Visiting Yakutat

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!

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Chickadees

A friend and I stood in a small muskeg on Douglas, checking out some deer tracks, when little twitterings announced the arrival of chickadees. Two of them scoured the twisted trunk of a dead pine right next to us, but we soon saw that there were two more—no, four more—no, maybe six or eight more—thronging the foliage of nearby hemlocks. They might be finding overwintering spiders or insect pupae and even adults.

I enjoy watching the flock that hang out around my house, too, as they diligently pick out little black sunflowers seeds from the feeders and flit into the adjacent spruces. They may eat some of those seeds immediately but sometimes the return trip to the feeder happens so quickly that there was only time to stash the seed in a hand crevice for a later snack.

Watching these chickadees stirred me to dig for more information. The species that lives in our area is the chestnut-backed chickadee, which lives principally in the Pacific coastal rainforest. Of the seven species of chickadee in North American, four (including ours) breed regularly in Alaska.

Chestnut-backed chickadee. Photo by Bob Armstrong

All the chickadees share the habit of nesting in tree cavities. The cavities may be natural ones left by a broken branch or a woodpecker, or they may be excavated in soft, decaying wood by the chickadees themselves. Clutch sizes tend to be large, averaging seven or eight eggs per nest. Both parents care for the chicks, but in some cases, not all the chicks in a nest have the same father because, as in many other birds, some hanky-panky goes on! Predation on nest contents of cavity-nesting birds is commonly lower than for open-cup nesters, but nest predation on chestnut-backed chickadee nests can be as high as fifty or sixty percent of nests; red squirrels are a principal predator on eggs and chicks.

When chickadees forage through the canopy, they often hang upside down to glean from the undersides of twigs and leaves. They can do this very agilely, reportedly thanks to well-developed special leg muscles. Chestnut-backs often forage in flocks in winter, sometimes joined by other species such as nuthatches and kinglets. In the southern part of their geographic range, as many as fifteen other species have been recorded in mixed-species flocks with chestnut-backs.

Where chestnut-backs overlap with black-capped chickadees in Washington, their foraging patterns differ slightly. Chestnut-backs have slightly smaller bills and are more closely associated with conifers. They forage especially on foliage and twigs, while the blackcap forages more often on the bark of tree trunks and branches. Although both of them hang upside down to reach the undersides of leaves, the blackcap reportedly does so more often.

Chestnut-backs apparently have been much less intensively studied than blackcaps, which is arguably the best-studied songbird in North America. Because detailed information about chestnut-backs is hard to find, I thought I’d summarize some of the details about blackcaps, which range all across North America and nest in the Interior of Alaska. It seems likely that much of what is known about blackcaps also applies to chestnut-backs, but that remains to be ascertained. In the meantime, here is some cool stuff on blackcaps, particularly their winter flocking and its consequences, food storage behavior, how they get through the cold season, and their calls.

The winter flocks of black-capped chickadees are strongly hierarchical, with males generally dominant to females and older birds dominant to younger ones. Winter ranks have carry-over effects to the subsequent breeding season. Dominant male breeders are in better body condition than subordinates and tend to have better nesting success, at least in some habitats. They also participate more than subordinates in hanky-panky outside of the socially monogamous pair. Higher winter ranks of females also lead to their better survival in the breeding season.

Black-capped chickadees store food in fall and winter, each one stashing hundreds and sometimes thousands of seeds and insects in bark crevices or among conifer needles or in cracks in trunks and branches. Unlike red squirrels, which create piles of cones, the chickadees generally store items singly. They are very good at remembering where these items are stashed, being able to retrieve them after several days or even weeks, if one of the many potential thieves (squirrels, mice, nuthatches…) has not stolen them.

The part of the brain associated with memory is called the hippocampus, which increases in size in the fall, when food storage is a common activity. Blackcaps in the north store more food and have larger hippocampi than those in the southern part of their range. Blackcaps also have larger hippocampi than chickadee species that do less food storage.

Dealing with cold winter temperatures requires metabolic energy, and the colder the weather, the higher the metabolic costs. Blackcaps in Alaska are reported to have a metabolic rate about fifteen percent higher than those farther south. Heat generated by the muscular activity of foraging, during the day, also contributes to staying warm on winter days. At night, however, blackcaps allow their body temperatures to drop ten or twelve degrees centigrade, saving substantial energy; however, the blackcaps in Alaska are a bit different (of course?), and only let their temperature drop about three degrees. At night, they roost in cavities or in thick vegetation, usually singly.

The calls of black-capped chickadees may sound to us like indistinguishable twitterings. But not so, among themselves. They can distinguish the subtle variations in each other’s calls and identify specific individuals (as can many other songbirds). Furthermore, the “chick-a-dee” alarm call varies according to the relative risk from a potential predator that is visible; a different call indicates a predator that has been heard. Other species, such as nuthatches, eavesdrop on blackcap alarm calls and respond to the signal. Recent research has shown the male black-capped chickadees sing at higher pitches when the level of anthropogenic noise is high (for example, near heavy traffic, construction, logging activity, and so on), which may have consequences for breeding (as it does in some other songbird species too).

Vocalization and predation

Four baby juncos, in a nest tucked under a dropping clump of grass, lie low and are very quiet. Only when their parents come with food do they raise their heads and beg. When the parents leave, the chicks again are still. There’s a good reason for this: a nestful of lively, loud chicks would probably attract predators, who are always on the watch for succulent little morsels. Even the repeated back-and-forth trips of attentive parents are often enough to alert watchful predators to the location of a nest.

The nestlings of many other songbirds (robins, sparrows, warblers, etc.) behave in the same way, for the same reasons. They nest in open-cup nests, which are vulnerable to all comers. Cavity-nesters, such as woodpeckers, can be a little more brash in their protective holes. Predators may come, but only some of them can enter or reach into a deep cavity, and if they do, they may face a barrage of sharp beaks. Predations rates on cavity-nesters are much lower than on open-cup nesters. As the chicks get bigger, they sometimes perch right next to their front door, poking their heads out and yelling for food (that’s how I easily found the nest of a black-backed woodpecker, some years ago).

Ducks and shorebirds do it differently. Wherever they nest, the chicks leave the nest soon after hatching, typically following a parent around but feeding themselves. When incubation is done, there are no back-and-forth parental feeding trips to lure a predator to a particular place. The family is now a moving target, not a stationary one.

Among mammals that are subject to predation, we find a similar dichotomy. The young of some species follow their mothers, but in other species the babies cuddle in a nest. Humpback whale calves stay close to their mothers, and recent research shows that they talk to them in ‘whispers’—soft vocalizations that cannot be heard at any distance. This may reduce the risk of killer whale attacks. The young of deer, moose, zebras, elephants and other large herbivores are also able to accompany their mothers soon after birth; I wonder if they whisper too!

Young marmots stay near the den, which offers a quick retreat when danger threatens, and young beavers gain some protection from the pond outside the lodge, a haven, when the alarm sounds. Smaller mammals have a variety of arrangements, mostly depending on being cryptic and hard to find.

But some small rodents add another feature that improves safety: They can produce ultrasound: too high-pitched for human ears (hence, “ultra”), these sounds have a very short wavelength along with the very high frequency. Such sounds attenuate rapidly with distance, so they do not carry very far; they are more directional than low-frequency sounds, but they get scattered by reflecting off twigs and leaves. Young lemmings, mice, and rats emit ultrasounds to call their mothers, if they have become separated too long; the calls prompt the mother to retrieve the wandering pups. Although many predators of small rodents cannot hear ultrasound, some can (e.g., dogs and cats and their relatives), and a short-range call of distress might reduce the risk of predation from such carnivores.

Adult small rodents also use ultrasound as a form of social communication within a group, quiet talk among companions. Certain ground squirrels emit ultrasounds that alert others to the presence of a distant threat, the rapid attenuation ensuring that the sound does not carry as far as the potential threat.

On the other hand, some predators have evolved the ability to use ultrasound in hunting—as an aid to predation (rather than a way to avoid it). The toothed whales use echolocation (sonar), much of it in the ultrasonic range, to navigate in turbid waters and to detect their prey. Our resident killer whales, for instance, use ultrasound to locate and capture their fish; the transient killer whales, however, seldom use it while hunting their prey of marine mammals. Not only are the prey mammals much larger and easier to see than the prey fish, typically, they are also more likely to be able to hear the sonar calls of the hunting killer whales. So the transients usually hunt silently.

Bats are perhaps the best-studied predators that hunt using ultrasound. The short wavelengths permit the sounds to bounce off small prey, such as insects, and bats emit very high intensity (‘loud’) ultrasounds as they close in on a hapless bug. Not all insects are hapless, however! Some toxic tiger moths make ultrasonic clicks to warn off approaching bats, which then often abort their attack. Other, nontoxic, tiger moths use their ultrasound to jam the sonar of an attacking bat, making the attack less likely to be successful.

Echolocating calls sometimes also allow the bats to communicate with each other, as they are looking for roosts or food. Because the calls can be individually recognizable, young bats can communicate with their mothers, and friends can talk to each other (although others may eavesdrop). There remains much to be learned about the social uses of sound in bats.