Beetle-mania

expression of an inordinate fondness

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There are many more species of fish (about twenty-eight thousand species) than of any other kind of vertebrate (amphibians, reptiles, birds, and mammals). And there are about thirty thousand species of orchid, in a single taxonomic family. But those seemingly impressive numbers fade into the background in comparison to beetles.

Numbering well over three hundred fifty thousand (and counting), there’s a species of beetle for every ecological job—predators and parasites, herbivores and detritivores, scavengers and pollinators. They range in size from a giant six or eight inches long down to a wee thing only a fraction of a millimeter in length. Beetles have been around for a long time. Their fossil history begins before that of bees and ants and long before that of butterflies. Beetles appeared at least two hundred thirty million years ago, already diversified in their ecologies. Their diversity got a boost from the appearance of conifers, and then again from the arrival of the flowering plants, as they began to exploit these new resources. In fact, they were probably the first insects to pollinate the early flowering plants, since there were no bees or butterflies yet.

The phenomenal diversity of beetles is impossible to capture in a short essay. So let’s reduce the problem (slightly) by considering selected taxonomic families: the weevils or snout beetles (Curculionidae) and the rove beetles (Staphylinidae). These two families are probably the largest, in terms of the numbers of species. And I can’t altogether leave out three other interesting, large families…

Consider first the weevils, with over eighty thousand species, according to some taxonomists. Most weevils feed on the flowers and leaves of flowering plants (which now number hundreds of thousands of species). With that long snout, they bite and chew the plant tissues. The most notorious species is perhaps the boll weevil, which feeds on flower buds and fruit of cotton and ravaged U.S. cotton crops in the 1900s. A few weevils are aquatic, including some that feed on native and introduced water milfoil. One acts like a dung beetle, collecting the dung of Australian wallabies for raising their larvae.

One branch of the weevil family includes the bark and ambrosia beetles, which can wreak havoc in conifer forests. There’s a variety of ambrosia beetles, whose adults and larvae feed on ambrosia fungi that grow on wood. Some of these beetles even carry bits of the fungus in special pockets, and so they inoculate new tunnels under the tree bark.

The rove beetles number at least sixty thousand species, with vast numbers still uncatalogued by taxonomists. Most of them are small and inconspicuous, often living in leaf litter, under loose bark, in caves, and other places that are usually beneath our notice, scavenging whatever they can find. Some feed on carrion, a few are external parasites on fly larvae, some feed on fungal spores, and some burrow in shoreline sand to feed on algae and diatoms. Here in Southeast, one species of rove beetle is the chief pollinator of western skunk cabbage.

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Rove beetles on skunk cabbage. Photo by Bob Armstrong
beetles-mating-on-skunk-cabbage-by-bob-armstrong
Rove beetles mating. Photo by Bob Armstrong

Many rove beetles are predaceous, often on mites, round worms, and fly larvae. For example, some species hang out in the dung of ungulates (deer, cattle etc.) and eat fly larvae while others maim and eat adult scarab beetles. Some species are specialized to live in the nests of birds, rodents, and even gopher tortoises, where they prey on the larvae of fleas and flies. One type of rove beetle has a very specialized and obligate relationship with neotropical figs, which are pollinated by specialized wasps, whose larvae grow up inside the fig. Inside the fig, the beetle adults and larvae feed on the pollinating wasps.

Many species of rove beetle live in the colonies of termites, ants, bees; one even inhabits the nests of a communally nesting butterfly in Central America. They are ‘inquilines’ or tenants in the host nests. Although some of them just scavenge in the middens of the ants and termites, others are predators, parasites, or kleptoparasites (stealing the food of the hosts); these species are well disguised, so that the hosts do not eject or kill them. They actually smell like their hosts, and in some cases they also look like them. Some rove beetle tenants secrete substances that calm the worker ants or even entice the workers to retrieve tenants that wander too far away. The rove beetles that live in certain termite colonies have huge glands that secrete drops that the termites love to eat. Some tenants are even treated as members of the colony, fed and protected as if they really belonged; in fact, these tenant beetles sometimes tap on the mouthparts of the host ants to elicit a feeding.

Two other large taxa are somewhat related to the weevils: The leaf beetles (Chrysomelidae), with at least thirty-eight thousand and perhaps as many as fifty thousand species, feed on plant material in a variety of ways, including leaf mining. The longhorn beetles (Cerambycidae), with maybe thirty-five thousand species, are plant-feeders too; the larvae dig into wood or mine the nutritious under-bark.

I can’t omit the so-called ground beetles (Carabidae), with over forty thousand species. Many of them are ground predators, but some eat seeds, some are inquilines in ant nests, some feed on slime molds, and some have parasitic larvae. Some eat snails by sticking the long snout into the snail shell and pulling out the resident snail. The well-known tiger beetles are thought to be the fastest running insects, chasing down their prey out in the open. One species is so quick that it can catch springtails in mid-jump. This family includes the famous bombardier beetles, which spray hot and caustic secretions at any attackers.

That’s just a sketchy introduction to some of the diversity of beetles. Beetle taxonomists and other researchers spend lifetimes immersed in the relationships and ecological stories about beetles. There is always more to learn and some of that will be surprising.

Seasonal body modifications

surprising changes in size and shape

A relatively simple –and familiar to most of us –kind of seasonal and reversible body-modeling occurs in bears preparing for hibernation, and beavers getting ready for snoozing in their lodges, or deer anticipating food shortages in winter. These species all put on fat in fall, becoming distinctly more portly. Come spring, they are more svelte, having burned up that winter fat. Humpback whale females migrating from Hawaii to the food-rich northern waters are much slimmer than in fall when on their way south. Similarly, migrating birds typically put on fat before they migrate and arrive at their seasonal destinations in trimmer condition.

Sometimes the reversible remodeling occurs in internal organs. Bar-tailed godwits and other birds that migrate very long distances without feeding on the way markedly reduce their digestive organs and regenerate them and resume feeding upon arrival. Chickadees, jays, nuthatches, and nutcrackers get bigger brains in fall; the part of the brain associated with processing spatial information is the hippocampus, which actually acquires more neurons. The temporarily larger hippocampus allows them to remember the widely scattered locations where they have stored seeds and retrieve them during the winter.

Brood-parasitic birds, which lay eggs in other birds’ nests, also have improved spatial memories—just in the nesting season. Two species of cowbirds in which the females monitor the locations of potential host nests have enlarged brains (hippocampus) in the nesting season. But in a third species of cowbird, in which both male and female monitor host nests, both sexes have seasonal changes in brain size.

Males of other birds (for example, starlings), get temporarily enlarged brains, especially the parts associated with singing, in spring, when males sing to advertise territory and attract females. European titmice that engage in strongly seasonal singing have corresponding seasonal changes in brain size, while those that vocalize year-round do not. Captive house sparrow males kept near females sang more often and had bigger brains than those isolated from females. These studies have focused on male birds and the production of song, but what about the females that listen to those songs?

It seems that the more we look, the more instances of seasonal remodeling we find. Nevertheless, I was not prepared to learn of recent work showing that skulls, specifically the brain case (and the enclosed brain) get seasonal changes too. Even though these bones are well-ossified and hard, with good, firm sutures between the various cranial bones, they too can be reversibly remodeled on a seasonal basis. These studies were done with the common red-toothed shrew of Europe and with two species of weasel (one called stoat in Europe and ermine or short-tailed weasel in North America, and one called weasel in Europe but least weasel here). Although all three species show the seasonal changes, there are interesting differences among them and between male and female in one species.

All three species showed a change in skull shape as the animals matured, from a more rounded and relatively large juvenile skull in their first summer–when they disperse and establish their individual territories–to a more flattened, relatively smaller adult form in their first winter. Then, each species showed a temporary, reversible increase in braincase size in the second spring and summer, with the acquisition of an increased behavioral repertoire involving mating and territoriality. There is then a subsequent winter decrease, accompanied by thinner skull bones—with hints that there were greater seasonal changes in geographic areas with more severe winters. At least in the shrews, there is no evidence of increased numbers of neurons, but in all three species different parts of the brain are involved in the increase and in the decrease. Precisely how this is achieved is not clear.

The researchers suggest that this skull remodeling is a way to conserve energy for these small mammals that have extremely high metabolic rates and high levels of activity all year long. Their slim body design, with short legs, is not conducive to putting on much fat and hibernation is not feasible.

However, while both male and female shrews exhibited approximately the same pattern, the weasels differed from each other. In the least weasel, after the winter decrease in braincase size, only males showed the spring-summer regrowth. There was no regrowth in the skulls of females. By contrast, in the ermine/stoat, both sexes exhibited a summer increase after a winter decrease.

The researchers related the variation in gender differences to the life histories of the respective species and genders. Both male and females shrews defend territories vigorously requiring much activity and perhaps recognition of neighboring individuals. Least weasels are very short-lived, seldom living more than a year or two, and females often invest resources in reproduction even in their first summer. They may not have enough resources to invest also in skull regrowth and little chance to gain by it, given the short life expectancy. Males, on the other hand, are busy with territorial defense, for which a larger appearance is often effective. Stoats/ermine are longer-lived and females don’t reproduce so quickly in the life history. Resource expenditure in reproduction is more spread out in time, and investment in skull regrowth may be more possible and more likely to lead to a possibility of future reproduction.

Winter wanderings

In early January, the ice on the ponds in the Dredge Lake area was good and solid, although there were isolated spots of open water where upwellings slowed the formation of ice. I traipsed around some of the trails and ponds, finding tracks of shrews, hares, and a mouse. Otters had slid over a beaver dam and then up a frozen slough, no doubt hoping to find a fish or two.

One day in mid-January, a friend and I explored a frozen pond, walking on snowshoes to spread out our weight, in case of a spot of weak ice. A little snow was falling, so it was a beautiful walk.

Beavers had made a small food cache near their lodge, including some hemlock branches. There were lots of spider webs and long, trailing silk threads used by airborne spiders. We wondered if any critters, in addition to some spiders, eat that silk to recycle the protein.

Around the bases of several trees at the edge of the pond, we noted the tracks of a small bird, probably a junco. It had apparently inspected each tree base quite closely, possibly picking insects from the spider webs that curtaining the gaps between the upper roots or searching for stray seeds.

A vole had crept out of one bank of a frozen rivulet, crossed he ice, and scuttled back to where it came from. My companion had observed such behavior in other places when the animal was seen to be a red-backed vole, so we assigned that perpetrator to those tracks. Deer tracks crisscrossed the pond ice, and deer had been feeding on the witches’ hair lichens that grew on small trees at the pond edge. My sharp-eared companion heard a brown creeper, which we soon saw as it hitched its way up a spruce trunk.

Many of the alders in this area had neither cones from last summer nor any male catkins for next spring. This was unlike other alder stands we’d seen, so we wondered why this stand was evidently reproducing very poorly. Perhaps the high level of water in the pond was too much for them.

We also noticed that here and in some other places the alders had retained many of their dried and shriveled leaves, instead of letting them drop to the ground. Blueberry shrubs sometimes do this too. In other regions, oaks, beeches, and other trees also retain many of their dead leaves throughout the winter. The term for retention of withered old flowers or leaves is ‘marcescence’. Marcescent leaves have attracted a good deal of speculation about why these plants do this, such as deterring deer and moose browsing, trapping snow for release of moisture in spring, or delaying decomposition until spring, when nutrients are most needed for growth. However, apparently very little investigation has explored those ideas. In some cases, particularly when marcescence is occasional and not regular, the retention of dead leaves may just happen incidentally because the weather suddenly changed in a way that prevented the usual mechanism of leaf-drop (formation of the cut-off or abscission layer at the base of the leaf).

A few days later, along the Auke Lake trail, (and later in other places) we noticed that many of the blueberry bushes had small galls on the twigs, often at the bases of marcescent leaves. The galls are really quite small, and I have to wonder how many times I have walked past them without noticing. They do seem to be more conspicuous against a snowy background…Some blueberry galls are made by midges or wasps, but these did not fit the descriptions of such galls, so the makers of these galls remain to be determined.

Toward the end of January, I went with a friend on the Pt. Bridget trail. Near the trailhead, we found a place where a weasel (I think) had fossicked about in the mud at the bottom of a hole in the snow, and come up to leave a string of its small, muddy footprints on the snow, before diving back down under the deep snow in a new spot. Somewhat to my surprise, the lower branch of the trail, along the edge of the big beaver meadow, was quite passable, provided one didn’t mind a couple of inches of water here and there. A moose had used the trail too, taking advantage of a deeply trenched part of the path—and a small wooden bridge—to avoid some of the post-holing that was required in the rest of the meadow. The bible-camp horses had left ample evidence of time spent on this side of Cowee Creek, on the beach fringe as well as in sheltered places under the conifers. Pawing away the snow and stirring the long, dead grasses, they also had clearly been looking for precocious green shoots under the snow…and had found a few.

As we left the area near the cabin, my companion spotted an owl, probably a short-eared owl, as it swooped down to some bare ground next to a tidal slough (the tide was out). It was probably trying to catch an unwary rodent, but we could not be sure it was successful. It soon flew up into the nearby trees, changed perches, and eventually took off across the wide meadows, screened from clear view by tall spruces.

A day or two later, when Plan A for a beach-walk was foiled by ferocious north winds on Lynn Canal, another friend and I eventually found a sheltered beach near Amalga Harbor. Moving slowly and quietly, we managed to share the beach with a trio of common mergansers that paddled slowly along the tide line. Then they all hauled out and snuggled up in a close-packed row to sun themselves.

I have learned a new word for verbal bric a brac like that found in this essay: bricolage. ‘Tis a very useful word for assortments of diverse things brought together in some more or less unifying way. There may be more bricolages here in the future.

Avian mate choice and plumage

how feathers shape species

Mating among birds is usually a matter of mutual agreement: both male and female are being selective in their choice of mates (although their criteria are likely to differ). Selectivity in mate choice is central to the Darwinian process of sexual selection, determining which individuals will mate and produce offspring. The chosen individuals are more successful in mating and reproduction. Thus, their genes are passed on to the next generation while the genes of un-chosen individuals are not. As the process continues, the genes that determine both the winning traits and the choosiness become more frequent in the population.

The outcomes of all that choosing vary enormously, depending on the ecology of the species, the previous evolutionary history, and the occurrence of genetic variation upon which selection can happen. If there is no plumage variation, there is nothing to choose! Avian feathers serve various functions, one of which is visual display during courtship. Genetic variation in plumage among potential mates provided birds with choices of color and pattern as they decide with whom to mate. Those choices, together with variations in other traits, shape the appearance and behavior of the lineage.

Imagine a species (Species A) that makes open-cup nests (as do all related species…that’s an evolutionary history factor) in shrubs (instead of under logs or roots; that’s an ecology factor). Suppose that in this species it is (for whatever historical reason) the female that incubates the eggs and cares for the nestlings. In an open-cup nests (compared to a cavity nest, for instance), the incubating female would be exposed to searching predators, and her frequent feeding visits to a particular location would also be noted by lurking predators. So inconspicuous, perhaps camouflaged, plumage would lead to better survival of the female and the eggs and chicks. And a male that preferred an inconspicuous female would have better reproductive success than one that somehow preferred a female that flashes a noticeable red crest or a long, bright blue tail.

If there is some variation among the males in the colorfulness of their plumage, those drab females might prefer males that are a bit colorful, perhaps with a yellow head or vivid magenta wings, rather than males that are more like the females. If those plumage patterns are heritable, the sons and daughters of such adults would bear the same traits, and eventually the whole population would have drab females and colorful males.

However, if (in species B) the males also do some of the incubation and parental care, they and their eggs and nestlings might suffer more predation. If they were colorful, then they and any female that somehow preferred a gaudy male would probably have lowered reproductive success. And so their genes would become less frequent in the population, and males and females would look similar in color.

Now go back to species A. Imagine that the population is spread over quite a large geographic area, such that the birds in one area just don’t get to another area, or vice versa. Now it is possible for the birds in that area to become different from the rest of the population. Suppose that some males don’t have simple yellow heads, they have additional blue crests on top. Then females there might find that they like males with blue crests (instead of plain yellow heads), for example. Then these more fancy males would come to predominate in that area. That might happen in several different areas, with different outcomes in each. If some of these fancy males just happened to wander into a different area, they might not be preferred by the females there. So thus, species A has begun to diversify into several new species, each with different male ornaments (and female preferences).

The classic example of diversification driven principally by mate choice is in the neotropical manakins. There are over fifty species of manakins. In general, the females are greenish and plain, while the males sport a spectacular array of plumage patterns and colors, often with behaviors that show off those features. By being very choosy, females maintain the dramatic differences among the males, and interbreeding is rare to non-existent.

Another example might be the wood warblers of North America, in which the males of different species are generally somewhat more colorful and distinctive than the females. Again, interbreeding between species is not common, but in a few cases, hybridization occurs between two species (e.g., Townsend’s and hermit warblers). Here in Juneau, a few years ago, observers noted that a warbler nest was tended by a mixed set of parents belonging to the same species (yellow-rumped warbler) but of two different varieties. One seemed to conform to the plumage patterns of Audubon’s warbler, while the other one was either a typical myrtle warbler, or the result of a previous mixed-mating of the two forms. In either case, more hybrids were being produced by this pair.

yellow-rumped-warblers,-male-and-female-at-nest-with-very-young
Two different subspecies of warbler tend their chicks together

Evolution by mate choice is common and widespread among birds. However, two other kinds of mating behavior tend to obscure the typical patterns. The first is that, even among ostensibly monogamous pairs, both sexes may go gallivanting, and do some of their copulations outside of the pair bond, and broods of mixed parentage occur. The choices for intra-pair copulations and extra-pair copulations may or may not be the same.

A second kind of mating behavior totally subverts the normal patterns of mate choice. In many ducks and some geese, there are forced copulations, in which males attack and try to copulate with females, which struggle and resist, but commonly suffer injury (sometimes lethal). There is clearly no female preference involved. The extraordinary complexity of the female reproductive tract in these species probably evolved as a way of reducing the fertilization success of the forced copulations; nevertheless, some small percentage of the embryos can be fathered by these violent males. Injury to the violated females is likely to reduce their nesting success, but I have not found data on that. The origin and continuation of this behavior of males is not entirely clear.

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This female Barrow’s Goldeneye (left) has made her choice from among competing males

Live-bearing and egg-laying

variation that defies generalization

Animals produce offspring by two principal modes of reproduction. Vivipary (or viviparity) means producing ‘live young’—readily recognized as ‘living’ because newly produced offspring wriggle, squirm, squall, or squeak. The intended contrast is with ovipary (or oviparity)—producing eggs that house an embryo inside a shell; usually the eggs do not wriggle or squall. Of course, fertilized eggs are not dead, as might be supposed by the contrast with ‘living’ young! Fertilized eggs are very much alive, but early development takes place inside the shell instead of inside a parent. All the nutrition for early development inside an egg must come from the egg yolk and therefore be provided by the parent before the embryo is enclosed in the eggshell.

(There is an intermediate condition –ovovivpary/ovoviviparity—in which fertilized eggs are held within a female and hatch inside her. The embryo may be nourished by eating other eggs or embryos or perhaps by a kind of placenta, with a direct connection to the mother. This might indicate ways that, in the course of evolutionary time, vivipary evolved from ovipary. But leave that aside for present purposes.)

Vivipary and ovipary—these two modes of reproduction are scattered widely in the animal kingdom. It would be convenient if we could make lots of solid generalizations about either of these modes of reproduction, either about their taxonomic distribution or about their advantages and disadvantages. But alas, not so. There are only a few strong generalizations and there are almost always exceptions. Consider first the birds and then the mammals.

All birds lay eggs. That’s one good generalization with respect to taxonomy. But how birds treat their eggs varies. Most birds make a nest in which the eggs and then the chicks are tended—ducks, hawks, most songbirds are examples. However, brush turkeys and mallee fowl in Australia don’t incubate their eggs in the conventional way. Instead they build a huge mound of dirt and vegetation, in which the heat of decomposition incubates the eggs. An adult may guard the nest and regulate temperature in the mound by opening or covering it, but that’s the extent of parental care.

In fact, not all birds make nests; several species of songbird and duck are brood-parasites: they avoid all matters of nest-building and parental care by laying their eggs in the nests of other birds. Penguins provide another exception. Emperor penguins and king penguins make no nest; they lay single, large eggs that are incubated on a parent’s feet, with a fold of skin covering them. The incubating adult can even shuffle around with its egg carefully held in place.

All mammals nurse their young; that’s the very definition of a mammal. But although most mammals are viviparous, not all of them are. The platypus and echidnas in Australia are exceptions, laying eggs. Some mammals make nests or dens for their young, some carry their offspring around, but others do not do either of those things.

There is also variation among the other vertebrates; for example, some snakes and some fishes are viviparous while others are oviparous. Among the invertebrates, vivipary is widespread, having evolved many times and occurring in many different taxonomic groups, but ovipary seems to be more common.

One broad generalization does seem to hold true: vivipary apparently necessitates internal fertilization of the eggs by sperm that are placed inside the body of the female. No such limitation applies to ovipary; some oviparous animals have internal fertilization and others do not, releasing sperm and eggs into water at the same time.

Scientists have long discussed the relative advantages and disadvantages of each mode of reproduction, but to my knowledge, they have not come up with a comprehensive explanation for the evolution of either mode. There seem to be exceptions to almost any general statement, and it is likely that different factors and different conditions have led to the evolution of one habit or the other in different evolutionary lineages.

Among vertebrates, egg-laying commonly means eggs are placed in some kind of nest while the eggs are incubated or tended by a parent (exceptions above). That means the adult is temporarily tied to one place (the nest) until the eggs hatch and, in many species, the chicks are also fed until they can be independent. Especially for an animal that flies, a clutch of relatively large eggs is difficult for a parent bird to carry around while the embryos develop, so a central place can be useful. A nest can also help keep the young animals warm. However, there is a risk involved—predators often learn to focus on parental activity as a clue about nest location, and an entire clutch of eggs or brood of chicks may be wiped out. Similar statements apply to mammals that use nests or dens. Some mobile invertebrates, however, simply lug a batch of eggs around, carrying them on hooks or in folds or whatever.

Vivipary, on the other hand, might mean that young are born in a relatively advanced stage of development (compared to egg-layers), having been nurtured inside the mother for some time. But no, although some viviparous mammals are born fully capable of running or swimming, others are born in a totally helpless condition that requires weeks or even years of parental care. Furthermore, there are birds, such as ducks, whose young hatch from eggs in condition to run about and feed themselves.

Pregnant mothers carry the fetus wherever they go, enabling them to move around to find places with more comfortable temperatures or better food or safer refuges—all things that they could not do with eggs in a nest. That applies also to invertebrates that carry their eggs with them, wherever they go. But there are risks to the parent, too, if the developing young impair mobility or, in some cases, require the mother to have a special diet. Pregnant bears avoid the mobility problem because they den in winter and birth relatively tiny young (but run a risk from human predators that seek out their dens).

The bottom line seems to be that, although some good generalizations emerge, there is much variation that defies wide generalization. There are balances to be found, playing this advantage against that disadvantage, and they vary with circumstances. As usual, there are many questions to ponder, and some answers may emerge from studying the details of particular species.

Long-distance migration

The Arctic terns that nest near our local glacier (and around the whole Arctic) are champion long-distance migrants; they are said to have the longest regular migration of any bird species. They fly from Arctic and subarctic summer nesting areas to the southern oceans around Antarctica to feed during the winter (southern-hemisphere summer), and then they fly back. They do this gigantic circuit every year. The average flight distances they cover are huge: one estimate is about twelve thousand miles (one-way) but another estimate found distances over twenty-two thousand miles in a zig-zag route over the Atlantic.

Short-tailed shearwaters do quite well too, flying up to the Bering and Chukchi seas (to feed during our summers) from their nesting areas around southern Australia. The distances covered are estimated at about nine thousand miles, one-way. Both the shearwaters and the Arctic terns feed in the open ocean and make stopovers to feed along the way, fueling up for the next leg of the journey.

Bar-tailed godwits are even more remarkable! These are large shorebirds that nest on the tundra in western Alaska and Eurasia. They feed in shallow waters in wetlands and along the coast. The Alaska nesters fly to New Zealand waters for the southern summer (our winter) and then come back in the spring. On the way back north, they often stop over in the Yellow Sea (between China and Korea)—a rapidly disappearing resource, because of shoreline development by China. One bird clocked over six thousand miles—non-stop– from New Zealand to the Yellow Sea remaining wetlands and then went another three thousand miles back to Alaska. Still more impressive was a godwit that made the southward migration directly over the open Pacific Ocean, a non-stop (!) trip of over nine thousand miles, taking about nine days without eating or drinking!

How is that possible??

We are used to the idea that migrating birds put on a lot of fat before migrating, sometimes doubling their body weight, and some (like the terns and shearwaters) can eat along the way. But godwits cannot feed in the open ocean. They put on some fat, of course, but that is not all they do: they also lose weight from various body parts: the digestive system, liver, and kidneys atrophy, shriveling up to a fraction of their former weights. Fat and protein from those organs are recycled and used as a source of energy. This also reduces the wing-loading or the ‘freight’ carried by the (non-feeding) migrant.

This weight-saving trick is used by some other fairly long-distance migrants as well, including some other shorebirds and songbirds. Furthermore, as migration continues, protein and fat from the muscles—including the flight muscles and heart!—are gradually metabolized and used as fuel for the journey.

The fascinating thing is that when these birds arrive at their destination, the atrophied digestive tract and associated organs are restored to their former functional size and condition! Lost muscle mass is restored too. The birds are able to “turn off” the internal organs and turn them back on again.

That kind of information has some medical researchers thinking about a human affliction called cachexia, which is a dramatic, potentially catastrophic, loss of muscle mass and fat that often occurs along with other afflictions, such as certain kinds of cancer, HIV, or multiple sclerosis. If research could figure out how migrating birds can turn off and then restore digestive tissues and rebuild muscle mass, they might figure out a means of mitigating cachexia in human patients. That’s a long way in the future, but it is interesting and significant that knowledge from avian migrations—seemingly quite far removed from cancer wards and hospitals—might yet contribute to human health.

Still an open question is how did such tremendously long-distance migrations evolve?

Tracks in December

tracings of life in an unusually warm winter

A warm, very wet spell in early December made the lichens and mosses all perky and colorful. Beavers left their distinctive foot marks in a thin dusting of snow and swam out around their winter caches of twigs, tail-slapping when we passed by. In a ‘real’ winter, they would be tucked up into their lodges, snoozing a lot, talking quietly with their offspring, and occasionally nibbling a twig from the cache. The kits of the year, however, would be chewing twigs all winter long, as they continue to grow. Bears were out and about too, mom and cub leaving their tracks near Dredge Lake, instead of entering into serious hibernation. That entails a profound reduction of metabolic rate, shutting down digestive processes, and very little activity inside the den, quite a contrast with beavers.

Then, in mid-December came a lovely and welcome snowfall, just a few inches at sea level. It wouldn’t last, of course, in this time of warming climate, so I dug up my snowshoes and headed to Eaglecrest. There the snow was maybe a foot or so deep and just right for poking around on a day when the lifts weren’t running. Snow was falling thick and fast, quickly covering any little tracks of mouse or shrew. But under the trees were prints of snowshoe hares. A small-footed canine creature had run across a wide open area, leaving a long, straight line of well-spaced prints. There was no evidence of any human anywhere nearby, so I guessed that a coyote had raced along. But very few critters made themselves visible—a porcupine that seemed to think that if it could not see me, then I could not see it; and one flying insect, probably a stonefly. Nary a bird to be heard or seen not even a hopeful, attendant raven.

A couple of days later, a nice little cold snap meant that even at sea level, there remained a few inches of snow cover. I went out the road to some meadows, where I plonked along on snowshoes—a convenient way to deal with snowy humps of frozen grass. Oddly, there were no shrew tunnels to be seen, nor any squirrel tracks, and again not a bird could be found.

But otters had been quite busy. They had fossicked along a tiny rivulet, trampling some spots quite flat; there were more than one of them, apparently, so perhaps a family of mom and well-grown pups. I lost their trail when it went under the trees where there was no snow. However, a few minutes later, I encountered their characteristic slide marks where they had crossed a snowy, open area, pushing off strongly with the hind legs and gliding smoothly even over flat ground. This is probably more fun than stomping around on snowshoes! A bit farther on, otters had come up out of a tiny stream and snuffled all around the nearly buried ends of several low, trailing spruce branches. What was going on there, I wonder.

Some days later, I looked for tracks in another meadow out the road, but there had been little recent activity. A couple of squirrels had explored the meadow edges, out of the trees and back again, diving under humps of bent-over grasses. Before the last little snowfall, porcupines had trundled over the meadow in several places, on their usual meanderings. They seem to travel quite extensively, perhaps in search of just the right twig to nibble (?). Along a small creek, some critter had burrowed into the bank in several spots—possibly an otter.

Surprisingly, there were no little shrew-size grooves on the surface of the snow, no tiny holes where a shrew dove under the white blanket. Yet this was a meadow that, in previous years, had been laced with trackways of shrews. One shrew had even taken a dive off a vertical mudbank and gone skittering over a gravel bar in a creek. But where are all those shrews now?

A fluttering on the creek-bank caught my eye and eventually turned into a dipper. This bird was foraging along the water’s edge but apparently found little of interest, because it soon took off, upstream. That was the only living animal to be seen, except for one red squirrel crossing the creek on a broken-branch bridge.

Later that day, on another stream, I checked a long-occupied beaver lodge. There were no signs of recent beaver activity here, although the lodge may be currently occupied. However, other woodland folks were interested in the place: porcupines and mink had visited on more than one occasion in recent days. Was this perhaps a multi-species condo? It wouldn’t be the first time that happened.

The slanting light of midwinter that stabs one blindingly in the eye at certain times of day on Egan Drive, did some beautiful things out by the meadows. Some conifer-clad hilltops were brilliantly lit, contrasting with darker slopes below. Light mists collected in the valleys caught the light rays and turned golden. Overhead, some dark clouds gathered amid some white fluffy ones, but bright rays came through the many unclouded areas, where blue sky was a cheery sight.