1994 Proceedings
North American Conference on Savannas and Barrens

The objective of this talk is to provide an overview of the birds and bird communities associated with savannas and savanna-like woodlands. The scope of this review is North America, but emphasis will be placed on oak savannas. A central question will be: What types of birds are associated with savannas and is the welfare of these species truly dependent on the availability of savanna habitat? Similarly, are savanna bird communities discrete or do they represent a mix of grassland, shrub, and woodland species? Analyses for these questions will include a review of savanna birds with respect to taxonomic affiliation, life-history traits, and geographic distribution. The dependency of birds on savannas will be assessed by reviewing the conservation status of savanna birds and examining the breadth of habitat associations for selected species. The role of fire or periodic disturbance will be discussed in detail. Research needs and unanswered management questions will also be reviewed with suggestions for future studies.

RESULTS AND DISCUSSION

Over 100 species associated with savannas and open woodlands have been identified. These species comprise a taxonomically diverse sample that includes 10 Orders and 23 Families. The sample ranges from hawks, owls, and hummingbirds to several families of songbirds (Order Passeriformes). In general, the diversity of this group is greater in western North America where species are associated with deciduous (oak), coniferous, and mixed forests. The range of types of ecological adaptations related to foraging and nesting also is high. Moreover, permanent residents, short distance migrants, and several species of neotropical migrants are represented in the group.

Categorizing these species as savanna-dependent is not straight-forward. The ambiguity stems in large part from diverse definitions of savannas. For example, if an oak savanna is defined as an area with 10-80% canopy cover, then many birds are characteristic of this forest type. More parochial definitions decrease the number of species that are found in only in savannas. Regardless, several birds appear highly dependent on the open woodlands that fit most definitions of savanna.

In the Midwest, the conservation status of birds associated with savannas and open woodlands is not promising. For example, from 1966-1991, Red-headed Woodpeckers (Melanerpes erythrocephalus) have been decreasing at a rate of nearly 2%/year within the physiographic region known as Till Plains (see Robbins et al. 1987) which includes much of Illinois, Indiana, and Ohio. The rate of decrease was especially steep in the 1980s. Whereas decreases such as these are typical for savanna birds in the Midwest, most species exhibit considerable geographic variation in the direction and magnitude of changes in their abundances.

The direct effect of fire and periodic disturbance on local abundance of savanna or open forest birds is unclear. In western forests, such as the pine forests of the southwest, it is apparent that cool fires can change species composition and relative abundances within bird communities. In midwestern oak forests, however, less information is available and the effects of fire less understood.

Research needs for savanna birds are many, and in certain geographic areas, urgent. In the midwest, for example, the effects of fire and the accompanying changes in forest structure may have positive as well as negative effects on the reproductive success of songbirds. A critical question concerns the role that birds play as seed dispersers or pollinators in the perpetuation and structure of savannas. Co-evolutionary links between birds and oaks are well known, but the importance of these associations in the context of management and conservation requires further study. The question of scale is also important: how large do savannas have to be for ecosystem-level properties to emerge?

LITERATURE CITED

Robbins, C. S., D. Bystrak, and P. H. Geissler. 1987. The breeding bird survey: its first 15 years, 1965-1979. United State Fish and Wildlife Service Resource Publication, Number 157.