A new study showed that the West African Royal Tern is not closely related to the American Royal Tern and thus it should be split as a ‘new’ species.
The Royal Tern is traditionally known to comprise two geographically separated subspecies: the nominate Thalasseus maximus maximus in the Americas (distributed from the USA south to Patagonia, Argentina) and Thalasseus maximus albididorsalis in coastal West Africa.
The birds of the two subspecies are morphologically near-identical except for some differences in bill morphology (redder and deeper in American birds) and biometric variations in mass and wing (the American Royal Tern is on average slightly bigger).
A new research, published in the Biological Journal of the Linnean Society, analysed the DNA from birds of the two populations to show if these are related to each other or not (to see if they indeed belong to the same species as currently recognised or not). Surprisingly, the result showed that the two populations are not each other’s closest relatives but two distinct species. The study thus proposed the split of the Royal Tern, as it’s currently recognised, into two species by elevating the West African Royal Tern to the species rank: Thalasseus albididorsalis.
This is not the only surprise from the research. The study showed also that the West African Royal Tern is actually more closely related to the Lesser Crested Tern (Thalasseus bengalensis) than to the American Royal Tern. The Lesser Crested Tern, although similar in structure, it’s smaller and with a yellower bill.
The study authors declared that “the discovery could have immediate conservation consequences for the West African Royal Tern as its population in The Gambia and Senegal is threatened by the eroding of its breeding grounds due to climate change and human activity”.
Collinson, J. M., Dufour, P., Hamza, A. A., Lawrie, Y., Elliott, M., Barlow, C. & Crochet, P.-A. 2017. When morphology is not reflected by molecular phylogeny: the case of three ‘orange-billed terns’ Thalasseus maximus, Thalasseus bergii and Thalasseus bengalensis (Charadriiformes: Laridae). Biological Journal of the Linnean Society 121: 439-445. doi: 10.1093/biolinnean/blw049
Updates (Dec. 2018):
- The full text is now freely available at the publisher’s website.
- The split is already under consideration by the ‘IOC World Bird List’. They suggested the English name ‘West African Crested Tern’. It makes sense because these are more related to the Lesser Crested Tern than to the American Royal Tern.
The following photo was taken from this publication:
Shoch, D.T. & Howell, S.N.G. 2013. Occurrence and identification of vagrant “orange-billed terns” in eastern North America. North American Birds 67: 188-209.