Monitoring, modeling, and management: why base avian management on vital rates and how should it be done?
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In this paper we argue that effective management of landbirds should be based on assessing and monitoring their vital rates (primary demographic parameters) as well as population trends. This is because environmental stressors and management actions affect vital rates directly and usually without time lags, and because monitoring vital rates provides a) information on the stage of the life cycle where population change is being effected, b) a good measure of the health and viability of populations, and c) a clear index of habitat quality. We suggest that modeling lambda (λ, the rate of change in population size) as a function of vital rates provides useful information on potential responses of populations to management actions, but because of covariation among vital rates and density dependence, the predicted responses may not occur. We suggest that modeling spatial variation in vital rates as a function of spatial variation in lambda provides added insight into the proximate demographic “cause(s)” of population change and permits identification of “deficient” vital rates. We illustrate this at two spatial scales with analyses of BBS and MAPS data on Gray Catbird and MAPS data on five other species. We then suggest that the formulation of effective avian management actions should be based on modeling vital rates as functions of habitat characteristics and, because of substantial amounts of annual variation in vital rates, as functions of weather and climate variables. We illustrate these concepts with threshold relationships between productivity and mean forest/woodland patch size in four forest-inhabiting species; relationships between precipitation and annual productivity indices for two landbird species in Texas; and relationships between reproductive indices in Pacific Northwest landbirds and both the El Niño/Southern Oscillation and the North Atlantic Oscillation. These latter results indicate that annual variation in the productivity of Neotropical wintering birds may be driven more by events and conditions on their wintering grounds and migration routes than on their breeding grounds. Finally, we suggest that, because avian management should be based on vital rates as well as population trends, effectiveness monitoring must include the monitoring of the targeted vital rates along with monitoring the appropriate population trends.