Gibraltar buzzard

By | 16 September 2012

Interesting news posted by Dick Forsman in his website following his short visit with Javier Elorriaga and Antonio-Roman Muñoz from Fundación Migrés to the Moroccan side of the Strait of Gibraltar this month. The aim of this visit was to study the controversial ‘Gibraltar buzzard’ which occurs in the areas around the Strait. Dick commented:

“Javier Elorriaga and his colleagues have been studying these buzzards for years now, and their paper on the identification of the ‘Gibraltar buzzard’ and the Atlas Long-legged Buzzards (Buteo rufinus cirtensis) is on its way”.

Dick added that: “’Gibraltar buzzards’ are extremely variable, and combine to a variable degree features from Atlas Long-legged Buzzards (a.k.a. African Long-legged Buzzard) and Steppe Buzzards” (Buteo buteo vulpinus). And he believes that the “’Gibraltar buzzards’ to be a self-maintaining hybrid population between these two buzzard taxa, in a way a new species formed by two existing species”.

Update 1: Ostrich article:

Elorriaga, J. & Muñoz, A.-R. 2013. Hybridisation between the Common Buzzard Buteo buteo buteo and the North African race of Long-legged Buzzard Buteo rufinus cirtensis in the Strait of Gibraltar: prelude or preclude to colonisation? Ostrich 84: 41-45. PDF

Abstract:

Natural hybridisation in Old World buzzards (Buteo) is an uncommon phenomenon with important ecological implications. This genus constitutes an intricate radiation of genetically poorly differentiated raptors whose taxonomic classification is a frequent subject of debate. We report the first case of successful hybridisation between the African subspecies of the Long-legged Buzzard Buteo rufinus cirtensis and Common Buzzard Buteo buteo buteo in a new contact zone in the Strait of Gibraltar (southern Spain). The hybrid offspring showed mixed characters from parental species indicating that, among others, hybridisation could explain the increasing presence of phenotypically odd reddish buzzards in southern Spain and northern Morocco. Given their close phylogenetic relation and their recently reduced allopatry, an increase in the hybridisation rate, fertile descendants and genetic introgression seem to be viable. We identify the potential contact zones where genetic monitoring is needed to gain insight on the real extent of this hybridisation and its possible effects on the current climate change scenario.

Update 2: Birding World article

Rodriguez, G., Elorriaga, J. & Ramirez, J. 2013. Identification of Atlas Long-legged Buzzard and its status in Europe. Birding World 26: 147-173. PDF

The following summary of this article is based on the Spanish summary published by Reservoir Birds under the title ”Gibraltar buzzard’: sobre los Ratoneros Moros del Estrecho” (PDF):

“The keys for the identification of the Atlas Long-legged Buzzard (Buteo rufinus cirtensis) have received little attention in the literature. The main bird guides describe it as a smaller taxon in comparison with the nominate rufinus, often difficult to distinguish from Steppe Buzzard (Buteo buteo vulpinus). Not surprisingly, both field identification and taxonomy of the genus Buteo in Europe and Africa are controversial issues and recurring objects of debate.

In this extensive Birding World article, unpublished ideas on how to differentiate cirtensis from similar taxa (rufinus, vulpinus and to a lesser extent, buteo) have been presented. The ideas put forward in this paper are illustrated with over 70 photographs, showing buzzards from around the Western Palearctic.

It reveals that, while southern Morocco cirtensis are remarkably distinct and clearly distinguishable from both vulpinus and buteo (being in fact very similar to rufinus), northern populations close to the Strait of Gibraltar show obvious phenotypic differences. So, many of these individuals have barred and darker tails, more uniformly brownish upperparts and a number of features close to buteo, including the typical light pectoral band, under-wing coverts not uniform, showing contrast between lesser coverts (dark) and median coverts (clear). These phenotypes have been mainly detected in the triangle Tangier-Larache-Tétouan, while determining their actual distribution range requires further exploration effort.

The authors postulated that the existence of this phenotypic difference is due to genetic introgression from buteo in the contact zone between the two species in the African coast of the Strait of Gibraltar. These differences are consistent at the population level and particularly evident in juveniles. However, there is a remarkable variation at the individual level.

In this article, the authors proposed to call this apparently hybrid population ‘Gibraltar buzzard‘ (Buteo rufinus cirtensis x Buteo buteo). The article also highlights the need for progress in the genetic characterization of these populations to determine their taxonomic classification.

Adult breeding 'Gibraltar buzzard' at the southern shore of the Strait of Gibraltar, September 2012. (Dick Forsman)

Adult breeding ‘Gibraltar buzzard’ at the southern shore of the Strait of Gibraltar, September 2012. (Dick Forsman)

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