|Population and Habitat
Assessment: Monitoring Bird Populations over Large Areas
John R. Sauer1 and Robert J. Cooper2
Monitoring provides essential information about status and change in bird populations. For Neotropical Migrant Birds (NTMBs), the North American Breeding Bird Survey (BBS) has been particularly influential in documenting regional population change (e.g., Robbins et al. 1989), and often is cited as justification for management actions. However, as with most bird surveys, the design of the BBS, and the geographic scale of the information, often limits its use either in evaluating the response of bird populations to management, or in identifying causes of population change.
In the study of NTMB population change, limitations of the landscape-scale BBS data are all too apparent. Adequately documenting patterns of change in populations using survey data is often difficult due to controversy about methods and limitations of the count-based survey design (e.g., Böhning-Gaese et al. 1993, James et al. 1995, Sauer et al. 1996, Link and Sauer 1997). Also, analyses of population change from the BBS often end with frustrating statements about the surveys inability to establish causes of population change (e.g., Peterjohn et al. 1995), clearly emphasizing the lack of linkages of the data collection to management. Many monitoring programs (1) are too poorly designed to allow us to adequately evaluate population change; (2) provide data collected at the wrong scale for appropriate management; and (3) are difficult to interpret unless their data are collected in a specific management context, for example, in conjunction with an experimental design or adaptive management. Developing additional monitoring programs, and fitting BBS information into management contexts, will improve our ability to understand bird population dynamics. The collection of monitoring papers in this volume outline some innovative approaches to gathering information using designs and scales appropriate for management.
Design of surveys, and connecting survey design to management objectives, is the primary concern of several of the papers. Johnson discusses some of the challenges associated with developing a local or regional monitoring program. Often, if objectives are not well defined before the survey is initiated, the results will not be useful for any objective. Methods need to be chosen appropriate to the stated objectives, and principles of experimental design must be followed if monitoring is to be used to assess the consequences of management activities. Nichols suggests that retrospective studies based on monitoring results often do not lead to reliable knowledge. Instead, monitoring is most useful when incorporated into experimentation or adaptive management, in that it then allows us to evaluate population responses to management actions. Often, management for birds involves habitat management, and Twedt and Loesch advocate habitat monitoring using Geographic Information Systems as an essential element of bird conservation planning. Evans and Rosenberg describe their efforts to develop acoustic monitoring programs, and document some initial successes of the procedure.
Scale-specific monitoring and integration of monitoring programs is addressed by several papers. Sauer uses information from the BBS to argue that monitoring data often do not interpolate from regional to local scales, and that management needs at each scale require scale-specific monitoring. Sauer, Hadidian, Droege, Handly, Williams, Swarth, Didden, and Huff describe a monitoring program for birds in urban environments of Washington, DC. Urban areas are generally not well monitored by the BBS, but data from these areas often play an important role in defining public and scientific perceptions of bird population change. Hamel, Brunswig, Dawson, and Staten review several case studies of monitoring at local and regional scales, documenting the benefits of several programs in the southeastern United States. Downes describes the Canadian Landbird Monitoring Strategy, which is designed to provide information on status and trends of bird populations for species and geographic scales of management interest. The Strategy extends beyond counting birds, to include monitoring demographic parameters such as survival and productivity, monitoring habitats along with count data from the BBS, and information transfer and educational activities associated with bird monitoring. Handel describes regional research and monitoring for landbirds in Alaska, with the goal of combining count data and demographic data to develop a comprehensive monitoring program within logistical and physical constraints imposed by the large area of interest and limited access by roads. A variety of research and management questions were specified, and monitoring at several geographic scales has been implemented to provide information to address the questions.
These papers indicate a clear advance in monitoring. Rather than simply documenting population change using methods with unknown sampling properties, the authors suggest that reliable information can be derived only from sampling with well defined goals, statistically valid sampling methods, and with a clear experimental or adaptive management context. They also express the need for scale-specific information, and information on demography rather than just counts of birds. Following these recommendations should result in clarification of the causes of population changes in landbird populations.
Wildlife Research Center
2 Warnell School of Forest Resources