The tools and techniques for bird conservation described in this booklet can be applied to just about any kind of bird. The impetus for this book, however, came from a particular group of birds known as “neotropical migrants.” Indeed, concern for these birds is so great that an entire program to conserve them was initiated in 1990. It’s called Partners in Flight, and is described on page 5.
What is a neotropical migrant, anyway?
Quite simply, neotropical migrants are birds that spend their summers in Canada and the United States and their winters in Mexico, the Caribbean, Central America and South America (the region known as the New World tropics, or neotropics). Although the name “neotropical migrant” sounds exotic, we’re actually talking about common birds, and lots of them — at least 250 species, nearly one-third of the birds that breed in North America (see the list on pg. 31). These include many familiar birds such as warblers, tanagers, thrushes, and orioles.
Why the concern about neotropical migrants?
Because in recent years, some have declined in numbers. To understand why it helps to know a little about the birds’ complex life cycles. First, migratory birds require summer habitat in temperate North America where they can nest and raise their young. Then, during spring and fall they need stopover habitats on their migration routes — places that are safe to rest in and rich in insects or berries to fuel their long-distance flights. Migration routes run for hundreds or even thousands of miles, crossing numerous political boundaries, until the birds reach their destinations — the wintering grounds. There, they must identify new food sources in unfamiliar surroundings and compete for food with residents such as White-tailed Trogons and Broad-billed Motmots.
It’s a complicated scenario, one that can be easily disrupted by human activities. Indeed, some species of neotropical migrants have shown significant declines. Consider the Breeding Bird Survey (BBS), a volunteer bird-counting effort conducted by about 2,000 birders each June (see page 16). In eastern North America, where some of the best information is available, the BBS suggests that 75 percent of populations of forest-dwelling neotropical migrant species declined between 1978 and 1987. More recently, several of these species increased in number, but some, such as the Cerulean Warbler, have not recovered. And woodland birds are not the only species experiencing declines. Grassland birds such as the Grasshopper Sparrow, which declined 4.5 percent each year between 1966 and 1991, are also in trouble.
Further concern arises from the work of Sidney Gauthreaux, an ornithologist who studies bird migration with radar. His research suggests that the number of birds migrating over the Gulf of Mexico in spring has decreased by half since the mid 1960s.
Let’s look at why the declines are occurring.
Obstacles in Latin America
Throughout much of Latin America, tropical forests are rapidly being converted to cropland and open grazing land by slash-and-burn agricultural techniques. Such forest destruction obviously creates problems for migrant birds that depend on forests for winter habitat. Another problem is geographical. The land mass inhabited by migrants in winter is much smaller than the vast breeding area — all of North America. this means that wintering areas are often packed with five to eight times as many birds as are found in the same area on the breeding grounds. Therefore, the destruction of just a small amount of tropical forest can have a huge effect on some bird populations. Species restricted to a small wintering range, such as the Cerulean Warbler, are at the greatest risk. And areas with the greatest concentrations of migrants – Mexico, Central America, the Greater Antilles, and portions of the Andean mountain range in South America – also have some of the highest rates of deforestation.
Neotropical migrants wintering near cropland area are also threatened by pesticides, because the toxins concentrate in the birds’ fat reserves. Some pesticides, including chlorinated hydrocarbons such as DDT, have been outlawed for use in the United States but are still used legally in Latin American and Caribbean countries. U.S. companies supply these pesticides.
Obstacles Along Migration Routes
During migration, birds use an astonishing array of habitats, from boreal coniferous forests and temperate-zone deciduous forests to grasslands, scrublands, and tropical rainforest. All these habitats must support the birds’ need s for food and protection from weather and predators. Clearly, the presence of suitable habitat along migratory routes is crucial to the birds’ ability to survive and reproduce successfully each year. The longer a bird must search for a satisfactory stopover area, the less time and energy it has to complete migration, set up and defend a territory, and raise young.
During spring and fall, neotropical migrants funnel through small areas where they rest and feed before beginning nonstop flights over land or water. Many species make 20-, 40-, and even 80-hour nonstop flights over water, so coastal habitats are particularly important stopover zones. Unfortunately, these areas are disappearing under a welter of condominiums and vacation homes. Other prime stopover sites, such as those along rivers, are being destroyed as well.
Obstacles in Temperate North America
Migrant birds face tremendous threats on their breeding grounds. Only 250 years ago, the forests of North America provided ideal habitat for many migrants. By 1920, however, much of the landscape had been deforested. In recent decades, many of the forests cut in the 19th and 20th centuries have regrown or been replanted, especially in the Northeast. But problems for forest-dwelling birds remain.
Why? Much of the forest that does remain has been fragmented, that is, parceled into small blocks by urbanization, agriculture, timber harvesting, and other human activities. Such fragmentation seems to be a serious problem for some neotropical migrants. Unlike large forest tracts, small, scattered woodlands present numerous edges — boundaries created by roads, fields, housing developments, and possibly clearcuts. these edges can allow open-land predators such as jays and crows, which feed on songbirds and their nestlings, to intrude into the forest. Creeping urbanization has also allowed increases in predators that live and thrive around humans, such as raccoons, opossums, and cats.
Fragmentation is a particular problem for neotropical migrants because of their nesting habits. Most neotropical migrants build open, cup-shaped nests that are relatively easy for predators to spot. They also tend to lay only a few eggs each year. Many nest on the ground, making them susceptible to predation.
Edge habitat and open-cup nests also cause birds to be susceptible to cowbird parasitism. Unlike most other birds, Brown-headed Cowbirds do not build their own nests; instead, they lay their eggs in the nests of other birds, sometimes destroying the eggs of the unwitting host. And even if the host eggs are not destroyed the cowbird eggs generally hatch first and the large, aggressive cowbird checks crowd out the host young, killing them directly, or killing them indirectly by eating all the food brought by the parents.
At the time of European settlement, Brown-headed Cowbirds lived in the Great Plains of North America. in the past 150 years, however, as forest has been cleared for agriculture, cowbirds have expanded their range dramatically. The number of cowbirds has skyrocketed, and so has the number of bird species they are known to parasitize — now over 200. In central Illinois, where very little forest remains, cowbirds parasitize 75 percent of the nests of some species of migratory birds, such as the Wood Thrush.
Forest fragmentation seems to be less of a problem in western North America, where migrants face a different set of challenges. The West is made up of diverse habitats — montane forest, riparian (streamside) habitat, desert, grassland, and shrubsteppe, to name a few. Neotropical migrants live in all of these habitats at some time of year, but most species nest in montane forests and riparian areas, which make up just a small percentage of western lands. Consequently, populations of western migratory birds may be smaller than those of eastern species.
As in the East, habitat degradation is a key factor in the declines of some western species. For example, disruption of riparian habitat by cattle grazing and agriculture has enabled cowbirds to take advantage of several species of migrants that nest in these areas. As much as 95 percent of the riparian habitat has been lost in many western states. As a result, populations of species that depend on riparian habitat, such as the southwestern Willow Flycatcher and Yellow Warbler, are in trouble. Riparian woodlands in California have lost most of their bird species.
Declines of grassland species, such as Grasshopper and Lark Sparrows, are also cause for concern. According to Breeding Bird Survey data, grassland bird species are showing steeper and more consistent declines over the past 25 years than are other birds. While these trends are not entirely understood, biologists suspect that changes such as the disappearance of the great bison herds from the Great Plans and habitat loss due to agricultural activity are factors in teh declines. In many states grassland habitat has nearly vanished. In others, grasslands have become fragmented, a process analogous to forest fragmentation, so bird species that require large areas of this habitat are unable to nest successfully. the growing body of scientific research will shed more light on grassland birds and their populations changes in the years to come.
The Solution: Partners in Flight
But here is the good news. Most species of neotropical migrants are still common, and very few species are endangered or even threatened. We are concerned about declining species because we want to avoid reaching a crisis situation — we want to maintain populations while they are still healthy. We therefore have the opportunity to conserve bird diversity in North America without putting an additional strain on our economic and social institutions.
Recognizing that conserving neotropical migratory birds is too big of a problem for any one agency, organization, state, or even country, the National Fish and Wildlife Foundation launched a new program in 1990 called Partners in Flight. This massive program is not an organization. It has no single address or employees. Rather, it is a cooperative effort among numerous state and federal government agencies, non-governmental conservation organizations, and private industry. The goal of Partners in Flight is to improve our understanding of neotropical migrants, identify species most at risk, and develop and carry out cooperative plans to protect their habitat.
Already great strides have been made in identifying the bird species needing the most help. A species prioritization scheme, available from the Colorado Bird Observatory, has shown which species are at greatest risk in every part of North America. This complex scheme takes into account many factors, including global abundance, breeding and winter distributions, and threats to habitats on wintering and breeding grounds. Identifying the species that are most vulnerable shows conservationists which habitats most need protection or restoration.
Progress also has been made toward developing regional and national migratory bird habitat conservation plans. These plans are based on the concept of management at the landscape level. In this context, “landscape” refers to a large area such as you might see while flying in an airplane, an area with a mosaic of habitat patches. Each of these habitats predictably harbors certain bird species, and individual birds of each species use habitat not just within their own breeding territory, but also in neighboring habitat patches. So the spacial arrangement of habitat patches, as well as the quality of the habitats, is important to birds.
Because landscape-level management crosses political and economic boundaries, the plans call for public, private, and intergovernmental cooperation. Indeed, Partners in Flight is a model of partnerships for conservation. Participants include more than 15 federal agencies, over 60 state and provincial agencies, 16 companies representing the forest products industry, and more than 30 private conservation groups.
There is one more important partner: you. As someone concerned about birds and their habitat, you can make a big difference. This booklet explains exactly how you can become involved in Partners in Flight — because every activity descried will lead toward migratory bird conservation.
Many Partners in Flight contacts are listed on page 32. For an even more complete list of contacts, write for a copy of the Partners in Flight newsletter (ordering information is on the inside back cover). The newsletter will also keep you up to date on all Partners in Flight activities.