The Atlas Long-legged Buzzard is more closely related to Common Buzzard than to Long-legged Buzzard according to a new study. The taxon cirtensis should be treated therefore as an allospecies of the Common Buzzard superspecies.
La Buse du Maghreb est une alloespèce de la Buse variable
Selon cette étude, la Buse du Maghreb (cirtensis) est en fait le résultat d’une hybridation entre la Buse féroce (Buteo rufinus) et la Buse variable (Buteo b. buteo et Buteo b. vulpinus). Bien que la délimitation génétique entre ces espèces n’est pas nette, l’étude a démontré toutefois que la Buse du Maghreb est plus apparentée avec la Buse variable qu’avec la Buse féroce. L’étude a donc suggéré que cirtensis soit considérée comme une alloespèce de la Buse variable. En d’autre terme, le nom scientifique de la Buse du Maghreb devrait être ‘Buteo (buteo) cirtensis’ au lieu de ‘Buteo rufinus cirtensis’.
[Les alloespèces sont des espèces à distribution allopatriques (géographiquement isolées) mais étroitement apparentées formant une super-espèce. Voir le concept de la spéciation allopatrique].
The Old World buzzards of the genus Buteo are relatively a young radiation and poorly differentiated genetically. However, they are well differentiated morphologically – both within and between the recognized species. Unfortunately, morphology does not necessarily reflect the true phylogenetic relationship between species as has been shown in many groups.
The current taxonomy and subspecies arrangements of the Common (Buteo buteo) and Long-legged Buzzards (Buteo rufinus), and especially the taxonomic treatment of the Atlas Long-legged Buzzard as a subspecies of the latter were considered unjustified by many experienced raptor specialists. For example, there are some anomalies in the geographical distribution of the different taxa. First, there are Common Buzzards in the Iberian Peninsula and the Canary Islands, but separated by the “Atlas Long-legged Buzzard” in Morocco. And second, the distribution ranges of the two subspecies of the Long-legged Buzzard as currently accepted are widely separated.
The genetic relationship between three buzzard species
Jowers and his coauthors, using different genetic markers, studied the relationship between three buzzard species: Upland Buzzard (Buteo hemilasius), Common Buzzard (buteo and vulpinus) and Long-legged Buzzard (rufinus and cirtensis). Their study has just been published in Molecular Phylogenetics and Evolution journal.
The mitochondrial (mtDNA) data showed that Upland Buzzard is clearly differentiated from the Common and Long-legged Buzzards. This species was considered as subspecies of Long-legged Buzzard in the past, and this study confirmed that the two are not the closest relatives to each other.
For the Long-legged Buzzard, the mtDNA analysis disagreed with the current taxonomy of the species: the nominate subspecies (rufinus) formed its own separate group, while the Atlas Long-legged Buzzard (cirtensis) clustered with Common Buzzard (buteo and vulpinus) in a third group. The hybridisation between cirtensis and buteo might have been the cause of this introgression (gene flow between the two taxa).
The documentation of this hybridisation in the Strait of Sicily and the Strait of Gibraltar is recent, but the phenomenon itself is not recent. In fact, this study showed that old museum samples of cirtensis from Algeria and Tunisia are intermixed with buteo, suggesting that the hybridization has been ongoing for thousands of years. It also shows that hybridisation is not restricted to the suggested contact zones between these two taxa (namely the Strait of Gibraltar area and northern Tunisia).
The historical demographic analysis showed that the effective population sizes of Upland Buzzard, Long-legged Buzzard (ssp. rufinus) and Steppe Buzzard (B. b. vulpinus) have remained relatively constant for the last 10 thousand years. In contrast, cirtensis – which has a more recent population history – has undergone a dramatic population expansion during the last 3 thousand years. This expansion is still ongoing and predicted to increase in the Iberian Peninsula as a result of several factors including climate warming (see for example Chamorro et al. 2017).
The study concluded that cirtensis should be treated as an allospecies of the Common Buzzard superspecies complex. [Alloespecies are allopatric (geographically isolated) but closely related species forming a super-species. See the concept of allopatric speciation].
What the plumage and morphology says?
Morphometric studies showed long ago that rufinus and cirtensis differ significantly in size (the former being very heavy, while the latter resembles Common Buzzard). Plumage traits also differ between the two taxa. For example, Andea Corso wrote this comment about the subject in 2010: “If you look into the plumage and morphological treats, you would never think cirtensis has nothing to do with rufinus but some similarities… However, there are many plumages that indeed are much closer to Common Buzzard….The [Atlas Long-legged Buzzard] seems to be like a mix between buteo and rufinus”. A. Corso has been researching this subject since many years, but as far as I known it hasn’t been published yet. It’s very interesting that this genetic study in some sort confirmed what has been suggested by morphological studies and experienced observers since many years.
Unfortunately, the geographical sampling still far for complete, and some important lineages and/or regions were not included in this study:
Northern Morocco where the so-called ‘Gibraltar buzzard’ occurs is not included. However, this is probably not a big issue because the study showed that the hybridisation and introgression occurred across North Africa. No samples from the Canary Islands as well, where the local buzzard subspecies is considered a Common Buzzard (B. b. insularum).
Similarly, no samples from Cape Verde. The taxonomic status of Cape Verde Buzzard is even less clear than in the previous two regions. It’s given its own species status (Buteo bannermani) by some authors (e.g. IOC Checklist, Dutch Birding), but still considered as a subspecies of Common Buzzard by others (e.g. HBW Alive)
Suggested common names
This study confirmed that the North African Buzzard (cirtensis) is more closely related to the Common Buzzard. In my opinion, changing common names are inevitable. Here are my suggestions (comments are welcome as always!):
In English, the qualifier “Long-legged” should be dropped from the name. I think ‘North African Buzzard’ is a better and more appropriate name than ‘Atlas Buzzard’ or ‘Maghreb Buzzard’ for example. (It’s disadvantage is that it’s composed with three words).
In French, there are two names already in use: ‘Buse du Maghteb’ and ‘Buse féroce du Maghreb’. I think the first name should be used which does not include ‘féroce’ in it.
In Spanish and Portuguese, Buteo rufinus (the “parent” species not just cirtensis) is called ‘Busardo moro’ and ‘Bútio-mourisco’ respectively. In both languages, I think keeping these names which literally means “Moorish or Moroccan Buzzard” for the eastern Long-legged Buzzard would be a real misnomer. See under these two languages in this blog-post: Maghreb endemic birds.
Jowers, M.J., Sánchez-Ramírez, S., Lopes, S., Karyakin, I., Dombrovski, V., Qninba, A., Valkenburg, T., Onofre, N., Ferrand, N., Beja, P., Palma, L., Godinho, R. 2019. Unravelling population processes over the Late Pleistocene driving contemporary genetic divergence in Palearctic Buzzards, Molecular Phylogenetics and Evolution 134: 269-281. doi: 10.1016/j.ympev.2019.02.004
The North African Buzzard is split from the Long-legged Buzzard by OSME (The Ornithological Society of the Middle East, the Caucasus and Central Asia) based on this study. It’s nice to see that they adopted the same English name we suggested in this blog two months ago.
The OSME List largely follows the International Ornithological Congress (IOC World Bird List), but they depart from this source when new research reveals new understanding,…etc. As anything in science, this is of course not final and can change when new information is published.
See the ‘OSME Region List Update 4.4’ at the OSME website here (PDF at the bottom of the page).