Population dynamics and habitat conservation for the golden-cheeked warbler (Setophaga chrysoparia)
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Fundamental to species’ conservation and management is an understanding of the factors driving population dynamics. The objective of this dissertation is to update and extend our knowledge on population and habitat dynamics for the federally endangered golden-cheeked warbler (Setophaga chrysoparia). In order to achieve this, I carried out 4 interrelated multidisciplinary studies that used modern statistical and geospatial methodologies.
Habitat availability limits the distribution and abundance of wildlife species. Thus, for the first study I quantified the degree of change in range-wide warbler breeding habitat over the past decade using available GIS data and Landsat imagery. Here, I provided quantitative evidence for large-scale reduction in total warbler breeding habitat during the last decade, determining that warbler breeding habitat was removed and became more fragmented at uneven rates across the warbler’s breeding range. This information will assist researchers and managers in prioritizing breeding habitat conservation efforts for the species and provides a foundation for more realistic carrying-capacity scenarios when modeling warbler populations over time.
In my second study, I estimated more current, precise adult and juvenile male warbler apparent survival estimates and tested hypotheses about spatial and temporal variation in apparent survival by analyzing long-term warbler capture-resight data. This study did not provide evidence of site-specific variation in warbler apparent survival on the study area. Nor did it provide strong evidence for temporal association between warbler abundance and apparent survival. Although juvenile apparent survival did not differ greatly from previous estimates, the adult apparent survival estimate suggests previous warbler population models were overly optimistic with respect to adult survival.
After my first two studies, it was apparent that movement among habitat patches was essential for warbler persistence. Unfortunately, movement rates had not been previously estimated for the species. Therefore, for my third study I focused on warbler population dynamics at the local spatial scale using a new extension of integrated population models. This study provided quantitative evidence of the importance of immigration to stabilize local warbler populations, indicating warbler conservation and management programs need to be implemented at larger spatial scales to be effective. This study also demonstrates that by using limited data within integrated population models, biologists are able to monitor multiple key demographic parameters simultaneously to gauge the efficacy of strategies designed to maximize warbler viability in a changing landscape.
Finally, for my fourth study I refocused on warbler population and habitat dynamics at the range-wide scale. Specifically, I estimated habitat-transition probabilities across the warbler’s breeding range by combining National Land Cover Database classifications with multistate capture-recapture analyses. This enabled a determination of warbler viability into the next 50 years given the current conditions and an evaluation of whether protecting a greater amount of habitat at present day would increase the number of warblers that can be supported in the future. The estimated habitat-transition probabilities indicated habitat transitions are directional, whereby habitat is more likely to diminish than regenerate. The model results also indicated that population viability could be achieved under current conditions. However, there is considerable uncertainty associated with the population projections due to parametric uncertainty. Further, the model results suggested that increasing the amount of protected lands would have a substantial impact on terminal carrying capacities at the end of a 50-year simulation. This study highlights the importance of prioritizing the conservation of existing, large tracts of warbler breeding habitat due to the directional nature of habitat transitions and the positive outcome of protecting a greater amount of habitat on the future population.