Monthly Archives: April 2015

Den Emergence on Kodiak


Bears exhibit two notable springtime behaviors.  The first is emergence from their dens, and the second is courtship and mating.  In this post, I will discuss hibernation and den emergence of brown bears on Kodiak Island, and I will cover courtship and mating in a later post.

Normally, you don’t see a bear leave his den.  All you see is a hole in the snow high on the mountainside with dirt trailing out of the hole and tracks leading away from it.  Occasionally, you might be lucky enough to observe a head sticking out of a den entrance, or you may see a bear sitting right in front of or next to the den entrance.  Sometimes, you see the bear disappear back into the den and then reappear later.  This is often the behavior of a sow with newborn cubs, as the mother slowly acclimates the cubs to the world outside the den.

While I don’t plan to cover bear hibernation in detail in this post, I must mention that when bears hibernate, they do not experience the extreme dormancy that many rodents do.  While most bears spend the winter in hibernation, they can and do go in and out of hibernation, and on Kodiak where winters are relatively mild, some bears (mostly older males) do not hibernate at all.  It is common to see bear tracks all winter on Kodiak.


There are very few natural rock caves on Kodiak, so bears dig their dens either into the side of a mountain or the side of a snow bank.  Research on Kodiak has shown that bears on the north end of the island usually dig their dens at a high elevation, where the soil remains frozen all winter, and the den remains stable.  On the south end of the island where the mountains are not as high, bears tend to dig dens in mid-slope habitat in alder thickets, where the dens are stabilized by alder roots.

Pregnant females are usually the first to enter their dens, followed by lone females and females with cubs.  Males normally are the last to enter their dens.  The time of den emergence in the spring is dependent on temperature and weather conditions, but males typically leave their dens first, followed by single females and sows with cubs.  Sows with newborn cubs are the last to emerge.  Males on Kodiak spend an average of three to five months in hibernation, while pregnant females may hibernate as long as seven months.

Pregnant sows give birth while in hibernation; which is an amazing feat of nature, since the sow must provide nutrients to her unborn young while she is hibernating and not eating.  She provides these nutrients by breaking down her own body proteins, and this causes her to lose muscle mass.  Since she would not be able to move if she lost too much muscle mass, a sow gives birth to very under-developed cubs.  No other mammals except marsupials have such immature offspring at birth.  A newborn cub weighs one pound (.5 kg).  They are blind, deaf, and unable to smell.  They are covered by a very fine hair and are toothless, weak, and uncoordinated.  They can detect temperature changes, so they move closer to their mother to seek warmth, and they are also able to find the sow’s nipples to nurse.  A bear’s milk is very rich, and cubs gain weight quickly, but they are still small and fragile by the time they leave the den, and their mother is very protective of them.


During hibernation, bears do not eat, urinate, or defecate.  When they leave their dens in the spring, they are groggy and sluggish, and it takes time for their bodily functions to return to normal.  Soon after leaving their dens, bears often pass a fecal plug that may be as long as two feet (61 cm) in length.  This plug consists of digested food that has accumulated in the lower intestine as a result of not defecating all winter.

After bears leave their dens, they drink large amounts of water but eat very little, concentrating on emerging plants and roots.  As spring progresses, they begin grazing on sedges and grasses as well as other plants, and by summer, they are voracious eaters, consuming protein-rich salmon and berries loaded with sugar.  By late summer and fall, a bear may consume 20,000 calories per day and add six to eight inches (15.24 to 20.32 cm) of fat to his body as he prepares for his next hibernation.


Bald Eagle Courtship, Mating, and Chicks

Bald Eagle in Flight

The piercing, high-pitched call causes me look up at the sky, where I see two bald eagles flying in circles several hundred feet above my head.  One eagle dives at the other.  They touch talons and then separate and soar higher. A few minutes later, one eagle again dives at the other, and this time their talons lock, causing the birds to spiral downward in a motion much like a cart-wheel.  I hold my breath as they plummet toward earth, but they finally pull away from each other and fly in opposite directions.

I assume I’ve just observed a courting display, and maybe I have, but biologists have a tough time differentiating between the aerial acrobatics of courting and those of aggression, and it is believed that the two behavioral displays may be closely related.  Eagles also display other much-less aggressive forms of courtship, such as perching beside each other on a branch and stroking and pecking at each other’s bills.  They also use their bills to stroke the heads, necks, and breasts of their mates.

Bald eagles sometimes mate for life, but if one member of the pair dies, the surviving member will often find a new mate within a year, and if a pair does not produce offspring after several seasons, they may change mates.



Copulation usually takes place near the nest site, and females lay between one and three eggs in mid-May on Kodiak.  The male and female take turns incubating the eggs, and each mate hunts for its own food.  The incubation period lasts 34 to 36 days, and it takes 12 to 48 hours for a chick to fully emerge from the egg.

During hatching, a chick must undergo several physiological adaptations.  Before it hatches, the chick absorbs oxygen through the shell by way of the mat of membranes under the shell.  During the hatching process, the chick must cut the blood supply to these membrane and trap the blood within its body.  At the same time, it must also inflate its lungs and begin breathing air once it has cracked the shell.  The chick must also absorb the yolk sack into its body and seal off the umbilicus.

Eagle in Nest

A newborn chick is helpless and dependent on its parents.  It cannot regulate its body temperature, so the parents must keep it warm.  Chicks grow rapidly as long as the parents can supply adequate food, and as the chicks develop and grow, the parents spend less time at the nest and more time hunting for food.

By the age of two weeks, most young eagles weigh one to two pounds (500 to 900 grams).  Between 18 to 24 days, chicks gain four ounces (100 to 130 grams) per day, the fastest weight gain of any stage of their development.  They begin feeding themselves by the sixth or seventh week and can stand and walk around the nest when they are eight weeks old.  At sixty days, eaglets are well-feathered and weigh 90% of their adult weight.

Chicks remain in the nest for ten to twelve weeks, and we often see fledglings making their first flights in late August.  Most nests where we live are located near the tops of tall cottonwood trees, and I wonder what it must be like for a young eagle to take that first step out of the nest.  Their first flights are often very clumsy and quite humorous to watch as they learn how to use their huge wings to fly and master landing on a branch.  Juveniles have longer wings and tails than adults, which makes it easier for them to learn how to fly, but it takes a while before they hone their skills, and they make several crash landings before they figure it out.  They often continue to receive food from their parents while they learn to fly and hunt.

Springtime on Kodiak

Kodiak Bear Sow and Cub

I’m sitting next to the heater and looking out the window at a blizzard, so it seems strange to write a post about spring.  I know, though, that over the next few weeks, spring will unfold in this corner of the world, and springtime on Kodiak is spectacular.  It is, without question, my favorite time of the year.  True, the weather is much nicer in the summer, but nothing can compare to the awakening of nature that spring brings.

All I have to do is look out the front window or walk out into the yard to watch the breath-taking aerobatics of mating bald eagles.  On the beach, I can see raucous, funny black oystercatchers, squawking and strutting to protect their territories.  The black-legged kittiwakes arrived yesterday at their rookery in front of our home, and the Arctic terns should arrive in the next two weeks.  We will soon begin seeing horned and tufted puffins paddling through the water and launching their fat little bodies into the air for their short, awkward flights.  Of course bears will be leaving their dens, and before too long, we hopefully will catch a glimpse of a sow with tiny, newborn cubs.

Fin Whale near Kodiak Island

All of this is fantastic to see, but perhaps the most amazing displays of spring occur in the ocean.  As the sea temperature slowly rises, phytoplankton bloom, providing a food supply for spawning zooplankton. Soon, the ocean is full of these small crustaceans that provide a food, for everything from herring to whales.  Spring is also when adult herring return to the marshy heads of bays to spawn and lay their eggs on eel grass and other plants.  It seems as if overnight we begin seeing masses of zooplankton washed up on our beach and notice huge schools of herring in the bay, and following the herring and zooplankton are fin whales, humpbacks, and other whales, along with seals and sea lions.  Some years we even see Orcas chasing and feeding on the oil-rich herring.  There are days in the spring when the last sounds I hear before I fall asleep at night and the first sounds I hear when I awake in the morning are whales blowing.  Life doesn’t get much better than that.

Over the next few weeks, I plan to go into more detail about springtime on Kodiak Island.  How do eagles court and mate, and when will their chicks hatch?  What do bears do when they first come out of their dens?  When do the Sitka black-tailed deer give birth to their fawns, and when are red fox kits born?  I’ll also let you know about the whales and other wildlife we see and tell you a bit more about Arctic terns and some of the other birds in our neighborhood.  The snow is relentless today, but I’m certain spring is around the corner!

Please let me know if there is any particular Kodiak animal you would like me to cover.