Arriving at the peak of low tide the other evening gave us some great looks at a diversity of shorebirds foraging along the shore of Eloise Roemer bird sanctuary on Alameda Island in San Francisco Bay.
It is often said that “variety is the spice of life”, and we recognize that almost all individuals of a single animal species exhibit some variation from one another. But sometimes that variation is markedly and drastically different — and we wonder how that variation came about and what the consequences of it are. For example, we came across a large flock of wild turkey hens at Sax-Zim bog, foraging along the side of a field, almost all of them identical to one another, except….
The turkey hen on the far right is a “smoke” color morph, a bird that lacks the normal expression of the rich browns and reds we usually see in turkey feathers.
How did this happen? Coloration of feathers in birds is a complex process, and can be completely different in males and females (leading to the basis for why males are so much “prettier” than females). A given stretch of genetic code for feather color in birds can be “alternatively spliced” as the pigment is being expressed in newly developing feathers, leading to wildly different outcomes between the two sexes and at different times of year in male birds or between juvenile and adult birds. But that isn’t the entire explanation for “smoke” color morphs in wild turkeys.
Coloration of bird feathers is largely dependent on eumelanin pigments that produce brown, black, and gray colors and pheomelanin pigments that produce yellowish and reddish coloration. Combining amounts of these pigments like an artist does with a paint palette is what results in the variety of rich color in the plumage.
The “smoke” morph plumage lacks the full expression of a lot of browns and blacks, and it has virtually no red and yellow highlights in its plumage. The morph is very infrequently seen in the wild population, occurring in only about 1 in 100 birds on average, and thus, it is a recessive mutation of melanin expression, especially pheomelanin. More interesting is the fact that the “smoke” morph seems to occur only in females, which probably means it is a sex-linked recessive trait.
There aren’t enough of these birds in the wild population to determine whether the “smoke” morph is at a distinct disadvantage in the winter, or whether they are more or less attractive to breeding males in the spring. But this color morph has been seen by turkey hunters from Oregon to Tennessee, so the mutation must occur in most wild populations.
Watching Black-capped Chickadees flitting about in the vegetation in the winter, you have to marvel at how successful they are at finding food and staying warm in such a challenging environment. I wrote a lot more about this in an earlier blog post: “Baby, it’s cold out there”.
But there is another cousin of the Black-capped species that winters even farther north, in even more intemperate (in the winter) habitat: the Boreal Chickadee – named for the fact that it is a permanent resident of the coniferous boreal forests of Canada and Alaska.
Boreal Chickadees spend most of their time in the spruce and balsam fir forests, where they forage for insects and spiders in the middle of the trees, rather than out on the tips of branches like the Black-capped species. When food is plentiful in the summer, Boreal Chickadees will cache food items in cracks in the bark of the underside of tree limbs where it is protected from winter snowfall, and then they secure them in place with their saliva. It is thought that these storage sites are communal property of the flock, so the birds don’t have to remember exactly where they cached individual stores. This food reserve is critical to their winter survival, in addition to seeds and hibernating insects they might find. Most of their European relatives, the titmice, and Mountain Chickadees have also been observed to use food caches as a winter food reserve.
Not much is known about the behavior and physiology of this lesser-known relative of our popular Black-capped Chickadee, especially their strategy for surviving in the intemperate environment of the boreal forest in winter. I guess not many researchers are willing to brave the conditions where Boreal Chickadees live in the winter — I certainly wouldn’t!
In the Minnesota boreal forest around Sax-Zim bog, we finally found and photographed the hawk counterpart of the Great Gray Owl (from the last post). Rough-legged Hawks are also mouse specialists, but use a completely different strategy to hunt their prey compared to the owls. Where the owls use auditory cues to localize mice under the snow, these particular hawks use visual ones, even honing in on urine trails of voles, which reflect UV light the hawks can detect. Then they perch, sit and wait, and pounce when movements in the snow indicate mouse (in this case, vole) activity.
Rough-legged Hawks are the most northerly breeding Buteo (broad-winged) hawks in North America, setting up breeding territories in the far northern Canadian and Alaskan tundra areas to prey almost exclusively on lemmings there. But they leave the tundra and migrate south to boreal areas of southern Canada and the northern U.S. that have lots of marsh and prairie expanse where they can hunt for voles and other mice where there is less snow cover.
Rough-legged Hawks have very long wings for their body size (up to 60 inches in a large, 3.5 pound female) and they are adept at soaring effortlessly over long distances to hunt for mouse activity. Winter birds on a foraging territory in Idaho had home ranges of up to 200 square miles that they traversed over the course of several days of hunting. Researchers estimated that the bird could sustain itself in the winter on a diet of about 5 mice per day. On days when hunting success was limited, the hawks did much more perching than flying, conserving energy for the next day’s hunting attempts.
I won’t forget this bird — we’ve made four trips to Sax-Zim bog to see it, and finally found one right next to the road, rather than sitting a 1/2 mile away or flying hundreds of feet over our heads. Its striking plumage, feathered feet, and black and white wing patterns should make it easy to ID in the future.
The best way to catch a mouse is to be a Great Gray Owl, with hearing out of this world to localize the mouse under a foot of snow, a dive bomb attack force that can break through a crust of snow hard enough to support the weight of a 180 pound man, sharp talons to grab the mouse scurrying along under all that snow, and a crushing beak that can separate the mouse brain from its spinal cord.
On a one-day trip to Sax-Zim bog, we were lucky to find a champion mouser Great Gray Owl hunting right next to the road along one of the boundaries of the bog. It caught and ate an amazing four mice in under an hour. In fact, it was 100% successful in its mousing attempts!
I’ve put together a series of images into a very short video, accompanied by special “hunting” music so you can enjoy what I was able to see and photograph. If you’re looking at this post in your email, you might need to go to the Backyard Biology website to view the video (click on the title of the post in your email to get to the site). The video is best viewed in full screen (rectangular icon in the lower right corner of the video as it plays), then hit ESC to return to the blog post.
In the video sequence you see the owl take off, from a perch, fly quickly to a site and dive to the snow feet first, dip its head down to the feet to grab the mouse in its beak, fluff its wings above the snow level to take off, fly to a perch, spend some time looking around (not shown in the video), take the vole’s head into its mouth and crush it, transfer the vole to its feet and squeeze it some, then back to the mouth where it is swallowed.
Our Great Gray caught four voles in a very short span of time. But on average they may catch and eat up to seven voles a day while hunting in the early morning and late dusk hours during the coldest winter days.
That’s what we say in the MN northland, when the temperatures drop below 0F. The other day when I ventured out in the early morning, it was -17F (-27C). When I got back in the early afternoon, it had made it all the way up to -3F (-19C), which is just barely tolerable if the sun is out and there is no wind.
And the wildlife aren’t enjoying the cold temperatures any more than I am. Little birds don’t show up at the feeders until mid-morning, and the squirrels (both gray and red) are usually found huddled next to the tree trunk with tails curled over their backs, or basking along the trunk to soak up warmth in the early morning hours.
For those animals (and humans) that can afford to do so, the best solution to surviving cold temperature extremes is to fire up the metabolic furnace. No one enjoys standing out in the cold shivering intensely, but that and the physical exertion of exercise are the first line of defense in staying warm. The trick is to preserve the heat inside the body by improving insulation with a nice layer of subdermal fat, a thick fur coat, and minimizing the surface area exposed to the air.
Another strategy for staying warm in mammals (but rarely in birds) is metabolizing brown fat, which is a special kind of adipose tissue located along the vertebral column, heart, and kidneys. Brown fat is highly vascularized and contains lots of heat producing mitochondrial organelles. The heat produced by a process of non-shivering thermogenesis in the central core of the body can then be circulated to other parts of the body.
So, bundle up and think warm thoughts — the days are getting longer and the sun is getting higher in the sky each day. Winter won’t last too much longer.
Another year of Covid prohibitions on activities, but not such a bad year for seeing new places and new species. The highlights month by month look like this:
Some misconceptions to the usual assumptions of what powers Santa’s sleigh need to be addressed:
Fact #1: those antlered reindeer pulling Santa’s sleigh are all females. How do we know this? Fact #2: both male and female reindeer have antlers — although the males’ antlers are usually much bigger. And Fact #3: male reindeer shed their antlers in late fall, so that by December, they are antler-less. Ergo — the powerful ones pulling the sleigh are the girls.
And this leads inquiring minds to wonder — a) why do female reindeer have antlers at all? (other female members of the deer family do not), and b) why do they have them all winter, only to drop them after their calves are born in the spring?
It would seem to be a great advantage for females to keep those antlers over the winter as they gestate next year’s offspring. They need energy for reproduction, and the food is buried under the snow. Antlers would certainly be useful for removing snow so the reindeer can get to the forage. Larger-bodied males can withstand periods of low food availability better, and need to start re-growing antlers immediately in the spring so they will be ready to compete for mates in the summer and fall.
Now — about that red-nosed leader of Santa’s team. Rudolph, created by Robert May in 1939, is also pictured with antlers, so we must assume he is a she, as well as the rest of the team. But why make such a big deal about the red nose? Is there such a thing as a red-nosed reindeer?
The rosy pink nose of reindeer in the winter is due to high blood flow to the nasal area, which warms the nasal cavity, and thus the warms up the frigid air reindeer breathe in before it goes to the lungs. In addition, flushing the nasal cavity and head with blood from the central core of the reindeer’s body helps keep the animal’s brain warm. I suspect if we did the same thing when eating a slushy drink (like Jamba juice), we wouldn’t get an ice-cream headache.
So, let your kids and grandkids in on the real power behind Santa’s trip around the world on Christmas eve — female reindeer!
The backyard has been really quiet the past couple of weeks, as colder weather sets in and the daylight hours get shorter and shorter. Some days the birds don’t start visiting the feeders until after 9 a.m. Even the squirrels are quiescent, having long ago dug holes all over the backyard to store their walnuts.
But the red foxes make regular treks through the backyard early in the morning, looking for whatever they can find — which apparently isn’t much because they don’t stay more than a minute and then move on to the wetland area in back of the backyard.
Photographers usually try to shoot with the sun behind them, but occasionally the scene may be more dramatic when shooting directly into the light. That was the case the other day when I was walking in Reservoir Woods and came upon a field of Indian grass and Showy Goldenod seedheads that shimmered in the backlit afternoon light.
Look at the difference in this scene when I turn around and shoot with the sun directly behind me. The seedheads of the grasses and goldenrod disappear into a monotonous expanse of yellow stems.
There’s an important lesson here — don’t always follow the rules because you might miss some of the drama in nature.