Birds and the gypsy moth outbreak
How did you fare during the gypsy moth caterpillar outbreak? I guess everybody got tired of sweeping tiny bits of leaves off their steps, hosing down their cars, and slipping on the millions of droppings. My neighborhood was so bad that the trees are defoliated, but I refuse to let it get me down.
In fact, the recent die-off of the larvae (caterpillars) from the entomopathogenic fungus means there is hope that next year won’t be bad at all. Yet, if you are like me, you are probably concerned about the impact the outbreak may have had on our birds. Fortunately, that, too, isn’t as grim as you might think, and some birds did benefit.
Gypsy moth caterpillars were introduced from Europe to North America 120 years ago in Medford, Mass., where their population quickly exploded free from the ecosystem it evolved in. But, unlike other invasive species that often lack adequate predation, 41 species of Connecticut birds eat gypsy moths.
Among them are the chickadees, diligently at work consuming gypsy moth caterpillars as a regular part of their diet. They join a long list of birds that take the caterpillars in years when there is no outbreak. These species include blue jays, eastern towhees, Baltimore orioles, and gray catbirds.
Only a few species of birds eat the pupae, and they include eastern wood pewee, hairy woodpecker, red-eyed vireo, and both black-billed and yellow billed cuckoos. Fewer species eat the actual moths: they are less common species from a variety of habitats and include the ovenbird, indigo bunting, common yellowthroat, and eastern phoebe. Chickadees and house sparrows are known to eat the egg masses.
During an actual outbreak, it is the black-billed and yellow-billed cuckoos that thrive on the infestations. Cuckoos are caterpillar specialists, and are well suited for eating soft and prickly caterpillars. They eat the larger late-stage caterpillars that most birds neglect because they have stomach linings that shed when full of caterpillar hairs. The cuckoos regurgitate their stomach linings and grow new ones.
So why can’t our local birds save us from this horrible infestation of caterpillars?
Despite the consumption of
caterpillars, pupae and eggs by our native birds, gypsy moths are important food sources for only a few, and so the overall effect on gypsy moths is limited. Birds have little impact against the invasive gypsy moth because there is preferable native food available.
Fortunately, outbreaks have a temporary effect on birds, unless we have three consecutive years of defoliation, then trees often die. This causes a complete habitat change that eliminates many birds and benefits only a select few.
For humans, the outbreak has been like an Alfred Hitchcock horror film, with caterpillars crawling on everything. But with a sense of humor, I made it through by considering the free fertilizer that rained down on the lawn from the tree tops day and night. How about all that great mulch from the half-eaten leaves covering the garden? And just think what the extra sunshine will do for those tomato plants now that the trees are bare.
Overall, there are gains and losses, in the complex relationship between gypsy moths and birds. I think we are lucky there wasn’t complete destruction and that some birds did gain by eating them. In a few weeks, the trees will send forth new leaves, and our lives, too, will return to normal.