The spicebush swallowtail butterfly’s caterpillar is one of numerous moth and butterfly caterpillar species that emerge in spring and provide abundant food for songbirds and nestlings. PHOTO CREDIT: Greg Schechter, Creative Commons

Wild Georgia: Birds have big appetites for caterpillars

Oaks, hickories and other hardwoods that were leafless only a few weeks ago now are sporting their bright green canopies of spring.

The leafing out, in turn, has triggered another springtime phenomenon, the “great munching.” Countless hordes of voracious caterpillars are emerging and devouring the tender new foliage for nourishment to grow into adult moths and butterflies (which make up the Lepidoptera order).

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Unchecked, super-hungry caterpillars would denude forest foliage within weeks. Fortunately, some equally hungry creatures are anxious to snatch up caterpillars by the tons to feed themselves and their babies.

They are the songbirds. Most songbirds do not reproduce on berries and seeds. Instead, more than 95 percent of them and other terrestrial birds turn to diets of protein-rich caterpillars and other insects during the breeding and nesting seasons, scientists say.

Warblers and chickadees, for instance, may rely on caterpillars — eating hundreds per day — for 90 percent of their diet during breeding and nesting periods.

Other larval and adult insects — beetles, flies, crickets — also may be on the menus of nesting birds. But of all the insect food, caterpillars are the best sustenance for baby birds, says University of Delaware entomologist Doug Tallamy, who spoke recently at the Atlanta History Center.

“Caterpillars are soft, high in protein and easy to digest,” Tallamy said. Over a long span of time, most songbirds have learned to time their breeding seasons to coincide with the emergence of caterpillars to provide abundant food for nestlings.

That is especially true for neo-tropical songbirds, such as warblers and tanagers, which are arriving now from winter homes in Latin America for spring nesting in Georgia. A readily available food source is critical because they will quickly commence nesting soon after arrival.

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IN THE SKY — From David Dundee, Tellus Science Museum astronomer: The Lyrid meteor is visible this weekend — in the northeast from 2 a.m. until dawn. The moon will be new on Wednesday. Mercury is low, and Venus and Mars are very low, in the west just after dark. Venus appears near the moon on Sunday morning. Jupiter is in the east at dusk. Saturn is in the east just before midnight.

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