Neotropical Migrants:
Checklist for Survival

---

by Marlene Ehresman

NOTE: This article was published in fall 2000. Since then, INHF has completed an entire book on this subject. The book is available online or free by mail.

As days shorten, many of us cringe at the thought of another cold, blustery Iowa winter. We watch the birds begin to gather in large groups that dip and dart over ripened fields. We ponder plans-some instinctive, some not-to stay or leave for warmer climates.

Human checklist: buy airline tickets, hold mail, cancel newspaper. Avian checklist: double body weight by feverishly feeding on buzzing insects. Human flight: unpredictable schedules, tight seating, too many peanuts. Avian flight: unpredictable calamities, exposure and exhaustion. Human tropical stay: tropical sun, food and fun. Avian tropical stay: intense competition for food and shelter in rapidly disappearing habitats.

With the coming of spring and promise of warmth, the fellow travelers migrate back north: more inconveniences, more hardships. What will they find upon their return to the Midwest? Ample shelter, food, water and space-we hope.

Why it matters
More than half the bird species that breed in North America spend part of every year away from their breeding grounds. In other words, more than 350 species that nest in Canada and the United States make that daunting journey thousands of miles to their winter homes in Mexico, the Caribbean, or Central or South America. These birds are known as neotropical migratory birds, or neotrops for short.

Protecting migrants isn't a new idea. Spurred by dwindling waterfowl populations, citizens demanded laws and wildlife refuges to protect waterfowl's migratory stopover and wintering habitats starting in the early 1900s. For decades, a great deal of attention and funding has gone to the Mississippi River basin, a migratory flyway for 40 percent of all North American waterfowl. However, other migratory birds, such as the songbirds, shorebirds and raptors, weren't afforded the same attention as migratory waterfowl. While migratory waterfowl numbers have generally stabilized or increased, many less "popular" migrant species are dwindling rapidly. Some of these other migrants have familiar names, such as the Bobolink and Baltimore Oriole, while others have names known mostly to birdwatchers, like the Cerulean Warbler and Scarlet Tanager. Whatever their name, they need our help.

Why should we care? In areas where natural resources are more abundant, such as in the Mississippi River blufflands, birding ecotourism could be a valuable addition to the economy. Migration "watch weekends" and everyday birdwatching attract millions of tourists, and their money, to wildlife refuges, parks, and other natural areas each year.

More importantly, neotropical migrants play vital roles in their ecosystems. During the summer, the diet of many species is insects-often leaf-chewing insects. Even the seed-eating birds add insects to their diet in summer or feed them to their nestlings. These birds help maintain the health of our prairies, savannas and forests.

Project goals
Because of its importance as a major migratory route and because it still contains fairly large contiguous tracts of woodlands, the Mississippi River bluffland area may be one of the last best hopes for neotropical migratory bird conservation in the Midwest. This rugged landform encompasses some 400 river-miles between the Twin Cities of Minnesota and the Quad Cities of Iowa and Illinois. It impacts four states and 23 counties and is in the center of a ring of cities considered the fourth fastest growing region in the US.

The Iowa Natural Heritage Foundation is an active member of the Blufflands Alliance, a partnership working to protect and enhance the resources of this important region. With a grant from the National Fish and Wildlife Foundation, the Alliance groups will gain the information needed to know which acres need protection most and the funds to protect at least 1200 acres of important neotropical migrant habitat.

INHF is conducting a literature review, gathering information on what neotrops need to survive and how to best provide it. Soon available to private landowners, public agencies and interested citizens, INHF is preparing a publication that outlines the study's results. This publication and related workshops will increase public understanding of the blufflands ecosystem and its importance to neotropical migrants. They will also help individuals and organizations understand and implement land management and protection efforts to support neotrops, especially the most threatened species.

Unfortunately, little is known about ideal habitat size, distribution or quality for most neotrop species. For example, no one knows exactly how many acres of mature woodland are needed to keep the Cerulean Warbler population stable or increasing. There are complex relationships involved and much research that needs to be done, and soon. In the meantime, we need to do our best with available studies to theorize and protect bird habitat before these species decline beyond recovery.

Threats to survival
Some neotropical migrants are considered generalists-able to thrive in different habitats. Most of the rarer ones, however, are specialists -with specific habitat or food requirements. For the purposes of this study, INHF is most concerned about the specialists. Some specialists are adapted to deep forest interior and are called area-sensitive, or forest-interior, species. For example, the Cerulean Warbler seems to require the extensive, unbroken mature woodlands with sparse understory to nest successfully. The Loggerhead Shrike, another specialist, is adapted to savannas and other habitats with open country and scattered trees and shrubs.

Neotrops face major problems here and south of the border. Pollution, pesticides and collisions with human-made structures all create threats. But the worst threats are habitat loss (especially loss of breeding habitat) and fragmentation (the isolation of a particular piece of habitat). These changes in the natural system especially threaten the survival of the specialists. Habitat loss can occur when a forest is cleared for development or agriculture. It can also occur when deer become over-populated and destroy the forest understory in which many migrants nest. Suitable breeding habitat can be lost when we suppress fires and forests reclaim savannas and prairies. Fragmentation can be a result of habitat loss.

Habitat fragmentation
The big problems occur when large, contiguous ecosystems are "fragmented," creating habitat "islands." The subject of fragmentation is complex. Landforms, such as a river, and natural disturbances can cause fragmentation. So do roads, developments, utility lines and rowcrops. Unfortunately, these human-caused changes occurred in a blink of the evolutionary eye, and specialists have not had time to adapt. People began to notice that some birds were suddenly less abundant.

Fragmentation causes edge effect. Many predators, such as domestic cats, raccoons, and skunks, prefer the easier hunt along the edges where plant communities meet. Brown-headed Cowbirds, birds that don't build their own nest nor rear their own young but lay their eggs in the nest of other species, also take advantage of these edge areas. In fact, most of the nest parasitism and predation takes place on the edge of forests, usually within the first 165 feet. Exotic plant species tend to move into disturbed edge areas, quickly taking over native plant species and leaving our native birds with poorer or fewer choices of food. Here, too, the more abundant generalists compete with the specialists. For many species, habitat size matters-and bigger is better.

Unfortunately, people have been taught that edges have the greatest abundance and diversity of wildlife in general. So, wildlife managers and landowners have actually created edge in the name of doing something beneficial, while some of our rarer species have suffered for this practice.

Habitat type
In addition to size, habitat type and quality also matter. Large healthy ecosystems include mosaics of habitats, which are, in turn, mosaics of plant types and ages. The bluffland region is a complex ecosystem. Mixed in with the forests, you can still find remnant hilltop "goat" prairies. Some of what we consider forests may actually be "degraded" oak savannas.

Therefore, habitat protection includes not only the type of land protected but the way in which that land is managed-whether the forest canopy should be kept closed or open or whether controlled burns should be used to defend prairies and savannas from invading forest.

There are many unanswered questions, but we know that the future of neotropical migrants depends on the availability of suitable breeding and wintering habitat as well as migration stopover areas. Since neotrops are adapted to a wide range of breeding habitats, protecting large blocks of each habitat type is probably the best conservation strategy while further research fills in details. With the completion of this project, INHF will protect some of these "best-bet" areas and encourage others to do the same.

As we think about this year's winter checklist, we must consider the neotrop's checklist as well. Come spring, will all the snowbirds feel welcomed home?

The Foundation plans to have the publication on neotropical migrants available by year-end. If you'd like to receive a copy, please email INHF or call 515/288-1846 to get your name on the list.


Marlene Ehresman is the Foundation's Program Associate. She and her husband Bruce, also a biologist, enjoy watching birds. Although they may argue about what species just flitted in front of them, they agree habitat is the key.