CONTENTS Introduction ………………………………………………………………………………………………………………………….. 409 Methodological Approach………………………………………………………………………………………………………. 411 Results …………………………………………………………………………………………………………………………………. 411Benefits of Using Waterbirds as Indicators in Estuarine Systems………………………………………. 411 Pitfalls of Using Waterbirds as Indicators in Estuarine Systems………………………………………… 413 Case Study 1: Long-Term Monitoring of Nesting Wading-Bird Populations inEverglades/Florida Bay Ecosystem …………………………………………………………………….. 414 Case Study 2: Using Wading Birds to Monitor Estuarine Habitat Restoration ……………………. 415Conclusions ………………………………………………………………………………………………………………………….. 417 Acknowledgments…………………………………………………………………………………………………………………. 417 References ……………………………………………………………………………………………………………………………. 420Estuarine resource managers need reliable information about the state of the ecosystem and how it is changing over time due to natural or anthropogenic perturbations. Animal indicators are often used for this purpose, as they are highly visible, reactive, easily measured, and of intuitive value to the wider public (Morrison, 1986; Landres et al., 1988; Kushlan, 1993; Frederick and Ogden, 2003). Various attributes of animal populations or communities (e.g., population size, reproductive success, habitat use, species composition) may provide information about other ecosystem attributes that are more difficult to measure (e.g., trophic structure, hydrology, contamination). When one or a small number of species are used to provide information about other members or attributes of an ecosystem, they are referred to as “surrogate species” (Caro and O’Doherty, 1999). The role of surrogate species may fall into one of the following categories: health indicator, biodiversity indicator, umbrella species, keystone species, or flagship species. There is much literature on the use of surrogate species; Table 26.1 provides definitions of terms commonly used when referring to vertebrate indicator species, and Table 26.2 lists attributes that must be considered when choosing an appropriate indicator species within a specific ecological system.