Tuesday, July 22, 2014

WATCH OUT, IT STINGS—OR DOES IT?


We all know when yellowjacket season rolls around, with pesky wasps that bother us on every picnic. You can usually chase them away easily, but they come back again and again. They are relatively innocuous when you’re trying to give them the brush-off, but don’t ever disturb one of their nests in the ground!








Western yellowjackets (Vespula pensylvanica) are members of the insect order Hymenoptera, the bees and wasps. Other wasps that are common in our area are bald-faced hornets (Dolichovespula maculata), bigger and fiercer than the yellowjackets and with a big turnip-shaped paper nest up in the trees; and introduced European paper wasps (Polistes dominula), with a much smaller paper nest with chambers open below.




All these species have in common a black and yellow or black and white banded abdomen. That coloration is common in wasps and bees and is thought to be aposematic (Greek ‘away sign’), a word used to denote a warning coloration. “Don’t mess with me” is a loose translation.
Some birds, for example kingbirds, are able to take stinging insects in their stride, catching them in flight and beating them to death, even squeezing out their stinger, but a lot of animals doubtless leave them alone because they pack such a punch at the end of their abdomen. The warning coloration assures that they are safe either because the predator species has a genetic memory of them or has tried to capture one previously and was stung by it, a much more immediate memory!

As these wasps move through our environment, relatively impervious to predation, other insects have benefitted by evolving coloration, shape, and even wing sound that mimic the wasps. Most of them in our area are flies (Diptera), especially hover flies of the family Syrphidae. Here are a few of them. They look very much like the wasps as they fly around, and even seasoned entomologists often have to look closely. I for one have grabbed what I thought was a fly from an insect net and been stung for my mistake.

By mimicking stinging wasps and bees, these so-called Batesian mimics (from Henry Bates, early student of this phenomenon) gain protection from predators, mostly birds, that mistake them for their models and leave them alone. It must work very well, as there are so many kinds of flies that mimic wasps. There are also grasshoppers, beetlees, moths, and other insects that do the same, especially in the tropics, where there are so many more species of insects and so many more birds that eat them.

A study done in Illinois that involved extensive collecting of model Hymenoptera and mimic Diptera showed that the mimics are common in the spring, when adult birds are present as predators, but virtually absent during the period in midsummer when young birds are fledging. Some of them appear again in fall. The authors speculated that the mimic flight seasons were adjusted to miss the time when young, na├»ve birds were everywhere, birds that wouldn’t know enough not to catch them!

Dennis Paulson 

Tuesday, July 8, 2014

THE PACIFIC NORTHWEST IS SLUG COUNTRY


With our very wet climate (favorable for terrestrial mollusks) and our relatively acid soils (not so favorable for forming snail shells), we furnish great habitat for slugs.

The ones most of us see are garden slugs (Arion ater). This slug, native to northern Europe, comes in two forms, a black and a reddish one. Long thought to be subspecies of one another, Arion ater ater and Arion ater rufus, they have recently been split as two separate species Arion ater and Arion rufus. Unfortunately for the field worker, both of them come in a great variety of colors and can only be distinguished by dissection or molecular analysis.


So we’ll just call them all garden slugs. They have proven to be very successful imports to our region but aren’t well liked by gardeners because of their predilection for garden plants. In fact, it’s the easiest thing in the world to go online to find out how to get rid of slugs. I am choosing to extol their virtues, perhaps the most important one just to familiarize people with slugs.

Our big native slug is the banana slug, Ariolimax columbianus. After a European species that grows to a foot (30 centimeters) in length, ours is the second largest in the world, reaching lengths of 25 centimeters. Four of these in a cup would weigh a pound! Rarely are such monsters seen, though; most that we encounter are in the range of 10-15 centimeters, just a bit larger than the much more familiar garden slugs.

But walk into a mature wet forest, and if it’s a moist day, you are likely to find lots of banana slugs. They come in a variety of colors, from white to plain yellow to heavily spotted with black. There must be some genetic differences among these color types, as often all the ones you see in one spot look about the same.

The big hole on the right side of these slugs is the pneumostome (breathing hole). An active slug shows two eyestalks above that detect light or movement and two tentacles below that are chemosensitive. They have mucous glands all over the body that keep them protected from dehydration and that can lay down a trail for easier locomotion.


Most slugs are herbivorous, feeding directly on plant tissue (garden slugs) or on detritus and mushrooms (banana slug). The leopard slug (Limax maximus), a large pale brown, black-spotted species that is also introduced in our region, feeds on other slugs as well as detritus and garden plants. In turn, garter snakes and ducks eat a lot of slugs, apparently able to combat the mucous that protects them from many other predators.

Slugs are hermaphrodites, both sexes present in the same animal, and when they mate each one contributes sperm to the other. The lack of separate sexes may make sense in slow-moving animals that might have trouble finding a mate. In this case, every slug encountered would be a potential mate, not every other one!

Dennis Paulson

Wednesday, February 12, 2014

SEA STARS WINKING OUT


Sea stars (you may know them as starfish) are prominent features of the marine environment all over the world. They are especially prominent in Pacific Northwest waters, where our species are among the largest, most diverse and best studied. In fact, the Pacific Northwest marine environment shelters the highest diversity of this group (class Asteroidea, phylum Echinodermata) anywhere in the world.

Perhaps this prominence made even more startling the discovery in 2013 that sea stars were dying off in great numbers in our waters. Sunflower stars (Pycnopodia helianthoides) were the first to be discovered. This largest of all sea stars is a top-level predator in our intertidal zone, eating just about everything smaller than it, so its disappearance could have profound ecological effects.

Just as important and much more abundant, the ochre sea star (Pisaster ochraceus) has long been known to control the distribution of mussels in the intertidal zone. By preying upon them in the lower intertidal and thus opening up substrates that would otherwise be completely covered by mussels, the sea stars provide habitat for many other species. The ochre sea star has been called a keystone species because of its importance. This species too has been dying off, in many cases completely disappearing from areas where it was once abundant.

These echinoderms are dying from sea star wasting disease, which causes the animal to deteriorate rapidly. Lesions form on the outer surface, and the arms begin to writhe around and eventually pull loose, spilling the internal organs. Death follows very soon, the animal turning to mush. This is a horrible thing to see, and you’ll have to go online elsewhere to see photos of it, as this is a family blog.


Other sea stars known to be affected include the sun stars (Solaster spp.). Some common species seem to be less affected or perhaps not at all, for example the blood star (Henricia leviuscula), leather star (Dermasterias imbricata) and bat star (Patiria miniata). Why would this be? Like everything else about this puzzle, no one knows.

The animals are being monitored in many areas now, both from shore and under water, and as spring comes and the intertidal begins to be exposed more during the daytime, it will be even easier to determine the fates of sea star populations all along the coast. Divers and remote underwater cameras have reported mass mortality in numerous places, with sea stars going from common to virtually absent in a shockingly short time, as if an epidemic swept through them en masse. Their dermal ossicles (the only hard part of a sea star) litter the bottom in some areas where they were once common.



Dead and dying animals have been brought into several laboratories, where efforts are being made to determine what pathogen(s) might be causing this disease. Earlier die-offs of sea stars were blamed on higher than usual ocean temperatures, but that’s not the case now.

So far, no bacterium or virus has been incriminated in these searches, but the search goes on. Stay tuned for more about this ongoing and very disconcerting drama.

Dennis Paulson

Thursday, January 23, 2014

WHITE PELICAN—ANOTHER SUCCESS STORY


Just as happened with their cousins the Brown Pelicans, American White Pelican populations fluctuated greatly during the 20th Century. Having bred at Moses Lake and probably Sprague Lake in the interior of Washington early in the century, by the middle of it they had disappeared from the state as a breeding bird.

As the second half of the century crept along, these pelicans remained in the state as nonbreeding visitors, sometimes as many as hundreds of them at fish-rich lakes of the Columbia Basin. Oddly, there is no evidence that American White Pelicans suffered from DDT poisoning as did North American Brown Pelicans. So there must have been other reasons for a general decline in their populations, and human disturbance of breeding colonies is considered a very likely factor.


However, late in the century a turn-around was observed, and White Pelican populations began to increase all across the range of the species. In the 1990s, a few breeding colonies were discovered along the Columbia River in the Tri-Cities area. The primary one now is on Badger Island in McNary National Wildlife Refuge, where as many as 1,000 pairs have bred. An injured flightless Bald Eagle spent the summer of 2013 there, and the pelican population may have suffered from that.

In 2010, a small colony formed on Miller Sands Spit, in the Lower Columbia River, reaching a few hundred pairs by 2012. The Army Corp of Engineers covered the nesting area with dredge spoil that fall, but small numbers continued to be seen the next summer.

A great number of nonbreeding birds, up to a few thousand, occur in the state every summer along the Columbia River and some of its tributaries. It would have been unheard of to see White Pelicans in the Yakima River 20 years ago, but now they feed all along its length. Small numbers even spend the winter along the Lower Columbia River, something never observed before the last few years.


The species has increased all over the continent in recent years. Counts made in 1998-2001 totaled about twice as many birds as in 1979-1981. Those counts, now 15 years old, estimated over 150,000 birds, a respectable number of individuals for a very large bird such as this. And the estimate is conservative, as some known colonies were not surveyed. Further surveys are to be carried out.

Brown Pelicans and their close relative Peruvian Pelicans are both confined to the marine environment. They forage by flying, often in small flocks, well above the water surface and diving into it when prey are sighted. American White Pelicans, on the other hand, feed like other species of pelicans all over the world.

American White Pelicans spend much time on fresh water, although they are equally at home on salt water, and large numbers winter coastally. When foraging, several birds move through shallow water, dipping the bill in the water rapidly to capture nearby fish. Sometimes a whole line of birds forms and moves forward steadily, individuals dipping their bills one after another as they herd schools of fishes ahead of them.

Like gulls and other fish-eating birds, they also collect at dam spillways where their prey is delivered to them, often too stunned to escape. Dams are usually not good for fish but often good for birds!

Dennis Paulson

Wednesday, January 15, 2014

BROWN PELICANS IN WASHINGTON


When I moved to Washington in 1967, Brown Pelicans were rare in the state. Formerly common and widespread on all coasts of the US, their populations had crashed over a period of decades. Only after some time and much research did the cause become clear. Beginning soon after the Second World War, DDT was developed as the first of the modern synthetic pesticides. Within a short time, it had been liberally applied to crops all over the continent and to settled areas to combat the mosquitoes that transmitted diseases such as malaria.

DDT accumulates in tissues and becomes concentrated as it passes up the food chain. Fish picked it up from the water and passed it on to the pelicans that ate them, concentrating the chemical in pelicans more and more. One of its byproducts, DDE, interferes with calcium metabolism and as a consequence, the birds weren’t able to produce sufficient calcium for their eggshells. The thin-shelled eggs cracked when the adults attempted to incubate them, and reproductive success dropped precipitously all around our coasts.

The consequences of using this pesticide became so obvious that in 1972 the Environmental Protection Agency banned its use in the US. Fish took up less of it, eventually pelicans were pretty much free of it, and their nesting success improved greatly.

By the end of the 20th Century, Brown Pelicans had become common again on the Pacific coast and were coming up to Northwest waters in numbers never seen before. Now thousands of them visit our outer coast every summer to take advantage of fish populations apparently greater than those around their breeding grounds in southern California and Mexico. A small number of birds make their way all the way down to southern Puget Sound, and a few even stay through the winter now.

Our pelicans are a good mixture of adult birds with white heads and dark underparts and juveniles with brown heads and white underparts. They roost in large flocks on sand islands, jetties and piers and launch into the air to feed after long sessions of resting and preening.

This unmistakable bird is an aerial plunge diver. Single pelicans, sometimes in groups, fly several meters above the water and, when they spot a fish or school of fish below, they fold their wings and drop like a plummet, piercing the water with their long bill and almost completely submerging. When the bill reaches one or more fish, it opens and water rushes into the huge pouch. The pelican lifts its head and lets the water drain out, keeping the fish inside to be swallowed.


Heermann’s Gulls, breeding in the Gulf of California, also move north along the Pacific coast, becoming common in Washington waters while the pelicans are here and then moving south again in late fall.

When a pelican dives, it may be accompanied by one or more of these kleptoparasitic gulls. If a fish falls out of a pelican pouch, a gull is often there to grab it.

Dennis Paulson

Tuesday, November 26, 2013

RETURN OF THE JUNCOS


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 AND THEIR PREDATORS


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