The story is one of expanding protection, moving from the Land and Water Conservation Fund Act's recognition of species threatened with extinction, through the protection of migratory birds, to the first federal statutes to protect endangered species-the Endangered Species Preservation Act (Act of October 15, 1966a), the Endangered Species Conservation Act (Act of December 5, 1969), and the Endangered Species Act itself in 1973. In this progression, federallaw has moved from protection of only fish and game to include nearly all at-risk plants and animals.

The enactment of the ESA in 1973 was not the end of the story, however. The act has been amended several times over the past thirty years and administrative actions have also modified its on-the-ground application. The original ESA embodied a top-down regulatory approach but the subsequent amendments have increased incentives that would encourage private landowners, government agencies, and other organizations to collaborate in recovery efforts for endangered species.

This chapter presents a graphical summary encapsulating thirty years of species protection and restoration under the ESA. The summary reveals both gains and losses. For some species, such as the Aleutian Canada goose (Branta canadensis leucopareia), the process worked as it was meant to, reversing decline and restoring populations to healthy levels (USFWS 2001a); for others, such as the dusky seaside sparrow (Ammodramus maritimus nigrescens), the process failed, and despite being listed the species continued to spiral toward eventual extinction (USFWS 1983; Walters 1992).

What follows is an assessment of the state of species protection as it has evolved under the ESA. This includes the taxonomie and demographie distribution of listed species, and the number of critical habitat designations. We also examine newer legal tools for conserving habitat on private land (such as habitat conservation plans), various measures of the act's success, and funding levels for species protection.

A certain humility, and a sense of urgency seem indicated .... One might analogize the case to one in which one copy of all the books ever printed were gathered together in one huge building. The position in which we find ourselves today is that of custodians of this building, and our choice is between exercising our responsibilities and ignoring them. If these theoretical custodians were to permit a madman to enter, build a bonfire and throw in at random any volume he selected, one might with justification suggest that others be found, or at least that they be censored and told to be more careful in the future. So it is with mankind. Like it or not, we are our brothers' keepers, and we are also keepers of the rest of the house. (U.S. Congress 1973,4-5)

Species conservation was already a difficult challenge in 1973. The human population of the United States had inereased from less than 4 million in the first census of 1790 to roughly 212 million by 1973 (Census Bureau 2000). This increase was accompanied by even more dramatic increases in per capita consumption of resources. The combination of population growth and increased consumption has driven a precipitous loss of nonhuman species that continues today: more than five hundred species formerly found in the United States are presumed to be extinct and an additional 47 percent of the species unique to this country are at risk (Master et al. 2000).

There are two key steps to determining critical habitat. The first is to characterize habitat requirements of a species based on its ecology and life history. Ideally, this is achieved by identif)ring variables that contribute to presence, density, and demography in different landscapes. The end product is a set of quantitative, functional relationships that predict presence or abundance. When sufficient data are lacking, descriptive habitat preferences based on known occurrences of the species are used to identify habitat requirements and elicit structured opinions from experts.

The second step is to evaluate how different amounts and configurations of habitat affect survival or recovery of the species. In making this determination, different scenarios for the amount and configuration of habitat under protection, and/or characteristics of the population inhabiting that area, are compared to each other and to a criterion, a threshold, or a critical level that embodies an acceptable risk of decline or loss. Again, when sufficient data are lacking, expert opinion can be used, cautiously, to evaluate risks of different scenarios for protecting critical habitat.

The Endangered Species Act mandates designating critical habitat based on the best available scientific data (Ruckelshaus and Darm, this volume). Data availability differs by species, which in turn affects the approach used for determining suitable and critical habitats (Karl et al. 2002; Scott et al. 2002). Models are the primary means of assessing habitat relationships and predicting consequences of habitat change (Wiens 2002). Ideally, sufficient data are needed to effectively determine if the designated habitat would support a viable population. However, often we cannot wait for these data to be collected. As Ruckelshaus and Darm (this volume) point out, logistics of model selection and development for determining critical habitat can be daunting.

In this chapter, we discuss a hierarchical approach to predicting species occurrence and designating critical habitat appropriate for the type and amount of data available to managers.

How the Endangered Species Act (ESA) should treat hybrids has been a topic of intense debate since its passage in 1973 (see box 12.1). The word "hybrid" does not occur in the definition of "species" in the ESA (sec. 3) nor are hybrids considered anywhere in the act. In fact, hybrids are not considered in endangered species legislation of any other nation (Haig, unpublished data) with the exception of the Biodiversity Act recently adopted by the Republic of South Africa (Republic of South Africa Act No. 8, 2004). In this chapter, we review the history of discussions related to listing hybrids under the Endangered Species Act, outline current legislation that may particularly address this issue, and explore new approaches to resolving this debate.

Management of the refuge system has changed significantly since the presidency of Teddy Roosevelt, evolving from the creation of "inviolate sanctuar[ies]" (Act ofFebruary 18, 1929, sec. 715d) through aperiod in which conservation of wildlife and natural communities was balanced with public uses, often to the detriment of conservation (Curtin 1993), to the current period in which the refuge system is to be managed to protect biological integrity, diversity, and environmental health, the management mandates enacted in the National Wildlife Refuge System Improvement Act of 1997 (Act ofOctober 9, 1997; Gergely et al. 2000).

This chapter describes the role the National Wildlife Refuge System plays in conserving species listed under the ESA, identifies factors that limit the refuge system's effectiveness in achieving that objective, and identifies opportunities to increase imperiled species conservation within the refuge system.

As described in The Endangered Species Act at 30: Renewing the Conservation Promise, the act has proven remarkably durable in spite of nearly continuous political assaults and legal and scientific challenges (Goble et al. 2006). The contributing authors to that volume describe a variety of factors responsible for the act's endurance. Public support for species conservation has remained strong, especially for high-visibility species such as the bald eagle (Haliaeetus leucocephalus) and grizzly bear (Ursus arctos horribilis) but also for less-charismatic taxa. The act has been championed by environmental groups in part for its power to control development, a role supported by a majority of the American public (Czech and Krausman 1997). Reforms have also been important to the act's continuance. In particular, implementation has evolved over the years from an absolute prohibition on take of endangered species to a more flexible permitting system, thereby defusing potentially explosive conservation conflicts on private lands. The act has also catalyzed administrative and legal reforms at all levels of government that have led to positive changes in natural resource management in rural areas and in urban open space planning.