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Natural Observations–Life in the birch trees

by KTNA Staff ~ March 17th, 2014

 

photos by Robin Song

Natural Observations host and producer Robin Song tells about the birds and animals that she observes using the cavities and branches of the birches outside her cabin. Audio is 9:43.

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Trees are vital to many species of birds and mammals. I’ve been observing two birch trees in particular, for a few years, now. They live east and west of the cabin in which I live as caretaker on Birch Creek Ranch. The one to the east is very tall and years ago lost its crown in a wind storm. It has seven large branches jutting out from its trunk, going down below what used to be its crown.  Early in the spring, four years ago, a pair of Hairy Woodpeckers began excavating a hole in its trunk just below the lowest branch. The hole faces due south. It took a month for them to finish the nearly perfectly round hole. The male did most of the work, with his mate taking shorter shifts. Doing research later, I read that the males of most cavity-dwelling woodpecker species do most of the nest-hole excavating, then – after  all the eggs are laid – the male usually takes over the night shift, sitting on the egg

 

I also read that woodpecker nest holes are in great demand by other cavity nesting species, (like swallows) and so woodpeckers face competition for the nest holes they excavate from the moment the holes become usable. Woodpeckers may aggressively harass potential competitors, and they may also use other strategies, such as digging the nest in the underside of a branch where it meets the trunk and is hidden from obvious view. Woodpeckers make one hole per nesting season. They line their nest with wood chips from the excavating. The eggs are incubated for a couple of weeks, and the nestlings stay in the nest hole for a month before they fledge.

 

I watched the pair of Hairys through binoculars, coming and going to their nest high up in the trunk. As the nestlings grew larger and stronger, their calls became louder. I quickly learned not to go near the tree to get a better look, for both parents would then dive-bomb me, screaming loudly as they dived straight at me. It was unnerving, and I left hastily, deciding it was better to watch the Hairys through binoculars. While I didn’t get to see the nestlings fledge, I did get to see the three fledglings shortly after they left the nest hole. They were on a nearby branch together, begging food from their parents, who dutifully brought them food throughout the day. The family was there on the branch the next morning, but by early afternoon they had all flown to the forest nearby.

 

The next spring swallows found the nest hole. It was a pair of Tree Swallows, and for the following three springs a pair of Tree Swallows has raised a family in that nest hole. Each spring a large flock of swallows arrives at the ranch, consisting of both Tree and Violet-green swallows. For a while the birds are checking out every nook and cranny for potential nest sites. That nest hole in the birch is quite a prize and is fought over vigorously. I’ve watched three or four pairs of swallows squabbling over nesting rights, and it looks like it gets downright nasty, with swallows duking it out in the air, swooping at each other and tumbling together, wings flashing as they dive, screaming insults until they finally break apart, then flying up to chase each other again. Sometimes it looks like a pair has claimed the nest hole, with one going inside, its mate clinging to the bark just outside the hole. But then another pair will come diving at the tree, bringing the swallow inside the hole flying out, she and her mate giving chase to the incoming pair, all four chattering with high-pitched calls. Last spring it looked like a pair of Violet-greens had won the battle, but a few days later they were usurped by a pair of Tree Swallows. I wonder who win will nesting rights this spring.

 

Meanwhile, the broken crown of the tree serves as a great lookout perch. In winter it has been used by Ravens, Magpies, Pine Grosbeaks, a Merlin, a Sharp-shinned Hawk, and a Great Horned Owl. When the Snow Buntings migrate through the ranch on their way to the tundra in April or May, that perch and the branches below it can be filled with the snowy white birds. The tree does not have any close neighbors, and so any bird using it as a lookout has a clear view for three hundred and sixty degrees. Until the resident pair of ravens go off in the spring to their nest site, they often use that birch as a lookout perch through the winter, especially in the early morning. The ravens roost in the rafters of the hay storage barn at night, then one or both will fly to that birch just after leaving their roost, there to sit on the lookout perch and survey their domain. From there they can spot any ravens who might dare approach the ranch from any direction, and launch to fly to the offender and escort them on out of the territory.

 

In the summer the seven branches leaf out, but offer sparse shelter to birds. Its main use is as a lookout perch for birds passing by, and as a home to that year’s swallow family. Once in a while a squirrel will make the mistake of running up its trunk, but is soon sent leaping for the tall spruce a few yards away when the squirrel is mobbed by diving, screaming swallows. Swallows are very good at bringing in help from their nesting neighbors to drive off any would-be intruders.

 

Meanwhile, the birch I’m observing on the west side of the cabin is nestled amongst a crowd of trees, both birch and spruce. In the spring of 2012 I watched a pair of Hairy Woodpeckers begin excavating a hole in its trunk, facing southeast. But this hole wasn’t very high up the trunk. Around twelve feet off the ground. Most of the woodpecker nest holes I’d seen were considerably higher, but I figured the birds had their reason. They made a beautiful hole and worked at it diligently. Then, to my surprise, they abandoned it. Just like that. A couple of days later I heard them working on another tree farther out in the forest. The abandoned nest hole didn’t interest the swallows at all. Too many trees and branches nearby, I surmised, and too close to the ground to be safe. The beautiful hole sat empty. Occasionally I’d see a chickadee or a nuthatch land on the bark near it, then go explore it, disappearing inside for a little while, then emerging again, flying away to another tree. Perhaps they were finding insects inside. The hole is much too large for either of these small birds to use it as a nest site.

 

Then, in mid-February of this year, I watched the pair of resident red squirrels chasing each other through the trees. All winter they had been squabbling, running each other away from the suet feeders I have hanging in various locales. The dominant squirrel wouldn’t tolerate the presence of the other squirrel and would give vigorous chase up, down and around the trees, the subordinate squirrel looking like it was fleeing for its life. But then the chase took on a different tone in February. It became more playful. Then I watched one squirrel sitting at a suet feeder while the other sat on a branch close by, nibbling on a sunflower seed from the bird feeder. That wouldn’t have been tolerated just a couple of weeks before. A couple of mornings after that I watched a squirrel climbing in that curious staccato fashion of theirs down the birch and approach that hole in the trunk. It poked its head in, pulled it back out, glanced around, and then popped inside the hole. I expected the squirrel to come right back out, but it stayed inside the hole for quite a while. I kept an eye on the birch, and that afternoon I saw a squirrel again approaching the hole, this time carrying a spruce cone. Inside it went. It poked its head back out after a few moments, minus the cone. It was a classic scene- the squirrel’s furry head looking out from the hole in the birch trunk, whiskers bristling. In a few moments the squirrel emerged and dashed up the trunk, disappearing from my view amongst the thicket of branches above. What this means, I’m not sure. Will the squirrels use this hole as a nest or a storage site? I guess time will tell.

 

It’s a privilege, for me, to watch these two particular birch trees and see what happens to them. Even though a wind storm damaged one, it still has served a vital purpose as a lookout perch and home to families of woodpeckers and swallows. The other, while selected as a potential nest site by woodpeckers, but then abandoned, is still serving a multi-layered purpose for small birds and squirrels. I’ve read that chickadees will seek out cavities during winter cold snaps and birds will cram into that cavity until it is full, thereby keeping each other warm with body heat until the cold snap ends. I’m sure that nest hole has kept several chickadees alive through many a cold snap, by now. Maybe this summer it will be the cradle to a new squirrel family.

 

Perhaps the next time you spot a hole in a tree trunk, you can take a moment to ponder the marvel of this creation, from the bird which chiseled it out, to its many uses thereafter. And study the tree, too. Does it have a lookout perch? Or perhaps the remnant of a robin’s nest? Are there small holes drilled in the bark where a woodpecker has searched for insects? Are there scars from the claws of a bear, or scratches marking where a porcupine climbed up to a limb? A tree can have quite a story to tell you, if you take the time to study it.

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Here is an update on last week’s “Owls of Winter” story: an astute birder contacted me and pointed out that Short-eared Owls don’t winter in Alaska. Sure enough, when I researched that, I found that these owls migrate Outside and generally winter in the Great Plains region of the Lower forty-eight. I included the calls of the Boreal and the Short-eared Owls in my story, but we’ll need to wait until later in the spring, when the migrants are returning to the State and setting up territories, to hear the calls of the Short-eared Owls. Thanks to my fellow-birder for helping me keep my facts accurate.

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KTNANatObs031614The Life of Trees, by Robin Song

 

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