The soil has begun thawing enough to unlock the food supplies of earthworms and insects for newly arrived American woodcocks.

They are stocky birds, about 11 inches long, with 3-inch bills, short necks and a dead-leaf pattern on their upper bodies. Their calling and display flights begin soon after they arrive from southern states.

Spring's emergence is widely announced by the noisy courtship displays and vocalizations of many bird species. House finches and northern cardinals sing, and woodpeckers drum. With much honking and fanfare, pairs of Canada geese claim their wetlands nesting territories. The male American woodcock adds its special music to this chorus at a quiet time of day. It begins its performance soon after sunset, and it ceases when the glow in the western sky disappears, only to begin again in the morning twilight or on moonlit nights when it continues throughout the night.

Woodcocks nest in wooded or brushy uplands not far from wetlands. They perform their courtship displays in open pastures or fields. The loud, nasally peent sound is uttered every few seconds as the woodcock struts about. Suddenly the bird rises and flies off at an angle, circling higher and higher until it reaches a height of 200 to 300 feet. The flight is accompanied by twittering musical notes made by the wings. As the bird flutters back to the ground, a series of chipping whistles completes its elaborate performance. The bird soon begins to court a hen with the peent call, and the whole act is repeated over and over.

These woodcock concerts might continue into June, but April is the liveliest month because the female nests in May. I have taken school groups out to experience spring woodcock displays in Carver Park near Victoria, and also in Minnesota's Arrowhead. For many people fortunate enough to witness this rite of spring, the memory lasts a lifetime. This year, Tom and Lisa Boevers, two very capable outdoor observers, witnessed their first woodcock display of this year at about 8 p.m. March 23 at River Bend Nature Center in Faribault, Minn.

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.