Big Bad Bald Eagle Mums

A female Bald Eagle broods her two chicks during a spring rain. One chick is peeking out from underneath.

(Mother's Day special edition)

In spite of what you may have heard, size really does matter, especially to female Bald Eagles. But in this case she has the advantage. Her extra heft has major impacts during nesting, when it's time to incubate delicate eggs and brood young eaglets - exactly what Montana's eagle moms are doing during Mother's Day. Two factors, weight discrepancy between the pair, and the weather during nesting season, can have a huge effect on how the eagle parents divvy up the family-rearing chores.

After the female lays 1-3 eggs, she and her mate both take turns incubating them. Montana's Bald Eagles generally incubate for 31 (mostly warm weather) to 35 days (mostly inclement weather). Chicks hatch between mid-March and mid-May. So by today, Mothers' Day, most of our successful Bald eagle nests should be cradling a baby or two that are really ugly, in a cute sort of way.

Bald Eagles incubate their eggs for about 95% of the daylight hours. If you average the hours, then the female spends about 10% more time incubating than the male, during daytime. She also takes the late shift and incubates their eggs through the night.

When their eggs finally hatch, both parents take turns brooding, or covering the chicks with their bodies to keep the little guys warm and dry. During the first 10 days after hatching, the parents will spend almost 80% of each day brooding their wobbly youngsters. As the voracious toddlers gain weight and grow feathers (downy feathers, body feathers, flight feathers), the time spent brooding falls to 3% at 51-60 days after hatching.

During that early, critical nestling stage, male Bald eagles handle about 30% of the brooding hours, while females work the other 70%. But before you judge these dads, this is actually a pretty good showing by Bald Eagles. By comparison, female brooding rates are 100% for Golden Eagles, 99% for Peregrine Falcons, and 95-100% for Osprey.

The steepest drop in brooding time happens 11-20 days after hatching, because this is age when chicks are finally fat enough to maintain their own internal body temperature, or "thermoregulate." The young eagles will fledge from their nest a little more than two months after hatching, but they'll still depend on their parents to feed them for another 2-3 weeks before wandering off to discover the world. In other words, typical teenagers.

Can you tell which eagle parent is mom?

Here in Montana, female eagles can weigh up to 30% more than males. Our nesting females average 11.5 lbs, while adult males weigh in at just 9 lbs. And as you may recall from high school biology, a larger body is more efficient at maintaining a constant internal temperature, so female Bald Eagles have a substantial, built-in advantage in the heat-maintenance department.

This size disparity shows up as a gradient as you look from south to north, from warmer areas to colder ones. Female Bald Eagles nesting in balmy Arizona weigh 20% less, an average, than our Montana females (males only 8% less). And the females that migrate through Montana on their way to nests in cooler Canada weigh up to 13% more than our Montana gals. So an eagle pair's individual weights are fairly similar in the south, but they diverge more and more the farther north they nest.

Larger body size contributes to a second built-in advantage for females over males, at least while nesting - they show more skin. Most nesting birds either molt or pluck most of the small body feathers from their breast area in preparation for incubation. This patch of bare skin is called a "brood patch," and a nesting female Bald Eagle has a brood patch that's three times larger than her mate's.

Give dad credit for having a brood patch, but mom has much more bare skin to press against the eggs without insulating feathers getting in the way. This one-sided heating is the reason that Bald Eagles, like all birds, need to turn their eggs frequently during incubation.

To this point, we've been talking about averages. But averages fly out the window when bad weather rolls in. Because of their built-in physical advantages - more weight to produce heat, and larger brood patches - female Bald Eagles take over almost all of the incubation and brood duties during periods of precipitation (rain or snow), high winds or low temperatures. This is especially pronounced at nests that are more exposed to the sky (no overhead branches) and the elements.

During spells of wet, windy or cold weather, mom is simply the best-equipped parent to keep eggs and chicks alive. Dad pitches in by delivering food to her at the nest, but that's indirect care of the young, so he tends to get less credit for this labor. However, during good weather, the males might more than double the daylight hours that they spend tending to eggs and eaglets.

Basically, Bald Eagle parenting is a flex schedule, especially for mom. Her plus-size body means she's well-equipped to micro-manage the family nest environment, and she changes her behavior to fit the family's needs. Diminutive dad just pitches in wherever he can help out. And of course, that's why we have Mother's Day. We pause one day each year to recognize that, in most families, mom rules the roost.

We could end there, but I'll add a bonus note from the Bald Eagle world. Size also matters to the sub-adult Bald Eagles, but not body size. Young Bald Eagles weigh less than adult eagles of the same sex, but they actually have longer wing and tail feathers than the adults.

Instead of parenting, young birds are in flight school for their first four years. Less weight and longer feathers make it easier to fly at slower speeds. And slower flight speed is a great benefit for young eagles who are learning how to fly, chase, fish and hunt. The young guns who master all of these flight skills will earn a turn as the future Bald Eagle moms and dads.

Montana Eagle and Osprey Cams

Still image from Miles City Bald Eagle cam

4/21/14 UPDATE: We have a baby Bald Eagle this morning! Either someone reported the wrong egg-laying date, or the eagles have learned how to use a microwave for incubation. While the chick is young, watch for frequent feeding bouts, as they can't eat much at one time - yet.

A pair of Bald Eagles nesting in Miles City, in eastern Montana, laid their second egg about one week ago. The two adults will take turns keeping the eggs at a constant 99.5F degrees for approximately 35 days. Incubating eagles also roll their eggs over about every two hours. If the eggs make it, there should be chicks in the nest starting around May 12th. You can follow their progress on a live eagle cam here.

More eagle cams can be found here and here. The eagle cam at the Libby Dam is currently offline, but more information can be found here. Eagle information here.

The Osprey have returned to their Montana nests as well. Iris has returned to her Missoula nest (webcam here), and Ozzie and Harriet are back in their Lolo nest (webcam here).

Eagles on Ice

A young Bald Eagle (right) harasses an adult that was trying hard to eat a fish.

The surface ice that's covered our lake all winter finally blew off this week, here at the end of the road. High winds and rising temperatures were more than the rotting ice could withstand, and it all broke apart over two afternoons (time-lapse video below).

One one side of the lake, our white-headed neighbors have been refurbishing their nest for a couple of cold and snowy weeks now. When the first cracks appeared in the ice, one the eagles flew out, plucked a fish from the narrow lead, and landed on the lake ice nearby. No doubt hungry, he had just set about tearing the fish apart when a young, sub-adult eagle landed a few meters away.

Now we had a stand-off.

Whenever the adult turned his attention to lunch, the younger eagle would feign a mild bluff charge. Sometimes this just meant jumping a few steps towards the adult. Other times the youngster would fly at and over the adult. After 15-20 minutes of intermingled stare downs, feeding bouts and food mantling (covering the fish with spread wings), the adult gave up and flew off to his nest. The youngster quickly hopped over to eat what was left of the fish.

What intrigued me about the young bird's behavior was how it resembled the Bald Eagles' duck hunting technique in spring. When there are large rafts of tightly-grouped ducks - especially Coots - the Bald Eagles make frequent flights over the nervous ducks. (I know, Coots are rails not ducks, but stick with me here.) Eagles fly towards these rafts at a moderate speed and altitude, just low enough to make the ducks skitter in a semi-mild panic.

The eagles are essentially shuffling the deck, looking for the odd duck that does not move like the rest. Most of the time, the ducks just skitter off a ways and the eagle returns to a tree branch, still hungry. The eagle spent very little energy in the effort. But every now and again the shuffle allows an eagle to spot a weak or injured duck, and the chase begins for real. Now the eagle focuses intense efforts on the odd duck, and he stooping in fast and low. If he misses the first time, he'll keep circling and stooping until succeeding or giving up.

The eagle's high-energy efforts were saved for the duck that stood a better chance of becoming lunch. Until then, he just made low-energy bluff charges. Efficient behaviors are well-honed in wild animals, and inefficient animals are soon removed from the gene pool - guess it's a good thing that I'm somewhat domesticated instead.

Sharing a Snag

(Click to find the dragonfly)

Two songbirds and a dragonfly (you have to look closely) share the afternoon view from a Douglas fir snag, along with a sub-adult Bald Eagle.

Cloudless, blue-sky days are a summertime specialty here in western Montana. And dead trees left standing are a valuable commodity for many of our native animals, including: owls, marten, fishers, black bears, flying squirrels, Vaux's Swifts, porcupine. Snags are especially valuable to our raptors and woodpeckers for foraging, nesting sites and hunting perches. This four-month-old Bald Eagle learned to use this favorite, shoreline hunting perch by watching both parents catch fish from here.

Back in 1997, the US Forest Service put together a guide to snag identification in the Pacific Northwest. It helps you figure out what tree species the snag is, and it tells you a little bit about what kinds of wildlife use each tree species. You can read it here.

(Hint: the dragonfly is just to the right of the Eagle's head.)

Big Daddies

I wrote a pleasant little story for Fathers' Day, and one week early to boot. I explained how our current Loon dad is better at raising his young than the previous Loon dad. And I described how he kept his offspring warm and well-fed. About how he was big enough and aggressive enough to protect his little chick.

Did I mention that I wrote it a week early?

A few days before Fathers' Day, one of the resident Bald Eagles snatched the week-old Loon chick from the water's surface. It wasn't supposed to end this way, I thought. But watching wild animals means learning to distinguish between natural behaviors and human judgements.

Our "Big Daddy" Loon covering his chick under a wing last week.

Here at the end of the road, Big Daddy rules over our little lake with a keen eye and a big beak. For the past three summers, he's been the resident male of our nesting Loon pair. His kingdom isn't big enough to share with another pair. Loons are very territorial, especially Big Daddy.

Before his arrival, the previous Loon pair failed to raise any chicks after the Bald Eagles moved in and built a nest of their own. Just as soon as the Loon chicks hatched, the Eagles would take notice. The two Eagles tag-teamed the Loon parents, stooping at them repeatedly. These previous Loons would do what they always did to avoid danger - dive underwater. But this left their chick bobbing alone on the surface, unprotected, and it seldom lasted more than a day.

Enter Big Daddy.

He was unbanded upon arrival, so we don't know where he came from. But Big Daddy was visibly larger and more aggressive than any other Loon we'd seen on the lake. He apparently claimed this territory by chasing off the previous pair, along with a number of visiting Loons.

We were never sure if he already had a mate, or if he courted a female after winning the territory. Loons are monogamous, with new pairs typically forming on the breeding territory and established pairs rejoining there each spring. Loon courtship is a ritualized form of aggression, and it's hard (for us, at least) to distinguish courtship from hostility.

Once this new, more aggressive pair moved in, we watched and waited through almost a month of incubation. We were dreading a repeat of previous years. Loon chicks often hatch at night, and an early-morning commotion across the lake got everyone's attention. Eagles screeching, Loons yodelling, water splashing - and me paddling across in our faded canoe.

But that first year, Big Daddy carried the day!

Each time the Eagles stooped to drive the Loons away, Big Daddy lept skyward instead of diving underwater, stabbing at the attackers with his long beak. The Eagles broke off their attack before I made it across the lake. During the next week, the Eagles attempted a few more attacks that declined in number and effort. 

Nowadays, as soon as any Eagle leaves a branch anywhere on his lake, Big Daddy yodels his alarm before scooping up the chick and hiding him under a protective wing. One pair of Bald Eagles can't catch this dad off duty.

That first summer, Big Daddy and his mate hatched one egg and fledged one youngster. When he was banded later that summer, Big Daddy weighed in at a whopping 11.44 pounds (5200 kg). (Adult Bald Eagles in Montana weigh 9 to 14 pounds.) He weighed three pounds more than his mate, moving Big Daddy into third place all-time for Montana Loons. The business end of his beak measured just over 3.25 inches (82.6 mm) long, and that was two years ago.

Last summer, Big Daddy tried to do it all. His mate vanished mysteriously on the very night that their first egg hatched. Big Daddy alternated between feeding the first chick, incubating the second egg, and chasing off visiting Loons. For three days. In the cold and rain. But even this super-dad couldn't do it alone. After dark on the third night, the little Loon chick disappeared, and we never found any clues to his demise.

Early the next morning, Big Daddy allowed an adult Loon to swim up to the nest, where he was still attempting to hatch a second egg. But his mate had returned one day too late. After a few more days, they gave up on the second, apparently non-viable egg. They abandoned their nest and eventually left their lake to spend winter somewhere along the Pacific coast.

Our Loons feeding their three-day old chick last week in the rain.

This summer, Big Daddy looked to be in charge again.

Once again, he and his mate hatched one chick. They tended the little guy through a precarious first few days of cold rain and snow squalls. He received a steady diet of tiny insects with an occasional leach thrown in. (Big Daddy had to fetch the leech a couple of times before the little guy figured out how to gulp it down.) At three days old we watched him make his first brief dive underwater - but it wasn't enough.

On the morning on his eighth day, three extra adult Loons appeared approached the nursery area and the resident Loon family. This set off a cacophony of Loon yodels and counter-yodels. And all of this racket caught the attention of the Bald Eagle pair.

What happened next is not exactly clear. Several different neighbors reported several different versions of the event. But somehow, while the parent Loons were distracted by the trespassing Loons, the Bald Eagles swept in and snatched the Loon chick amid the confusion.

Once again, despite Big Daddy's best efforts, no young Loons will grow up on his lake this summer. The trespassing Loons left the lake. The resident Loons left the nursery area and began feeding farther apart. One would call out occasionally, but they gradually grew quiet.

This year's 2nd Loon egg

We eventually paddled our faded red canoe across the lake, over to the marshy area where the Loons had nested. Floating next to their nest was an intact, olive-green egg. It fell out of the nest somehow, and no one knows if it was before or after the first chick hatched. We collected the egg (it will be sent to Maine for analysis) and removed the area closure signs.

A few days later, I searched the ground around the giant larch tree, an area I normally avoid. I found a few fish bones and lots of whitewash under the massive Bald Eagle nest, but no Loon parts. I wondered, might the little guy might be up there in the nest?

But when we peered into the eagle nest from some distance away, we had to manage a smile. Through the binoculars we could easily make out two clumsy, comical, brown lumps of feathers.

Two baby Bald Eagles.

Regardless of our human judgements, there are also Big Daddy Bald Eagles, doing what Eagles do, working to keep their chicks fed.

We removed the area closure signs for another year. The Loon nest is the brown mat just right of the canoe bow.

A Montana Mother's Day

Mothers' Day dawned as a warm, blue-sky morning, so we celebrated by paddling our faded pink canoe around the lake to check on the neighbors. This is our holiday update on motherhood in northwestern Montana.

Mother Loon on her nest on Mother's Day morning

One of the adult Loons was incubating eggs on their reedy nest at the edge of the cattails. The adults are hard to tell apart, but we decided it must be the female because bird moms don't get holidays. Her beak was open slightly and she appeared to be panting in the windless heat, which both adults will need to patiently endure for another 17-18 days before their eggs hatch.

Loons normally lay two eggs, but sometimes only one and -- rarely -- three eggs. The 28 days of incubation is the passive portion of Loon parenthood. The real test begins on the morning after the last egg hatches. That's when the family will leave the nest for good, and the adults will have to defend their little chicks from the resident Bald Eagles, who also have young to feed.

Click to see two fuzzy Bald Eagle chicks

One of the adult Bald Eagles -- probably the male -- delivered a fish to their massive stick nest just as we floated past. The female began tearing off small pieces to feed to their two chicks. Both parents spent about the same amount of time incubated their eggs, but now the female will feed the chicks 80-90 percent of the time, and the male will do most of the hunting.

Eagle eggs hatch 1-2 days apart, and the elder chick should be about 8 days old today. Both of the wobbly chicks are standing up in the nest, just now becoming visible. The chicks have downy feathers, but both parents will take turns keeping the youngsters warm by brooding them about 80% of the time during their first 10 days. Time spent brooding will gradually decrease over the next six weeks, as the youngsters grow big enough to maintain their own body temperature. Before fledging from their nest, a female juvenile will be bigger and heavier than her father.

Male Bufflehead

We turned our old canoe towards home, passing a male Bufflehead on patrol at the mouth of the creek. Just a few days ago, we caught a glimpse of his mate flying into a hole in the old larch snag -- 40 feet off the ground. That's where she's doing her motherly duty, incubating their eggs in her high-rise nest. She makes a daily trip down to the lake where she'll feed and preen for an hour or two. While on the water, the male will mate-guard her from other Buffleheads. This protects his paternity while allowing her to forage more efficiently. It also allows him to avoid nest tending, but it exposes him to the hazards of fighting with the other male Buffleheads on patrol nearby.

Just a short distance uphill from the Bufflehead, thousands of Arctic Grayling were busy spawning in the little creek that flows into our lake. The adult males and females began working upstream two weeks ago, and their numbers are just now peaking in the neighborhood of 5,000 to 7,000 fish. It'll be another two weeks before they've all returned to the lake. Spawning in the shallow creek is dangerous and difficult, but most of the grayling will survive to spawn another day.

A male Arctic Grayling (front) fertilizes the eggs released by a female (rear) in a shallow stream.

Grayling don't spawn until they're 2 to 5 years old, and they only live for 5 or 6 years. When they move up into the spawning stream, the dominant, older males defend territories over the best gravel beds for almost a week, while the females swim freely among them. Instead of excavating "reds" in the gravel, they will broadcast spawn. The female swims up next to the male(s) of her choice, and both will begin a trembling dance -- the result of straining to squeeze out the eggs and sperm that briefly mingle before settling into the tiny crevices between the rocks and gravel.

After the tiny fry hatch, they'll spend 3 to 4 days hiding in the gravel before emerging to swim up or downstream to a refuge. Fry disproportionately select stream reaches that have slower, shallower water with some sort of vegetative cover. The limbs and branches will help to hide them from the eyes of our resident Kingfishers, at least until they are big enough to swim down to the lake.

Female Belted Kingfisher

As we slowly paddled our canoe towards home, the female Kingfisher flew over and announced her presence with a rattling call. We're smiling now -- it was exactly one year ago today that we released a female Kingfisher who needed rehabilitation after she'd flown into a window. She and her mate spent last summer catching crawdads along our shore, but they apparently did not nest.

Could this bird be her?  Is she nesting in the neighborhood this year?  Will we get to watch her feeding youngsters sometime soon?

Last year, watching the Kingfisher fly from our hands made Mothers' Day for both of us. This year, watching her fly over our canoe was just the icing on a many-layered cake.

Scrapping for Scraps

It's been a long, lean winter for many of Montana's animals. Here at the end of the road, our resident pair of Bald Eagles started incubating eggs almost two weeks ago, but the lake ice won't break up for another week or two. So when a subadult eagle found some sort of morsel today in the melting ice, a battle broke out quickly over a little scrap of food.

An adult Bald eagle drives a subadult away from a small food item on the surface of a frozen lake.

One adult flew over from their nest, knocked the youngster on its side, and took possession of the food. The subadult mounted a counter-attack and managed to retake the morsel that remained. The adults then exchanged places, with one returning to the nest and the other flying across the lake to mob the subadult. The second adult bit the youngster in the butt and scored a small scrap before flying off again. As the younger eagle stood on the ice, three more subadults flew out to join him - and to look for more scraps.

When nesting, adult Bald eagles are very territorial towards other adults, chasing trespassing adults away post haste. But even nesting adults are somewhat tolerant of younger eagles hanging around in their territory, at least when food is plentiful.

Down the road a ways, the creek is melted and flowing below another eagle nest. And most of the nests on larger lakes already have open water for fishing. But our little lake is still quite frozen. When it finally ices out, there will be plenty of fish available for the catching. Until then, food is a valuable commodity that's worth fighting over.

All Those Not-so-bald Eagles

A courageous Magpie joins a two-and-one-half year old Bald Eagle for lunch on a deer carcass.

This evening I watched no fewer than nine Bald Eagles take turns feeding on a deer carcass in a foggy field of stubble. One or two at a time would fill their crops with red meat - in some unspoken eagle pecking order - while the rest watched from favorite trees along the river.

Banding juvenile Bald Eagle.
(Click to see the dark beak.)

A lot of people I know think Bald Eagles have white heads and tails and Golden Eagles are just that, golden-brown. That makes life real simple. The only problem is that it leaves out the majority of Bald Eagles, the many sub-adults that aren't old enough to have solid white head feathers.

Bald eagle plumage basically goes from dark to light with age. They start off chocolate-brown with various amounts of white feathers here and there during their first three years - but not just in those areas that will be white in adult plumage. With all the variability in feather colors, it's easier to focus on eye and beak colors.

Juvenile Bald Eagle with dark eye and beak.
(Click to raptorize.)

Juveniles just off the nest (first-year birds) have dark eyes (irides) and black beaks from the nose holes (nares) forward. A second-year bird will still have a dark beak, but its eyes will lighten to a buffy brown. A third-year bird will start showing some yellow on the forward half of its beak, and its eyes will lighten even more to a creamy tan.

A forth-year bird is finally starting to look the way we think a Bald Eagle should. A few dark feathers remain on an otherwise white head and tail, the beak is mostly yellow, and the eyes are dull yellow. And if the Bald eagle lives to be five years old, it will finally look very distinguished with its bright white head and tail, solid brown body, and bright yellow eyes and beak.

If the eagle in question is anywhere near water, you're almost certainly looking at a Bald Eagle. They are mostly denizens of large lakes and rivers. Golden Eagles are denizens of high desert plateaus and mountains. as they prefer higher and dryer terrain. About the only notable overlap in is the high desert winter, where some Bald Eagles spend the icy months dining on jackrabbits.

You can find a detailed description of Bald Eagle ages here, and you can find the answer to just about any question you might have about them here.  Information on aging Golden Eagles is found here.

One and one-half year old Bald Eagle with dark beak and buffy brown eye.