By John Keeling
First Fall Warblers
I know fall has arrived when the first Wilson’s Warblers arrive in my garden in Ajijic. These are fairly common yellow birds somewhat smaller than a sparrow. The lower parts are yellow to greenish yellow, and the upper parts are greenish yellow to olive. The male has a distinctive small black cap on top of its head, while the female and immatures have either no cap or a hint of a cap.
In spring and summer the male develops a bright yellow body as its breeding plumage, which is what is typically shown in the bird books. You may notice the tail is often cocked, and has a characteristic tail wave or tail flip. The call is a high pitched: “chik, chik, chik.”
You can observe these little birds in bushes and vines from two to six feet off the ground, always on the move, hopping from branch to branch, continuously foraging. They are looking principally for small insects, leaf hoppers, caterpillars, wasps, ants and also minor quantities of seeds and small berries.
They spend the summer in sub-artic regions from Alaska to Newfoundland, as well as along the pacific coast from Oregon to California. They build nests on or just above ground level well hidden under willow trees, tall grasses or blackberry tangles near water. Designed for a quick turn-around in the short, unpredictable northern summer, the eggs take only 14 days to hatch and the young are flying within another 12 days. Researchers studying nesting habits of Wilson’s Warblers near the Arctic Circle one year found five chicks in a nest wiped out by an unexpected heavy snowfall in July.
When the far north cools off in August, these birds start migrating nocturnally, following major flyways through the central states, heading for winter feeding grounds from Mexico to Panama. They will rest at spots where they find plentiful insects, stopping for four days at a time to replenish body fat to use on the next stage of the journey. A month later, in September, when it gets cooler in Oregon, the Pacific Coast birds move down the coast to winter in Western Mexico and Ajijic.
In March the West-Coast birds start heading north, while the others in Central America wait another month for the far north to start defrosting before they travel. The males go about two weeks ahead of the females in order to select nesting territories. They will often go back to the same nesting area they used in the previous year.
Wilson’s Warblers are not afraid of humans, so you will often see them in your garden, approaching close to your house, particularly if you have vines or bushes for them to hunt for insects. Look out for them.
Editor’s Note: John and Rosemary Keeling lead ‘Los Audubonistas del Lago’ which is a loose-knit group of people interested in birds. To receive notices of bird-walks please leave your e-mail address at www.avesajijic.com.