The end of August

a cheery end to a dismal month

A rather dismal August finally dripped to a finish. The sodden ground could hold no more water, so the streams were raging torrents and trails were squishy. The lovely long days of summer were just a memory, as day-lengths shortened rapidly. The fall season in Juneau can be pretty gloomy, but instead of pouting and whining (well, mostly instead), I found some cheering things to see.

Out near the glacier, a very late brood of barn swallows lined the edge of their nest with five widely gaping beaks every time a parent bird arrived. Each time, one lucky nestling would get a bug or two from a busy adult; feeding five big chicks took a lot of work. But all five chicks fledged a day later and were lined up on a fence railing, awaiting food deliveries.

On my home pond, there was another late brood, this one of mallards. A female appeared, trailed by two large offspring that were getting their real feathers. All that was left of the babyish down was a small poof on the rump. These two, about half the size of the female, were the remainder of a brood of five or six ducklings, but both of them, with mama, appeared for many days and finally looked just like her in both size and plumage.

The star of the show near the Visitor Center was a young porcupine, recently abandoned by its mother. That’s normal for this time in the porcupine year. Junior could be seen by numerous enchanted visitors, as it steadily gobbled alder leaves right next to the trail. For variety, it nibbled on some cottonwood leaves or climbed up a willow to demolish more leaves. Its right front leg seemed to be sore and was seldom used, but that didn’t deter the little guy from climbing trees and roaming around the area in search of green delicacies.

A whale-watching tour near Shelter Island found several humpbacks, and soon we were surrounded by them. The adults were placidly diving and coasting along, while a calf was showing off. It breached many time, it lunged repeatedly, and it rolled again and again. Its youthful exuberance entertained us well.

Mixed flocks of migrant songbirds flitted through the shrubbery in several places. Yellow-rumped warblers, ruby-crowned kinglets, Wilson’s warblers, and probably others searched for insects in the foliage. A friend watched an orange-crowned warbler probing both ends of a rolled-up cottonwood leaf in hopes of extracting the caterpillar within. Those masters of fast, erratic flight, the dragonflies, were no match for the wily olive-sided flycatchers, which perched in dead treetops and nabbed the big ‘darner’ dragonflies as they hunted small insects over a creek.

Those of us who hang out near Steep Creek and the glacier were pleased to see an old ‘friend’ appear, strolling on the beach (or what beach there was, given the high waters). This was Na Tláa, the Clan Mother, a.k.a. the grandma bear, who is about twenty-three years old and has not had cubs for several years. She was not very plump and, long after other local bears had their new coats, she was still molting; her back was covered with long, bleached-out, reddish fur, while the rest of her showed shiny black new fur. This old bear foraged on this and that in the vegetation, caught a fish and ate it, looked at more fish in the ex-beaver pond, and eventually wandered on down the lakeshore.

High on the list of fun stuff was an encounter on the Perseverance Trail on the very last day of August. Two friends and I were coming down the trail, just below the Horn (where two benches provide a view of Snowslide Gulch). Some distance ahead of us there appeared a large black lump, followed by two smaller black lumps, moving slowly up the trail. Ooooops! What now?! Steep cliff up on our right, steep cliff down on our left, and nowhere to go but back. So we quietly backed up a hundred yards or so to the Horn, intercepted two other down-hikers, and waited. And there they came, mom and two cubs.

I suggested that we all go up on the little rubble slope on the inside of the curve, to allow the bruins plenty of room between us and the railing. Bad idea! Mom took one look at us and turned around, heading back down the trail. But she hesitated and looked back, as if she really wanted to continue upward. So we all scuttled into a corner of the fence behind the benches. Ah! Much better! The family turned back uphill and sauntered past us—Mom completely calm and owning the trail, the kids a bit skittish. So on they marched, right up the trail. There had been clear signs that some bears had used the trail above, bears that had been eating loads of stink currants. Nevertheless, we hoped they’d find a good place to leave the trail, so as not to be bothered by other hikers.

She was presumably a Town Bear, because she had an ear tag. This female bear was very well-behaved, from our perspective. And we had respected her space. A good encounter!


Visiting Yakutat

a festival of terns… and lots more to see

In early June, I had the privilege of participating in the Yakutat Tern Festival. This gave me the opportunity of visiting an area of Southeast that I’d never explored before (as well as meeting some new and interesting folks). There were only two familiar faces, one of which belonged to Linda Rosenthal; she was there as a visiting musical artist, and her violin wizardry kindly provided the introduction to my seminar!

From my little explorations, several natural history items stand out. Brown bears lived up to their reputation of being very common. In just over four days, I saw nine of them, at least one every day. Some were grazing in the meadows, including three young cubs whose mother was not in evidence but must have been somewhere nearby.

We saw several Caspian terns—huge (for a tern), with a big red bill and a raucous voice. Much more common are two smaller terns: the Arctic tern, which also nests in Juneau, and the Aleutian tern. Yakutat is reputed to be the southernmost nesting colony of the Aleutian species on mainland North America; this species also nests along the Aleutian chain and the coasts of western Alaska and eastern Russia.

Aleutian tern. Photo by Bob Armstrong

The small terns look quite similar to each other, but the Aleutian tern has a distinguishing white forehead mark on its black cap; it also has a slightly shorter tail and a darker back, as well as a call that differs from that of the Arctic tern. Both species feed on small fishes and sometimes shrimp-like invertebrates. Both species are long-distance migrants: our familiar Arctic terns go all the way to Antarctica after the summer nesting season here, so they enjoy perpetual summer (when it is winter here, it’s summer down there, of course). The Aleutian tern migrates from here down the coast of eastern Asia to the seas around Indonesia. I wonder what they eat down there: tropical seas are usually said to be less productive than high-latitude waters, which is why our humpback whales come up here from their winter quarters in Hawaii.

Because they usually nest on the ground on sparsely vegetated sandflats (Arctics reportedly in slightly more open areas than Aleutians), both species are too easily subject to disturbances that ruin their nesting attempts—humans and their dogs can have devastating effects on a whole colony of terns. Of course, wily predators such as ravens are eager eaters of eggs; coyotes (and foxes is some areas) like both eggs and adults if they can get them. Sometimes a whole colony deserts a traditional nesting area and goes elsewhere, and sometimes the whole group just gets wiped out. So little is currently known about Aleutian terns that the loss or reduction of known colonies raises concern about the population status of the species, so studies are now underway in Alaska to discover if the birds have established new colonies to replace the lost ones.

We saw several parasitic jaegers (in German, jaeger means ‘hunter’), harassing gulls that were actively fishing. Jaegers are kleptoparasites, stealing prey from other birds that catch prey for themselves. One jaeger dove repeatedly at a small gull that held a just-caught fish, following every evasive action of the gull, until the gull finally gave up and the jaeger got the fish. Parasitic jaegers nest on the tundra up north, where they are quite capable of catching their own prey; their kleptoparasitic habits are exercised chiefly on migration and in winter.

In among the several kinds of gulls were black-legged kittiwakes, which resemble gulls but technically are not gulls. I seldom see them in Juneau, although they nest in Glacier Bay. Kittiwakes are typically cliff- nesters, but the Yakutat forelands do not offer many cliffs, so these individuals may nest across the bay near the glacier or perhaps they are non-breeders.

Other sightings that provoked thought include the observation of large differences among beaches in the animal remains that were left by a receding tide. One large sandy beach yielded shells and claws of Dungeness crabs and the shells of razor clams. Another had some mussels and clam shells (more like many Juneau beaches). And one had nothing at all except one long-dead sea star—that seemed very odd.

On one large sandflat there were moonworts growing among other sparsely distributed plants. Moonworts are rather peculiar fern relatives about which relatively little is known. Recent research has found two new species of moonwort in Southeast (I was told that Yakutat is one place where they live), but for those of us who are not specialists, they look very much alike.

We found a small colony of cliff swallows, which stick their gourd-shaped mud nests to rocky cliffs or the sides of buildings and I-beams under bridges. From almost every nest opening peered the face of an adult bird, while other adults flew back and forth, sometimes delivering a tasty morsel to the nest occupant. We inferred that one adult was incubating eggs or brooding very small chicks while the other adult of the pair went hunting. Male and female cliff swallows equally share the parental tasks of incubation and feeding chicks.

Barn swallows were tending their nests too, and every morning brought a chorus of bird song from several species of sparrow and warbler, especially in the alder and willow thickets. Worth getting up for!

Barn swallows and thixotropy

dabbing and daubing for stable nests

One day in early September, I was fascinated by a pair of barn swallows still feeding big chicks in the pavilion by the visitor center. All the other pairs there had long since fledged their chicks, and those chicks would be experienced foragers by the time of migrations to southern climes. The September chicks would leave the nest soon, but they would have a lot to learn about catching insects on the wing, and it seemed unlikely that they’d be proficient foragers by migration time. An uncertain fate!

As I looked at that nest, I began to wonder about how barn swallows manage to build such a nest. Their nests are shallow cups made of little mud balls stuck together, and lined with feathers. Their relatives, the cliff swallows, build a more elaborate, gourd-shaped nest with a narrow entrance, but they use the same basic technique—mud pellets stuck together and the whole edifice stuck to the side of a building or cliff.

But what makes the pellets stick to each other? In a nest under construction, the first pellets to be placed have had a chance to dry a little, and when they dry, they shrink a bit. If a swallow just plopped new, wet pellets into place, the shrinkage rates of the new and old pellets would differ, and this creates weakness and cracks in the structure (a result well known to human potters). Not a good result.

That’s where thixotropy comes in. It’s a fancy but concise way of describing what happens to some seemingly stable materials when they are mechanically agitated. They become fluid, temporarily, and a little later become stable again, often in a new configuration. It turns out that thixotropy (from the Greek words for ‘touch’ and ‘change’) is characteristic of many materials and situations. It’s involved with some metal casting, certain printing processes, and some foods, for example. Perhaps most famously, it can happen during earthquakes, which shake and liquefy wet soils, causing buildings and trees and everything else to sink or tip or slide, sometimes catastrophically.

Animals use this curious phenomenon too. When bald eagles dance up and down on wet sand in order to capture buried sand lance, one effect of their prancing is liquefying the sand, making the fish more accessible. Gulls can use the same trick.

Mud dauber wasps build little cells of mud, stuck to walls. When they add new pellets to the cells, they add a bit of water from their crop, and they buzz. The vibrations liquefy the mud, letting it spread into the earlier, drier pellets. Then old and new pellets vibrate together, achieve the same consistency, and are stable when vibration stops.

Gathering mud. Photo by Bob Armstrong

That brings us back to barn swallows. They collect mud pellets from puddles and gradually add several rows of pellets to form the nest cup. But they apparently don’t just whack each new pellet into place. Instead, when they add pellets to the growing base, they use a dabbing or dabbling motion. This jiggles the old (drier) and new (wetter) pellets until the water content is similar and their consistency is equalized. As soon as the dabbling stops, the junction of new and old pellets becomes stable. Wouldn’t it be fun to find out if young adult barn swallows know to do this automatically or if they have to learn the hard way (if their first nest-building attempts collapse)!

Barn swallows

a complicated society

I like to go up around the Mendenhall Glacier Visitor Center for lots of natural history reasons, and one of them is to watch the barn swallows that nest in the pavilion, the bus shelter, on the sides of the center itself, and sometimes on the kiosk. The insect-catching adults swoop high and low, sometimes playing ‘chicken’ with the numerous cars and buses, which typically exceed the posted speed limits. Most of the thousands of tourists are oblivious to these birds, but a few do pay attention.

In mid July, some of the nests had big chicks, either just leaving the nest or just about to do so. Other pairs still had eggs, in some cases because vandals had destroyed their first nests and these pairs had to begin anew.

Photo by Bob Armstrong

Originally, barn swallows nested in caves, cliff crevices, and hollow trees, but now they have converted to using human structures almost entirely. They build inside culverts, under bridges, and on buildings; use of natural sites has become unusual and noteworthy. Historically, as North American became more populated by humans, barn swallows also spread into new areas.

Barn swallows occur all over the northern hemisphere in the nesting season (but migrate to South America or Africa in winter), and they are among the most intensively studied songbirds. European birds have white breast and belly feathers, but in North America these feathers are rusty orange. It turns out that in North America, a dark rusty breast on a male is attractive to females, and females mated to dark rusty males produce more chicks than those mated to paler males.

In this species, the elegant tail is long and forked, and males have longer tails than females. A deeply forked tail is said to increase lift and allow tighter turns, and if the fork is symmetrical, maneuverability is enhanced. Long, symmetrical tails develop on males that have few external parasites. Females really go for males with long, symmetrical tails—the best fliers with the fewest parasites. So males with such tails have a high probability of getting a mate, they get better mates, and they indulge in more extracurricular copulations as well. Females that are socially bonded to short-tailed males actively seek extra-pair copulations with better-endowed males.

However, those studly males with big tails don’t invest much time and energy in the chicks of their ‘official’ mate: they’re too busy running around. The short-tailed males are more attentive fathers; they also reportedly build better nests, and females are also more attentive moms when they have better nests. So there is some compensation to females for not being mated to the studliest guy. But the nests of short-tailed males often contain some other male’s chicks, so the short-tailed males end up investing effort in chicks that are not their own.

If all that were not enough complexity, barn swallow nests are sometimes subject to hostile takeovers by intruding males. The marauding male may belong to another species, such as a wren, or house sparrow, or cliff swallow. And sometimes the intruder is another barn swallow. If the intruder pushes out the original male, he generally destroys any eggs or small chicks, and then mates with the widowed female.

Nests are built of pellets of mud, cemented to the wall or beam, and lined with grass and especially feathers. Both parents incubate the eggs, although only the female has a featherless, highly vascularized brood patch on her belly. Incubation takes about two weeks and chicks are in the nest roughly three weeks. After leaving the nest, the juveniles are tended by their putative parents for about two more weeks. Chicks in a second brood are sometimes also tended by older siblings from the first brood. Parents (and older sibs) can recognize their fledglings, not by voice, but by variation in plumage color patterns on the chest—no two chicks are exactly alike.

Barn swallows nest in several locations in Juneau and are easily seen. Next time you see one, just think a moment about how complex their lives are.