Predicting patch occupancy in fragmented landscapes at the rangewide scale for an endangered species: an example of an American warbler

Abstract

AIM: Our objective was to identify the distribution of the endangered golden-cheeked warbler (Setophaga chrysoparia) in fragmented oak-juniper woodlands by applying a geoadditive semiparametric occupancy model to better assist decision-makers in identifying suitable habitat across the species breeding range on which conservation or mitigation activities can be focused and thus prioritize management and conservation planning. LOCATION: Texas, USA. METHODS: We used repeated double-observer detection/non-detection surveys of randomly selected (n = 287) patches of potential habitat to evaluate warbler patch-scale presence across the species breeding range. We used a geoadditive semiparametric occupancy model with remotely sensed habitat metrics (patch size and landscape composition) to predict patch-scale occupancy of golden-cheeked warblers in the fragmented oak-juniper woodlands of central Texas, USA. RESULTS: Our spatially explicit model indicated that golden-cheeked warbler patch occupancy declined from south to north within the breeding range concomitant with reductions in the availability of large habitat patches. We found that 59% of woodland patches, primarily in the northern and central portions of the warbler's range, were predicted to have occupancy probabilities ≤0.10 with only 3% of patches predicted to have occupancy probabilities >0.90. Our model exhibited high prediction accuracy (area under curve = 0.91) when validated using independently collected warbler occurrence data. MAIN CONCLUSIONS: We have identified a distinct spatial occurrence gradient for golden-cheeked warblers as well as a relationship between two measurable landscape characteristics. Because habitat-occupancy relationships were key drivers of our model, our results can be used to identify potential areas where conservation actions supporting habitat mitigation can occur and identify areas where conservation of future potential habitat is possible. Additionally, our results can be used to focus resources on maintenance and creation of patches that are more likely to harbour viable local warbler populations.

Figure 1

Distribution (a) of woodland patches (n = 63,616) and posterior predicted spatial process (b) centred at the regression means for the geoadditive semiparametric model containing patch size, landscape composition, X and Y location, and the interaction between patch size and landscape composition within the 35-county breeding range of the golden-cheeked warbler in Texas, USA.

Figure 2

Estimated patch-specific occupancy probability for the golden-cheeked warbler in the 35-county breeding range in Texas, USA.

Figure 3

Visualization of classification accuracy (area under curve =0.91) for patch-scale surveys (n = 143) relative to predictions from the semiparametric model showing (a) the ROC curve and (b) model sensitivity-specificity trade-off.