Tree sparrows and bluebirds

…a scrapbook of spring bird stories

In the early part of April, there were sometimes two dozen mallards on my mostly-icy home pond. There was one male who was not fully ‘dressed’—while all the other males in the group had long since acquired their glossy green heads, rusty chests, and so on, this one was only part-way into the typical breeding dress. Was he just a very late hatchling last fall, lagging in maturation, or did he have a metabolic deficiency of some sort?

By late April, the mallard mob had dispersed, leaving one pair in charge of the now-ice-free pond. The male was seriously aggressive toward a visiting solo male, defending both his female and, perhaps, the seed-fall from the feeder hanging over the water.

Out at Eagle Beach, a mixed crowd of six species of waterfowl moved offshore, as a gamboling puppy approached along the water line. A scattering of American pipits foraged over the tideflats, readily distinguished from other small, brown songbirds by their characteristic gait—they walk and run, rather than hop. At the edge of a mown grassy area, I found a mixed flock of juncos, both Oregon and slate-colored, and American tree sparrows. They were all scouring the turf for food and flitting hastily to the surrounding brush when startled. I hadn’t seen a tree sparrow for ages, so this was fun.

Tree sparrows nest way up north, on open tundra with scattered shrubs and thickets of willow, birch, or alder. The nest is usually on the ground, and the female incubates the eggs for about twelve days. Nestlings are fed by both parents and stay in the nest only about nine days, then hopping out to follow the adults on foot. Tended by the parents, they begin to fly when they are about two weeks old. Tree sparrows feed on the ground and also by hopping up to grab seeds from the seed-heads of low-growing plants. In season, they also feed in trees, to eat small berries. This species has not been very thoroughly studied, so there are lots of details to discover.

Through much of April, there were reports of migrating mountain bluebirds on their way north, seen now here, now there, and in some other place. I tried several times in several places to find them, but they continued to elude me. Then, the day after finding the tree sparrows, I strolled out toward the Boy Scout beach. In addition to seeing a fox sparrow, two Townsend’s solitaires, some Bonaparte’s gulls, and a flock of snow geese, I encountered two friends who were intently watching a patch of dead cow parsnip stalks and a few little spruces. They had found a male bluebird, which was foraging in classic bluebird style: watching from an elevated perch, just a few meters above the ground, then dropping down to the ground to pick up an insect and flying back up to an observation perch. Later, I spotted a female bluebird in the same area, and she too was foraging in the traditional way. So, at last, I had found them.

Photo by Kerry Howard

Bluebirds have other foraging techniques too. Sometimes they hover a couple of meters above the ground to scan for bugs or occasionally chase bugs in the air. In the non-breeding season, they add seeds and fruits (of many species) to the diet. To augment calcium in the diet, egg-laying females may eat bits of egg shell or snail shell to help build the shells of developing eggs, and nesting females may feed shell bits to the chicks to help develop good bones.

Mountain bluebirds nest primarily in the mountains of Montana, Wyoming, and so forth, but some of them range more widely, coming in small numbers to northern B.C., Yukon, and interior Alaska. They are cavity nesters, loving old woodpecker holes but also nesting in cliff crevices, nest boxes, and sometimes other human structures. They favor habitats with short grass and scattered trees or snags offering nesting cavities. They are reported to arrive early on the nesting ground, probably because suitable cavities are limited in number, so the early arrivals get the best choices.

Male bluebirds are territorial, defending an area around potential nest sites, and females can then choose among them. Nests are built primarily by females, often guarded by their mates against potential predators and intrusions by other males. Females incubate for about two weeks, usually fed by their mates, and they brood the tiny hatchlings. Both parents feed the nestlings, which stay in the nest about three weeks, and the fledglings.

Mountain bluebirds are socially monogamous, meaning that they form pairs but both partners may go philandering–seeking occasional matings outside the pair bond. This arrangement turns out to be rather common among species that were once thought to be strictly monogamous. A bluebird pair bond typically lasts for a season, including replacement nests or second nests, but a pair does not necessarily stay together the following year.

That blue color that we love is not produced by pigments but by the micro-structure of the feather barbs; both UV and blue wavelengths are reflected. Males within a population differ in the amount and reflectance of their plumage. Now things get more intriguing: In two studies, done in two different geographical areas, brighter males were more likely to go philandering, engaging in more extra-pair copulations, than less-brightly colored males. Their brightness was not related to age or body condition. In one of those two studies, the more colorful males sired more of the chicks in their own nests and more extra-pair chicks. In the other study, the more colorful males were also early nesting and achieved more extra-pair copulations, but the paternity of chicks in their own nests was not enhanced, compared to less colorful males nesting later. Thus, in both cases, the payoff for bright coloration was greater numbers of offspring sired, and potentially greater evolutionary fitness, although the size of the payoff differed between the two areas.

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Beaches and tideflats

sightings and discoveries in a sudden spring

Several sunny (!!) days in a row in mid April. I’ve now hacked most of the ice off my driveway and trimmed back the piles of snow on my terraces from two feet deep to a few inches. Mallards are thronging to my pond, which has ice only in the middle, with wide open channels around the edge. I hear juncos, ruby-crowned kinglets, varied thrushes, and nuthatches in my yard. Maybe it’s really spring!

All that sunny weather drew me out to soak up the sunshine. On Boy Scout beach, while a group of friends perched to have lunch, a beautiful, huge queen bumblebee checked us out—she particularly liked a certain blue/purple jacket, to the consternation of the human inside. Those bees just love that hue and come buzzing around, as if it were one huge flower. They usually figure things out fairly quickly and go away.

On another day, I visited Eagle Beach and found a partial skeleton near the high tide line—one forelimb and a body sans skull. The bones were quite well picked-over by scavengers. I was puzzled—they clearly didn’t’ come from a deer or a seal; otter and bear were quickly ruled out; so who was it? A little bony detective work on the internet later found a likely prospect—a small Steller sea lion. The clues were the short, stout bones of the forelimb, a curve at the back edge of the shoulder-blade, and the lack of well-developed flanges (neural spines) on the outer part of the vertebrae. That tentative ID was later confirmed by a photographer-friend who had seen the carcass. The forelimb was especially interesting—the upper arm bone (humerus) was very short (maybe five inches long); the two lower arm bones (ulna and radius) were not quite so short but quite thick. That morphology might be related to how they use their forelimbs on land, hoisting the heavy body over the ground.

A couple of days later, I walked the dike trail with a friend, and the place had really come alive. Ruby-crowned kinglets serenaded us all along the trail, helped by a song sparrow or two. Golden-crowned sparrows scratched around in the thickets for fallen seeds and occasional bugs. Four pipits explored a channel left dry by the low tide. Robins were scattered widely over the grassy tideflats, foraging, and scolding when disturbed. A male yellow-rumped warbler hawked for flying insects over a pond and a female flitted about in a semi-dry channel after bugs that apparently jumped around. Two shorebirds got away from me but a greater yellowlegs was poking around in some shallows. All that warm sun had made green shoots of several species begin to rise from the soil, and on the trees a few leaf and flower buds were ready to open.

The next day I walked Eagle Beach again. Things were very quiet until a northern harrier coursed over the flats, scattering a few small birds and provoking the geese into vociferous protests. Harriers often cruise the beaches at this time of year, no doubt hoping to nab migrating shorebirds. Although I’d missed (sadly) the migrating mountain bluebirds reported from several beach areas, I did score a minor coup—a Townsend’s solitaire was hanging out in the brush at the edge of the big meadow at Eagle Beach, making occasional forays into the open in pursuit of small flying insects. This species typically nests in the Interior, often in open forest habitats, placing its nests in cutbanks and steep rocky slopes; the nests are on the ground but usually have some overhanging rocks or stumps.

Townsend’s solitaire. Photo by Scott Ranger

A few more fine, sunny days, and there were blueberries in flower, skunk cabbages up and open for their female-phase flowers, a flock of snow geese on the wetlands, and reports of wood frogs chorusing in a pond over on Douglas. It’s happening!

Eagle Beach at equinox time

swans and lugworms on a lovely day

Just before the vernal equinox, I strolled in the Eagle Beach area with a couple of friends. The lower reaches of the river bore a few cakes of ice drifting to the sea. We stood on the bank, looking toward the Chilkats, enjoying the view. Then, down around a bend, one of those ice cakes surprised us as it suddenly sprouted a long neck and a head. Oh. Not an ice cake. Presently, the swan spread its big wings and set sail over the estuary. It was too far away to be sure of the species, but it was probably a trumpeter swan, which appear to be more common here than the smaller tundra swan.

Trumpeters migrate through here in spring and fall, and occasionally overwinter in estuaries and ice-free freshwater ponds. We see them in various places, including Amalga and the Dredge Lakes area. They are probably from the population that nests in coastal areas farther north; those that nest in the Interior are more likely to migrate inland. They have a huge wingspan, similar to that of eagles, but they are much heavier; they are said to be the heaviest flying bird in the world.

Trumpeter swans once nested in marshes and ponds across much of North America, but hunting (for meat, feathers, skin), habitat destruction, and lead-poisoning (from ingesting shotgun pellets that sank to the pond bottoms, where swans often feed) decimated their numbers. Thanks to conservation efforts, the species is not endangered now, and many breeding populations are thriving.

They can live to be more than twenty years old, but they mature slowly; they usually mature when four to seven years old, occasionally sooner. They are monogamous, the pair bond usually lasting as long as both birds are alive and well, and the pair often staying together year-round.

On the nesting grounds, they choose freshwater marshes, ponds, and small rivers, building nests on beaver dams and lodges, hummocks, and platforms of floating vegetation. The nests are typically surrounded by water, giving them room for a running take-off when departing. Both male and female work on nest-building, both birds collecting material but the female doing most of the construction. The big eggs are laid at intervals of one and a half to two days (not daily, as in most birds). Both members of the pair incubate the clutch of (usually) four to six eggs, but neither develops an incubation patch on the body…they incubate the eggs with their huge, well-vascularized feet!  

They are territorial, fiercely defending their chosen area at least until the eggs hatch and often, with declining intensity, until the chick fledge. That takes three or four months. Both adults tend the chicks, but become flightless for a few weeks during the summer molt. The young birds stay with their parents throughout their first winter. They forage on submerged and emergent aquatic vegetation, sometimes grubbing up tubers. Birds that winter farther south often forage in agricultural fields, and even digging up potatoes and carrots.

A bit later that day, we wandered out onto the sand flats exposed at low tide. And there was the swan again, walking slowly toward a group of grazing Canada geese. We imagined that it had thoughts of joining the group; swans sometimes migrate and forage in flocks of geese, ducks, and cranes. But these geese would not have it! They went on full alert and eventually took off. The swan then ran across the flats and took off toward the estuary.

Photo by Aaron Baldwin

Along the bank of the lower river, we found a lugworm, lying on the sediments. I don’t know why it was there…They normally they live in J-shaped or U-shaped tubes within the sediment, although they can move out and build a new tube at times. At one end of the tube, they deposit coiled fecal castings on the surface, which we often see when the tides have not washed them away. Fecal deposition may sometimes be a slightly dangerous activity, because a foraging bird or crab may snap up the tail end; however, the worm can regenerate a new one. At the other end of the body is an eversible pharynx with a mouth that engulfs the sediment. The worm then digests some of the tiny organisms and perhaps organic detritus, passing out the partially cleaned-up sediment grains in the castings. Some lugworms can also feed on suspended particles. These worms breathe water, using their external gills alongside the body, when inundated by the tide, but reportedly can breathe air through the skin, when the tube is exposed at low tide.

The sexes are separate, raising the question of how these burrow-dwellers manage to make offspring. The available online reports are contradictory and confusing. The males simply eject sperm out into the water, hoping they can find eggs to fertilize. By some reports, the eggs are held in a female’s burrow and released sperm have to find and enter the burrow; that’s a system that probably works best when the worms live at high densities and spawn at about the same time, as indeed they often do. Then what? The fertilized eggs and larvae may be brooded in a female’s burrow; when still small, they leave and make a burrow of their own. However, we often see gelatinous sacs lying on the surface at low tide; they are tethered somehow to a female’s burrow. The sacs contain eggs or embryos; but why are they lying on the sediments?

April Scrapbook

a sea lion necropsy, grazing geese, and other fascinations

In mid-April, I had the privilege of observing a necropsy of a subadult male sea lion that had recently died. The carcass lay near the end of a rocky point. I was fascinated not only to see the big beast close-up but also to watch the well-organized NOAA necropsy team in action (lead veterinarian Kate Savage). The animal had no perceptible wounds, but it was very thin and its stomach held nothing more than a stone, a small clam, and a cluster of round worms. Was it unable to feed, for some reason, or could it not find enough food? The lab reports might identify some ailment but we may never know why the big fellow came to lie on the rocks.

Several days later, I went back out to see if the remains were still there. The carcass had washed up on a high tide nearly to the trees. The bones had been picked quite clean, except for the flippers, which were still covered with skin. Two immature eagles tugged at stringy tissues but could nip off only tiny morsels—hardly worth fighting for. Despite the poor rewards to be had, the trees held several other eagles that were keeping a close eye on the bones. As often happens at carcasses, the intestines had not been eaten, even though the bones were picked bare. What makes that body part undesirable?

The next day, I went to Eagle Beach. Circling a bunch of grazing geese in the meadow (so as not to disturb them) and arriving at the berm near the mouth of the river, I saw a group of fourteen snow geese, resting on a sand bar and wondered if the solo bird that had been around in previous weeks had finally found some friends of its own kind. Walking the beach past the day-use area, I noted that some irresponsible person had dumped an eight-cylinder engine from the highway lookout down onto the upper beach. What are the prospects of getting that big piece of junk out of there?!

As I returned to my car, I saw a very dark bird perched at the top of a small spruce. A merlin! Merlins of the Pacific race are charcoal-black on wings and back, and the chest streaks are thick and dark. This bird looked very burly and husky. Checking a bird guide, I found out that merlins are a bit bigger than kestrels in linear dimensions but considerably heavier. Merlins typically prey on small birds, which seemed rather scarce that day. This sighting was my good prize for the day (my other ‘prize’ was a five-gallon bucket full of trash from the beach).

The following day, I went out on the Boy Scout/Crow Point trail with two friends. Good weather, this time, in contrast to a few days before, when stiff, cold winds had us hiding the trees and sent the ducks and geese into shelter well up the river. On this day, however, the waterfowl were spread out over the sand bars near the mouth of the river. Eagles stood at the edges of the sand bars exposed by the dropping tide. One of them was attended by two or three quick and daring crows that darted in to snatch bits from the big bird’s prey. Six snow geese, heads down, grubbed up food from the meadow soils while several Canada geese stood watch. Later, more snow geese flew in, gliding elegantly on black-tipped wings, bringing the total back to fourteen.

Some sea lions, large and small, cruised along the southern end of the beach, tightly packed together. They were soon joined by another group. The whole gang dithered back and forth but did not appear to be foraging. We wondered if the second group had brought word of a pod of transient killer whales somewhere not far away.

The sands were full of animal track: shorebirds of two sizes (although we saw none of the makers), geese, gulls, ravens, a mystery critter. The wrack line from the last high tide was a very thin line of small debris. We could see that a crow had marched along the line for some distance, no doubt looking for things edible.

The goose-flat meadow was empty of geese, so we strolled across it, looking for signs of emerging green shoots. A sharp whistle brought us bolt-upright and looking toward some trees, where three marmots stood on a small rise. There is presumably a colony of beach marmots nearby, perhaps under tree roots in a sand bank.

Songs of ruby-crowned kinglets and robins entertained out ears, filling out a good early-spring walk.