A moose darts into the forest on Beaver Loop Road in Kenai, Alaska, during the Kenai River Marathon on Sunday, Sept. 26, 2021. (Photo by Jeff Helminiak/Peninsula Clarion)

A moose darts into the forest on Beaver Loop Road in Kenai, Alaska, during the Kenai River Marathon on Sunday, Sept. 26, 2021. (Photo by Jeff Helminiak/Peninsula Clarion)

Refuge Notebook: Mating systems of moose and caribou

Driving home the other day, my friend and I came across a big bull caribou chasing several cows down Kalifornsky Beach Road. One hundred yards behind them lagged a young bull trailing the group.

As the young bull attempted to approach the group of cows, the older bull wheeled around and slammed into the younger bull, driving him to the ground with his massive antlers. Having no chance in the fight, the smaller bull sprinted away as soon as he regained his footing.

That sighting quickly turned into a discussion of the caribou breeding system, commonly referred to as the rut, and how it differs from the more familiar moose rut on the Kenai Peninsula.

For caribou, pre-rut behaviors begin during late August and early September, when many caribou herds start their seasonal migrations between summer and winter ranges. While on these migrations, bulls begin to strip the velvet from their antlers and rake vegetation in order to strengthen their neck muscles and harden their antlers that will be used in fights for dominance during the coming months.

During this time, bulls also begin to produce increased amounts of testosterone and other steroid hormones, increasing muscle strength and giving rutting bulls their thick-necked appearance during the rut. As these hormones continue to take effect, bulls become increasingly irritable and aggressive, particularly toward other bulls.

By late September, sparring with other males begins to get more serious. By October, cow caribou come into estrus, and the rut goes into full swing. Most fights between bulls are brief and do not result in serious injuries. However, skirmishes between equally matched dominant bulls vying for access to cows can turn violent.

Compared to many other deer species, the caribou rut is a loosely organized affair. Caribou move into general rutting areas and form large aggregations with bulls and cows mixed together. Bull caribou are not territorial, but they do attempt to control a personal space around themselves and breed any receptive cows within this area.

Larger bulls follow groups of cows and try to prevent other bulls from breeding with the females within their perceived area. Cows generally want to breed with the more dominant bulls in the area, and so groups of receptive cows will often congregate around larger or more dominant bulls.

In contrast to caribou’s relatively disorganized breeding system, moose in Alaska use a more structured breeding system. Similar to caribou, bull moose begin to strip the velvet from their antlers in late August and early September. Again, bulls begin to produce more testosterone and other steroid hormones in preparation for the rut.

During September, bull moose begin moving into rutting areas, searching for cows, and they start marking these areas. Bulls rake vegetation to strengthen their neck muscles, but dominant bulls also begin to scent mark their rutting areas with urine.

Dominant bulls use their forefeet and antlers to scrape out large pits in the ground called wallows. Bulls also urinate in wallows and often roll around in the mud and urine to spread their scent and advertise their presence in the area.

As the bulls prepare their rutting areas and the rut gets into full swing, cow moose congregate in these open areas and form rutting groups around dominant bulls. Caribou typically don’t vocalize much, even during the rut. However, both cow and bull moose make interesting vocalizations to announce their presence and attract one another.

Dominant bull moose defend their rutting area and their group of cows, known as a harem, from other bulls. The dominant bull keeps his cows close and breeds the cows in his group as they come into estrus. Younger bulls, commonly called satellite bulls, will linger on the periphery of rutting areas trying to gain access to the females when the dominant bull is distracted.

However, the dominant bull will generally keep other bulls away from the cows and will do most of the breeding. When two dominant bulls meet in a rutting area, the battle for dominance and access to the harem can be epic.

For both caribou and moose, the energetic costs of the rut are great. During the productive summer months, bulls of both species build up remarkable fat stores. However, the energetic demands of the rut and injuries sustained during bouts for dominance can take their toll.

Bulls are sometimes seriously injured during these fights and may even die from their wounds. Some bulls will also expend too much energy during the rut and exhaust their fat stores before the end of winter. Injured or exhausted bulls often become easy prey for wolves and bears.

But, for those that make it through, the cycle begins again in spring when bulls of both species begin to grow their antlers for the next rut.

Dom Watts is a pilot and wildlife biologist at Kenai National Wildlife Refuge. Find more Refuge Notebook articles (1999–present) at https://www.fws.gov/refuge/Kenai/community/refuge_notebook.html.

More in Sports

Soldotna's Wayne Mellon works to a pin of Kenai Central's Zoticus Active at 189 pounds in a dual meet at Soldotna High School on Tuesday, Nov. 30, 2021, in Soldotna, Alaska. (Photo by Jeff Helminiak/Peninsula Clarion)
SoHi wrestling honors seniors in matchup with Kenai

Thanksgiving weekend gives many the opportunity to see family. The holiday gave… Continue reading

Strausbaugh, Hippchen take Turkey Skate

Soldotna hosted Kenai Central for the Turkey Skate at Tsalteshi Trails on… Continue reading

Kenai Central's Sawyer Vann controls Nikiski's Wyatt Maguire at 125 pounds Tuesday, Nov. 23, 2021, at Nikiski High School in Nikiski, Alaska. Vann notched a 7-6 victory. (Photo by Jeff Helminiak/Peninsula Clarion)
Area wrestlers collect mat time before Thanksgiving break

Area wrestlers got in some mat time Tuesday before the Thanksgiving break.… Continue reading

Assistant coach Taylor Shaw leads the Kenai River Brown Bears during a game Thursday, Nov. 18, 2021, against the Springfield (Illinois) Jr. Blues at the Soldotna Regional Sports Complex in Soldotna, Alaska. (Photo by Jeff Helminiak/Peninsula Clarion)
Brown Bears start search for new head coach

The Kenai River Brown Bears issued a press release Friday about staff… Continue reading

Kenai River Brown Bears forward Bryce Monrean tries to find a way through the defense of the Springfield (Illinois) Jr. Blues during a first-period power play Friday, Nov. 19, 2021, at the Soldotna Regional Sports Complex. (Photo by Jeff Helminiak/Peninsula Clarion)
Jr. Blues come back to take series from Bears

The Springfield (Illinois) Jr. Blues lost not only a 2020-21 season to… Continue reading

Soldotna junior Liam Babitt holds a grip on South Anchorage’s Britten Hamilton during the 215-pound final of the Lancer Smith Fall Varsity 2021 Invite on Saturday, Nov. 20, 2021 at the Menard Arena in Wasilla, Alaska. (Photo by Jeremiah Bartz/Frontiersman)
Soldotna crowns 4 champions at Lancer Smith

The Soldotna wrestling team finished fourth Friday and Saturday at the Lancer… Continue reading

Hockey roundup: SoHi sweeps in Kodiak; West wins End of Road tourney

The Soldotna hockey team swept Kodiak in the first high school games… Continue reading

A brown bear feeds on a salmon. (Photo by C. Canterbury/USFWS)
Refuge Notebook: Bears, uniquely built to respond to winter

With the new snow and temperatures dipping into the single digits, you… Continue reading

Kenai Central's Caden Warren surveys the ice against West at the End of the Road Tournament at Kevin Bell Arena in Homer, Alaska. (Photo by Sarah Knapp/Homer News)
Kenai, Homer hockey lose to open tourney

The Kenai Central and Homer hockey teams both opened the End of… Continue reading

Caden Triggs of the Kenai River Brown Bears celebrates his first-period goal against the Springfield (Illinois) Jr. Blues on Thursday, Nov. 18, 2021, at the Soldotna Regional Sports Complex in Soldotna, Alaska. (Photo by Jeff Helminiak/Peninsula Clarion)
Brown Bears topple Jr. Blues

By JEFF HELMINIAK Peninsula Clarion The Kenai River Brown Bears received two… Continue reading

Michael proposes to Sarah at the Kenai National Wildlife Refuge on Sunday, Nov. 7, 2021. (Photo by Ashlyn O’Hara/Peninsula Clarion)
Out of the Office: Falling in love one snowflake at a time

Do you want to know what I’ve been looking forward to the… Continue reading