Tuesday, November 26, 2013


People who feed birds in the Pacific Northwest look forward to the return of flocks of Dark-eyed Juncos (Junco hyemalis) to their feeders every year. Great numbers of them descend on our towns and cities each fall, both from our own mountain conifer forests, where they are abundant breeders, and from similar habitats farther north.

Juncos are great birds to show social interactions. Aggression between individuals is usually expressed by flicking the tail, exposing the white outer feathers and by using the sharp, metallic chip call. By watching a flock around a feeder, you can learn a lot about dominance hierarchies. The dominant bird sleeks its plumage, extends its neck and moves toward the subordinate one. If the subordinate bird does not retreat, a peck may occur, or even a brief flight.
Years ago, when it was noticed that chickens exhibited aggressive behavior around food, researchers discovered that each chicken had a place in a dominance hierarchy. It was called “pecking order,” as chicken A would peck every other bird in the flock to displace it from food. Chicken B would peck every other bird but chicken A, etc. Poor Chicken F, at the bottom of the pecking order, was destined to feed only when all the other birds were satiated.

This dominance hierarchy has subsequently been found to be typical of flocking birds. You only have to watch a flock for a while to see it at work. Dark-eyed Juncos have been extensively studied, and it turns out that males are dominant to females and adults to immatures. Dominance is related to hood color, the pink bill standing out dramatically against a black (male) or gray (female, immature) hood. In such a highly social bird one can easily see how this color pattern would have evolved from ancestral sparrows with their more subdued and camouflaged patterns.

Interestingly, there seems to be little cost to being subordinate, as several studies showed that subordinate birds survived through the winter as well as dominant ones.
Our common birds are what used to be called Oregon Juncos when five species were recognized. Males have black hoods, rich brown backs and buffy sides. Females are similar but with gray hoods. All five have been lumped into a single species now, the Dark-eyed Junco. North of here, in the boreal forests of Alaska and Canada, juncos have dark gray hoods with gray sides and gray are brown backs. These are called Slate-colored Juncos. It’s easy to distinguish them because the hood and sides are the same color. Watch for them at your feeders.

Juncos typically build nests on the ground, well sheltered by the surrounding vegetation, and lay their 4-5 eggs there. They commonly raise two broods of young each in a summer, and the young are streaked like their sparrow ancestors. As they have become more common breeders in Northwest cities in recent years, watch for the young in your own yard in midsummer.

Dennis Paulson

Tuesday, September 17, 2013


Jellyfish are amazing animals. Almost entirely made of water, without a brain or central nervous system, they manage to get around the oceans very successfully.

One of the common species in the eastern North Pacific is the sea nettle, Chrysaora fuscescens. This species is among the better known Pacific coast jellyfish because it can be kept in aquaria. It can become superabundant in our waters, presumably when the zooplankton on which it feeds are similarly abundant, but it also may be because of the vagaries of ocean currents. Jellyfish generally swim upcurrent so they encounter a regular supply of the tiny animals on which they feed.

Not very many animals feed on jellyfish because of a combination of their fairly effective antipredator adaptions and their very low nutrient content. Two of these that do so are actually specialists, large animals that roam slowly around the world’s oceans and eventually run into single or even concentrations of jellyfish.

The Ocean Sunfish (Mola mola) is the more common of these two species. This is the largest and best-known species of its family and in fact the heaviest bony fish in the world, with an average weight of 1,000 kilograms. It looks about like a head with fins, swimming with a sculling motion of the big dorsal and anal fins. A long fin waving at the water surface is usually a good indication of one of these two-meter monsters.

Ocean sunfish are usually found floating at the surface on their side, perhaps taking advantage of the warmest surface water to more effectively digest the great amount of jellyfish they have to eat to gain adequate nutrition. We see them when they are at the surface, but in fact they spend much of their time well below the surface and perhaps come up just to warm up!

Ocean Sunfish are known to lay the most eggs of any animal in the world, up to 300 million eggs at one time. The larvae look nothing like the adults but are more like the larvae of other members of their order, including puffers and porcupine fish. It is rare to sight groups of juveniles, but five such groups were seen off Grays Harbor in September 2013; presumably like other fish, they school for protection from predators, among them sharks and sea lions.

The other main medusivore, as a jellyfish-eater should be called, is the Leatherback Turtle (Dermochelys coriacea). This is also huge for its group, the largest living turtle at an average weight of 400 kilograms. The largest ever recorded had a carapace length of over 2.2 meters. These animals are very different from the sunfish in that they have to go to shore to nest, and the ones in our waters are migrants from, amazingly, the Southwest Pacific.

Of all the sea turtles, this is the one most capable of living in cold waters, even north to the Gulf of Alaska. They generate metabolic heat by swimming, and they are insulated by fat as well as warmed by counter-current heat exchange in their blood vessels. Although “cold-blooded” like other reptiles, their body temperature has been recorded as up to 18° C. warmer than the water in which they swam.

Northern Fulmars (Fulmarus glacialis) also eat large jellyfish, among the few birds that do so. The cnidarians because of their watery nature are poorly represented in stomach contents, but observers have seen them picking at jellies. They appear to go after the gonads, which are doubtless more nutritious and oil-rich than the rest of the animal.

And all these animals eat their jelly without peanut butter!

Dennis Paulson

Tuesday, September 10, 2013


In fact, southbound migratory shorebirds have been back in the Pacific Northwest since the last week of June, but it is timely to write about them, as they are probably at their peak at the beginning of September.

The adults come back as soon as their young fledge, but of course some nests fail, and those adults are the first to return. Why stay in the Arctic, with all those mosquitoes and arctic foxes, when where you really should be is on a mud flat in Grays Harbor or a sandy beach in Sinaloa? Some of them are going farther, well into South America, so they had better get an early start for that long flight.

In quite a few shorebird species, one sex deserts the other adult and the offspring soon after the eggs hatch. The majority of these are females, presumably because females have expended much energy producing the eggs, so to balance parental investment, the males are left to raise the young. Most shorebirds don’t feed their young, so raising young shorebirds consists of shepherding them around to feeding sites and warning them about potential predators. It’s still a lot of work (imagine keeping track of four kids when you can’t see them much of the time).

Perhaps because they are big enough to potentially ward off predators, large shorebirds such as curlews and godwits divide parental responsibility, and the sexes migrate together. This is also true of most plovers. But the first Western Sandpipers you see in fall are probably those that failed at nesting, then a large wave of females that have left their families, then the males.

Many of these species undergo body molt while they are migrating, so in the fall we see birds in breeding plumage, in nonbreeding plumage, and at all stages in between. In addition, another plumage complicates the issue. These are the juveniles, young of the year that migrate after the adults. The peaks of their migration are often about a month apart, so in some species that continue south after passing through our region, we see a lot of adults and then a lot of juveniles, but not much mixing.

When trying to identify unknown shorebirds, it is extremely important to place them in a plumage, or at least an age stage. In fall, the adults have very worn body feathers until they are all replaced, and many of them don’t replace all their feathers until some time in the winter. Of the flight feathers, both the primaries and the tertials (the feathers of the inner wing that cover the primaries when the wing is folded) become very worn, and that wear is easily seen. Juveniles, on the other hand, have neat unworn feathers, including the primaries and tertials.

Get out to the coast and savor the shorebirds. You can easily see one to two dozen species on a good day, and identification is much facilitated because they are often in mixed-species flocks.

Dennis Paulson

Tuesday, August 13, 2013


Many insects are predators on other insects. Dragonflies and damselflies (order Odonata) come to mind immediately, as all of them eat smaller insects and spiders. But put them up against robber flies (order Diptera, family Asilidae), and they have not only met their match but been bested with ease.

Robber flies eat dragonflies and damselflies regularly, but there are almost no records of odonates turning the tables. One type of predator is clearly superior to the other. I have seen robber flies take insects from most orders, including their own. Size is no limit, as an inch-long robber fly can latch onto a flying dragonfly three times its size and bring it down to the ground instantly with a paralyzing bite. Presumably if the fly was captured, it could do the same thing to its captor.

The two wings of a robber fly are narrow but strong, and they propel their owner through the air with an audible—sometimes impressively loud—buzz. Their flights are usually short, and when you hear that buzz you can often find its source resting on a branch, rock or the ground. They usually perch right out in the open, again like a dragonfly, where they can see potential prey. They have relatively large, forward-pointing eyes as befits a predator.

The thick, tubular proboscis injects venom that is both proteolytic and neurotoxic. The neurotoxin paralyzes the prey almost immediately, and the proteolytic enzymes digest the innards into a liquid soup that the fly sucks out. The proboscis is strong and sharp enough to penetrate the hard cuticle of a beetle.

Many insects are poisonous and distasteful and brightly colored to advertise their unpalatibility. This adaptation must be against birds, because robber flies freely feed on such insects, as do dragonflies.

Robber flies are very bristly. The legs have long, sharp spines to hold onto the prey, much as in dragonflies. The face has a dense coat of bristles, called the mystax, presumably to protect it from the legs and mandibles of struggling prey (but it’s a sure thing that they don’t struggle for long).

Many robber flies are sleek and pointed at the rear, the jet fighters of the insect world. Others are fat and fuzzy, very effective mimics of bumble bees but just as effective as predators. They have been called aggressive mimics, mimicking their favored prey species to get close enough to make a kill.

Fly larvae are legless and look like maggots, and robber flies are no exception. Slim and pointed at both ends, at least some of them feed on the larvae of other insects, usually in rotting organic material such as logs and dead trees or in the soil. Surprisingly little is known about the larval life of this group, however.

With over 7000 species in the world, robber flies are diverse on all the continents. They are relatively uncommon in the wet western lowlands of the Pacific Northwest, just as many groups of insects are less common in our cool, cloudy summer climate. Head across the Cascades to see a lot more of them in the dry, open areas that they prefer.

Robber flies are easily observable, as they are fairly tame, but capturing one in an insect net and looking at it closely allows you to appreciate its adaptations even more. Be cautious, however, as their bite can be painful. I know enough about their adaptations that I have never allowed one to bite me!

Dennis Paulson

Tuesday, July 30, 2013


Dragonflies (including damselflies, both in the order Odonata) are aquatic as larvae and terrestrial (and aerial) as adults. These are very different environments, and organisms need different adaptations to be successful in each one.

Dragonflies, like amphibians, have successfully colonized these two different environments. Some amphibians remain in water, and their immature and mature stages are very similar. Others undergo a dramatic metamorphosis when they move from water to land, for example tadpoles to frogs.

In dragonflies the changes are even more dramatic. A dragonfly larva (nymph) is so different from an adult that you would never think they were the same organism. Each is perfectly adapted to its environment, but they must change radically to move from one to the other.

Most dragonfly larvae spend months, in some cases years, in the water. Very tiny when they hatch from the egg, they begin feeding on other small organisms immediately. With an inflexible exoskeleton, they have to molt to grow, so they enlarge each time they shed their cuticle and grow a new one. Each of these stages is called an instar. Larvae usually go through 10-12 instars before they are full size.

While in the last instar, they begin the amazing transformation of metamorphosis. Within the larval body, tissues are transformed from larval to adult tissues. All this happens while the larva continues to move around, feed, and try to avoid being eaten by some other predator. Finally, the change becomes such that the larva switches from aquatic to aerial respiration. It cannot feed any more by that time, and it heads for a place to emerge from the water.

The larva crawls up onto shore or onto a stem emerging from the water and begins its transformation. It anchors itself in place by its sharp claws. Soon a split appears in the cuticle of the thorax, and the adult within enlarges and begins to emerge. The thorax and then the head emerge, and the dragonfly rests in that position for some time, presumably waiting for muscles to firm up.

It then reaches forward and grabs its own skin or the stem in front of it and pulls itself completely out of the larva (the cast skin is called an exuvia). It is still more or less the shape of the larva, but then it begins to enlarge still more while still soft. First it pumps body fluids into the wings, which had been accordioned into very small wing pads. The wings get bigger and bigger, finally reaching full size.

The fluids then are pumped from the wings into the abdomen, which lengthens greatly. Eventually the fully developed wings open up, and the dragonfly remains that way for a while. Finally it lifts into the air and flies away. The entire process may take only a half hour in a small damselfly, up to several hours in a large dragonfly, but the result is the same. Free of the water at last, the dragonfly undertakes a completely different life from then on.

That life will be much shorter than the larval life, in the range of a week to a few months, but it will involve dispersal away from the water to feed and mature, then back to the water to mate and, for the females, to lay eggs. The cycle is complete.

Dennis Paulson

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