Late September notes

quiet trails, fall colors, and dragonfly migration

It’s been rather quiet along the trails in late September: here a pair of hermit thrushes, there a trio of varied thrushes, and a stray robin or two. Coho were milling about in Mendenhall Lake, rumpling the water surface. From the beach on the west side, I watched a seal or two making bigger rumples as they tried to grab a fish. I saw no coho going up the west-side streams, as they usually do, but they were going up Dredge Creek on the other side of the lake.

I met a dog-walking fellow who remarked on his enjoyment of the fall colors, as we looked at the golden cottonwoods, yellow willow leaves, and the red/pink/yellow leaves of highbush cranberry. Dwarf dogwood has been spectacularly red along some trails, with small spots of color from trailing raspberry and nagoons. Along the lakeshore trail, new willow-roses were developing, showing brilliant red on a background of still-mostly-green willow leaves. The midge larvae inside will emerge next spring, having fed on the inside of the gall, and face the world as adults.

Willow “rose” midge gall

Meanwhile, I was sent a link to an article in a Wisconsin newspaper about huge swarms of dragonflies headed south on their fall migration. Tens and maybe hundreds of thousands of dragonflies were on their way, attracting so much public attention that they even made it into the newspaper (and there are other migrating swarms, on the east coast, near the west coast, and in between). Several species had joined the swarm, but the great majority of them were green darners (Anax junius)—possibly my favorite dragon, very snazzy. The Latin name means June king—“king” perhaps because of its large size, with a wingspan of almost twelve centimeters, bigger than most other North American dragons. They typically breed in quiet waters of vernal pools and marshes, where the females lay their eggs on aquatic plants. These mighty predators are able to capture and eat other adult dragonflies, as well as many other insects. They range over most of North America, coast to coast, from southern Canada to Mexico, Hawaii, and beyond. They don’t get to Alaska except by accident of vagrant winds. But their regular migrations take them from the northern part of the range to the southern part in fall, and back again in spring.

Green darners are well-known for making long-distance migrations and we now know a little more about their fall travels. The advent of miniature radio transmitters, small enough to be glued onto a dragon’s back, allowed researchers to follow their progress for several days. The dragons made an average of about twelve kilometers per day, with stopover days for foraging in between the flight days. They took advantage of northerly winds, after a cool night or two, and typically flew with the wind, although they seldom flew on very windy days.

The swarms are apparently more common in fall than in spring. Swarms are composed of individuals from widespread areas, gathered together in fall to follow shorelines, ridgelines, and other landmarks. Individual dragons bore natural markers in the form of isotopes that could be identified to their approximate sources; natural isotopes of hydrogen, for instance, can have one, two, or three neutrons, changing their atomic mass (‘weight’). The proportion of hydrogen isotopes (in water, for example) varies geographically (e.g., latitudinally), and this is reflected in the body composition of the critters that grew up in different areas.

A simple version of green darner migration divides things into three generations. Generation #1 emerges in the south in February to May, flies north, where it breeds and dies. Generation #2 emerges from that breeding activity in the north, flies south to breed and die. Generation #3 are the offspring of fall migrants and do not migrate; these residents breed and die in the south and their offspring migrate north in spring.

But it’s not really quite that simple! Individuals in the green darner population of some places (data from two studies in the north) seem to be comprised of individuals with two different migratory patterns. A given population may have some adults emerging and breeding in summer, whose slowly growing larvae overwinter in the breeding pond, emerging the next summer to breed there as adults. Other individuals in the same pond are small larvae in early summer (whose parents were spring migrants); these grow quickly, with adults emerging and breeding in late summer and fall, and then disappearing on fall migration. This makes it seem that these northern populations contain both residents and migrants.

Studies of the population genetics have shown that green darners have not differentiated into distinguishable populations but rather exhibit widespread similarities, which indicates genetic mixing throughout the whole population. Spring migrants probably do not go back to where the previous generation of their parental lineage came from; they may settle to breed somewhere along the way. Their offspring therefore cannot be closely adapted to particular rearing conditions in various geographic areas. So researchers now consider the possibility that the life-history differences (resident vs migrant) may be flexible. Perhaps the early larvae decide which life history to take on the basis of some environmental trigger.

There is much to be learned about migratory strategies in green darners. What cues do the migrants use for orientation on the long flights? How do they decide where to settle and breed? Do the offspring of a given female actually embark on differing life histories, depending on circumstances? If life histories are flexible, what are the triggers that determine which alternative prevails? Will the relative frequencies of the two pathways change as the climate changes?


Early fall in Cowee Meadows

burying beetles, sweetgale ecology, and dragonfly sex

A trip to Cowee Meadows usually provides a curious naturalist with something to contemplate. It’s also a good idea to keep an eye out for large, brown, sometimes temperamental, mammals with claws or hooves.

A stroll out there in mid-August discovered several things of interest.

A desiccated toad carcass lay in the trail, cause of death unknown. The body was attended by two big, orange and black, sexton beetles, maybe just looking for a meaty snack but possibly foraging for a carcass on which to rear a brood of larvae. Sexton beetles are also called burying beetles; they bury the bodies of small mammals and birds (or chunks of dead salmon), denuding them of fur and feathers, which are used to line a chamber housing the carcass. Eggs are laid near the buried carcass and the larvae crawl into the food-filled chamber. Unusual among insects, both parents feed the larvae on liquefied, partially digested meat, as the larvae also feed for themselves on the stored carcass. The number of larvae feeding on a carcass may be regulated by parental infanticide; if there are too many for the available food pile, the parents reportedly reduce the numbers. If for some reason, a female beetle does not have an active partner, she can raise a brood by herself, fertilizing her eggs with stored sperm. In this case, the question in my head was whether or not a desiccated toad would make good larval meals.

The low wetland before the beach berm is thronged with aromatic sweetgale shrubs. They harbor symbiotic bacteria in the root system; the bacteria take atmospheric nitrogen and ‘fix’ it into a form that plants can use. This species usually (but not always) has male and female flowers on different individuals. Male plants have already set their flower buds for next year, while female plants bear cone-like structures with small one-seeds fruits attached to the core. Some small critter had feasted on the seeds of a few plants, leaving the cone-core and fragments in a heap. A fat green caterpillar grazed steadily along the edge of one leaf, not deterred by the reported insect-repellent properties of this species. I was interested to find out that two field guides and two tomes on the flora of Alaska do not instruct a field naturalist how to tell male from female flowers—but the Trees and Shrubs of Alaska by Viereck and Little does!

Out on the beach, it was time for tea and snacks on a favorite log. The tide was low, and far out on a distant rock there was a black lump, which turned out to be an oystercatcher, able to loaf now that the chicks have been raised.

Instead of hobbling over the cobbles around the point, the return trip came back through the grassy/sedgey meadow, where the trails of trampled vegetation left by wandering horses made easy walking in most places. Sparrows popped up out of the tall grass and quickly dove back into the next dense cover. Closer to the river, the vegetation is shorter and marsh felwort flowers began to show up, not only on gravelly soils (as the books say) but also in deep black muck.

The old trail next to the beaver pond has been abandoned, but the water level was very low; there was not even any water in the stream below the dam that makes the pond. That encouraged a little exploration at the edge of the wet meadow along the old trail, which was apparently built (or rebuilt?) without consideration of beaver activity. In recent years, beavers had raised the pond level so the trail was often flooded well over ankle-deep; water was often trapped between the log rails on the trail margins. Rows of young alders have now sprouted up along the edges of that trail, making most of it rather impassible. But the low water level made it quite easy to tromp through the sedges on a parallel route. The newer, improved trail along the hillside would still be the trail of choice most of the time.

Near the beaver pond, dragonflies zipped to and fro, some of them in copula. Male dragons (and damselflies) chase whatever female flies by. If a female is not interested, she may evade the male by running away or hiding; in some species she just plays dead! A successful male grabs a female behind her head with claspers at the end of his abdomen, and they may fly in tandem for a while. The female, if willing, bends her body under his to bring her genitalia (near the end of her abdomen) next to where he has previously stored his sperm in the anterior part of his abdomen, so sperm can be transferred. Copulating dragons make a circle or ‘wheel’ of their bodies. If the female had mated previously, the present male may try to scrape out the sperm of the first male; the ‘opinion’ of the female with respect to this action apparently has not been recorded.

Photo by Bob Armstrong

Some days later, I watched a pair of bluet damselflies in tandem, perched on a sedge blade in a mid-elevation muskeg pond. The female bent her body up to touch his, in the copulatory position, several times, but they did not form the mating wheel. Three other bluet males patrolled this pond, sometimes zooming in closely on the pair, and even contacting them, as if to try to steal the female away. This is a behavior I’d not seen before. At the edge of the pond lay a dead female, possibly drowned in the act of laying her eggs in underwater vegetation. Some bluets lay eggs in vegetation near or on the surface, but some species of bluet actually submerge the whole body while egg-laying, and upon occasion need to be pulled out by their partner or perhaps by a nearby unmated male.

Solstice at Cowee Meadows

surrounded by abundance

Around the time of the summer solstice, I spent a couple of nights in the Cowee Meadow cabin, along with some friends and my visiting niece. We like the flower show in the meadows. This year, everything was a bit early (after the sunny, hot month of May) and flowering was somewhat past its best, but nevertheless we noted as many species of plants in flower or just past flowering as we found last year (over 75 species, barring grasses and sedges).

The cabin needed some attention, so we swept it out and washed the windows with plain water, having neglected to bring window cleaner. We brought in window screening and duct tape, so we were able to cobble together screens to exclude the flying bugs and thus keep the windows open. As it happened, however, there were astonishingly few mosquitoes and such (what a difference from last year!). Sitting outside for breakfast, lunch, and dinner was very pleasant.

Every day we cruised around the trails, seeing what we could see. A major highlight was the discovery of a sizable patch of RIPE strawberries—just one big patch; the plants all around this site held only green, unripe berries. This discovery caused a significant delay in our progress but there were big smiles all ‘round!

Photo by Katherine Hocker

These coastal strawberries have a very interesting distribution: they occur naturally along our coasts but different subspecies or varieties also occur on the coasts of Chile and Argentina and, reportedly, in the mountains of Hawaii. The species is thought to have originated in North America, but it was probably carried to South America by migrating birds. There is good evidence that migratory shorebirds can carry seeds and spores of a variety of plants on their long-distance seasonal journeys. Some seeds may stick to feathers and escape being preened off. Strawberries (and other fleshy fruits) are adapted to be eaten by vertebrates, which snack on the fruits and pass the seeds through their guts. Most small birds pass seeds rather quickly, in just a few hours, so viable strawberry seeds travelling all the way from the northern hemisphere across the equator to the southern would require a really quick flight or a long residence time in the gut. I observe, with interest, that the coastal strawberry, Fragaria chiloensis, bears the name of the Chilean island where I spent many happy austral field seasons. Historically, this strawberry was widely used and cultivated in Chile and reportedly was hybridized with another species to create the domestic strawberry.

A small botanical mystery confounded us. We noted that the oysterplants (a.k. oysterleaf) on the upper beach fringe made smaller leaves on the parts of the stems that bore flowers. But on saltbush (a.k.a. orache) plants, flowers were borne on stems with both small and large leaves. Why the difference?

We had a report from later hikers of a sickly bear cub beside the main trail and eventually learned that ADF&G had picked it up. Their investigations failed to reveal any obvious cause of the distress, but clearly the little cub was malnourished and in a very bad way. Nothing could be done to save it, and it was a public safety concern to leave the cub where it was as long as the mother was nearby, so it was euthanized. Some observers later saw a female with one cub and thought that the family of the dying cub had moved on.

Along Cowee Creek a doe with two fawns come out of the woods to the sand bars. The doe was limping from a wound on a hind leg, but she was able to lead her fawns back into the thickets when she detected us a hundred yards upstream.

The meadows were popping with savanna sparrows, including lots of recent fledglings. Lincoln sparrows burbled their complex song along the shrubby edges, maybe contemplating a second brood. As we sat on the beach for a while, a male belted kingfisher came over our heads and landed on a big rock partly exposed by a low tide. Presently, he dove and came up with a long, thin fish. Then he headed overland toward an upstream part of the creek. The next day, we were walking up along the creek and heard a group of kingfishers raising a ruckus. We surmised that the chicks had fledged and were begging, but they all went around a bend of the creek and out of sight before we could be sure.

We watched dragonflies laying eggs: the females repeatedly dipped down to touch the end of the abdomen to the chosen substrate. One species dropped her eggs into open water, while another, larger one (a blue darner, I think) chose to put her eggs in decaying wood.

The wonderfully long days of solstice time gave us lots of time to wander about, including a stroll out to the beach in the evening to watch the sun setting—and anything else that came our way.

The last throes of summer

in the ecotone between seasons

Early September—and Gold Ridge earned its name in a botanical (rather than a mineral) way; the open slopes were covered with the golden leaves of deer cabbage. Color accents came from the scarlet berries and crimson leaves of dwarf dogwood. There were even a few scattered flowers of about ten species still in bloom, with little hope of pollination, but swathes of partridgefoot, still flowering, clothed a few protected pockets.

Black crowberries and two kinds of low-bush blueberries offered snacks to foraging birds and hikers. The very last salmon berries hid under drooping foliage.

A female grouse and a big chick tried to be invisible at the edge of an alder thicket; their patience outlasted ours, and we eventually went on up the trail. A very small marmot hustled into its burrow with a big mouthful of dry grass for a winter bed, while an adult marmot posed regally on a rock right next to the trail. The marmots will disappear for the winter very soon now.

Swarms of minute insects danced in the open spaces between the canes of salmonberry. I have no idea what they were, but surely they were in reproductive mode, trying to beat the onset of low temperatures.

On another day in early September, a stroll through the lower muskegs at Eaglecrest found some good patches of still-unripe bog cranberries and some low-bush blueberries. We saw that a few of the dwarf dogwood berries had been sampled by some small animal, leaving a hole but without removing the seed—very different from the more usual rodent foraging, which focuses on the seed, leaving a hollow fruit behind. I have to wonder who might eat the dogwood berries; I’ve seldom found the seeds in the hundreds of bird or bear scats that I’ve inspected.

A few swamp gentians were still tightly furled in bud and were probably too late for pollination, as were the one or two bog kalmias that were still open. We searched for sundews and found only three decrepit specimens where earlier there had been thousands, so we concluded that they had gone to bed for the season.

Dragonflies—the big, blue darners, mostly—still cruised the ponds and waterways in search of occasional prey. One enterprising couple flew by in copula: the male clasped the female behind her head with the grasping appendages at the end of his body, and the female looped up her abdomen under the male’s thorax where his sperm are stored. He carried her around while his sperm were being transferred to her ovaries (and perhaps he also displaced or removed sperm from a previous mating!). She would probably lay her eggs in dead wood or vegetation, where they would overwinter.

Meanwhile, the sockeye run in Steep Creek ended, and we await the arrival of the coho. The mallard ducks that visit my home pond are all in brown, eclipse plumage. A few, however, are starting to show rusty chests and darker heads that will turn green as the males don their courtship feathers. Mallards begin their courtship and mate-choice in winter—it seems to be a gradual process.

Cottonwood and devil’s club leaves are turning golden, willows sprinkle their crowns with yellow leaves, and the maples glow with yellows, orange, and several shades of red. Highbush cranberry leaves turn to pink and red, and the wild crabapple leaves get a characteristic shade of rather grubby, rusty red. Even some of the blueberries, especially in the alpine zone, are colorful. The alders get left out of this color show; their leaves turn dull brown and crinkled. Why are they so different?

Amid hundreds of ripening rose hips, I saw a single, lonely pink blossom.

“Tis the last rose of summer

Left blooming alone.

All her lovely companions

Are faded and gone”

Dragons and Damsels

extraordinary lives of odonates

A few days ago, I stood beside a small pond, watching showy insects zoom around. There was a small blue damselfly, checking out the weeds in the shallows. And there were two of its larger dragonfly cousins: a couple of big darners and several smaller emeralds, so-named for the intensely green eyes and greenish body of mature adults.

There are over 30 species of dragonflies and damselflies in Alaska, and in Southeast we have around 19 species (3 damsels and 16 dragons). As they become better studied, more species will probably be added to the lists. The state dragonfly is the four-spotted skimmer.

Dragon- and damsel-watching is an increasingly popular recreation. Even without bothering about taxonomic details and the minutiae of species identification (which commonly requires having the creature in hand), the behavior of these conspicuous insects can be fun to observe.

My own introduction to this group, collectively called odonates (”toothy”), came several short eons ago, when I was a graduate student. I was studying yellow-headed blackbirds in the marshy potholes of eastern Washington, where these birds, along with red-winged blackbirds, were abundant. Perhaps the most important prey the blackbird parents fed to their chicks were recently emerged odonates.

Odonate larvae are aquatic predators, capturing prey with a huge, extensible, hooked lip. They may spend a year or two, or sometimes more, in the water, feeding and growing.

Damselfly larvae breathe by means of three external gills at the back end of the slender body; the gills also help in swimming. Dragonfly larvae have internal gills, and they breathe through the back end of the digestive tract.

When they are ready to become adults, the larvae crawl up on a plant stem or rock, the larval ‘skin’ or exoskeleton splits open, and the new adult pulls itself out. Blood is pumped into the long abdomen and into the wings, which gradually expand and slowly harden. These newly emerged adults are called tenerals. They fly very weakly until their body and wings harden. So this is the stage of their life when they are extremely vulnerable to predators, such as the blackbirds. The blackbirds I was observing stuffed their chicks with tenerals all day long.

As fully mature adults, odonates are much harder for birds to catch. Odonates have four wings, which can be moved independently of each other, giving them great maneuverability in the air. Adult odonates are terrific predators of other insects, catching the prey in a basket formed by their spiny legs, and munching them up in strong jaws. They have huge eyes of multiple facets, which are fine motion-detectors. Some odonates hunt by almost constant flying and searching, and others are sit-and-wait predators, perching on a lookout spot and darting out after a passing bug.

Each adult flies for only a few weeks. During that time it forages and plays the mating game. Males of some species are territorial, defending part of a pond from other males, and waiting for females to visit. Others cruise around, looking for potential mates.

The mating process in odonates is unique among insects. The male produces sperm, which he transfers to a special chamber at the front part of the abdomen. He does this by bending forward and placing the tip of his abdomen at the entrance of the storage chamber. When he finds a female, he grabs her with special appendages on his ‘tail’, holding her by the top or back of the head. The pair may fly around in tandem for a while.

Bluets mating. Photo by Bob Armstrong

The female then loops her abdomen forward to connect with the special sperm storage chamber. In this circular or ‘wheel’ position, a pair may fly around some more. The sperm are transferred to the female, where they fertilize her eggs.

But that’s not all: females can mate with more than one male. Competition for females is intense, and males have a nifty way of beating out competitors. Their penis does more than transfer sperm. It also can remove or push aside the sperm of males that mated with this female previously. So, if this male is the last one to mate with her, he ensures that he is the father of her eggs.

In some species, the male stays with the female, either in tandem or nearby, keeping guard on his paternity while she lays the eggs. In other species, females just sneak off on their own and try to avoid getting grabbed by other males. Given what goes on in many birds and mammals, I have to wonder if some females might not let themselves get caught by a new male, if he looks like a better specimen and potential father.

Females lay their eggs in several ways. Some typically insert their eggs into plant tissue, using a sharp structure called an ovipositor (egg-placer). Other species just drop their eggs into water or dap them onto mud or moss.

It is easy to observe territorial aggression, tandem and wheel flights, and sometimes oviposition in these insects. Such behaviors are often easier to watch in odonates than in many birds.

Here are three nice introductory guides to odonate watching:

Dragonflies of Alaska (second edition), Hudson and Armstrong;

Introducing the Dragonflies of British Columbia and the Yukon, Cannings;

Dragons in the Ponds, Armstrong, Hudson, and Hermans (for children).