Wednesday, June 8, 2016

THE ANGELIC AND DEVILISH PIED-BILLED GREBE

Pied-billed Grebes, Podilymbus podiceps, breed at several lakes within the city of Seattle and doubtless within many other cities in the Pacific Northwest. One of our breeding sites is Magnuson Park, where one or two pairs of grebes began to breed just last year at the Shore Lagoon, the pond closest to Lake Washington. The male started calling early this spring.



And in mid May I saw the adults taking care of 5 downy young. They are very striking, with their striped heads and reddish markings. The young grebes have a strong predilection for riding on the back of the female, and I saw this numerous times. Four young at once would try to crowd onto her back, a logistical impossibility, but I saw her holding three on a few occasions. As they got larger, of course, this behavior became less likely. But it was very cute to see, a picture of parental care in a bird that can't be beat.



For several years this pond, the result of a wetland mitigation, had no fish in it. Last year the grebes fed their young primarily large dragonfly larvae, and these common insects were apparently sufficient food for the family. By this summer, Oriental weatherfish, Misgurnus anguillicaudatus, an introduced member of the loach family, had found their way into the pond somehow, perhaps through a drain into Lake Washington. So they have been the hot items on the diet this summer.


The young laze around until an adult comes up with a fish, then immediately crowd in. At first the loaches were too large, and I saw the female attempt to offer them to one young after another with no success. They swallow their food whole, so this wasn't doing it, and I assume there must have been smaller food items fed to the young when I wasn't watching. There were originally five young, but two weeks later I could see only four, so a predator may have taken one. A young bird that fledges may have moved from one narrow escape to another.


However, these grebes, especially the male, dominated the pond. He would call often and loud, sounding like a challenge to me. One day I saw something I wish I had been able to photograph. Two Mallard ducklings were following their mother across the pond, when one of them disappeared. I wondered if someone had introduced a large bass or snapping turtle into the pond, when a few seconds later the male grebe surfaced right at that spot. I didn't see the duckling again, and 10 minutes later I found it floating dead on the surface, with wounds on its head.

In additional visits, I saw the grebe chase both ducklings and adults ducks numerous times, and one of my friends saw the grebe kill two ducklings in a row. The literature about Pied-billed Grebes makes it clear that they are fiercely territorial against each other and other water birds, and a case of a Pied-billed killing the chicks of a Least Grebe was reported. The male that I watched regularly was astonishingly aggressive, chasing every bird that it came near, and I started calling it the Devil Grebe. Of course it was just exercising normal behavior for the species, and it's not the only water bird that has been reported to kill the chicks of other species. Nature is something else.



Dennis Paulson

Tuesday, June 16, 2015

VIREOS, INCONSPICUOUS SIGNS OF SUMMER


Now that summer has come around, it’s time to look at breeding birds, of which we have plenty in the Pacific Northwest. One such group is the vireos, Vireonidae. Members of this family, at least out of the tropics, are quite plain, olive to gray-brown, perhaps with a bit of brighter greenish or yellow thrown in. Some species have a combination of eye rings and wing bars, others have a supercilium (pale eye stripe) and no wing bars.

We have two each of these types. Of the eye ring/wing bar group, Cassin’s Vireos have a white throat contrasting with a leaden gray head and bright white “spectacles,” while Hutton’s Vireos are duller, with no contrast in the head/throat area and a less conspicuous and broken eye ring. In the second group, Warbling Viros are dull gray-brown above, with the white supercilium their only conspicuous mark. Red-eyed Vireos are much more brightly marked, rather greenish above and with a gray cap and rather conspicuous dark lines above and below the white supercilium. This species is the only one of our vireos that doesn’t have a dark brown eye.


More interesting than the differences in appearance are the differences in ecology. Cassin’s breed in somewhat open conifer forests and are quite common well up into the mountains. Hutton’s breed in lowland conifer and mixed forests and are uncommon even as high as the foothills. Warbling breed widely in mixed forests with a high deciduous component, much more commonly to the east of the range of Hutton’s, and Red-eyed are characteristic of tall cottonwoods in riparian situations along rivers and around lakes.



Red-eyed and Cassin’s are birds of the canopy, while Warbling and Hutton’s are more typical of the subcanopy and even understory. The consequences of these differences are that each species has a habitat in the Northwest where the others usually aren’t found. This is the ecological separation, presumably by each species being best adapted to its own habitat and foraging height, that is discussed in ecology texts. Our vireos show it particularly well.


In addition, three of the species are migratory, moving out of the region in winter and wintering in Mexico (Cassin’s and Warbling) and even far into the Amazon Basin in South America (Red-eyed). These long migrations are typical of most of our insect-eating birds, which would have trouble finding food in the winter when most insects are hidden well away from a leaf-gleaning bird such as a vireo. Hutton’s is resident, on the other hand, apparently able to find enough to eat in the moist forests where it occurs. We are at the northern end of its range, and it is doubtful if it could be resident any farther north. Perhaps because it is the smallest vireo, it can find insects in places in which the larger species couldn’t forage.

Vireos build nests supported by their rims, often in the fork of a branch and often enough in the open that they are findable by an observant naturalist. They are also findable by female Brown-headed Cowbirds, brood parasites that parasitize a large percentage of vireo nests. Our vireos seem to be doing fine in spite of this.

Dennis Paulson

Tuesday, May 5, 2015

TOO MUCH WIND FOR BY-THE-WIND SAILORS


For more than a month now, Pacific Northwest outer ocean beaches have been the scene of a massive stranding of by-the-wind sailors, Velella velella. These little blue critters are washing up on our beaches by the billions. Each time a new high tide comes in, they are deposited at the upper end of the waves in windrows on the beach.

     Velella wrecks are commonplace on the Pacific coast, usually happening in the spring of most years. But this year has produced a bumper crop of them, many more than usual, from Vancouver Island to California. First noticed in August of 2014, they came in in stupendous numbers in the spring of 2015 with unusually strong onshore winds. They are everywhere in tropical and temperate oceans, but their strandings seem to be most common on the American Pacific coast.


     Velella is a colonial animal, each sailor made up of hydroids attached together under a chitinous float, the individuals thought to be specialized for prey capture, digestion and reproduction. A stiff semicircular sail projects upward from the float, so any breeze blows the sailor across the surface. The sail is set at a bit of a diagonal, so the Velella is actually tacking off the downwind direction. It is speculated that the direction of tacking is such that the animals are kept offshore for the most part, but changing winds can undo that safety factor.

     One of the most characteristic things about Velella is its beautiful blue color. The blue pigment is apparently a protection against harmful ultraviolet radiation from the sun that streams down through the day.

     Velella are typical cnidarians, possessing nematocysts in their tentacles that kill tiny planktonic prey, including crustacean larvae and fish eggs, and digest them in a central stomach area. This nutrition is shared among the individuals and is augmented by algae (zooxanthellae) in the colony that photosynthesize and produce organic carbon and nitrogen. In the class Hydrozoa, they are more closely related to hydras than to jellyfish, although not as closely related to Portuguese man-o’-war as previously believed.

     They feature alternation of generations, reproducing like typical members of the phylum Cnidaria. The sailors that we see bud off tiny medusae (“jellyfish”) that then produce male and female gametes that fuse and form larvae that at some point presumably assemble into the animals that we see. Exactly how this happens is still quite unknown, and the smallest ones that are usually seen are fully developed.


     You might guess that Velella, just because of its abundance, would be attractive as prey, yet much of the animal is inedible chitin, the same protein that makes up the exoskeleton of insects. Their best-known predators are spectacular pelagic nudibranchs (Glaucus) and a group of unusual snails (Janthina) called violet snails that produce mucus with their foot that forms into bubbles that support them. They float on the surface darkside up, countershaded like oceanic fish!


     Two jellyfish predators, ocean sunfish (Mola mola) and leatherback turtle (Dermochelys coriacea), are said also to consume Velella, but there seems little evidence for this. Many sandpipers fed among the Velella at Grays Harbor recently, and some poked into the tentacles, perhaps finding small prey among them.



     These Velella velella are not to be mistaken for the Seattle musical group of the same name!

Dennis Paulson

Tuesday, April 14, 2015

LONG-HORNED BEETLES


Beetles are the most diverse animals in the world, with surely over a million species, although only about 350,000 have been described to date. Any collection of tropical insects contains undescribed species, and beetles often make up a good part of this, even though they have been favorites with collectors ever since specimens were first collected for museums.

One explanation for the great diversity of beetles is their long association with angiosperm plants. It appears that a taxonomic group that is associated with these very diverse vascular plants has an unlimited array of niches available for speciation, furnished by both the many different species and their many parts—leaves, stems, roots, flowers, fruits—on which to specialize.


Long-horned beetles, family Cerambycidae, are strongly associated with these plants and one of the most diverse beetle families, with about 35,000 species known to date (1,200 or so in North America). Almost all of them have larvae that bore in plant stems. They are distinguished by—guess what—their long antennae as well as C-shaped eyes that curve around the antennal bases. They range in length from a few millimeters to over 17 centimeters and because of their size, beauty, and those looong antennae, are among the most charismatic and well-liked of beetles.

The family is common in the Pacific Northwest, and some of the species are striking. A large black and white one, the cottonwood borer Plectrodera scalator, breeds in cottonwood trees, so look for it along rivers with associated riparian forest. Originally distributed east of the Rockies, the species has become established in the Pacific Northwest.

The eggs of Plectrodera are laid in the fall, and the larvae bore into the bases of cottonwoods and willows. They pupate beneath the bark and emerge as adults in 2-3 years. The larvae may girdle and kill trees and are considered a pest in some areas.

The larvae of Monochamus scutellatus, the white-spotted sawyer, bore into pines and spruces, and the adults are attracted to trees that have been burned in forest fires. Apparently the burned trees release chemicals that attract the beetles from long distances. The species is considered an economic pest because the boring larvae make the wood, which might otherwise be harvested, unsightly, as well as allowing access to fungi. Wood-boring beetles cause the timber industry to lose millions of dollars annually.




The elderberry borer Desmocerus auripennis lays its eggs in elderberry bushes. The larvae bore in the stems just like their larger relatives do in trees. The locust borer Megacyllene robiniae is also native to eastern North America but has spread into the West with the planting of black locust trees. This and the cottonwood borer are spectacular species, and it’s a bit disappointing to find out that they came from somewhere else!






Check patches of milkweed for milkweed beetles, Tetraopes femoratus. A related eastern species is shown here. The larvae of these beetles live in milkweed stems, and both larvae and adults are distasteful because of the chemicals ingested with the milkweed tissue. The bright red coloration is surely an aposematic advertisement of this.







A very large number of species of cerambycids are flower visitors, eating the pollen and probably in some cases effecting pollination even as they destroy the reproductive efforts of the plant. Lepturobosca chrysocoma, Pseudogaurotina cressoni, and Xestoleptura behrensii are examples of this group. Many are brightly colored and tapered behind, perhaps giving them some resemblance to bees or wasps, especially in flight. By that mimicry, they fool some avian predators that normally leave stinging hymenopterans alone.

Dennis Paulson