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.

Fountains of Youth

nature’s take on everlasting life

Myths and legends abound concerning magical waters that restore youthful appearances and sometimes might increase longevity. Over two thousand years ago, an historian of ancient Greece wrote about such a miraculous pool, and later European writers carried on the tradition. Similar stories of wonderful springs or poolsare reported from elsewhere, too; miracle waters have been thought to occur in many places, from Japan and India to North America.

Some mineral springs may have healing and soothing properties, but the hope of actual rejuvenation remains in the realm of myth (barring genetic engineering). So humans, at least for now, are stuck with myths and false hopes and the superficialities of face-lifts and cosmetics.

However, in the rest of the animal kingdom, there are thousands of species that have evolved life histories reminiscent of the fountain-of-youth myth, in which juvenile morphology is retained throughout the life of an animal. Technically, this is called paedomorphosis. Paedomorphic individuals never achieve what would be the “expected” adult morphology, as seen in related species. Although they keep their youthful appearance, paedomorphic animals mature sexually and reproduce; their lifespans are not necessarily extended.

One example is the tiger salamander of North America. Some populations have the normal life history, in which the juvenile phase is aquatic, with frilly external gills; the juvenile metamorphoses into a terrestrial adult, losing the external gills. But in some populations, the juveniles never metamorphose at all; they mature sexually in their juvenile, aquatic form. Tiger salamanders are closely related to the Mexican axolotl, in which an adult, terrestrial form is unknown. Axolotls are native only to the region of Mexico City and are critically endangered from loss of habit to urbanization and its effluents.

Paedomorphic species are found among fishes, too. Some gobies, for instance, keep their larval form and habits and become sexually mature. But paedomorphic species do not occur in reptiles, birds, or mammals, which develop directly from hatchling to adult, without a distinct juvenile stage.

In the world of insects, paedomorphosis occurs regularly in a variety of flies and beetles, as well as in hundreds of species in a taxonomic group called ‘twisted-wings’, which are parasitic in other insects. In all of these cases, paedomorphosis in known only in females, which do not complete the customary process of metamorphosing from larva to pupa to winged adult but, instead, remain in larval form. Researchers suggest that females have made an evolutionary trade-off: instead of spending energy on the costly process of metamorphosis, they devote that saved energy to making eggs. But the ecological conditions that favored that trade-off in those particular species are not known.

In many, probably most, of the paedomorphic insect species, paedomorphosis is obligatory for females—all the females do it. But in some cases, paedomorphosis is ‘facultative’, meaning that it happens or doesn’t happen, according to circumstances. For example, the larvae of many gall-midges feed on fungal mycelia (the fine filaments that comprise the main body of fungi), and the life history of females depends on what the larvae feed on: a diet of older mycelia induces complete metamorphosis and leads to sexual reproduction but, on a diet of young mycelia, female larvae do not metamorphose, and these paedomorphic females mature very quickly, producing live, all-female offspring from unfertilized eggs. Why diet should trigger such a difference in life history is unclear.

Not to be outdone, various other invertebrates exhibit paedomorphosis too. For example, there’s a sand crab in which tiny larval males attach themselves to the legs of adult females and produce sperm (later, these “youthful” hitchhikers transform into females). Males are paedomorphic in some parasitic isopods, too. And there’s a whole group of tunicates known as larvaceans, which closely resemble the larvae of other tunicates but are sexually mature in that seemingly larval form.

Perhaps the prize-winner among the “fountain-of-youth” invertebrates is the so-called immortal jellyfish named Turritopsis dohrnii. As in typical jellyfish, the adult form is a tiny, free-swimming medusa, a bell-shaped body with dangling tentacles. From a fertilized egg, a swimming larva (called a planula) emerges, settles down on a rock or a shell, and begins its development as a polyp. When a polyp matures, it buds off new medusae. But here is the possibly unique and fascinating thing: if a one of those little medusae is injured, starved, or stressed by abnormal temperatures or salinity, it can revert to the polyp stage. The bell and tentacles deteriorate and the individual again settles onto a substrate, back-transformed into a polyp, which grows up and produces more medusae.* The cycle of medusa to polyp to medusa can be repeated many times, leading to the idea that this jellyfish is potentially immortal. The process has only been observed in laboratory conditions and not in the wild, which is not surprising, given that the jellyfish is so tiny and the transformations can happen very quickly–and furthermore, many of the medusae are probably eaten by predators.

Just as paedomorphosis does not necessarily engender longevity, extended longevity does not necessarily involve paedomorphosis. Individuals of many organisms, both animals and plants send their own unique genetic makeup into the future by cloning—and thus, in a sense, extend their own lives as individuals without showing signs of youthfulness. Some, such as aphids, produce offspring asexually, and the offspring are genetically identical to the mother. Some plants propagate by means of runners, stolons, and rhizomes (e.g., strawberries and aspens), creating genetically identical ‘satellite’ individuals. Still others, such as some lichens, can produces copies of themselves by fragmentation.

(*Somehow, the cells of this organism have undergone ‘transdifferentiation’, by which mature cells have become reprogrammed to another kind of cell altogether, an extraordinary feat that is not well understood.)

Moose in northern Southeast Alaska

latecomers to the coastal forest

In the past several years, the annual probability of sighting moose or their leavings has increased from something close to zero to a hundred percent. Moose have been reported from the shore of Mendenhall Lake and the airport area to Cowee Meadows and Echo Cove. Many, but not all, of these sightings were of bulls; I saw a cow followed by a young bull in Cowee Meadows a few years ago. I have also seen moose tracks in the Herbert River floodplain forest. It remains to be seen if moose will establish a resident population here; there are pockets of good moose habitat in several places, and I recently learned that moose can do quite well within conifer forests.

Moose arrived in Alaska just before the Bering Land Bridge flooded (14,000 to11,000 years ago). Eventually, by the early 1900s, they made their way down the Taku and Stikine river systems, and down the Alsek to the Yakutat coast a few years later. They arrived in the Chilkat Valley in the 1920s and the population was well established by the early 1930s, peaking in the mid 1960s.

Moose were introduced to Berners Bay almost six decades ago. In 1958 and 1960, twenty-two calves were released (but one died immediately) in the bay area. That local population increased steadily until it reached a point of relative stability in about twelve to fifteen years. Because female moose can reproduce when they are just two years old (occasionally even younger), a female can produce a calf every year, and twin calves are quite common, a rapid rate of population increase can be achieved, in good habitat. Through the 1970s and for the next thirty or more years, the population fluctuated roughly between 100 and 140 animals. Then the population declined sharply, after a couple of hard, snowy winters, but it rapidly re-stabilized at about the previous level.

The rapid rate of population increase in Berners Bay was similar to that following the introduction of moose to the Copper River delta. Mostly in the 1950s, twenty -four young moose were released there; in the following years, the population grew rapidly.

Over in Gustavus, moose were first noted in the 1960s. They are thought to have arrived by emigration from Haines, possibly moving through the Endicott Gap into Glacier Bay and thence to the Gustavus forelands. At first, the numbers were very low, presumably dependent upon occasional additional emigrants arriving in the area. It took several decades for the numbers to increase dramatically, despite the ability of moose to reproduce rapidly and despite what proved to be excellent moose habitat. The slow start in Gustavus, compared to the rapid increase in Berners Bay and the Copper River delta, might have been a result of the very small initial numbers in Gustavus. However, by the early 2000s, the population was extraordinarily high (several hundred moose per 100 square km), so high that a culling program was instituted, cutting the numbers down to about half the peak level (although the population density there is still relatively high, compared to the Interior).

moose-with-twins.jpg
GPS-collared moose with twin calves

It will be interesting to see what happens here in Juneau. The number of moose appears to be very low at the present time (2018), and population growth may be slow, at least at first, as it was in Gustavus.

But where did our moose come from? It’s not clear. Genetic studies would be needed to compare our local moose with those of other places. Previous genetic work has suggested that the established moose populations in Southeast are genetically distinct from each other. The emigrant individuals that founded each now-established population probably did not carry the entire array of genes from the source population but rather just a sample from that gene pool. Furthermore, our mountains and fjords restrict movement between populations, limiting gene flow. In any case, the genetic distinctiveness of established Southeast moose populations may allow future work to identify the source of our local animals.

Moose are herbivores that eat a variety of plant material. In summer, they consume many kinds of greens and twigs; in winter, when green things are scarce, they browse twigs. Their digestive system is very effective in extracting nutrition from plants, because bacteria in the stomach break down cellulose into digestible fragments. The stomach has four chambers: billions of symbiotic bacteria live in the first chamber (the rumen), which also starts to mix the food. The second chamber allows the animal to regurgitate a wad of partially digested food, to chew it again (chewing the cud), further breaking down the plant particles. Saliva from all the chewing helps to bind tannins, which are common defensive compounds of many plants but which can be toxic in high concentrations. The third chamber churns and mixes the processed material and passes it on to the fourth compartment, where the bacteria themselves are digested, releasing useful minerals and other items that moose need. Then all that material goes to the intestine, where nutrients are absorbed. There is not a lot of material left to be eliminated in the feces.

Dense populations of moose can have important effects on their ecosystem. Heavy browsing on willows reduces the number of catkins, an important source of food for bumblebees that pollinate many flowers, including blueberries. Intense browsing of shrubs and saplings might reduce the suitability of habitat for nesting birds by changing vegetation structure, reducing the amount of protective cover and reducing the abundance of insects that normally feed on vegetation. Leaf litter might be reduced, altering the nutrient quality of the soils—the consequences of such effects perhaps depending on the initial condition of the soils. At the present time, moose population density in Juneau seems likely to remain low, but we can be on the look-out for localized effects of browsing. Much more remains to be learned, as always.

Thanks to Kevin White, ADF&G, for helpful consultation and references.

Reluctant spring

…in Cowee Meadows

Early April and, despite some earlier signs of spring, we seemed to be stuck in the middle of a long cold spell—freezing at night and daytime temperatures in the thirties or low forties. All the trails were icy, and it seemed as if I would never get all the ice chipped off my driveway.

A friend who had missed a Parks and Rec hike to Cowee Meadows during a warm spell in March wanted to check out that area. Where P&R hikers had waded ankle-deep in meltwater on the trail, in early April it was all frozen solid. We walked securely over the beaver sloughs and ponds—easy going! The only down-side was a very stiff and cold north wind, with gusts strong enough to send me off-balance occasionally. So we didn’t go out on the beach at all, but just wandered around the meadows to see what we could see. We hid from the wind behind some dense spruces for a comfortable lunch in the sun.

There was plenty of evidence that the horses from the ranch across Cowee Creek had paid their usual visits. They too had taken shelter in the lee of spruce thickets, leaving digested evidence of their sheltered stay.

Bird life was scarce. A woodpecker drummed, but it eluded our sighting. A couple of chickadees flitted by, at the forest edge. A group of nervous mallards fled down the creek well ahead of us. Two ravens performed their classic rolls as they flew overhead.

A solitary, hapless robin poked along the fringe of a frozen pool, where the sun had loosened the ice along the edges. There was little there to feed on; maybe it was getting a drink. In fact, there’s not much for robins to eat when the weather is like this—some invertebrates on the beaches, perhaps, and a few frozen berries in the woods; I wonder how they manage to survive.

Two little sparrows, buffeted by the winds, dove into the shelter of bent-over dead grasses. From their pale brown backs, I guessed that they were savanna sparrows, which frequent these meadows. They stayed under cover for some time—smart birds!

Later in the morning, and a little farther on, we came upon a bunch of six crows, all gathered around the edge of a shallow, sun-warmed pool with some remaining ice. They looked like they were drinking: they’d dip the bill into the water, then raise it up and tip it back—which is how many birds drink fluids. But what was so special about this pool, when the creek and some other pools were nearby?

A few green shoots emerged from one small open-water slough. But all the skunk cabbage shoots that had emerged above the surface of the frozen meadow had been blasted by the cold temperatures. It’s not unusual to see frost damage on the tips of skunk cabbage shoots, but out in these meadows, the cold had killed and blackened several inches of new shoots. Not a good start of the season for them.

There were deposits of moose pellets on the snow in several places, clear evidence that moose had been visiting the meadows this winter. Moose have been recorded from Cowee Meadows for several years, as well as a few other places in Juneau, where moose are usually a rarity.

Sweet gale, a wetland shrub, is widespread in these meadows. The volatile oils of this aromatic plant are reported to repel midges and mosquitoes, but moth caterpillars are said to love eating the leaves. Insect damage induces the plant to increase its chemical defenses, reducing further attacks. The volatile oils can also reduce some fungal and bacterial infections. Vertebrate herbivores include beavers and moose; the European mountain hare eats it too, leading me to wonder if our snowshoe hares might do so also. We noted that some of the sweetgale shrubs in the meadow had been browsed, possibly by the visiting moose, but we could not exclude the possibility that ranch horses might have done so.

Sweetgale is an interesting plant in other ways too. It harbors symbiotic bacteria in root nodules; the bacteria fix atmospheric nitrogen, making it accessible to plants. Although some accounts say that male and female flowers are borne on separate plants, in reality, some individual plants have both male and female flowers and, to further confuse the matter of gender identity, sometimes both male and female sex organs are found in the same flower. However, I have not found any information about the factors that might control sex expression in sweetgale. In any case, propagation is said to be primarily by vegetative means, via underground stems called rhizomes, rather than by sexual means and seed production.

Although this excursion to the meadows was very wintery, I just had a cheering report from a friend that ruby-crowned kinglets have arrived! Now spring can get serious.

Birds of a feather

the benefits of flocking

It is said that “birds of a feather flock together”, and indeed they do. We see gangs of crows—sometimes a hundred or more—foraging together on the wetlands or at the tideline. A skein of Canada geese flies overhead, talking all the time. Better yet, a little troop of trumpeter swans flies up the channel, their whiteness contrasting well against the dark mountainsides.

Why do such birds do things in groups? There are (so far) three main kinds of reasons.

When geese or swans fly together on extended flights, they usually do it ‘in formation’—about a meter apart in a line or a V, they gain aerodynamic advantages. A vortex forms at each wing tip, creating down-drafts and up-drafts. By flying at the appropriate distance from another goose and timing its wing-flaps to catch the up-drafts, a goose that follows another one gains lift and saves energy.

When crows or buntings or shorebirds forage in bunches, one possible benefit lies in protection from both aerial predators, such as eagles, hawks, or owls and ground-based predators, such as coyotes or dogs. A bird foraging alone must keep a sharp lookout for possible predators, and the time spent being vigilant decreases the time available for feeding. In a group, however, there can be many eyes watching and everyone can spend more time eating. In a flock of geese, grazing with their heads down, there is almost always at least one with its head up, being vigilant; a few minutes later, a different bird will be the sentinel. Furthermore, if a group of birds is startled into flight by an approaching predator, the whirl of many frightened birds might distract the predator, making it harder for the attacker to focus on a particular bird.

There may also be advantages in locating and exploiting a food resource. In some cases, particularly in species that are quite sociable year-round, if one bird finds a really nice patch of food, that bird might signal to its friends and relations to come join the feast, and the rest of the gang just follows. I suspect that crows might do this.

Sometimes, the foraging activities of one bird might make food more available to its opportunistic companions. A bird fossicking about in the wrack line, for example, might stir up any number of invertebrates, making them vulnerable to the next comer. Then every bird in a foraging group may take advantage of that and, in so doing, stir up more prey. Another example: dense squadrons of scoters cluster on the surface of a bay or channel often make what I call ‘chain dives’—one bird at the edge of the flock dives deep and all the others, in a line, follow the lead, moving up to dive in the same spot as the first diver. I have to wonder if the foraging activity of the first birds might loosen up a congregation of mussels, for instance, and make it easier for the later divers in the chain to pluck them up.

There are also times (and places) when birds that are NOT of the same feather flock together. These mixed-species flocks occur most commonly in forests around the world. In North America, mixed-species flocks form in winter, and commonly include chickadees, which are often the focal or ‘nuclear’ species, accompanied by golden-crowned kinglets, and maybe nuthatches or brown creepers or even a downy woodpecker. The various species in such a flock are not related to each other nor do they forage in the same ways, although they typically all eat insects and spiders found in the forest canopy. In our local forests, I have found mixed flocks of chickadees and golden-crowned kinglets in winter, but I seldom detect the other likely follower-species (of course, I simply might miss them!).

Obviously, the ‘many eyes’ idea applies to multi-species flocks. In many cases the birds in the flock are foraging at some distance from each other, maybe even out of visual contact, but the cohesion of the flock is maintained by vocalizations. Each bird may be foraging independently, but if one bird spots a predator, the whole flock may be notified to be on watch. By joining such a flock, and depending on the watchfulness of everyone, each bird might gain more time for feeding; this had been shown to occur in some situations. In a few cases, the foraging of one species might create feeding opportunities for others: for example, the tapping and bark-scaling of a downy woodpecker could make hidden bugs accessible to birds that glean surfaces.

As usual, many questions remain. Why do chickadees usually serve as nuclear species, drawing other birds together in a foraging flock? Do nuclear species benefit as much as their followers do? What triggers the formation of a mixed flock at certain times or places? How long do these flocks stay together, and what leads to the eventual breakup of the flocks? Under what circumstances might the foraging activity of one species benefit another? A curious naturalist might not have a ready answer to such questions, but formulating questions is usually the first step in finding answers. Sometimes finding an answer is not even the most useful outcome of questioning; the very act of questioning can stimulate new insights and perspectives.