Non-monophyly and deep genetic differentiation across low-elevation barriers in a Neotropical montane bird (Basileuterus tristriatus; Aves: Parulidae).

Most widespread birds of Neotropical cloud forests exhibit phenotypic variation that is partitioned geographically suggesting allopatric divergence, but little is known about the extent to which such phenotypic differentiation is consistent with genetic variation. We studied geographic patterns of genetic differentiation in the Three-striped Warbler (Basileuterus tristriatus), a polytypic and widespread understory bird of the foothills and mid-elevation zone of the tropical Andes and adjacent mountains of Central and South America. We sequenced mitochondrial DNA for 196 samples covering the entire range of B. tristriatus, as well as 22 samples of its putative closest relatives: the Three-banded (B. trifasciatus) and Santa Marta (B. basilicus) warblers. We found deep genetic structure across the range of B. tristriatus, which consisted of ten major clades including B. trifasciatus, a species that was nested within B. tristriatus. In contrast, B. basilicus was not closely related to B. tristriatus but part of a clade of Myiothlypis warblers. Geographic boundaries among clades were clearly related to lowland gaps separating subspecies groups. The subspecies melanotis of the mountains of Central America was sister to a large clade including B. t. tacarcunae, and the rest of South American clades, including B. trifasciatus. Five clades are found in the northern Andes, where no signs of gene flow were found across barriers such as the Táchira Depression or the Magdalena valley. Our study highlights the importance of valleys in promoting and maintaining divergence in a lower montane forest bird. The substantial genetic and phenotypic differentiation, and the paraphyly uncovered in B. tristriatus, may call for revising its species boundaries.

How to deal with ground truthing affected by human-induced habitat change?: Identifying high-quality habitats for the Critically Endangered Red Siskin.

Species distribution models (SDM) can be valuable for identifying key habitats for conservation management of threatened taxa, but anthropogenic habitat change can undermine SDM accuracy. We used data for the Red Siskin (Spinus cucullatus), a critically endangered bird and ground truthing to examine anthropogenic habitat change as a source of SDM inaccuracy. We aimed to estimate: (1) the Red Siskin's historic distribution in Venezuela; (2) the portion of this historic distribution lost to vegetation degradation; and (3) the location of key habitats or areas with both, a high probability of historic occurrence and a low probability of vegetation degradation. We ground-truthed 191 locations and used expert opinion as well as landscape characteristics to classify species' habitat suitability as excellent, good, acceptable, or poor. We fit a Random Forest model (RF) and Enhanced Vegetation Index (EVI) time series to evaluate the accuracy and precision of the expert categorization of habitat suitability. We estimated the probability of historic occurrence by fitting a MaxLike model using 88 presence records (1960-2013) and data on forest cover and aridity index. Of the entire study area, 23% (20,696 km2) had a historic probability of Red Siskin occurrence over 0.743. Furthermore, 85% of ground-truthed locations had substantial reductions in mean EVI, resulting in key habitats totaling just 976 km2, in small blocks in the western and central regions. Decline in Area of Occupancy over 15 years was between 40% and 95%, corresponding to an extinction risk category between Vulnerable and Critically Endangered. Relating key habitats with other landscape features revealed significant risks and opportunities for proposed conservation interventions, including the fact that ongoing vegetation degradation could limit the establishment of reintroduced populations in eastern areas, while the conservation of remaining key habitats on private lands could be improved with biodiversity-friendly agri- and silviculture programs.