MERGANSERS, THE TOOTHY DUCKS

Mergansers are fish-eating ducks. They are closely related to Buffleheads and goldeneyes, but because they diverged sharply from their invertebrate-eating relatives, their anatomy has diverged sharply as well. The main point of divergence is in the bill. Buffleheads have a normal duck-shaped bill, only 2-3x as long as wide.

 A merganser bill, on the other hand, may be 4x as long as wide. But more than that, the structure of the bill has changed dramatically. Duck bills have plates or lamellae, fine transverse ridges on the cutting edges that let water escape from the bill when prey is brought to the surface. In mergansers, these plates have been modified to produce a saw-toothed effect. These aren’t true teeth, lacking in birds, but they are very toothlike, analogous to the teeth of barracudas, needlefish and dolphins, other fish-catching vertebrates.

We have three kinds of mergansers in the Pacific Northwest. Two of them are in the genus Mergus, the Common Merganser (M. merganser) and Red-breasted Merganser (M. serrator). Both of them are large ducks, the Common one of our largest. Both have relatively long, slender bills the edges of which look like saw blades. These toothy bills are perfectly adapted for capturing slippery fish, and mergansers feed only on fish.

The Common breeds in rivers all over the Northwest and extends its range in winter to lakes and marine environments, especially deep channels with swift currents. The Red-breasted breeds in the Arctic and Subarctic and descends on the PNW in the winter, primarily on salt water. It is one of the common and widespread wintering ducks on Puget Sound.

Both of these mergansers move around the landscape looking for fish, especially fish in large schools that are easier to capture than the individual fish that the ducks encounter most of the time. Thus herrings and sand lance, two of our common schooling fishes, are often prey. Like other ducks, these mergansers may be in flocks.

The Red-breasted is perhaps even better adapted as a fishing duck than the Common, as its bill is a bit more slender and cylindrical. The bills of these two duck species have converged on those of other fish-eaters such as loons, grebes and cormorants, but none of the latter have the “teeth.”

The least modified and smallest of the mergansers is the Hooded (Lophodytes cucullatus). It is close enough to the goldeneyes (Bucephala) to have hybridized with both Common Goldeneye (B. clangula) and Bufflehead (B. albeola) and is considered intermediate between the goldeneyes and the other mergansers.

The bill of the Hooded is also intermediate, with the “teeth” rounded or square and nowhere nearly as impressive as in the other mergansers. The species may eat as many invertebrates as fishes, especially crustaceans such as crayfish and aquatic insects. It is much more confined to fresh water than the other two, but small numbers winter in protected bays.

All three mergansers have nesting habits like the goldeneye group. Hooded Mergansers nest in tree holes like Buffleheads and goldeneyes, Common Mergansers, much larger, need much larger crevices in trees, but like Hooded, sometimes uses old Pileated Woodpecker holes. On the other hand, Red-breasted Mergansers nest on the ground, often in the shelter of rocks or fallen trees adjacent to their preferred breeding wetlands. With their northerly breeding range, there aren’t many trees big enough for a nest hole!

Dennis Paulson

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

COLONY-NESTING SWALLOWS

Finally, a swallow that nests only where it is supposed to. Bank Swallows (Riparia riparia) nest in sand banks, usually in colonies, sometimes in very large colonies. These vertical or near-vertical banks are typically along rivers but may be in dry areas as well, even sand quarries and piles of sand thrown up by construction and then abandoned. Thus like all other swallows, their nest sites can be augmented by human activities.

Bank Swallows are common breeding birds across northern North America. They winter mostly in South America and are common migrants in between. Breeding also all across Eurasia, they are one of the most widely distributed songbirds (like the Barn Swallow).

Bank Swallow colonies range from just a few birds to up to 1,500 active nests. The burrows can be quite near to one another but stretch for hundreds of feet along a bank.

At new sites, males begin excavating burrows as pairs are forming. A male with a burrow will fly after a female and attempt to attract her to the burrow, where he lands at the opening. If she is interested, she will accompany him inside, where copulation takes place.

Although Bank Swallows are socially monogamous, males constantly attempt extra-pair copulations. When a female leaves the nest, her mate often flies right on her tail to keep other males from attempted mating, and this is successful most of the time. These flights, usually with three or more birds, can be seen constantly around colonies early in the season. One researcher found that males could actually distinguish heavier females, apparently receptive to breeding, and preferentially chase them.

The burrow is dug with beak, feet and wings. The excavation takes about 4 or 5 days, and then the female begins to gather material for the nest at the end of the burrow, taking another few days. The four or five eggs are laid one each day, and incubation, mostly by the female, ensues for about two weeks after the last egg is laid.

Both adults gather food for the brood, and it has been estimated they bring about 60 prey items/visit and feed the entire brood about 7,000 insects in total. If you're worried about bugs, it would seem to pay to live near a Bank Swallow colony. 500 nests x 7,000 insects = 3.5 million fewer insects in three weeks! But what would the Society for the Prevention of Cruelty to Insects say about that?

The young leave the nest at about three weeks of age and gather in communal perching areas, where they are fed for up to another week. Adults recognize their own young vocally among the clamoring of many individuals, much like the case in a tern or gull or penguin colony.

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

FROM CAVES TO BARNS

Just as Cliff Swallows adjusted to the push of humans (and their structures) across North America, so did Barn Swallows (Hirundo rustica). This species, virtually worldwide in distribution, has been known to be associated with humans for over 2,000 years in Europe. But it may have had a limited breeding range in North America, thought to be primarily in the mouths of caves. Needless to say, these were very limited nesting habitats.

Nowadays, however, Barn Swallows nest throughout southern Canada and the United States, excepting the southwestern deserts and peninsular Florida. They are so successful because they nest on just about any structure provided by humans—houses, barns, overpasses, bridges, even small culverts. Drive across country, and there will be Barn Swallows nesting under just about every bridge you cross. But look for them in vain on natural substrates!

Like Cliff Swallows, Barn Swallows utilize mud for the foundation of their nest, and they gather it in the same way from the water's edge, although singly rather than in groups. The mud walls are usually about an inch thick. Rather than retort-shaped, their nest is cup-shaped, so the young spend their time looking out at a broader world, although still constricted by the ceiling of their nest site.

Some people think having Barn Swallows nest on their house brings good luck. Others are turned off by the mess they make. The parents collect fecal sacs from the nest for the first 12 days after the eggs hatch, but after that the young just stick their rear end over the edge and let fly. That's a lot of incremental excrement in the subsequent 8 days before they fledge.

With clutch sizes averaging around five eggs, the nest of a Barn Swallow fills up fairly rapidly with growing young, so the young need to leave the nest as soon as they can fly. The adults "park" them on nearby tree branches or fence wires and feed them for up to a week more. Then they are on their own.

Barn Swallows have been much studied in Europe, especially their mating behavior and sexual selection. Birds of both sexes with longer and more symmetrical tails have greater reproductive success, parental effort, annual survival, ability to withstand parasites, immunocompetence, and other measures of fitness. Thus an individual has a fairly good chance of judging the true quality of a prospective mate.

So Barn Swallows nested in caves, and Cliff Swallows nest on barns. Care to guess where Cave Swallows nest?

Dennis Paulson

SWALLOWS ON CLIFFS AND BRIDGES

In this era of human domination of the world, a successful animal or plant may be defined as one that has adapted in some way to human presence, even benefits by it.

Cliff Swallows (Petrochelidon pyrrhonota) may be one of those animals. They build mud nests that they attach to vertical substrates overhung sufficiently to provide shelter from rain. They were able to evolve this nesting habit because of the widespread abundance of rocky canyons in western North America. Cliff Swallows are still abundant in that habitat.

The species was probably restricted to western canyonlands until barns and bridges built by settlers advancing across the Great Plains a few hundred years ago provided nesting substrates comparable to those provided by nature. The birds took advantage of these newly furnished nest sites and moved eastward, encountering more and more artificial cliffs and canyons as they went. Today they nest through much of the East as well, on buildings but mostly under big bridges across rivers.

Cliff Swallows are among the most social of land birds, with colonies of up to 3,500 pairs reported. Their closely packed nests extend over lengthy sections of cliff walls and can fill up the sides of barns and bridges wherever there is overhead shelter. Because they nest so densely, they are more subject than most birds to ectoparasites, especially swallow bugs and ticks, in their nests. Because of high chick mortality from high densities of these parasites, whole colonies are sometimes abandoned and the birds settle elsewhere.

Their other "enemies" include House Sparrows, which take over Cliff Swallow nests and even kill their young, and automobiles, which take their toll of birds nesting adjacent to roads. Recent research has shown that Cliff Swallows in such situations are evolving shorter wings, making them more maneuverable and less likely to be struck down by a car.

Swallow nests are somewhat messy, because after about a week old, the young defecate off the edge of the nest. A pile of poop can build up rapidly below the nest, sometimes even blocking the entrance! Swallows that nest where people live and work aren't always well loved because of this, and whole colonies are sometimes removed from highway overpasses because of the mess they make. Living around humans brings mixed benefits.

Dennis Paulson

A CROW FAMILY

It’s not easy to get to observe the development of young birds in a nest, Most songbird nests are hidden away, hawk and eagle nests are high in trees, woodpeckers nest in holes, and ground-nesting birds tend to be precocial, the young leaving the nest soon after the eggs hatch. So when an opportunity presents itself, it’s worth taking advantage of it.

This nest of crows (American Crow, Corvus brachyrhynchos, or Northwestern Crow, Corvus caurinus) was discovered on the seventh floor of a building in the University of Washington Medical School in Seattle. The person whose office was above it alerted Netta Smith to the opportunity, and she brought a camera to work with her many days over the ensuing month to document the development of the crowlets. I was able to drop by on one occasion and watch the action when the birds were about to fledge.

Unfortunately, the eggs had already hatched when the nest was discovered. The average time until young crows leave their nest is about 32 days in the Pacific Northwest, so the eggs probably hatched on about May 1. Thus at the time of the first photo on May 5, they were about four days old. As the month progressed, the young birds looked more and more like crows.

The young developed rapidly with a constant input of food brought by the two parents, which must have had a busy time finding enough for them. Food items seemed to be mostly small and were difficult to identify, but at least some insect larvae were noted. Human garbage likely played a part, as crows in the city forage constantly in dumpsters, but they surely captured “natural” prey as well. No bird eggs or young were seen, but they play a significant part in the diet of crows.

One young disappeared from the nest and was subsequently seen on a ledge several floors below, presumably killed by a fall. This is surely more of a hazard in such a nesting place; tree branches might have stopped its fall. The other four young flourished until, one by one, they left the nest. They tussled with one another as they got larger, and when about ready to fledge, exercised their wings again and again. Netta did not see any of them actually leave the nest, but on one occasion one spent the day on a ledge across the courtyard and was fed again and again. Then they were gone.

One of the most notable things about young crows is their blue eyes. Young corvids often show signs of immaturity by having eye or bill color different from that of the adults.

Dennis Paulson