HOW DO SWALLOWS BUILD THEIR NESTS?

The 75 or so species of swallows are an energetic,capable clan of birds. They fly gracefully and rapidly, executing all sorts of aerial acrobatics. They are experts at nabbing insects on the wing, tend their young dutifully and seem to enjoy each other's company. When it comes to nests, however, there is great variety.

Swallows are noisy, frolick some birds who take to the air like ducks to the water. In fact they are ill at ease on the ground, moving quite clumsily on their weak legs. And they alight only to gather materials for their nests. Many species of swallows build their nests out of mud and other materials. Some, however, dig holes in sandbanks, particularly on the banks of rivers. Others lay their eggs in natural hollows of rocks or trees.

One of our North American songbirds, the barn swallow, mixes straw with mud to build the nest. Both mother and father work together, filling their beaks with mud from the edges of streams, ponds and puddles. They carry their cargo to a barn, bridge, church or other building where they use their bills to place it on .a beam or ledge. To construct one tiny cup shaped nest requires hundreds of trips. But the completed home is softly lined with feathers and hair, a lovely place to raise a family.

The barn swallow's nest is reinforced with straw; and since it is usually plastered to a rafter or beam under some cover, it rarely falls. The smaller red rumped swallow of southern Europe, Africa and Asia, however, nests in rocks and sand or mud banks. The nest, shaped like a ball, is entered through a long tube or extension instead of from a hole on top.

The tiny five inch long bank swallow nests with large colonies of its kind. Holes the size of tennis balls, one practically on top of the other, are dug in vertical sand or clay banks. Amazingly, the delicate bird scrapes out a tunnel about two feet deep in the hard material. At the end of the slightly upturned passage is a chamber to hold the eggs.

Swallows build their nests carefully, and generally speaking they are sturdy affairs. The mated pair share in the construction, as well as with the incubation and feeding chores. All swallows, if they survive their migration, will return to the same nest the following year.

Almost all swallows migrate to avoid chilly winters and to find more abundant food supplies. The tiny birds are strong flyers capable of up to 10,000 miles in a yearly migration. The San Juan Capistrano Mission in Southern California is famous for its swallows, which depart every year from the mission on Oct. 23 and return home on March 19.