last year. 

Levine was asked, if we’re worried about the state’s population of moose, why do they still allow hunting? She said with moose, Wyoming focuses on hunting bulls in populations that aren’t doing so well. 

“We actually don’t need as many males on the landscape as we do females. Females are the ones that are reproducing, they’re raising that calf and putting all that energy in,” she said.

If there were equal numbers of males and females in the environment, it wouldn’t be representative of how a natural habitat with an intact predator community works, she said. And despite there currently being predators in much of the available habitat, there are still far fewer predators than there would have been before humans entered the habitat.

In 2021, 39 cows and calves were harvested in the state while 287 bulls were harvested.

“Hunting simulates that lower number of males, which means that there’s less stress on the environment for females, and potentially, the females can do better,” she said.