AMPHIBIAN DEFENSES

One reason that amphibians in general are in trouble (well, with the exception of Bullfrogs and Cane Toads) is that they have very porous skin, so they are more likely to pick up environmental contaminants than are other vertebrates. The chytrid fungus that is killing so many of them attacks their skin, perhaps interfering with dermal respiration or water balance.

Thin-skinned and small, it would seem that amphibians would be almost defenseless against the whole array of predators with which they share their world. But they’re not!

In part because of their sensitivity to drying out, most amphibians are nocturnal. But this also is a first line of defense against diurnal predators, among which birds are by far the most important. There are many hawks that relish amphibians, and in the tropics members of many different bird groups eat frogs. Of course, by being nocturnal, the frogs are subject to owl predation; you can’t win them all!

Many species, even though active at night, spend the day at least partially exposed, and they are usually very well camouflaged, green for the leaf-sitting frogs and brown for those on the forest floor.

Frogs are also escape artists. The great leap forward that a frog can take with its long legs allows it to capture prey very effectively, but the leap is probably even more important for predator avoidance. A Wood Frog (Rana sylvatica) at the edge of a pond heads for the water at the least disturbance, arcing through the air on the way there. Plunging into the water, it immediately makes for the bottom sediments, where it disappears.

Nocturnal life style, camouflage colors, and escape locomotion notwithstanding, amphibians are still captured. For many species, the next line of defense is provided by their skin toxins. Many of them secrete chemicals in the skin that are poisonous to other vertebrates. Sometimes these are concentrated in particular glands, often around the head (predators often grab their prey by the head to dispatch it most quickly). Note the big toxin-secreting parotid glands behind the eyes, presented to the potential predator by this Northwestern Salamander (Ambystoma gracile).

Many of these amphibians are nocturnal and cryptically colored. But others are either active in the daytime or can be found where they spend the day only partially hidden. Toad tadpoles are toxic, and instead of scattering out and hiding as do the tads of other frogs, they congregate into big, black, wiggly masses, and a predator that captures one and then spits out the bitter-tasting morsel can easily learn to avoid such groups.

These include many species of poisonous frogs, for example the Strawberry Poison-dart Frog (Dendrobates pumilio). Many of these species are conspicuously, even garishly, colored. This is warning coloration (also called aposematic coloration), and predators that learn not to bother with this prey presumably leave more descendants.

Rough-skinned Newts (Taricha granulosa) of the Pacific Northwest are cryptic brown when viewed from above, but when disturbed, they display their bright orange undersurface as a warning coloration. These newts are extremely poisonous and have killed people who swallowed them (just on a dare, can you believe it?). The tetrodotoxins in their skin are poisonous to just about anything that tries to eat them and in fact are among the deadliest poisons known to have evolved.

But some populations of Common Garter Snakes (Thamnophis sirtalis) have evolved resistance to this toxin and can eat the newts with no ill effects! This “evolutionary arms race” has been won by the snakes in this case, but not in all populations.

Dennis Paulson

FROGS ARE JUMPING!

Spring in the Pacific Northwest was made for amphibians. They flourish in cooler temperatures than reptiles, and they do best where it’s wet, so the cool, wet springs of this region are great for them. And because amphibians need moisture and are small and have many predators, most of them are active at night, so that’s the time to be out looking for them. Most amphibian hunters use a headlamp to keep their hands free, as amphibians are elusive little critters.

There is a moderate diversity of frogs in this area, some of them common. The most ubiquitous is the Pacific Chorus Frog (Pseudacris regilla), and it seems as if they can hardly wait to start breeding. Individuals are heard calling during warmer winter days, and the choruses really start up by February. Their ribbit call is known to all because so many movies are made in Hollywood, where the species is common. The call is first heard individually and then swells into a chorus, as more and more males head for the wetlands in which they breed.

The Western Toad (Anaxyrus boreas [formerly Bufo boreas]) was also one of the most commonly seen frogs in the Northwest, but this is one of the species that has declined greatly in recent years, as part of the Great Amphibian Problem. We don’t see as many of them as we used to, but they are still widespread. If you can’t find an adult, you may see masses of little black tadpoles swimming together in a mountain lake or a shore lined with toadlets that have just undergone metamorphosis in late summer.

The Red-legged Frog (Rana aurora) is the common native frog that looks like a classical frog – a long-legged jumper with smooth skin. It is most common in wooded areas with abundant ponds, where you may find its big floating mass of around a thousand eggs in spring. You have to have one in the hand to see the conspicuous red colors on the underside of the legs and body. In the mountains and east of the Cascades you can find two related species, the Cascades Frog (Rana cascadae) and Columbia Spotted Frog (Rana luteiventris).

The Bullfrog (Lithobates catesbeianus [formerly Rana catesbeiana]) is one of the villains in the amphibian story. Brought from eastern North America for culinary and sporting reasons, this species seems to flourish almost anywhere it is introduced. Unfortunately, it does so at the expense of other amphibians and other aquatic creatures. A virtual eating machine, a Bullfrog will take in anything that fits in its capacious mouth, and it has been implicated in the decline of some other frogs that share its aquatic habitat.

One of the most interesting things about Northwestern frogs is their silence. Anyone coming from the East is used to frog choruses with multiple species calling, one of the real thrills of a rainy spring evening in Massachusetts or Florida or Missouri. But our frogs don’t say much. Although some toads have ear-splitting trilled calls, ours makes nothing more than chirps. Red-legged Frogs call from under water and can be heard only at very close range. In fact, our only noisy native frog is the chorus frog. Of course the introduced Bullfrog has added much to our soundscape, its loud jug-o-rum resounding from warm-water lakes all over the region.

The Tailed Frog (Ascaphus truei) is another silent species - it doesn’t even have ears. It lives in rushing streams, where almost any sound would be obscured by the sound of the water. Unlike many other frogs, the males don’t attract females by their calls, but instead go looking for them. They also can’t fertilize the eggs in the standard way by depositing sperm on them, as the current would wash the sperm away. Thus the males have evolved an extension, but it’s not a tail!

There is still much controversy about what has caused so many frog species all over the world to become rare or, in some cases, extinct. A special kind of fungus called a chytrid (Batrachochytrium dendrobatidis) is heavily involved, as infestations of this fungus can kill off all the individuals of some species in an area. Fortunately, our Northwest amphibians have not declined as thoroughly as have populations of many tropical montane species.

Dennis Paulson

IT’S SALAMANDER SEASON!

Spring has sprung, or at least it’s about to spring, and it’s the time of year when amphibian activity becomes most noticeable.

Washington supports populations of 14 species of salamanders and 11 frogs. Amphibians like wet climates, and we’ve got that. Salamanders are diverse in temperate latitudes, frogs a bit less so, but as usual, the tropics are the home of the greatest diversity (compare Costa Rica’s 43 salamanders and 133 frogs!).

Our rainy winter provides the water to allow frog and salamander breeding, and as soon as it warms up enough in spring, off they go. This happens in late February or March for a variety of species.

Northwestern Salamanders (Ambystoma gracile) live underground for much of the year but come to the surface to feed in spring and during fall rains. They are rarely seen but could be observable at night at breeding ponds, when the adults come to the water to breed. Males court females, then when both are ready, the male deposits a spermatophore which the female picks up in her cloaca. The sperms within fertilize her eggs as she lays a big clutch of around 100 eggs in a jelly envelope the size of an orange, usually wrapped around some underwater object. The larvae stay in the water for a year or more, then undergo metamorphosis to the terrestrial stage and breed in the next spring.

Meanwhile, Long-toed Salamanders (Ambystoma macrodactylum) are migrating to other ponds, often smaller ones. This species is more common and wide-ranging, occurring in drier parts of the Northwest and well up in the mountains as well as the wet western lowlands. Breeding occurs in the spring, but females lay much smaller egg masses, averaging only a dozen or so eggs. Being a smaller species, metamorphosis and maturation are quicker than in the Northwestern.

Rough-skinned Newts (Taricha granulosa) are also stirring from their winter retreats and heading for the water. Like the others, they migrate mostly on rainy evenings to their breeding lakes. Courtship is prolonged, even lasting a day or more, but usually ending with spermatophore pickup, fertilization, and egg-laying. Eggs are laid singly in aquatic vegetation. The larvae metamorphose and leave the water in fall and disperse away from the water, to which they return after 4 or 5 years. In this species, many breeding adults remain aquatic through the summer, developing smoother skin and tail crests that aid in swimming.

By contrast, two of the common salamanders of the Northwest are terrestrial, with no aquatic stage. They are lungless salamanders, breathing through their skin! Western Red-backed Salamander (Plethodon vehiculum) and Ensatina (Ensatina eschscholtzii) live in forests, where they can be found in spring by turning over logs (be sure to replace divots!). They breed during winter, laying their 10 eggs in a cluster in such sheltered places, and the female guards them from invertebrate predators until they hatch.

Most of the other salamanders of the Pacific Northwest are locally distributed and uncommon, but they are worthy of attention by any naturalist fascinated by creepy-crawly critters. There is a good reference book: Amphibians of the Pacific Northwest, by L. L. C. Jones, W. P. Leonard, and D. H. Olson, eds., Seattle Audubon Society, 2006.

Dennis Paulson

CORMORANTS

Cormorants are big black water birds with long necks. They dive for a living, and they float low in the water, with bill pointing up, while at the surface. All of them have all four toes connected by webs, characteristic of the Pelecaniformes, the avian order that includes pelicans and boobies. The bill is prominently hooked at the end, a “tool” to subdue the slippery fish they catch. All three species are fish-eaters, chasing down their prey with amazing underwater speed. At close range, their emerald-green eyes are a pleasant surprise.

Three species of cormorants inhabit Pacific Northwest waters. Two of them—Brandt’s and Pelagic—are entirely marine, and it would be a surprise to see either of them on fresh water at any time. The third—Double-crested—is one of the world’s more successful birds, occurring on all large water bodies, fresh and salt, all across the Northwest as well as throughout North America below the boreal zone. The other two species range along the Pacific coast.

Double-crested Cormorant (Phalacrocorax auritus) is the largest of the three and can be recognized by its yellow-orange face skin and throat pouch and somewhat pale bill. The feathers of the upperparts are very dark brown with black edges, producing a chevron pattern on the back. In breeding season, the adults have side-by-side curly crests. Immature Double-crests are the only cormorants that are pale beneath, the underparts becoming increasingly dark with age until they mature at three years.

Brandt’s (Phalacrocorax penicillatus) is a bit smaller, with a more slender bill, head, and neck and a distinctly shorter tail. The throat pouch is dark but becomes brilliant sky-blue in breeding season. The buffy patch around that can be seen all year. The back is glossier than that of the Double-crested, and the breeding plumes are white, arrayed along the neck and back. Immatures are dark brown above and a bit paler below but otherwise look like nonbreeding adults.

Pelagic (Phalacrocorax pelagicus) is much smaller than the other two, only half the weight of Double-crested, with a small head and very slender bill and neck. The plumage is iridescent, glossy green and purple. The tail is long, even longer than that of the Double-crested relative to the bird’s size. The throat pouch is dark, but the facial skin becomes red during the breeding season, fore-and-aft crests develop on the head, and a big patch of white feathers appears on either side of the tail base. Immatures are very dark brown, almost as dark as adults.

Breeding plumage in all species comes very early, so by February you can see signs of it, and they become easier to identify. After the birds are on their nesting colonies, even while still incubating eggs, they begin to molt the characteristic breeding plumage and are out of it by July or August.

At a distance, the three species can be difficult to identify, but the pale bill and throat of the Double-crested and the small size and glossy plumage of the Pelagic distinguishes them if they are anywhere near one another. And they often are, as they roost on pilings and rocks together all over Puget Sound. Double-crested is almost always much more common and usually perches higher than Pelagic. Brandt’s is less common in Puget Sound but still widespread in winter and often roosts with the other two. It looks about as large as the Double-crested but has a dark bill and throat and obvious short tail. Its head feathers often look puffy, in contrast to the flat head of the Pelagic.

Double-crested is the only one of the three that habitually spreads its wings to dry them as soon as it perches. One of the big puzzles in cormorant biology is why this behavior differs in birds with such similar habits and anatomy! Student research with salvaged cormorant carcasses at the Slater Museum was unable to find any difference in wetting or drying parameters in the three species.

In flight the Double-crested shows a thick, crooked neck. The Brandt’s neck is thinner and sometimes shows the crook but less pronounced. The Pelagic’s neck is straight, and the head is scarcely distinct from the neck. The shorter tail of the Brandt’s again is a good identifying mark. Double-crested often fly very high and often over land, probably going between lakes or between fresh and salt water, while the other two tend to fly just over the water. The two large species sometimes fly in small groups, usually arranged in a line; Pelagics fly by themselves or occasionally join groups of Brandt’s.

Cormorants in general feed on bottom fish such as sculpins, soles, and gunnels, which they pursue in all marine habitats. Pelagics tend to be more associated with rocky areas, Double-crested everywhere. Brandt’s tend to feed in open water on surface and midwater schooling fish such as herring and sand lance. Both of the larger cormorants often collect in groups to feed on abundant fish, while Pelagics tend to forage singly.

The most exciting way to view cormorants is at a breeding colony. All three breed in Washington, Brandt's on cliffs at the mouth of the Columbia River and the other two widely on cliffs (Pelagic) or islands (both) on the outer coast and in protected waters, south very locally into Puget Sound. The birds wave their heads around and hiss and grunt at one another, and their reptilian ancestry seems beyond debate. They lay 3-4 chalky white eggs and incubate them for about a month, then the young take another month and a half or more to leave the nest. Both parents participate fully in care for the young.

Dennis Paulson

A VOLATILE MIX

Dunlins (Calidris alpina) are sandpipers that winter in large flocks at and near the Washington coast. Because they are common, they represent an important part of the diet of wintering bird-eating falcons (especially Peregrine Falcons and Merlins). When you find a large flock of Dunlins, there is every chance that one or more falcons will be nearby, and you may be gifted with one of nature’s more spectacular shows.

This is what happened to us near Edison in Skagit County on January 2, 2010. A large flock of Dunlins (around 4,000) was feeding and roosting in the flooded fields along the Bayview-Edison Road, not far from Skagit Bay, so we stopped to watch them.

Almost immediately the flock flushed, and a Merlin flashed through them. It didn’t get one, then disappeared, maybe because too many of its big cousins were in the area. In the hour and a half we spent at the spot, we saw three different Peregrines.

An adult male and an adult female stooped on the flock several times each, scattering the sandpipers like confetti. But it was confetti with a purpose, as the birds flushed and then became dense moving objects, oscillating back and forth over the landscape in alternating brown camouflage and white flash as they showed their upper- or undersides.

The speed at which the falcons went through the flock was breathtaking. The male seemed faster than the female, perhaps only an illusion because of his smaller size. After each pass, the predator would gain altitude quickly, then come back through in a dive. It would level out not far above the ground or water and come shooting through in level flight.

One would think any capture would be because of a random meeting in the air, but the falcon often jinked sideways or up or down slightly, presumably going after an individual bird each time. Their success rate was low; we never saw either bird catch a Dunlin, but a bit later we saw the female eating one, so she must have succeeded when we weren’t watching.

The biggest show was put on by a young female, easily distinguished because of her brown upperparts and striped underparts. She shot through the Dunlin flocks again and again, stooping perhaps 25 times as we watched. A lightning pass at eye level, sometimes coming within 50 feet of our car, then up and down again for another pass. She never picked one out of the air, but then we saw her circle around and pick one up from the water, presumably a casualty of her strike or a midair Dunlin collision.

We saw a Glaucous-winged Gull carrying a Dunlin in its bill, presumably another bird that hadn't survived the aerial confusion.

It was impossible to follow a stooping falcon with the camera lens, but by focusing into the middle of the Dunlins and hitting the shutter button just as the immature Peregrine passed, I managed to get a few photos during the attacks. The two adults obligingly posed for photos on nearby utility poles.

There was also a nearby Prairie Falcon that we never saw harass the Dunlins, perhaps because it already had something for lunch. A male Northern Harrier also passed through the waves of Dunlins but with no luck.

What a way to begin the New Year!

Dennis Paulson

SWANS IN THE FARMLAND

The Trumpeter Swan (Cygnus buccinator) formerly bred widely across the North American boreal forest, but by early in the 20^th century it hovered on the brink of extinction because of overhunting, Since then it has been rigorously protected and managed, and it has bounced back and continues to increase.

When I arrived in Washington, we made special trips up to the Bellingham area to see Trumpeters at one of a few lakes where small wintering populations persisted. With four decades of additional protection, now thousands of them can be found wintering all over western Washington. It’s nice to have as many pluses as we can to compensate for the many minuses we suffer in overall biodiversity!

But we also have another species of swan in Washington, the arctic-breeding Tundra Swan (Cygnus columbianus). That species has remained more common over the years just because it is much more wide-ranging, but its populations seem more or less stable now, not increasing like those of the Trumpeter.

Nowadays both of these swans can be seen in large numbers in winter in northwest Washington. Trumpeters tend to winter on wooded lakes, Tundras on salt water or larger, open lakes, but here in Skagit and Whatcom counties, they find most of their food in farmlands. Some of these farmlands are managed specifically for the swans and Snow Geese that furnish spectacular displays of white winter waterfowl.

The two swans tend to forage in single-species flocks, but they also mix from time to time, usually a few of one species associated with a larger flock of the other. How do we tell them apart?

Tundra Swans are only about two-thirds the size of Trumpeters, as measured by weight, but they have to be seen in close proximity to be compared in this way. Their linear measurements are not so different, and all swans look big!

Most Tundra Swans have a small yellow spot between eye and bill, lacking in Trumpeter, but some Tundras lack that spot and look much like Trumpeters. The best way to distinguish these birds is by looking at the base of the bill adjacent to the eye. That area is broad in Trumpeter, so the eye looks like part of the bill, while it is usually distinctly constricted before the eye in Tundra, making the eye stand out.

This different configuration of the bill can present a different appearance at a distance, even in flight.

Being larger, Trumpeters may mature at a slightly later age, and they change more slowly from the gray immature to the white adult. In their first winter, Tundra Swans molt in many white or whitish feathers, so by midwinter the immatures are quite whitish. Trumpeters don’t do this, so by midwinter they are still leaden gray. Thus looking at the immatures is a good way to identify the species present in a flock. Even the whitest immatures are easily distinguished from adults by their dusky head.

Finally, the swan species have very different voices. That of the Trumpeter is a low-pitched sound that could be compared with an off-key trumpet. That of the Tundra is a higher-pitched honking, somewhat more musical than that of the Trumpeter, that might be likened to a flock of geese.

Dennis Paulson

5,000+ bullfrogs dying in desert potholes

At Potholes Reservoir, Grant Co, Washington I discovered a rather dramatic scene of thousands of bullfrog tadpoles that were trapped in drying mud holes on 29 Aug 2009 (Photo 1). The small mud hole at the top right was about 3 ft and the larger in the middle of the picture about 12 ft in diameter. The larger contained approx 5,000 bullfrog tadpoles based on counts of a few subsamples; most were dead. The two mud holes in the photo had water about 4” deep a week prior to the photo and the surface quivered with wriggling tadpoles when approached. 

Typically bullfrog tadpoles in the Northwest remain in ponds for at least one winter and grow to a total length of about 130 mm+ before morphing into froglets. Most of the tadpoles had small to medium size hind legs and were less than 110 mm in total length, which is the lower extreme of the size when bullfrog tadpoles could morph (Photo 2). Under normal conditions with plenty of food and no crowding, the tadpoles in the picture would be about one year old, but if food limited or crowded, they could be two years old. Although most were not ready to morph, a few had started the process and were hopping away from the drying mud holes. The closest pond was 100 ft away, but with the heat and predators, their chances were not good (Photo 3 and 4). The mud recorded tracks of great blue herons, great egrets, killdeer or yellowlegs, coyotes and black-billed magpies (Photo 5). Yellowlegs have small mouths, but eat the tadpoles by vigorous shaking the tadpoles to pieces.

The dead and dying tadpoles illustrate one limit to this invasive species’ success – they can’t survive in ephemeral ponds. Although the area is flooded as the level of the reservoir rises during winter and spring, as the water level drops through the summer, they move to deeper water. The mud holes were at a low spot so presumably the tadpoles moved to the deeper water as the water level dropped through the summer, but they moved to the wrong pond and were cut off.

Bullfrogs have recently expanded into the main reservoir and are now extremely common in Crab Creek beaver ponds and in ponds near Job Corp Dike, which is at the NW corner of the reservoir. There were none in 2002, but tadpoles starting showing up in traps in 2006, and 2009 was the first year I observed adult and juveniles widespread throughout the region. One 12 m dia pond at the Job Corps Dike had over 100 frog heads visible as they floated on the surface waiting for a prey object to venture near (Photo 6). There were none at Dodson Road/Winchester Wasteway (10 mi to the west) or at I-road/Frenchman Hills Wasteway (16 mi WSW). They were recorded in lower Crab Creek, south of O’Sullivan Dam, prior to 2005 (WA Gap analysis). The species was introduced into Washington from east North American in the 1920-30’s for food, sport and for pond features and have since spread throughout lower Puget Sound and the Columbia basin and are slowly spreading into new regions such as Potholes Reservoir.

It is generally assumed that the bullfrogs are harmful to native species. But at Potholes Reservoir, they are simply joining other introduced species in the reservoir such as large and smallmouth bass, yellow perch, pumpkinseed, and bluegill that I caught on the same trip (Photo 7). Additional introduction include are catfish, carp, crappie, and rainbow trout. In prior years, I found Pacific Chorus Frogs common around the beaver ponds and leopard frogs rare, but always present. I found neither of these species in 2009 searches, and it is possible they were supplanted or eaten by more common bullfrogs.

I happen to like bullfrogs and felt for the little guys as they struggled to survive, but that’s life in the desert. They were all turned into tadpole jerky by the sun and are now in December probably providing coyotes and magpies with snacks.

   

Gary Shugart