Saving Birds Thru Habitat

During a bird survey of the Leelanau Conservancy’s Lighthouse West property on Sunday, our group of five came upon one of the hordes of eastern tent caterpillar tents that have appeared across the region.   These caterpillars (also referred to as “bag worms”) are native to our continent and do not harm healthy trees or shrubs. They a natural part of our ecosystem, providing food for both black-billed and yellow-billed cuckoos.

On Sunday morning, our survey group had an opportunity to watch a black-billed cuckoo feeding from a tent filled with worms.  Because this is a big year for the tent worms, it should be a good year for cuckoos.  Since black-billed cuckoos are declining, this outbreak may give them a boost.  People who have tent worm caterpillars on their properties might want to think about the cuckoos before grabbing a can of insecticide.

Also spotted was a common nighthawk sleeping on a branch.  While cuckoos depend heavily on insects, nighthawks depend exclusively on insects.  Cuckoo and nighthawk populations are declining.   Efforts to eradicate insects are undoubtedly contributing to those loses.

Garlic Mustard is a rapidly spreading invasive alien plant that is displacing native woodland wildflowers in forests from the eastern seaboard to the Rocky Mountains.   This plant eventually dominates the forest floor, displacing virtually all native herbaceous species in as little as ten years. As it invades woodlands, spring ephemerals such as trillium, trout lily, Dutchman’s breeches, and jack-in-the-pulpit disappear along with other flora upon which our native depends.

The problem with this bioinvader is the same as it is with other non-native plants that have spread across the continent:  they do not support the ecological structure of the habitats they move into.  Non-native plants do not host the insect biomass required for birds, amphibians, fish and some reptiles and mammals.  Moreover, wildlife species that depend on early flowering plants for needed pollen, nectar, fruits and seeds are deprived of these essential food sources when garlic mustard replaces native vegetation.

There are two modes of spread: an advancing front and satellite population expansion by seeds, possibly facilitated by birds and small mammals. Unlike other plants that invade disturbed habitats, garlic mustard readily spreads into high quality forests.

Garlic mustard was introduced from Europe, likely for its supposed medicinal properties and for use in cooking. It naturalized and is now widely distributed throughout the northeastern and Midwestern U.S. from Canada to South Carolina and west as far the Rocky Mountains. It grows in upland and floodplain forests, savannas, yards, and along roadsides.  Although it is largely shade-tolerant, generally requiring at least some shade it occasionally tolerates full sun.  It cannot tolerate acidic soils. The invasion of forests usually begins along the wood’s edge, and progresses via streams, campgrounds, and trails.

For information on eradicating an infestation on your property, see the Wisconsin DNR website.  Scroll down the page to the heading “Controlling Garlic Mustard.”

Several years ago, the educational director of a state Audubon Society questioned my assertion that only native plants host the insects that support our migratory birds.  We were both attending the International Wildlife Conference in Columbus; one might reasonably assume that those in attendance would already understand that fact.

But the young man who served such an important role not only didn’t know it, he doubted it.

“Do we really know that’s true?” he asked.

We do know it is true.  Unfortunately, it seems to be a new concept, even for many who work in the field of conservation (such as the above biologist).  Dr. Douglas Tallamy, who chairs the Department of Entomology and Wildlife Ecology at University of Delaware, explained the disconnect when I interviewed him about his book, Bringing Nature Home (Timber Press, Inc., $27.95, 2007).

Tallamy confessed that during the very time he was studying the relationship between native plants and insects in college, he was busy filling his personal landscape with non-native ornamentals and cultivars.  He added that his epiphany; the moment the light came on about the importance of native plants only came after he and his wife purchased ten acres of old Pennsylvania farmland for their home.

The property was overgrown with alien plants like autumn olive, multiflora rose, and Japanese knotweed.  The vegetation was so dense that they had to cut trails in order to get inside of it.  One day, he took a walk to look for insects.  He was dismayed to find none except on the handful of native plants that struggled to survive under the stranglehold of invasives.  It was a defining moment for him.  He began to present programs to educate the general public about his discovery.  It was a rediscovery, actually; he already knew that our indigenous herbivorous fauna (insects, amphibians, mammals, etc.), with few exceptions, either cannot or will not eat plants from other continents.  He just hadn’t applied the concept to his own property.

In his book, Tallamy talks about the “insect biomass” which is the base of the food web.  A full 97% of all terrestrial birds (birds that live on land as opposed to seabirds like puffins) require insects during some part of their life cycles.  Nestling birds must have protein-rich insects in order to develop.  No bugs, no baby birds.  As well, many amphibians, reptiles and some mammals depend on insects.  Only native plants support this biomass.  Thus, whether we are homeowners, trying to create a little habitat for the wildlife around us, or an agricultural interest or corporation attempting to improve the land under its control, the message is the same.  If you use a variety of native plants, you will provide a haven for vastly more members of the wildlife community than if you don’t.

It’s important to bear in mind that migrating birds do not simply need the right habitat for nesting.  They must also have good places for winter homes (using shade-grown coffee helps provide that) and good stopover sites after their trans-Gulf crossings (your back yard can fill this part of the equation).

Our role is to join Dr. Tallamy in educating people to the fact that if it isn’t native, it might be beautiful, but it simply is not habitat.