Short days and fat bears

What do these animals have in common during the fall months?

A Black Bear scrounging for goodies on the forest floor in the Grand Tetons, WY, in September 2016. Black bears consume prodigious quantities of food before retreating to their dens for their winter “sleep”.

One of my many chipmunk friends that live in the backyard. This one had its cheeks stuffed full of sunflower seeds and peanuts from the bird feeder — probably taking them down its burrow to add to the food stores for the winter.

A female (or juvenile) Yellow-rumped Warbler was chowing down on Juniper berries in late September. The berries are consumed whole, but the bird’s digestive tract will separate seeds from pulp and excrete the seeds, while cleaving off and digesting the waxy coating of the fruit for a few extra calories. High sugar and fat diets help these migrants put on body fat quickly before they migrate.

Not all Robins migrate — some stay here all winter. But those that do fly south seek out the high carb fruits like crabapples and service berries that allow them to build their fat stores up quickly.

The answer to the question above is that all of these (and many more bird and mammal species) exhibit excessive consumption of food in the fall, technically becoming hyperphagic.

There really are only a few viable solutions to surviving the long, cold winters of the far north: 1) get out of town — migrate! 2) build fat stores to last you several months and sleep as much as possible, and 3) stay active to search for what little food remains, tolerate the cold, but enter a starvation state by metabolizing a lot of of your muscle (when you run out of fat).

The temporary condition of hyperphagia is brought on by decreasing photoperiod — i.e., the continually declining number of daylight hours in the transition from late summer to fall — that triggers the change in an animal’s eating habits. Fortunately, this also happens to be when food is most abundant with the ripening of seeds, fruits, excess numbers of young, naive juvenile animals roaming the countryside, etc. So food is easy to come by and fattening is easily accomplished by overeating.

To take Black bears as a good example of this strategy, consider the following comparisons of its diet and caloric consumption from summer to fall.

In the summer Black bears consume about 5,000-8,000 kilocalories per day. If food and water are restricted at this time, they break down their muscles for energy, may accumulate too much nitrogenous waste in their blood, and may die. They cannot “hibernate” at this time.

In the fall, Black bears become voracious, begin consuming 15,000-20,000 kilocalories and drink gallons of water per day, excreting 1-2 gallons of urine as they metabolize all those calories into fat stores. Then, they stop eating and enter a lethargic, hypo-metabolic state of winter sleep, in which their resting heart rate of 80-100 beats per minute falls to less than 22 per minute and their breathing slows down to 2 or 3 times per minute. For the duration of their winter “sleep” they don’t eat, don’t drink, don’t break down any muscle, and females give birth to their cubs. It’s an amazing physiological transformation.

This is Alaskan brown bear #901 from Katmai National Park, a winner of the Fat Bear annual contest for most immense Fall season body mass. Photo from the New York Times, Oct. 2022.

But have you ever wondered if we humans exhibit a similar response to the waning photoperiod and colder days of fall weather? It’s true that humans cannot hibernate the way small rodents do, but could they increase their consumption of carbohydrates and fatten up in the fall and then decrease their daily activity and sleep more in the winter to conserve energy — like bears do? [Side note: carb craving in the fall is a real thing for me — how about you?]

Well, here is the answer, in an article from the New York Times written more than a hundred years ago, back in November 1906. (Click on the image to enlarge it to be readable.)

Apparently, it has been common practice in some cultures (in the past?) that face temporary periods of starvation in winter to prepare multiple loaves of substantially nutritious bread in the fall, prior to beginning a routine of reduced activity and increased bouts of sleeping during long winters. Sleeping with farm animals for warmth was encouraged, I guess.

Drawing from the British Medical Journal May 3, 2000.

Hidden food

This is the time of year we see massive flocks of “black birds” (Starlings, Red-winged Blackbirds, Grackles) wending their way around the landscape in erratic plumes, descending on swamps and fields to feed, and roosting in noisy, dense colonies in the trees.

Red-winged Blackbirds gathered in trees lining some recently plowed fields.

A flock of Red-winged Blackbirds swarmed the cattail marshes at Crex Meadows — looking for what kind of food there?

I always wonder what kind of food birds are finding when they hunker down in the vegetation, probing into dry leaves and stems.

The birds seem to be concentrating their efforts on probing into the bases of the cattails. What would they find there at this time of year when all the vegetation has died back? Inquiring minds want to know — my photography buddy on this field trip insists that I write about it.

A little research into the annual cycle of the Cattail reveals what a wealth of invertebrate life associate with this plant.  Its starchy root stalks and rhizomes are fed upon by a variety of critters, but this underwater food source is not what the blackbirds are after.  Instead, it might be orb-web spiders and orange garden spiders that have built vertical webs in among the vertical stalks of the cattails at this time of year.  Burrowing Water Beetle pupae may be found at the base of cattail stalks, already settled down for their winter diapause, only to be dislodged by the sharp bill of a blackbird.  In addition, larvae of the cattail borer moth overwinter in the cattail heads feeding on the seeds all winter — this resource sustains a variety of birds, like Black-capped chickadees, throughout the winter.

A member of a big flock of birds searching extensive areas of potential food resource might locate food more quickly and easily than single individuals searching alone. And of course — there are more eyes to look for potential predators and more victims from which to choose when predators fly by. So dense flocks make a lot of sense at this time of year.

a day in the life of a Sandhill Crane

Sunrise on the Platte River near Grand Island, NE. Already, hundreds of Sandhill Cranes have launched themselves skyward to fly out to crop fields to forage.

One large flock of cranes flew off before sunrise, but several more flocks still remain on the sandbars. You can just barely see one group in the lower third of the photo.

From sunrise to sunset, Sandhill Cranes make their presence known with their loud rattle call (click here to sample the sounds of a single bird or that of a large flock of cranes).

All but a few of the Cranes in the foreground have taken off, but a huge flock in the background is still waiting for just the right time.

What are they doing, besides preening, calling to each other, and occasionally stabbing a bill into the mud to find a snack there? Waiting…waiting, for just the right time to take off.

Often still vocalizing, it’s follow the leader to the first foraging site at some farmer’s corn field.  These birds are strong flyers, and move quickly across the landscape!

Calling out….”follow me”

Large flocks accumulate in fields of corn stubble a few miles from the river, but often a small flock simply joins another larger flock if the foraging looks good there.  Here, this small flock is gliding in to land with another larger group.

Put down the landing gear…

Gliding in for the landing…

Heads down, the Cranes are intent on gobbling up every kernel they find. However, more efficient machinery for harvesting corn leaves far less waste on the ground these days than in previous decades. Cranes must search more intensively or stay longer on their stopover to gain adequate fat stores to complete their migration.

The Cranes spread themselves out in a straight line across the remains of last year’s corn crop. You can see there is not much in the way of edible nutrients left on the ground.

After a long day of foraging in the corn stubble, Sandhill Cranes head back to the river in huge flocks of hundreds of birds — for another night on the river’s sandbars.

Three subspecies of Sandhill Cranes converge on the shallow sandbars of the Platte River from their wintering grounds in New Mexico, Texas, and northern Mexico in late February to early March.  They might stay several weeks, depending on how quickly they can refuel their fat deposits, before taking off for prairies in central and western Canada and Alaska.

Cranes and other waterfowl funnel through the narrow channel of habitat along the Platte River in the Central Flyway.

Sandhill Cranes are one of the oldest bird species, with fossils (found in Nebraska) indistinguishable from living cranes dating back 9 million years, long after the the rise of the Rocky Mountains and the development of prairie grasslands.  It’s amazing to think that these birds may have been repeating this same migratory journey for millions of years — and hopefully will continue for years to come.

Another misplaced migrant

Earlier this winter, I commented on what I thought was a case of misplace migrants when I saw a juvenile Yellow-bellied Sapsucker in my Minnesota backyard. Similarly, among the bevy of birds that crowded into the feeders in the past couple of days was an unusual one — unusual to see at this time of year at any rate.

I tried hard to make this little bird into a Tree Sparrrow, imagining that black fleck in the middle of its breast was the tell-tale spot of a Tree Sparrow. But the facial markings are the wrong color for a Tree Sparrow.  Instead I think it is a misplaced, non-migratory Chipping Sparrow.

It turns out the confusion over which species of sparrow one is seeing in the winter is not uncommon — for two reasons:  first, among northern-breeding bird species, some juvenile and even adult birds apparently do not always migrate (which might be a fatal mistake); second, some birds find the opposite sex of a different species more attractive than their own, and produce hybrid offspring that share some of both parents’ characteristics. So what is going on here with this supposed Chipping Sparrow?

Tree Sparrows and Chipping Sparrows are two of the seven species of Spizella in North America.  But…The two species are not supposed to be found in the same places in winter. So is this a case of failure to migrate?  Has this bird been here all winter, toughing out the frigid conditions when it could be basking in the warmth of Floridian sunshine?

Tree Sparrows are the typical bird found in the northern U.S. in the winter, while Chipping Sparrows winter much further south, in Texas, the southeastern U.S., and Mexico.

The two species do look similar, except for a definite chestnut streak behind the eye in Tree Sparrows and a black one in Chipping Sparrows.  Tree Sparrows are somewhat bigger in body mass, although not necessarily longer in head to tail length and possess a definite central black breast spot.

Photo from Project FeederWatch, sponsored by the Cornell Lab. Chipping Sparrows apparently are increasingly found north of their traditional winter range according to this website.

Tree Sparrows have a bi-colored bill, yellow lower with gray/black upper parts. Breeding adult Chipping Sparrows have a solid black bill.  Is my backyard visitor some kind of hybrid, with its bi-colored bill and faint central breast spot?

Black central breast spot is less obvious in this shot.  It was difficult to get a decent shot of the bird on a gloomy, gray day.

Well, it turns out that Chipping Sparrows only show the solid black bill during the breeding season, and it is, in fact bi-colored during the non-breeding season.  In addition, Chipping Sparrow breast plumage is somewhat variable, and some individuals do show black spotting.  So I assume this is not a hybrid product of cross-species interactions, but is in fact, a misplaced migrant (or it failed to migrate).

Which just leads me to wonder why, if migratory species can, in fact, survive harsh winters like this, why do they bother to migrate where they have to crowd in with the already established resident birds?  Do all the backyard bird feeders enable seed-feeding birds to remain in their breeding areas all year?  Is this an example of the effect of climate change (hard to think of warming in the middle of a Minnesota winter!) on bird distributions?

Of fancy feathers and dancing feet

It’s hard to believe in the middle of this polar vortex weather that the birds think spring is coming.  I heard the Mr. Cardinal warming up his vocal cords the other day, and a chickadee “fee-bee” duet breaks the morning quiet every now and then.  A neighbor told me she heard a woodpecker drumming to attract his mate’s attention the other day. While we alternate almost daily between sub-zero cold and 6-8 inch snow storms, the sun climbs higher in the sky and stays out longer each day, so some message is getting through to the birds’ brains telling them to get ready for their spring fling.

Since it’s too early for animals here to start showing off to each other, I’ll go back to some photos from our visit to Safari West wildlife reserve in early January to illustrate.

What can a male bird do to attract his lady love?  Why show off his fancy feathers and dancing feet, like the Demoiselle Cranes.

Actually, like other bird species that mate for life, this pair of Demoiselle Cranes cement their pair bond by doing a programmed set of postures, steps, and dances with each other.

First, an open wing display to show off the fancy feathers.

Next, there is the courtship dance of the duo, a sort of pas de deux. it’s a turn-off if the steps are done incorrectly.

There is always an aerial component to the dance, as if to show how light and graceful the crane is.  Sometimes this involves jumping over each other — it’s bad form to actually land on the other bird.

Demoiselles are the smallest of the crane species and are notable for their migration in huge flocks of thousands of birds over the Himalayas from their breeding grounds in Mongolia to their wintering areas in India. Unfortunately for them, Golden Eagles have keyed in on this abundance of prey and attack them just as they clear the thin air of the tops of the Himalayas, as explained in this video from Planet Earth.

Why fly over the tallest mountains on earth instead of around them or through lower passes?  Migratory routes are hard-wired in bird brains, just as the sequence of dance steps in a courtship ritual is, and this crane species is older than the Himalayas are.  A few minor evolutionary tweaks to their already superior respiratory system, and cranes became adapted to soar above 30,000 feet.

Flyaway

A few minutes after a couple of Canada Geese took off from the marsh yesterday, I heard a really eerie call and turned around to find these two birds taking off.

And they sounded just like this…as they flew away. It’s not a sound you easily forget.

These birds may have bred near here this summer, but will soon be on their way south as well, to wintering grounds in Florida, Texas or northern Mexico. For more information about these birds, see “Dance of the Cranes“.

Short-winged fighter

Rufous Hummingbirds are built like jet fighters with short stubby wings and plenty of attitude.  The Cornell bird lab website calls them “the fiestiest hummingbird in North America”.

This was the perch from which this male defended his clump of flowers.

A trio of male Rufous Hummingbirds zipped around me trying to outdo each other is their competition of flowers, but they were so quick, it was really difficult to photograph them.

You can get an idea of just how small they are when you compare their size (about 3 inches) with that of the holes in a standard mesh fence.

Rufous hummers are very aggressive, and will drive away larger hummingbirds, as well as each other, from a nectar resource (feeder or patch of flowers).  Their short wings make them extremely agile in changing direction quickly, and the fast wing beat frequency propels them amazingly fast through aerial space.

Tail up and wings beating 60 times a second, this little male approaches a set of his defended flowers.

This little male spent 90% of his time defending his flower patch, and less than 10% actually foraging from it.

With his bright orange iridescent throat, brown head and belly, white chest, and metallic green back and shoulders, this male is handsomely decked out.

Rufous hummers are a western US species, but breed as far north as southern Alaska!  Then they undertake a 3900 mile migration to their wintering grounds in southern Mexico, quite a feat for such a small bird!

Flocking up

Is it time for fall already?  These birds seem to think so.

Bobolinks are actually members of the Blackbird family, although they look like stocky finches. These may be female bobolinks, and/or young birds just fledged from their prairie nest.

Female and juvenile bobolinks have yellow feathers on their breast and face; the male, however, looks like an entirely different species when he is dressed in his breeding plumage.  Bobolinks are one of the few species that molts all of its feathers twice a year, and his distinctive set of black, white, and yellow feathers will soon be replaced with drab brown and yellow ones before he migrates to southern South America for the winter.  Then he will re-decorate himself again with another new set of breeding plumage feathers before he undertakes the northward migration next spring.  A lot of energy just to make himself attractive to the ladies.

Male Bobolink in breeding plumage (by Andrea Westmoreland via Wikimedia Commons).

Bobolinks form large migratory flocks, feeding voraciously during the day on seeds of crops and prairie grasses to fuel their nocturnal flights.  Their preferred forage on the large grain fields in South America, earned them the name “rice-birds”.

But first, they have to lay on a layer of fat and build up those wing muscles before the late summer take-off.  Their migratory round-trip from the upper midwestern prairie and wheat fields to agricultural areas in Argentina, Paraguay, and Bolivia is about 12,000 miles.

Bon voyage, rice-eaters.

Dance of the cranes

We visited Sherburne National Wildlife Refuge on a cold, windy day this past weekend, hoping to see Sandhill Cranes that nest there.  Driving the wildlife loop, we got a glimpse of these stately birds.

Three Sandhill Cranes foraged in a grassy wetland area about 1/4 mile from us. This was as close as we got (with max telephoto).

Up to 40 pairs of Sandhill Cranes nest at Sherburne NWR each spring, migrating from their wintering area in Florida.  Sandhills that nest in northwestern Minnesota migrate there from Texas, so there are two subpopulations nesting in Minnesota.  In the fall, the refuge may host thousands of cranes as they return south for the winter, feeding on the remains of fall crops on nearby agricultural land.

Sandhill Cranes are large-bodied birds, weighing 5-8 lb and standing about 4 feet tall.  Their sharp bill enables them to grab and eat just about anything they can find:  small mammals, frogs, insects, snails, seeds, and berries.  Photo by Ken Thomas (Wikimedia Commons)

Cranes are highly social and  may congregate in the thousands during migration.  In fact, their name “Sandhill” comes from one of their stopover points on the Platte River near the sandhills of Nebraska.

Sandhill Cranes congregating at lake Andes in South Dakota. Photo by Gary Zahm

With their 6 foot wingspan, cranes are expert soarers and once they get altitude, their flight is fairly effortless. Their long wings make them graceful dancers as well, as they jump and flap around their partner in their own “pas de deux” that, as in the ballet, showcases the virtuosity of each of the partners.  We caught just a glimpse of this action at the wildlife refuge.

Cranes can become airborne with the slightest effort and easily jump over and around their partners.

Dancing, bowing, and posturing between cranes is important for development and maintenance of their social relationships.  Indigenous people are thought to have copied some of the actions of dancing cranes in marriage ceremonies or other rituals, perhaps for the same reasons.

Below is an illustration of the “pas de deux” of the cranes from YouTube. (Click on “skip ad” after a couple of seconds to play the crane dance.)  The rattling call that goes along with the dancing carries over amazingly long distances.

an amazing day

Finally! some sun after several days of cold rain.  It was a brisk, but clear, sunny day and the birds were obviously as happy about that as I was. I walked around Afton State Park for a couple of hours and saw 13 species of warblers, in addition to about 30 other species.

I must have seen about 200 of these American Redstarts — all of which were bouncing from limb to limb to ground, never still for a moment.  What an annoying bird to photograph.

Female Redstarts were much more sedate.

A black-throated green warbler — well named.

Blue-gray gnatcatchers copied the male Redstarts’ behavior, flitting continuously from branch to branch. This one almost flew out of the photo.

A Chestnut-sided Warbler whose chestnut sides have not quite developed (perhaps a first year male). He was either in the process of taking off or landing.

Eastern Towhee singing “drink your teeeeeeea”

A very cute flycatcher, one of many in the genus Empidonax that you can’t tell apart unless you hear and know their song.

An immature male or a female Yellow Warbler (faint red streaks on the breast) was one of the only cooperative warblers for the day.

Female Scarlet Tanagers look nothing like their bold crimson and black mates.

Meadowlarks are pretty eye-catching, but this guy didn’t want to show me his bright yellow breast.

The waves of migrants are still arriving, and what is interesting is that not only are there new species arriving, but we now have many more females than males of the earlier-arriving species (who left to set up their breeding territories).  I also see more first-year males with less well-developed color now than previously. What a delicate balance it is to arrive early, face cold weather and short food supply, but try to be first on the breeding ground … or die trying.