YAQUINA HEAD, PARADISE LOST?

The islands off Yaquina Head in Oregon have always been just right for nesting seabirds. Isolation from the mainland gives them safety from mammalian predators, a very important feature for colonial birds. Colonies of nesting birds would be sure to attract predators such as coyotes, foxes, raccoons, and other carnivorous mammals, but apparently most of these mammals are not inclined to swim to offshore islands, so birds that nest on these islands are relatively safe.

These are scenes from Yaquina Head on 6 May 2011. A great colony of Common Murres has been there for many years, occupying the tops of several of the islands. In addition, large numbers of Brandt’s Cormorants nest among the murres and on lower ledges, and Pelagic Cormorants and Pigeon Guillemots fill in other parts of the islands.

The colony was flourishing during our visit, probably several thousand murres and good numbers of the other species. But the colony faced threats like never before. Bald Eagles have continued to increase every year since the banning of DDT in North America, and they are proving very effective predators on colonial nesting birds. Once the birds began to lay eggs, eagles disturbed the colony daily, taking both adult and young murres as well as eggs, and the massive disturbances caused by their presence enabled crows, ravens and gulls to take additional eggs and young.

Unexpectedly, Brown Pelicans proved almost as great a threat. Immature birds, not old enough to return to breeding colonies, stayed at Yaquina Head through the summer and visited the murre colony regularly. Walking and flapping through the colony, they picked up dropped fish and then began picking up young birds to get them to disgorge their fish. If that wasn’t enough, they also began to swallow the chicks whole. Many more chicks fell from their nesting ledges and drowned in the surf. Further disturbance was caused by Turkey Vultures that visited the colony.

During 372 hours of monitoring the colony in 2011, observers from the Hatfield Marine Science Center recorded 186 disturbance events, during which 1034 eggs, 142 chicks, and 70 adult murres were taken. Depredation rates were three to ten times higher than in previous years. Researchers estimated that no more than 28% of murre pairs successfully raised chicks to fledging age. Cormorants, much more spread out and with larger chicks, appeared to suffer much less mortality.

Interestingly, not only Bald Eagles but also Brown Pelicans and Turkey Vultures are increasing in the Pacific Northwest in recent years, perhaps all as a result of the removal of DDT from the environment. A new balance may be struck as one set of species becomes less common as previously rare species increase. How will we protect the murres now that we have protected their predators?

Dennis Paulson

A HERONRY TO WATCH

I recently learned of a Great Blue Heron nesting colony in Kenmore, Washington, only 10 minutes from my house. But the colony, at the edge of a park and ride lot, was at some distance from the vantage point, so it would take a long telephoto to get good photos of them. So I went up there with my new Canon PowerShot SX50 HS camera with its 50x zoom lens.

The colony has about 50 obvious nests, although not that many pairs were present during my two morning visits. Activity levels were low, consisting mostly of birds flying out to gather additional nesting material. But that activity had birds flying in with twigs and branches often enough to be photogenic, and a few birds even landed in the nearby Douglas-firs to tug on live branches. Otherwise the herons stood quietly at their nests.

The nests are reused for many years, birds sometimes changing nests between years. I don't know what happens when a bird chooses a nest and its previous owner returns soon thereafter! You do see sparring in the colonies.

Males procure the nest material and females remain at the nest to put it in place, and I saw numerous such exchanges. The sexes can't be distinguished, so all one can do is make assumptions that are supported by previous research. The first eggs should be laid in March, according to the literature, so presumably in early April some of the birds had clutches already. Indeed, some birds were flat on the nest, presumably incubating.

Copulation takes place both before and during egg laying, and one such act was observed during a two-hour visit. Both sexes incubate, alternating during the 24-hour period (females more at night), and the total incubation period is about 27 days. Hatching is asynchonous, as incubation begins when the first egg is laid, so the youngest bird may be several days younger than the oldest.

Once the eggs hatch, the young remain in the nest 7-8 weeks, so there will be plenty of photo opportunities to come. One thing I will be looking for is siblicide, where a young bird attacks and actually kills a nestmate. The prey is often dropped into the nest in the midst of the young, and especially when the items are small, the young are more likely to fight over them. When food is limited, it makes evolutionary sense for the brood to be reduced, so the remaining young will have sufficient food to grow and fledge.

Great Blue Herons have had a hard time of it in the Seattle area, as Bald Eagles, which have increased tremendously in recent years, visit their colonies as they are forming and take eggs, young or adults if they can catch them. A few such disturbances will usually cause the adults to desert the colony. They can either move elsewhere or just fail to breed. The next season they try again at another spot, and there is a fair likelihood that eagles will find that spot as well.

I keep hoping that the eagles won't destroy this colony. It has been established for a decade at least, so there is hope. On occasion, herons nest very near an eagle nest, and apparently that keeps other eagles away from the heron colony. I don't know why the resident eagle doesn't take its toll.

Dennis Paulson

BALD EAGLE - HERO OR VILLAIN?

The Bald Eagle is the national symbol of the United States of America. It seems appropriate for a country to have such a majestic bird as a symbol. Long-lived, monogamous, good parent, characteristic of wild places, Bald Eagles excite awe and admiration wherever they fly.

There have been notable dissenters from this view, including Ben Franklin, in a letter to his daughter 20 June 1782: "For my own part I wish the Bald Eagle had not been chosen the Representative of our Country. He is a Bird of bad moral Character. He does not get his Living honestly. You may have seen him perched on some dead Tree near the River, where, too lazy to fish for himself, he watches the Labour of the Fishing Hawk; and when that diligent Bird has at length taken a Fish, and is bearing it to his Nest for the Support of his Mate and young Ones, the Bald Eagle pursues him and takes it from him."

Yes, Bald Eagles are inveterate kleptoparasites, robbing Ospreys and other raptors of their prey. Like all birds, they have terrific vision and are aware of what goes on all around them, even at some distance. Not even a swift and strong Peregrine Falcon can withstand the attack of an eagle determined to wrest a recently captured bird from it.

In the middle of the 20th Century, Bald Eagle populations were decimated by ingesting DDT along with the fish and fish-eating birds that they preyed on. DDT compromises calcium transport, and the eggs laid by the eagles, with inadequate calcium, were thin-shelled enough to crack under the weight of an incubating female. Reproductive success fell and populations declined along with it.

DDT was banned in the US in 1972, and eagle populations have been rebounding ever since, to levels greater than any previously documented. Their numbers have skyrocketed in particular in the Pacific Northwest, which must be optimal eagle country.

Unfortunately, the consequences of this are dire for some other bird species. Eagles are opportunists above all, and they have learned to make a living, at least in spring and summer, by hanging around bird colonies. With present eagle numbers, colonies of Great Blue Herons, Caspian Terns, and Common Murres on and near the coasts have been hit hard by these predators, sometimes just single birds taking advantage of the prey concentration.

The nesting birds have no way to withstand eagle predation, losing eggs, young and even adults to the predators. Even though eagles may eat a small percentage of the birds in a colony, their presence causes nesting to be disrupted to the point of complete colony abandonment. Because of this, numerous Great Blue Heron colonies have failed, and even huge colonies of thousands of murres and terns have been abandoned.

In the coming years, wildlife managers will have to figure out how to deal with this dilemma. Bald Eagles are not on the endangered species list any more, but they are still protected. The birds whose colonies they are destroying are also protected and of concern, and what should we do when one valued species affects another one so severely?

Dennis Paulson

SALMON AND EAGLES

One of the more spectacular natural phenomena of the Pacific Northwest is the annual spawning of five species of Pacific salmon (Oncorhynchus).

The Harrison River is one of the major tributaries of the Fraser River in southwestern British Columbia. Every fall my wife and I make a pilgrimage to the Harrison to see this phenomenon. The salmon are spectacular to watch, although we see very little actual spawning, just the great number of fish, both alive and dead. The dead ones have presumably spawned, as Pacific salmon spawn only once in their life and then die.

The attribute of breeding only once is called semelparity, and it is more typical of organisms that live only one year, usually called "annuals." There are many annual plants among our wild flowers and quite a few annual animals as well, mostly small ones. Hatch or sprout, grow rapidly, breed. and die are the usual course of events for an annual animal or plant.

Pacific salmon, on the other hand, have a fairly complex life cycle. They hatch in fresh water, where they may spend up to a few years, then move into the marine environment, where over an additional few years those that survive grow large and strong, prepared to come back to the river system and the very stream where they were hatched. They swim upriver some distance, spawn, and then die. That's what all those salmon are doing in the Harrison River.

Some of them are there because of human activities. Hatcheries on tributaries of the Harrison raise the young fish in tanks, where they are protected from predators, then release them when they are ready to travel downstream. When they come back as breeding adults, they are captured and bred artificially by applying sperm extracted from the males to eggs extracted from the females, and the cycle begins again.

The Harrison River system has many thousands of fish of four salmon species—chinook (O. tshawytscha), coho (O. kisutch), chum (O. keta) and sockeye (O. nerka). You'll notice the scientific names from Russian; all of our species occur as well on the other side of the Pacific Ocean.

When very large runs are in the river system, especially from October to December, the dead and dying fish support great populations of predators and scavengers. Among them are gulls, crows, ravens, and—most notably—Bald Eagles.

Eagles come to the Harrison in the late fall by the thousands. I have estimated as many as 500 visible from one spot, although that was a rare sighting. More likely, a visitor who stops at several places along the river may see a few hundred birds, sometimes a dozen roosting in the same tree or a hundred spread out over the river flat.

Interactions among the birds are commonplace and make the experience a memorable one. The whistled calls of the eagles, the flowing river, the conifer background, and, if you're lucky, the blue sky, all make the experience a memorable one. The smell of rotting salmon carcasses adds an extra dimension not available on all nature trips.

Dennis Paulson

RAPTORS IN THE CITY

One of the surprises in studies of urban wildlife in recent years is the invasion of our cities and suburbs by predatory birds such as hawks and owls. Perhaps "invasion" is too active a word, and a better word is "acceptance." More and more raptors are apparently becoming comfortable with living in the cities of the Pacific Northwest and, in fact, all across North America.

Bird feeders have become a dependable part of the urban/suburban environment, and many small birds are attracted to them. The juncos and finches and sparrows that abound at feeders attract Sharp-shinned Hawks in winter, but the hawks leave for the mountains in spring. However, their larger relatives Cooper's Hawks are year-round residents, feeding on pigeons, jays, and flickers and nesting in wooded areas that give them a sense of security. The males are conspicuous in spring, with display flights and vocalizations, so more and more of them are being detected living among us.

Merlins too are in the process of becoming city dwellers. These small falcons nest in forests near open country, where they usually capture their prey (small birds). Wintering Merlins probably moved into cities to take advantage of local concentrations of small birds, and eventually pairs remained throughout the year and nested because of that prey abundance. Their nesting efforts have been successful, and the population of urban-nesting Merlins has slowly risen.

Barred Owls have moved into the Pacific Northwest from the north, and they too appear to be comfortable in wooded parts of our cities. Preferred prey include the gray squirrels and rats that have been introduced into the region, and our bird feeders attract and concentrate these mammals as well. There are now pairs of Barred Owls, Cooper's Hawks, and Merlins nesting in wooded areas near my house in Seattle that weren't there 10 years ago.

Red-tailed Hawks do not live around dense housing developments, but large parks and open spaces furnish adequate hunting grounds for rats and squirrels, and if any trees in their territory are large enough to support their nests, they may nest in our cities. Many more of them appear in winter to hunt in open areas around parks and airports.

The Great Horned Owl is a top predator surprisingly willing to live in cities, mostly in relatively large parks. It is large enough and fierce enough to handle mid-sized mammals such as raccoons, opossums, and domestic cats that thrive in cities. Crows and pigeons furnish abundant prey populations as well. Nest sites (usually old Red-tailed Hawk nests) may be limiting, however.

Even more surprisingly, after a long period of decline during the DDT era, Bald Eagle populations have rebounded in the Northwest, and they not only visit but even nest in the cities, often in large parks near water where prey species such as waterfowl and fish are available. They need large trees for their huge stick nests.

Whenever a shift like this occurs, it is worth trying to distinguish between behavioral adaptation and genetic adaptation. Have these birds "learned" that cities are OK? Or are there genes for city living that have become favored? Are there genes for increased tameness, recognition of bird feeders as sources of bird concentrations, resistance to being mobbed by crows? Actually, cities aren't bad places to live for mobile predators such as these, as there may be local sources of abundant food and some of their own potential predators may be absent. Also, the first individuals to accept life in the cities have no competition from others of their species!

Dennis Paulson