A black bear mother and her three cubs on Skilak Lake Road in the Kenai National Wildlife Refuge (July 2017). Delayed implantation of the fertilized egg prevents pregnancy from starting until late fall, several months after mating. (Photo courtesy Kenai National Wildlife Refuge)

A black bear mother and her three cubs on Skilak Lake Road in the Kenai National Wildlife Refuge (July 2017). Delayed implantation of the fertilized egg prevents pregnancy from starting until late fall, several months after mating. (Photo courtesy Kenai National Wildlife Refuge)

Refuge Notebook: Winter wildlife babies on the Kenai National Wildlife Refuge

Being six months pregnant in the dead of winter (as I am) has its challenges — from trying to zip up a coat that’s too small over an ever growing belly, to hobbling around in the snow without falling to open and close the driveway gate. There is also continually braving the freezing temperatures in search of the novel foods I crave. All of this got me to wondering how Alaskan wildlife handle their winter pregnancies.

Most mammals mate during the fall and give birth in the spring, but a select few actually give birth in the late winter or early spring. Some of the earliest mammals to give birth are brown and black bears, and wolverines, because they have adapted the reproductive strategy called embryonic diapause or delayed implantation. This process allows the animals to mate early in the year without becoming pregnant right away. Instead of the fertilized egg implanting in the walls of the uterus immediately, the egg develops into an eight-celled blastocyst that remains floating in the uterus in this dormant stage. The blastocyst eventually implants in the uterine wall if certain physiological requirements are met; at that point, it becomes a fetus.

Bears mate between May and July but implantation will not occur until October or November. If the female bear is able to gain enough weight before hibernation, the blastocysts will implant into the walls of the uterus and proceed to develop into cubs; otherwise the pregnancy will be terminated. Once she enters her den she will not eat or drink again until she emerges in June. Pregnancy demands a significant amount of energy and nutrients from the mother, and the entirety of her 6- to 8-week pregnancy is spent in the den.

ADVERTISEMENT
0 seconds of 0 secondsVolume 0%
Press shift question mark to access a list of keyboard shortcuts
00:00
00:00
00:00
 

Between January and March she will give birth to up to four cubs that are only 13 ounces when born and will spend the next 3 to 5 months nursing in the den. There are eight months between mating and birth, but the female is actually pregnant for less than two months of that time.

Wolverines are solitary animals that roam around the Kenai Mountains at very low population densities. Delayed implantation allows them to take advantage of meetings by mating when they have the opportunity, anytime from May to August. Similar to bears, the embryo will not implant unless the female wolverine has gained enough weight before she burrows into a deep snow den. Pregnancy usually lasts 4 to 6 weeks, and babies or kits are born in February through mid-March. Wolverines typically have two but sometimes up to four kits in each litter. When born, the kits are tiny and pure white, relying on their mother’s milk until they emerge in mid-May.

One of the earliest birds to nest here on the Kenai Peninsula is the great horned owl. Like most owls, these do not construct their own nests. Instead, they must find a suitable nest in tree cavities, cliff ledges, or old nests of other large birds. Great horned owls begin courting near the end of February, lay 2 to 5 eggs in April, which they then incubate for a month. Juvenile great horned owls rely on their parents to care and feed them until the fall.

In contrast, songbirds like orange-crowned warblers usually lay eggs in June or July and the fledglings are ready to leave the nest within a few weeks. It’s likely that great horned owls nest so early because it takes so long for their young to grow and mature. This timing also allows juveniles to practice hunting when the weather is mild and prey is plentiful.

Insects are a different story, invoking many reproductive strategies. Depending on the species, they overwinter as adults, larvae, pupae, or even eggs. To me, an insect overwintering as an egg is the closest to being pregnant. One genus (Aedes) of mosquito on the Kenai Peninsula overwinters as eggs and are known as “snow melt pool” insects. These eggs hatch in the icy water that forms as snow melts in April or May, emerging as adults in late May and early June. The rusty tussock moth (Orgyia antiqua) also overwinters as eggs that are laid on the outside of the female’s cocoon. These hatch in early spring as soon as foliage appears.

Animals that birth in late winter or early spring have some interesting reproductive strategies. To be honest, though, I think bears have the right idea. I wouldn’t mind spending the majority of my pregnancy sleeping in a cozy den!

Kyra Clark is a seasonal biological technician at Kenai National Wildlife Refuge. Find more information about the Refuge at http://www.fws.gov/refuge/kenai/ or http://www.facebook.com/kenainationalwildliferefuge.

More in Life

A clay tea set on display at the Kenai Potters Guild exhibit, “River,” hosted by the Kenai Art Center. (Jonas Oyoumick/Peninsula Clarion)
Making art shaped by the river

Kenai Potters Guild Clay On Display exhibit focuses on a river’s effect on self and community.

A clipping from a Homer Death Cafe poster.
Homer group tackles death and dying through open conversations

The local group mirrors a growing worldwide trend of “Death Cafes.”

Peonies bloom on Friday, July 4, 2024, in the garden beside Cosmic Kitchen on Pioneer Avenue in Homer, Alaska. Photo by Christina Whiting
Homer chamber hosts 6th annual Peony Celebration

The weeks-long festival features art exhibits, events, flower sales, guided farm tours and more.

These fudgy brownies are a classic, decadent treat. (Photo by Tressa Dale/Peninsula Clarion)
Dessert for a thoughtful reader

These classic fudgy brownies are dense and decadent.

Volunteers scoop up ducks at the finish line during the annual Anchor River Duck Races on Saturday, July 5, in Anchor Point.
Locals win at 4th annual Anchor River duck races

The event is part of the Anchor Point VFW’s Fourth of July celebrations.

Photo courtesy of the Melchior Family Collection
Between 1879 and 1892, Stephan Melchior (far left, middle row) performed his mandatory Prussian military service. He was a member of the Eighth Rhineland Infantry Regiment No. 70 in Trier, Germany.
Steve Melchior: Treasured peninsula pioneer with a sketchy past — Part 1

Did anyone in Alaska know the real Steve Melchior? That is difficult to say.

File
Minister’s Message: ‘Be still and I will fight for you’

Letting go of control and embracing faith and silence can encourage us in peace and divine trust.

"Octopus" is an acrylic painting by new co-op member Heather Mann on display at Ptarmigan Arts in Homer, Alaska. Photo provided by Ptarmigan Arts
July First Friday in Homer

Homer’s galleries and public art spaces celebrate with new and ongoing exhibits.

Frank Rowley and his youngest child, Raymond, stand in knee-deep snow in front of the protective fence around the main substation for Mountain View Light & Power in Anchorage in 1948 or ’49. This photo was taken a year or two before Rowley moved to Kenai to begin supplying electrical power to the central peninsula. (Photo courtesy of the Rowley Family)
Let there be light: The electrifying Frank Rowley — Part 2

In July 1946, the soft-spoken Rowley was involved in an incident that for several consecutive days made the front page of the Anchorage Daily Times.

Most Read