Yellowthroat warblers are primarily insectivores. They migrate to tropical climates in the winter where insects are plentiful.Submitted photo

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It was a busy sunny lunchtime on the back screened porch one late September day. The bees had divided up the flowers: the honeybees were all over the New England asters, while the bumblebees were enjoying nectar from the zigzag goldenrod. The cedar waxwings were up top in the hawthorn tree, checking to see if its berries were ripe. Mature and immature goldfinches, the males beginning to look scraggly as they replace their beautiful yellow summer feathers, were taking over the coneflowers that had gone to seed; their young were begging to be fed. The Ruby-throated Hummingbird was savoring the last of the scarlet monarda blossoms. At least 10 robins were taking turns at the birdbath, crowding out the House Finches and sparrows. Occasionally other birds squeezed in. A young Northern Cardinal and a handsome adult male, a blue jay and a striking adult male grackle, with his glossy plumage and yellow eyering, replaced them for a few moments.  

Then, a burst of bird suddenly flew into the center garden beneath the asters. It was clear from the occasional waving of the asters that at least one bird was in there, but it, or they, were well hidden.  Watching carefully for about 10 minutes, and staying on the porch so as not to scare the birds, we finally got a good look at a handsome male Common Yellowthroat, a warbler, a first for my yard. Yellowthroats stay close to the ground as they scavenge for insects.

Unlike the other birds, who were chowing down on seeds or berries or nectar, most warblers are primarily insectivores. As days get colder, and insects are no longer available, warblers must migrate to tropical climates where insects are plentiful. Not only warblers, but over half of our breeding North American birds migrate to places with an abundance of insects. Even along the way, they need protein. When this Common Yellowthroat finally came into view, it had a medium-sized tan moth dangling from his beak, energy for its journey south.

A recent Science article documented the demise of 3 billion birds in North America since 1970, some of them common everyday backyard species. Reasons for the decline included collisions with glass buildings (Common Yellowthroats are common victims of building collisions), outdoor roaming cats, habitat loss, and pesticides.  

Habitat loss and pesticides drastically reduce the insect population on which, according to Doug Tallamy, a professor in the Department of Entomology and Wildlife Ecology at the University of Delaware, 96 percent of North American terrestrial bird species depend for essential protein. In fact, many seed-and berry-eating birds switch to insects to feed protein to their growing nestlings, and adults need protein for muscle tone and energy. More from Tallamy: Insects have up to twice as much protein, pound for pound, as does beef.  

Many people who have taken road trips have witnessed the severe decline in insects. Where 30 years ago, car grills would be splattered with insect bodies, now there are few, if any.

The decline in insects would most likely be a prime factor in the loss of 3 billion birds. But, it turns out, we are not helpless. We have the ability to create healthy habitats where insects can thrive. We can replace at least part of our grass lawns and our gardens with native plants to attract the insects that the birds need. We can eliminate the use of pesticides on the lawn that remains. And Common Yellowthroats and their kin will find buggy nutrition for breeding and for their hazardous migration to their wintering home and back.

Libby Hill

Libby Hill is the author of "The Chicago River: a Natural and Unnatural History. She has been writing about birds and trees and Evanston's natural history for the Roundtable since 2004.