SNOWY OWLS ARE ORNITHOPHAGOUS!

The Snowy Owls (Bubo scandiacus) that came down to Washington this winter, which I have written about before, finally contributed some pellets to the cause of science.

Of course, you know what owl pellets are. Birds of prey, and actually quite a few other birds, eat a lot of stuff that doesn't make it through their digestive tract. Hair and feathers are difficult to digest, as are bones and mollusk shells. So even if they are broken into smaller pieces when eaten and crushed by heavily muscled gizzards, even the smaller pieces can't pass through the hindgut very well. Rather than sharp-pointed bones coming up one by one, they are coated in hair or feathers and barfed, urped, hurled, vomited and/or regurgitated back into the environment.

It's not easy to find these pellets unless you know right where the bird has been roosting. After they are produced, they get covered up by detritus, even blown around, and eventually decay into pieces. But they hold together for a while, and ornithologists have long used them to get a handle on the diet of birds such as hawks and, especially, owls. Snowy Owl pellets look like fuzzy three-inch cigars. It's been said there is nothing like a good cigar, but I personally prefer owl pellets.

Paul Bannick, well-known bird photographer and author of The Owl and the Woodpecker, recently sent me three pellets he picked up from one spot at Ocean Shores. At the museum, we soaked them in water and stirred them up until the feathers floated and the bones sank. We recovered a surprising amount of bones, arranged them by type, and identified them by comparing with our skeleton collection.

I had a pretty good idea what birds were out there, and it wasn't difficult to identify the majority of the bones as sandpiper bones. The only confusion would have been between Sanderling and Dunlin, both common birds in Grays Harbor. Sanderlings were common right where the owls were roosting, so I favored them. Sure enough, there were several lower mandibles present, and they clearly belonged to Sanderlings.

In total, at least five Sanderlings were present in these pellets, as indicated by counts of tibiae and tarsometatarsi, long, slender bones that were well represented because birds of prey tend to swallow legs of smaller birds whole. In addition to all the sandpiper bones, there were quite a number of larger bones. Many of them were broken up, but a few were intact, and two coracoids and a femur allowed identification as a Horned Grebe. Probably all the bones, including many vertebrae, were from the same bird.

I also examined single pellets from Sandy Point, near Bellingham, furnished by Isa Werny and Andrea Warner. They were mostly feathers, but one of them contained a few Horned Grebe bones, the other a few Bufflehead bones. The second pellet was found at the foot of a utility pole along with parts of a dead Bufflehead, making the identification easier. Both of these species are known Snowy Owl prey.

Snowy Owls are well known to subsist largely on water birds in the winter on our coast, and there wasn't a trace of a mammal in these five pellets. By now you may have figured out that ornithophagous = bird eating.

Dennis Paulson

IT’S SHOREBIRD TIME AGAIN

Every year in April and May the Pacific Northwest experiences a mad rush of thousands and thousands of shorebirds—sandpipers and plovers—on their way north to their Arctic and Subarctic nesting grounds.

This is nowhere more obvious than around two big coastal estuaries, Grays Harbor and Willapa Bay. These estuaries are extremely productive of the invertebrates that the shorebirds eat. Prey animals are present at very high densities in the mud and sand of these estuaries, for example about 10,000/square meter at Bottle Beach, on the south side of Grays Harbor, one of the most productive areas.

This seems astronomical but pales in comparison with 100,000 individuals/square meter of one species of amphipod in the Bay of Fundy. Nevertheless, it is sufficient density to support the tens of thousands of shorebirds that visit the area for up to a month each spring. Individual birds stay only a few days, fattening up for a flight that may be only 200 kilometers to Roberts Bank in British Columbia or as much as 900 kilometers to the Copper River delta in Alaska, then on to arctic breeding grounds.

The invertebrates that fuel these birds are primarily amphipods and polychaete worms. The amphipods are about 5-6 mm long, and some of the polychaetes are in the same size range. Other polychaetes are called “thin worms,” up to 30 cm long but only 1 mm in diameter! They can be in such high densities as to almost bind the mud together.

The three most abundant species in spring migration are Western Sandpiper, Dunlin, and Short-billed Dowitcher, in descending order. Most of the big flocks you see will include these species. There are many other species present as well, and searching them out gives the observer variety as well as spectacle. Other common species include Black-bellied and Semipalmated Plovers, Greater Yellowlegs, Whimbrel, Marbled Godwit, Ruddy Turnstone, Red Knot, Sanderling, and Least Sandpiper, with numerous others even less common but out there somewhere.

No migration is evident at the beginning of April, but by the middle of the month, Greater Yellowlegs and Short-billed Dowitchers have arrived in numbers. During the last two weeks of the month, all the species move in, most of them in full breeding plumage, and peak right around the first of May. Numbers fall off after that but are still impressive through mid May, and some of the later migrants are present until the end of that month. Species that peak late include Red Knots and Long-billed Dowitchers.

Herb Wilson of Colby College, Maine, found that these hordes of shorebirds had little effect on the invertebrates on which they fed. He erected “exclusion cages” at Bottle Beach, meter-square cages that kept shorebirds out, and after the migration compared the numbers of invertebrates under each cage with the original numbers there and the numbers just outside. He found no fewer invertebrates outside than inside; thus the numbers had not been reduced by the birds.

The spectacle can be seen in feeding areas at lower tides and at roosts at higher tides. The ocean beach itself has throngs of shorebirds on peak migration days, but it is discouraging to see the high levels of human activities (joggers, horseback riders, dog runners, mopeds, pickup trucks) that disturb each flock again and again on a busy weekend day. The birds get back to feeding immediately after each disturbance, and we can only hope that they are able to take in enough nourishment to make it to their next destination on time.

Dennis Paulson

SHOREBIRDS ON THE MOVE

Every spring, about the beginning of April, flocks of shorebirds begin their annual migration up the Pacific coast on their way to Alaska and other points north. Sandpipers and plovers by the tens of thousands use the coastline as a pathway to their summer homes, feeding on the abundant populations of marine invertebrates and depositing fat to fuel their long-distance flights to their breeding grounds. Some birds leave the Washington coast and fly directly across the Gulf of Alaska to southern Alaska, where they stop at estuaries such as the Copper River Delta.

The most common species are Western Sandpipers, Dunlins, and Short-billed Dowitchers, in that order. At the same beaches, mudflats, and tidal pools are smaller but still substantial numbers of Black-bellied and Semipalmated Plovers, Greater Yellowlegs, Whimbrels, Marbled Godwits, Ruddy Turnstones, Red Knots, Sanderlings, Least Sandpipers, and Long-billed Dowitchers. At the same time, Black Turnstones, Surfbirds, and Wandering Tattlers feed along rocky shores as they move north, and Red-necked and Red Phalarope flocks settle on the ocean offshore.

These birds take advantage of a spring flush of invertebrate growth and recruitment, and they find no lack of goodies to help them put on weight. Amphipod crustaceans, polychaete worms, and small bivalves are among the most abundant fauna in birds that feed on and in sand and mud. These animals are so abundant that just about all the shorebird species using the area feed on them. Barnacles, mussels, and snails are staples of the rock shorebirds, and planktonic crustaceans fill the bellies of phalaropes.

Shorebird migration peaks on the Washington coast in the last week of April and first week of May, when the maximum number of species and individuals are present. Grays Harbor and Willapa Bay and the beaches adjacent to them always support the largest numbers, and the abundance of these birds provides a stirring spectacle every spring. Concentrations of some species in Grays Harbor are the highest south of Alaska.

And there is a Grays Harbor Shorebird Festival every spring to enjoy these concentrations: http://www.shorebirdfestival.com/.

Unfortunately, shorebird numbers have been declining, so the spectacle gets a little less spectacular every year. More importantly, we don’t have a good handle on the cause of the decline. Presumably it relates to loss of habitat on either the wintering grounds or at migration stopovers, as the arctic and subarctic breeding habitats are still relatively intact.

It’s also possible that anthropogenic changes are reducing the abundance of shorebird prey, another factor that we don’t know much about on a grand scale. There are still lots of shorebirds, so we have some time to work out an effective conservation plan, and there is such a plan for the U.S. (http://www.fws.gov/shorebirdplan/).

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