Population dynamics and conservation of Snail Kites in Florida: The importance of spatial and temporal scale

It has been suggested that the primary regulatory factor of Snail Kite (Rostrhamus sociabilis) populations in Florida is periodic drought. Consequently, the need for drought refugia has been previously identified as essential to the viability of kites. However, rainfall patterns across Florida are quite variable and the spatial and temporal patterns of drought have been largely ignored. We suggest that the primary response of Snail Kites to local drying events is behavioral; birds simply move to a different location. Small localized drying events occur at a relatively high frequency, whereas widespread droughts that encompass the entire range of Snail Kites in Florida are relatively rare. The occurrence of simultaneous drying events also is inversely correlated with distance between wetlands, resulting in greater asynchrony of drying events at larger spatial scales. Consequently, a large spatial extent helps to ensure that some refugia are available during most droughts. This enables individuals to escape the effects of droughts by moving. Several management recommendations have focused on maintaining continuous inundation of wetland habitats; however, the lack of periodic drying can detrimentally affect the kites' nesting and foraging habitat. We suggest that ensuring adequate refugia from drought can, and should, be accomplished by maintaining suitable habitat across a large enough area (including habitats in several different watersheds) to include climatic variability, rather than by prolonging local inundation. A broad spatial extent enables areas to incur periodic drying (necessary for plant communities) on a rotational basis through climatic variability. Monitoring also must occur over time periods long enough to detect not only the short-term response of birds to a given drying event, but also the long-term response of the habitat to water management regimes.