By MILLIE BASDEN

For just a few weeks each year, a small, bright yellow bird visits Mission Trails Regional Park.

Wilson’s Warbler (Cardellina pusilla) spends winters in Mexico and Central America. From about the middle of March until the end of May each year, Wilson’s Warblers can be seen in the park as they pass through the area on the way north to their breeding grounds. Some will nest in Northern California; others continue as far as northern areas of Alaska and Canada.

Like most warblers, they are active birds, hardly ever sitting still. They forage in willows, oaks, and other trees, usually near water, looking for caterpillars, spiders, aphids, flies, and other insects. In addition to gleaning prey from leaves, they will sometimes sally out to catch an insect in flight.

The male Wilson’s Warbler has a black cap. The top of the female’s head is olive, like the back and wings of both sexes. In both males and females, their black eyes really stand out in their solid yellow faces.

The warbler was named after Alexander Wilson, sometimes called the “Father of American Ornithology” who lived from 1766 to 1813.

As is true for many of our birds, the number of Wilson’s Warblers is in decline, mostly due to loss of habitat in all areas (breeding grounds, wintering grounds and migration path).

If you don’t catch sight of a Wilson’s Warbler this spring, you will have another chance for a few weeks beginning in mid-August when they pass through again on their way south for the winter.

— Millie Basden is a Trail Guide at Mission Trails Regional Park.