Studying processes acting on differentiated populations upon secondary contact, such as hybridization, is important to comprehensively understand how species are formed and maintained over time. However, avian speciation studies in the tropical Andes have largely focused on the role of topographic and ecological barriers promoting divergence in allopatry, seldom examining hybridization and introgression. We describe a hybrid zone involving 2 closely related Andean warblers (Parulidae), the Golden-fronted Redstart (Myioborus ornatus) and the Spectacled Redstart (Myioborus melanocephalus). Geographic ranges of these species abut near the Colombia-Ecuador border and many specimens from the region exhibit intermediate phenotypes, but a formal description of phenotypic variation in the contact zone were heretofore lacking. We collected specimens across a transect encompassing the area where ranges abut and areas where only “pure” parental phenotypes of M. ornatus chrysops and M. melanocephalus ruficoronatus occur. We described variation in plumage traits including patterns of head and ventral coloration and tail markings based on 321 specimens. To describe genetic variation in the contact zone and over a broader phylogeographic context, we used sequences of the mitochondrial ND2 gene for 219 individuals across the transect and the entire range of both species, including all subspecies, from Venezuela to Bolivia. We documented a hybrid zone ~200 km wide based on head coloration, where intermediate plumage phenotypes are most common and “pure” forms do not overlap geographically, consistent with extensive hybridization. Across the range of the M. ornatus–M. melanocephalus complex, mitochondrial genetic structure was shallow, with genetic breaks only coinciding clearly with one topographic feature. Such low genetic structure is striking given the high diversity in plumage phenotypes and current taxonomy of the group. Our phenotypic data suggest that barriers to hybridization are not strong, and allow us to postulate hypotheses to be tested using forthcoming genomic data.

The dataset was collected from museum specimens collected in our study and previously available in museum collections. Specimen information is on Supplementary Table 1 and Supplementary Table 2.

The head coloration data was obtained by using the scoring system described in the Table 1 of the paper. Was entered on Excel, and then processed on R. The data table included here was exported from R.

The underpart coloration data was obtained by using a reflectance spectrometer. Then, the colorimetric variables were calculated on R, using functions implemented in the package pavo. The data table included here was exported from R.

The tail coloration data was entered on Excel and then processed in R. Data table included here was exported from R.

- Additional specimen information is also available in Supplementary Table 1 and Supplementary Table 3.

- In all cases, “NA” refer to missing data.

- All data tables are in a tab delimited format (.txt) and can be directly imported in R without previous modifications.

- Detailed explanation of all data tables included in the repository is in the readme file.