Data from: Wintering grounds, population size and evolutionary history of a cryptic passerine species from isotopic and genetic data

Cryptic species pose a particular challenge to biologists in the context
of life history investigations because of the difficulty in their field
discrimination. Additionally, there is normally a lag in their widespread
acceptance by the scientific community once they are formally recognised.
These two factors might constrain our ability to properly assess the
conservation status of the different species conforming a cryptic complex.
In this study, we analysed isotopic and genetic data to shed light into
the still unclear wintering grounds, population size and evolutionary
history of the Iberian chiffchaff (Phylloscopus ibericus), a species
included within the Common chiffchaff (Phylloscopus collybita) until two
decades ago due to their phenotypic similarity. We used molecular methods
to identify spring-migrating Phylloscopus species captured in northern
Iberia, and by comparing the Hydrogen isotopic ratios of their claw tips
(δ2Hc; which would reflect the signatures of their wintering grounds), we
detected that δ2Hc values of Iberian chiffchaffs were similar to Willow
warblers (Phylloscopus trochilus; a renowned trans-Saharan migrant), and
higher than Common chiffchaffs (mostly a pre-Saharan migrant). These
results strongly support the idea that Iberian chiffchaffs winter in
tropical Africa. We additionally reconstructed the phylogeny and
evolutionary history of the Iberian chiffchaff’s clade using mitochondrial
and nuclear markers. Our results revealed relatively high values of
nucleotide diversity (and, hence, high Ne) for the species that were
greater than the values of the Common/Iberian most recent common ancestor.
This suggests that the Iberian chiffchaff did not experience strong
bottlenecks after diverging from the Common chiffchaff approximately one
million years ago. Ultimately, our study provides another illustrative
example of how isotopic and genetic analysis tools can help to enhance our
understanding of avian ecology and evolution.