Everglades hydrology influences population dynamics of wood storks in the southeastern U.S

Background/Question/Methods

Hydrological changes in the Florida Everglades and subsequent declines in habitat quality and prey availability has been linked to dramatic declines in Everglades wading bird abundance, including that of the wood stork (Mycteria americana).  Wood storks are tactile foragers, and as such require concentrated prey. This makes them extremely sensitive to hydrological changes in the Everglades and they are considered a key indicator species for evaluating restoration success. Models of wood stork response to hydrological changes in the Everglades are increasingly used to evaluate the potential benefits of alternate restoration scenarios. We used satellite telemetry to track the movements and breeding patterns of wood storks across the southeastern US. These data were then used to model habitat suitability in the Everglades in relation to a suite of hydrological and landscape variables. The resulting habitat suitability index (HSI) was then incorporated into a multi-state movement model to determine whether movements into and away from the Everglades were linked to habitat quality, and to model the resulting impacts on nesting and population dynamics. 

Results/Conclusions

Using satellite telemetry data from 2004-2011, we compared vegetation and daily hydrological characteristics at used and random locations in the Everglades using a proportional hazards model. When resulting HSI values were used as a covariate in a multistate state model to evaluate the probability of birds leaving the Everglades as a function of HSI, we found that movements into the Everglades appeared to occur seasonally independent of HSI, but that movements out of the Everglades were linked to low HSI values. These HSI-dependent transition probabilities were then incorporated into a demographic model to explore how increasing habitat quality in the Everglades influenced the persistence of birds during the nesting season. Preliminary results indicate that persistence increased with habitat suitability. Increasing HSI by 50% more than doubled the number of chicks produced in the Everglades and increased the size of the SE US population by roughly 8%, indicating that despite shifts in nesting away from the Everglades over the past 40 years, restoration should have positive effects on the population as a whole.