Studies in Avian Biology No. 19:2-26, 1999. CONSERVATION OF GRASSLAND BIRDS IN THE WESTERN HEMISPHERE PETER D. VICKERY, PABLO L. TUBARO, Jo& MARIA CARDOSO DA SILVA, BRUCE G. PETERJOHN,JAMESR. HERKERT, AND ROBERTOB. CAVALCANTI “The sweeping vista of the worlds’ natural grasslands-be they steppes, savannas, range- lands, punas or prairies-occupy nearly seven billion hectares; over half of the earths’ land surface. Add to that figure the vast area converted to habitats of low intensity agriculture and grasslands become second only to the oceans in terms of direct dominance of the planets’ ecosystems. They govern, directly, the livelihoods of hundreds of millions of neoole.” -C. Imboden (i988:vii). Research on and interest in grassland birds usual adaptations, such as large body size and have increased considerably in the past 20 yr. cursorial habits, have evolved in grassland birds. There are several reasons for this heightened in- And the ability to readily observe many behav- terest. Foremost, it is clear that populations of iors makes these species ideal for research (e.g., many grassland birds have declined sharply Wheelwright and Mauck 1998). throughout the Western Hemisphere (e.g., Buch- er and Nores 1988, Cavalcanti 1988, Fjeldsg GRASSLAND HABITATS IN THE 1988, McNicholl 1988, Knopf 1994, Peterjohn WESTERN HEMISPHERE and Sauer 1999). In North America, populations of at least 13 species of grassland birds declined Grassland ecosystems occur in a variety of significantly between 1966 and 1995 (Peterjohn forms and are affected by geology, geography, and Sauer 1999). And as a group, North Amer- moisture, soil type, elevation, climate, and dis- ican grassland birds have experienced “steeper, turbance regime (Kantrud 1981, Vickery et al. more consistent, and more geographically wide- in press). In this volume, we define a grassland spread declines than any other behavioral or habitat as any extensive area that is dominated ecological guild,” largely because of habitat loss by more than 50% grass (Poaceae) or sedge (Cy- and degradation (Knopf 1994:251). Similar de- peraceae) cover and that generally has few scat- clines are also occurring in South America, tered shrubs (< 4 m high) and trees. We have where species such as Pampas Meadowlark generally excluded habitats that are dominated (StumelZu dejilippii; Tubaro and Gabelli 1999), by more than 50% shrub cover, such as chap- Saffron-cowled Blackbird (Agelaius jlavus; Fra- arral. ga et al. 1998), and Sporophila seedeaters (Silva In addition to such obvious grassland habitats 1999) have declined in the past 20 yr. Indeed, as tallgrass and shortgrass prairies, pampas, and Collar et al. (1992:35) describe the “near-total Patagonian grassland, we include sedge-domi- destruction of open grasslands in south-east Bra- nated tundra, alpine ridges and barrens, puna, zil . and in the vast central planalto . as one and paramo. We also include the longleaf pine of the great ecological catastrophes in South (Pinus palustris) ecosystems of the southeastern America.” United States and the pine (Pinus spp.) forests Another reason for the increased research in- and savannas of Mexico because it is clear that terest in grassland birds is changing agricultural several species of birds, among them Bachmans’ practices. For example, the U.S. Department of Sparrow (Aimophih aestivalis), Striped Sparrow Agricultures’ Conservation Reserve Program (Oriturus superciliosus), and Sierra Madre Spar- (CRP), which has taken more than 14 million ha row (Xenospiza baileyi), have adapted to the of cropland out of production under IO-yr con- graminoid ground cover beneath these forests. tracts, has made it possible to examine regional, Although these ecosystems are generally viewed and even continental, effects of changing land- as forests, the above species appear to occupy scapes on grassland birds (e.g., Lauber 1991, them as a form of grassland, not forest, habitat. Reynolds et al. 1994, Herkert 1998). Addition- Bachmans’ Sparrow, for example, continues to ally, the CRP has provided excellent opportu- occupy clear-cut glades after forest removal nities to study bird colonization, habitat use, and (Dunning 1993). In North America, we also in- nesting success in different regions and under clude as grassland wet-mesic upland habitats different ecological conditions. Finally, grass- where the soil is often saturated but not inun- land birds are also fascinating from ecological dated for long periods; we do not include fresh- and evolutionary perspectives. Distinctive or un- water, brackish, and saltwater wetlands where 2 INTRODUCTION-Vickery et al. 3 FIGURE 1. Distribution of major grassland ecosystems in North America and Mexico prior to European settlement.Alpine zonesabove tree line have not been depicted. This map was adapted and modified from two primary sources, Risser et al. 1981 and Environment Canada 1998. standing water is present for long periods, how- grasslands in southern Argentina and Chile and ever. pampas in eastern Argentina, Uruguay, and Native grasslands in the Western Hemisphere southernmost Brazil. Brushier savanna grass- extend from high-arctic sedge meadows in the lands include chaco, cerrado (particularly “cam- tundra of North America to pampas and Pata- po limpo” and “camp0 sujo” in central Brazil), gonian grasslands in southern South America Beni savannas, Amazonian savannas, Guianan (Figs. 1 and 2). In North America, a mosaic of savannas, and espinal. Native South American tundra/barrens habitats forms the northernmost grasslands also include such mesic ecosystems grassland component. In the temperate region, as the llanos of Venezuela and Colombia and the the most extensive grasslands historically in- Pantanal of southwestern Brazil, where seasonal cluded the shortgrass prairie and southern mixed flooding for several months each year is fol- prairie of the western Great Plains and the tall- lowed by pronounced dry seasons when most grass prairie and northern mixed prairie of the surface water disappears (Soriano 1991, Diner- midwestem United States and Canada (Knopf stein et al. 1995, Stotz et al. 1996; Fig. 2). 1988; Fig. 1). Although they were less exten- sive, bunchgrass shrubsteppe (including palouse DEFINING GRASSLAND BIRDS prairie) and California grasslands in the west, “The difficulty in defining grassland species desert grasslands in the southern United States results from the fact that grassland itself is not and Mexico, and palmetto (Serenoa repens) dry easy to define precisely. How small may a prairie prairie in Florida were historically all major be before it is a mere opening? Where does grass- grassland types in North America (Fig. 1). land stop and very open woodland begin? In South America, major native grassland How much sage is required before grassland be- comes some form of desert scmb?” ecosystems include high-altitude paramo and -R. M. Mengel (1970:283) puna grasslands (listed as Andean grasslands; Fig. 2) and mid-elevation monte grasslands (Fig. Few would argue that species such as Lesser 2). Low-elevation grasslands include Patagonian Rhea (Rhea pennatu), Spragues’ Pipit (Anthus STUDIES IN AVIAN BIOLOGY NO. 19 FIGURE 2. Distribution of major grassland ecosystems in South America prior to European settlement. Puna and paramo grasslands have been classified as Andean grasslands. This map was adapted and modified from two primary sources, Cabrera and Willink 1980 and Dinerstein et al. 1995. spragueii), McCowns’ Longspur (Calcarius alized that grasslands extend along a moisture mccownii), and Wedge-tailed Grass-Finch (Em- gradient-from arid prairies to wet meadows berizoides herbicola) are completely adapted to and marshes-and that defining the limits of this grassland habitats and should be considered gradient in relation to the birds that occupy these grassland specialists. Classification seems obvi- habitats can be, and is, somewhat arbitrary. In ous in these cases, as all of these species use addition, he noted that grassland ecosystems fre- grassland habitat for all their life-history needs. quently intergrade with forested and other hab- But for many other species, determining which itat types, making it difficult to define the limits ones should be considered grassland birds quick- of some grassland types. In the Cerrado of cen- ly becomes complicated and invariably some- tral Brazil, for example, “camp0 limpo,” or what subjective. Are Western Kingbirds (Tyrun- open grasslands, are interspersed with “camp0 nus verticalis), Red-winged Blackbirds (Age- sujo,” or grasslands with scattered trees and Zuius phoeniceus), and Blue-black Grassquits shrubs; and campo sujo may blend into “cerra- (Volutinia jucarinu), for instance, also grassland dHo,” which is even more densely forested (Ei- birds? What about jaegers (Stercorurius spp.)? ten 1972). In the United States, tallgrass prairie Although each of the three jaeger species spends intergrades into oak (Quercus) savannas in the 9 mo a year on the open ocean, all require open Midwest, and in the Southeast the dry palmetto tundra for nesting. And nest success in Pomarine prairies of central Florida merge into longleaf Jaegers (S. pomarinus), as in Snowy Owls (Nyc- pine savannas, called “flatwoods.” Consequent- tea scandiucu), depends strongly on collared ly, it is often difficult to delineate where grass- lemming (Dicrostonyx torquatus) populations land ends and forest begins. Furthermore, dif- (Pitelka et al. 1955). ferent species of birds may respond differently Mengel (1970) recognized the difficulties in-