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

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