Both species are expanding their range and hybridizing in the periphery.
In March 2018 I received a message from Alexander Worm. He had just completed his Master thesis and informed me that “Scissor-tailed Flycatcher (Tyrannus forficatus) and the Western Kingbird (T. verticalis) are able to hybridize and produce viable offspring.” Recently, the genetic analyses behind this statement were published in the journal Ibis. Let’s have a look at the results!
The Scissor-tailed Flycatcher and the Western Kingbird are widely distributed across North America and their ranges overlap in several regions. Some putative hybrids have been reported in Texas, Oklahoma, Colorado and California. To see if hybrids actually occur and if they are fertile, Alexander Worm and his colleagues collected samples from a contact zone combined with several museum specimens, culminating in a final data set of 84 individuals.
Mosaic Hybrid Zone
Based on eight microsatellites and one mitochondrial marker, the researchers found convincing evidence for gene flow between these species. The analyses did not uncover first generation hybrids, but there were several backcrosses (in both directions).
The system can be regarded as a mosaic hybrid zone where two sympatric species interbreed in a patchy distribution. Moreover, both species are expanding their range (mostly it is only one species expanding into the range of another) and hybridizing at the periphery. This unusual situation offers many opportunities for further research.
Worm, A. J., Roeder, D. V., Husak, M. S., Fluker, B. L., & Boves, T. J. (2019). Characterizing patterns of introgressive hybridization between two species of Tyrannus following concurrent range expansion. Ibis, 161(4), 770-780.
This paper has been added to the Tyrannidae page.