EXTENDED PARENTAL CARE IN BIRDS

You may be surprised to see obviously immature (brown) gulls at the waterside at this time of year vigorously begging from some nearby adult. You can recognize begging by the bird's throwing its head back and giving loud, high-pitched calls. You may be even more surprised to know that the adult isn't necessarily the parent of that young bird. You may not be surprised to see that the adult ignores the young or chases it away if it remains persistent.

This begging behavior continues into the winter and even to the next spring in some Glaucous-winged and Western Gulls and their hybrids. After all, they have begged for food from their parents for several months, and the behavior is hard to turn off—especially if they are hungry!

Extended parental care after the young have left the nest area is rather rare in birds and seems to be restricted mostly to fish-eaters. It is not easy to catch fish—no bird has evolved a rod, reel, hook and line for the job—so a young bird just starting out to learn how to do this may have a difficult time of it. So although we see these gulls trying to get a little extra parental care, they don't usually get it.

However, young of some other types of birds are successful beggars well after the breeding season. Several species of crested terns have extraordinarily long dependence on their parents after fledging. Juvenile Elegant Terns fly around with their parents for up to six months or more, beg from them, and are fed.

Juvenile frigatebirds may return to their nesting colony for as long as a year after leaving the nest, to be fed by one or both of their parents. Frigatebirds forage by capturing squids and flying fishes at the sea surface, and they have to be very effective at scooping one of these fast-swimming fish from the water. Thus it takes a long time for the young birds to be effective foragers.

Tropicbirds also feed in the open ocean and on the same types of fishes and squids as frigatebirds, although they plunge into the water at high speed to capture them rather than picking them up with a long bill. Interestingly, tropicbird parents do not feed the young postfledging. Perhaps they should, as frigatebirds are thought to have low juvenile mortality for a seabird, presumably because of the extra help they get from their parents.

Dennis Paulson

CASPIAN TERNS – FABULOUS BIRDS BUT NOT ALWAYS APPRECIATED

The Caspian Tern (Hydroprogne caspia) is the largest of the world’s terns and one of the most widely distributed. The size of a medium-sized gull, it is a most impressive bird, with its striking silvery-white plumage, black crown, and big red bill. Its vocalizations are no less impressive, a loud rasping call that one could imagine pterodactyls made on their breeding grounds.

Caspian Terns breed on islands in lakes or bays, usually in colonies of hundreds to thousands of birds. The largest Pacific Northwest colony is on East Sand Island, at the mouth of the Columbia River, with about 10,000 pairs. This may be the largest colony in the world. The first eggs are laid in mid April, the first hatching about a month later and the first fledging about a month after that. Thousands of birds are still present in late July, but the colony empties shortly after that.

Most pairs lay three eggs, and when they hatch both adults are kept busy bringing in fish from surrounding waters. They fly well above the water, up to 10 meters or more, and dive when they see a fish near the surface, submerging their body completely. If they succeed, they head for the colony. The young have a high-pitched call, like most young birds, and in and around a colony the constant calling back and forth between parents and offspring brings to light the meaning of the word “cacophony.”

Terns are all fish-eaters, and big colonies of Caspians can only thrive where there are a lot of fish in the nearby waters. The Lower Columbia River is such a place, rich in many kinds of fish at the transition from fresh to salt water. Among them are salmon of several species. After their early growth in fresh water, salmonid smolts descend the river to spend some years in salt water before returning to spawn. It has been estimated that 100 million smolts come downriver each year, most of them released from hatcheries.

The terns, and other fish-eating birds nesting in the same area, are there to receive them. It has also been estimated that the tern colony on East Sand Island accounts for predation on about 5 million of these smolts. Although this is only 5% of the estimated smolt run, it is enough to greatly concern wildlife management personnel in both Washington and Oregon.

In fact, concern seems sufficiently great that the terns have been systematically persecuted. Over the past few decades, Caspian Tern colonies have formed at numerous sites along the Washington coast, and at each of them the birds have been hazed until the colony disbanded. Because they have been chased away from islands, they have tried to nest on rooftops and other humanmade structures, but each time they are discovered, they are soon displaced.

Because a few of the colonies on Columbia River islands are thriving, there are enough excess terns that they are still to be seen and heard flying over all of our coastal waters, but many of them fail to breed because they are not allowed to. Salmonid fishes are of great importance to the Pacific Northwest economy, and Caspian Terns are not; the equation does not favor the terns.

POSTSCRIPT (added 23 June 2011)

The largest PNW tern colony, on Sand Island at the mouth of the Columbia, has been severely disrupted by predators, especially Bald Eagles, and will probably fail this year. Fortunately, the terns are long-lived and will presumably breed next year, but the eagles are proving to be real villains in this case, disrupting colonies of terns and other seabirds severely enough that they pose a long-term threat to the populations of these birds. Anthropogenic changes may have made the situation worse, with a decline in other eagle prey and a reduction of the seabird colonies to few sites.

Dennis Paulson