DIVING BIRDS

Many kinds of birds dive for a living. Not from a diving board, but from the air or the water surface. Some of these birds fly over the water, see potential prey, and dive from the air to attempt capture. These birds are called plunge divers. Gulls plunge into the water to about their own body length and retrieve prey from near the surface. Terns, some pelicans, tropicbirds, and boobies dive from above the surface, the first three penetrating farther into the water column than the gulls do. Boobies (and their close relatives the gannets) penetrate well below the surface and actively chase fish underwater.

Many other birds dive from the water surface, including loons, grebes, cormorants, alcids (puffins and their relatives), diving-petrels, some shearwaters, coots, and many ducks. In this discussion let’s look at this group, so-called surface divers.

All diving birds have feet that are modified for swimming at the surface, and these same feet serve them well for underwater propulsion. The typical swimming foot is that of a duck, with the three forward toes joined by webs. The hind toe is much reduced. Among the diving birds, these webbed feet also characterize loons, gulls, terns, shearwaters, diving-petrels, and alcids (this last group lacks a hind toe).

A variation on this is to have the hind toe lengthened and all four toes connected by webs. This characterizes cormorants, pelicans, boobies, and tropicbirds. Finally, instead of webs, some birds have each of the toes, including the hind one, provided with large, flat lobes that are equally efficient in propelling the bird forward. Divers with lobed toes include grebes and coots.

Surface divers vary quite a bit in how they dive and how they locomote under water. Most of them just put their head down, slide under the surface, and propel themselves downward. Although the feet stroke alternately while swimming on the surface, when underwater they stroke in unison, like a pair of oars, and they are held out to either side. This must use different sets of muscles than those used for swimming on the surface. Smaller birds such as grebes, coots, and small cormorants may jump up into the air to enter the water with more momentum.

One group of birds exhibits a real variation in this theme. The alcids are wing-propelled surface divers, using their wings to swim just as if they were flying underwater. As they go below the surface, you can see their wings already open as their means of propulsion. In the guillemots, which feed on bottom fish, the feet are used along with the wings, but in murres and puffins and others that feed on midwater fish and krill, they are held behind and not used at all. The southern-hemisphere diving-petrels, related to true petrels, also use this method of propulsion, as do penguins. Not able to fly, penguins are the most highly modified birds for underwater living.

Scoters and some other sea ducks such as Long-tailed Ducks open their wings as they dive, easily seen. They may use them as diving planes underwater or may actually flap them just as alcids do. For the most part, diving birds surface just by stopping their underwater propulsion and, like a cork, popping back up to the surface. They go headfirst, the most streamlined way to go. Alcids sometimes swim actively upward and penguins always do.

Although you would think that fish are the fastest swimmers in the sea, the most amazing thing about diving birds to me is that they can swim faster than the fish, presumably a necessity if they are to catch them! Both animals streak through the water, and just like a smaller bird trying to escape from a hawk, the fish may or may not escape.

Still photos of birds swimming underwater are very hard to come by, although YouTube and other such online video sites show a variety of birds swimming underwater, very often misidentified (grebes and alcids called “ducks”). Notwithstanding these few videos, we have much to learn about how diving birds forage underwater.

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 day at the coast

Hello, all.

This is the first post from the Slater Museum of Natural History at the University of Puget Sound in Tacoma, Washington, USA.

These posts will be varied, but the theme is Northwest nature, information about natural ecosystems of the Pacific Northwest and their plants and animals. We encourage anyone with interest in this subject to join the blog and contribute to it. We also encourage civility and respect for the opinion of others. As most of our material will consist of facts rather than opinions, that should be easy!

I'm writing about a trip to the outer coast of Washington on 30 August 2009. Netta Smith and I wanted to get out of the house and see how the coastal bird migration was faring. It turned out there wasn't much migration going on, at least at most of the places we visited. We drove to Westport first, all the way at the end of the road around the marina to check out the breadth of Grays Harbor with our spotting scope. Out in the middle there were vast flocks of birds, underscoring the value of coastal estuaries for marine life. There must be a lot of prey out there to support hundreds, maybe thousands, of Brown Pelicans, Double-crested Cormorants, California and Heermann's Gulls, and Common Murres, all fish-eaters. There were also smaller numbers of Western Gulls, Pigeon Guillemots, and Rhinoceros Auklets on the relatively calm waters of the harbor. Heavy cloud cover made for gray sky and water, but visibility was good.

Small numbers of Brandt's and Pelagic Cormorants were roosting on channel markers and rock jetties, perhaps the beginning of the large numbers that arrive from the south each fall. No ducks, loons, or grebes were seen; they are yet to come. The only shorebird present was a welcome one, a juvenile Wandering Tattler (PHOTO) that probed among the rockweed. This bird is a far-journeying species that breeds in the Alaska mountains and winters on islands of the South Pacific, north to Hawaii and California. They pass along the Washington coast in small numbers every spring and fall, enhancing the sound of the ocean breaking on rocky shores with their loud, ringing calls.

Below us on the same rocks were scattered ochre seastars (Pisaster ochraceus), one of the dominant intertidal invertebrates in Pacific Northwest coastal waters. This is a polymorphic species, occurring in orange and purple morphs. We noted that the orange ones were very conspicuous, even below the water, but we didn't see the purple ones until the waves receded, exposing them, and even then we had to look quickly, as they blended with the rocks and algae. Why is the species polymorphic? Why are the purple ones more common here, when the orange ones are more common in Puget Sound? Does it have anything to do with their conspicuous to potential predators? One thing that Mother Nature bestows on us is a never-ending series of master's and doctor's research topics!

We headed for the ocean beach south of Westport. In some areas, driving on the beach is permitted, and that's a great way to see birds. Unfortunately, as our population has increased, too many of us are doing this now. We were shocked to see how many people were scattered along the beach. There were no shorebirds (sandpipers and plovers) at all, but there were roosts of hundreds of gulls of three species (Western [PHOTO], California, Heermann's) all along. As we would approach one of these roosts to try to get some photos and check for rare species, more times than not one or more people would walk right up to the birds, scaring them away. More often, a frolicking dog or two would do the same, and it was obvious that the resting gulls were irresistible to people and dogs alike. "Oh boy, let's go scare up those birds." If this was an opinion blog, I would relate in no uncertain terms what I thought of those people! Sharing the beach is great, but this wasn't sharing. Imagine just sitting down on your favorite couch to relax and digest your dinner, and someone comes running through the living room and says "up, up, up," so you walk around the house three times and then sit down again. Within a minute or two the pest comes again, and the scene is repeated. Some of the flocks were disturbed so often that I wondered, not for the first time, how birds and other wildlife will manage in the long run to coexist with our own species.

After this frustrating experience at several beach-access points, we motored down to Tokeland to look for the large roosting flock of Marbled Godwits and other shorebirds that are often present at the marina. Perhaps for the first time ever, there was not a single bird present. Other birders who we encountered had seen none of them earlier in the morning, and we arrived right around high tide, when the birds should have been roosting. But it was a low high tide, with plenty of mud flats in Willapa Bay still exposed, and why roost when you can feed? Shorebirds in migration feed until they are stuffed, laying down fat deposits all over their bodies, and after a few days of this, taking off on the next stage of their flight, often hundreds or even thousands of miles. They can burn their fat for "food" as they fly, and the longer they fly, the lighter they get!

Shorebirds are the world's best optimizers when it comes to feeding. A sandpiper's bill may actually be probing the substrate as it is coming to a landing, and they never stop probing, as long as there is a bit of room in their stomach. Many species have sensitive nerve bundles called Herbst corpuscles in little pits on their bill tip, and they can feel the wiggle of a worm or the curve of a snail as they probe the sand or mud.

Our final stop of the day was at Bottle Beach State Park on the south side of Grays Harbor, and that's where the migrants were. Flocks of hundreds of Western Sandpipers flew to newly exposed mud flats as the tide receded, and scattered among them were Semipalmated and Black-bellied Plovers, Whimbrels, Greater Yellowlegs, and other species. The sun never came out this day, but there were just enough birds that we headed home with a sense of accomplishment. Of course the birds were the ones accomplishing.

Dennis Paulson