By EBWG Naturalist Tammy Mercer
I have walked through native prairies, forests, oak savannas and wetlands. In these places I found many of the most interesting bird and animal species on my mental life list. In Bringing Nature Home, author Douglas Tallamy explains why; and more importantly, why the long-term survival of many species of birds and other wildlife depends on a diversity of native plants and the insects that feed on them.
Evolutionary Relationships. For thousands of years plants and animals have evolved together. Plants develop toxins to reduce being eaten; insects adapt with enzymes to counteract the toxins. The insects are then limited to eating only those plants for which they have adapted the right enzymes; all other plants are poisonous to them. In this way, some level of balance is maintained. Birds evolved along with plants and insects, coordinating their breeding with maximum food availability and developing the tools they needed to take advantage of available food.
Birds have bills of different shapes and sizes for eating different kinds of foods. Cardinals and finches have thick conical bills for cracking open seeds, while warblers and vireos have thin probing bills for grabbing insects. However, even seed-eating birds with thick bills rely on high-protein insects, mostly caterpillars and spiders that eat insects, to raise their young. Predators like hawks and owls feed their young small mammals and birds, many of which have been fattened up by eating insects. This is just part of the natural food web, and it all begins with plants.
Bird Migration: Billions of birds fly thousands of miles north every year to breed. These long migrations are treacherous, and fewer than half of the small land birds of the northern hemisphere will make it back to their breeding grounds (Gill 1995). So why have birds evolved to travel such great distances? Chickadees show us that small birds can survive a Minnesota winter, so it’s not just because of the cold. The reason is food. And the food that almost all birds require to raise their young is insects, which are produced in abundance on native plants during the northern hemisphere’s warm seasons each year.
Native Plants: Most insects cannot eat non-native plants. While this may sound ideal to gardeners, it is very bad news for the birds. Early results of Dr. Tallamy’s research have found that native plants produced 35 times more caterpillar biomass than non-natives (Tallamy 2007). When ecosystems are in balance, the visual damage to the plants is minimal.
Lawns and non-native ornamental shrubs, trees and plants do not produce enough insects for birds to raise their young and for their populations to survive. Too many backyards landscaped with exotic plants could literally starve our birds, very likely to the point of extinction. We can make a difference by reducing the size of mowed lawns and gradually replacing non-native trees, shrubs and other plants with native species. Native oak trees, for instance, top the list by supporting more than 500 species of caterpillars (Tallamy 2007).
Adaptation: Native insects may eventually adapt to alien plants, but not in our lifetimes—and not in time to preserve the diversity of birds we now enjoy. Many insect species can eat only one or two kinds of plant. For example, the comma butterfly caterpillar evolved to eat elm leaves.This insect might have been severely impacted because of Dutch elm disease if it weren’t for the fortunate fact that it could also eat leaves of the closely related hackberry tree and the nettles that grow in the forest understory. Elm trees support 213 species of caterpillars (Tallamy 2007), and birds need a lot of caterpillars to raise a brood of chicks. Insects must be able to find their food species and synchronize their life cycles and body chemistry with the plants they eat. They have achieved this over thousands of years of co-evolution with these plants.
Habitat: How much of the lower 48 states do you think has been developed or altered by humans? 50%? 75%? With the help of satellite images and global information systems, landscape ecologists have determined that humans have altered 95% or more of all land in the lower 48 states (Rosenzweig 2003). In the southern half of Minnesota, less than 1% of the prairies, wetlands and “Big Woods” forest remain (Tester 1995).
With residences, cities, farms, roads, etc., we have destroyed about 95% of the native plant communities that evolved in tandem with our native wildlife. We have replaced native plants with alien crops, ornamental trees, plants and grasses that cannot sustain wildlife. The 5% of the habitat left undisturbed could eventually leave us with just 5% of the species of birds and wildlife (Tallamy 2007). Even the few remaining wild places have been increasingly fragmented and degraded by invasive species. And the rate of development continues to increase. We can no longer trust that there are enough wild places somewhere else to support the wildlife we displace every time we develop new land.
Of course people need places to live too. But we can reduce our impact on wildlife by living as much as we can within the ecological relationships that have evolved on this continent over thousands of years. We can share our landscapes with wildlife by including native plants in the places we live, work, and play.
The Garden: In addition to being a repository for native plants and a bird sanctuary, the Eloise Butler Wildflower Garden is an important habitat that supports a remarkable diversity of plants, wildlife and birds. You can find many examples of native plant communities in EBWG. Come to the Garden this season and you will see ecosystems in action: examples of native plant communities that you might consider the next time you want to plant something new in your yard. And watch for programs about the native plants in the Eloise Butler Wildflower Garden website.
Gill, Frank B. 1999. Ornithology W. H. Freeman and Company. NY.
Rosenzweig, M. L. 2003. Win-Win Ecology: How the Earth’s Species can survive in the Midst of Human Enterprise. Oxford University Press, NY.
Tallamy, Douglas W. 2007. Bringing Nature Home: How You Can Sustain Wildlife with Native Plants. Timberline Press. Portland, OR.
Tester, John R. 1995. Minnesota’s Natural Heritage: an Ecological Perspective. University of Minnesota Press. Minneapolis, MN.
Allen, Thomas J. 2005. Caterpillars in the Field and Garden: a Field Guide to the Butterfly Caterpillars of North America. Oxford University Press. NY.
Dr. Tallamy’s Website: www.plantnative.com
Native Plant Society of Minnesota: www.mnnps.org
Nowak, Mariette. 2007. Birdscaping in the Midwest: a Guide to Gardening with Native Plants to Attract Birds. Itchy Cat Press. Blue Mounds, WI.
Steiner, Lynn M. 2005. Landscaping with Native Plants of Minnesota. Voyageur Press. Minneapolis, MN.
Wagner, David L. 2005. Caterpillars of Eastern North America. Princeton University Press. Princeton, NJ.
Gardening with Prairie Plants: How to Create Beautiful Native Landscapes. University of Minnesota Press. Minneapolis, MN.
Local native plant sources
Outback Nursery and Landscaping: www.outbacknursery.com
Prairie Moon Nursery: www.prairiemoon.com
Prairie Restorations, Inc.: www.prairieresto.com
Tammy Mercer is a naturalist who formerly worked at the Eloise Butler Wildflower Garden and led birding walks.
This article was published in the Fringed Gentian™ Vol. 58 #2, Spring 2010.
Other articles related to birds by Tammy Mercer:
A Great Place for Birding – why the Garden is great for birding, including in May after the Spring migration.
Early Birders Catch the Wonders – what wonders are seen during the year on the Saturday Morning Birding walks.
EBWG as a Migration Rest Stop – an article addressed to the birds about the benefits of Eloise Butler Wildflower Garden as a migration rest stop.
Many Colors of Feathers (The) – about the color of bird feathers and why we see the colors the way we do.
Rewards of Summer Birding – summer birding and distinguishing fledglings from adults.
Warblers - Spring Warblers and the little time there is to see them. (This is a 1.0mb pdf file)
Winter Survival of Warm-blooded Critters – how some of the birds and animals survive the winter in the Garden.