Posted by Nigel Collar
When species are split into two or more new species, there can be serious implications for the conservation status of the newly elevated taxa. For a start, each of the new species will have a smaller range and a smaller population ‒ therefore increasing the chance that it will be considered ‘Threatened’ according to the IUCN Red List. In the case of grey parrots, it also has serious implications in terms of trade monitoring. Here, Nigel Collar of BirdLife International explains the scoring system he uses for taxonomic assignment and why the two ‘old’ subspecies of African Grey Parrot Psittacus erithacus erithacus and P. e. timneh are now recognised by BirdLife as two distinct species.
Using the scoring system of Tobias et al. (2010), BirdLife staff measured the degree of phenotypic differentiation between West African timneh and nominotypical erithacus using a system in which an exceptional difference (a radically different coloration, pattern or vocalisation) scores 4, a major character (pronounced difference in body part colour or pattern, measurement or vocalisation) 3, a medium character (clear difference reflected, e.g., by a distinct hue rather than different colour) 2, and a minor character (weak difference, e.g. a change in shade) 1; a threshold of 7 is set to allow species status, species status cannot be triggered by minor characters alone, and only three plumage characters, two vocal characters, two biometric characters (assessed for effect size using Cohen’s d where 0.2–2 is minor, 2–5 medium, 5–10 major and >10 exceptional) and one behavioural or ecological character may be counted (Tobias et al. 2010). Moreover, under this scheme a parapatric range (where two taxa replace each other across an extremely narrow line, with no gap between populations) scores 3, a narrow zone of hybridisation 2 and a broad zone of hybridisation 1 (these degrees of hybridisation without full character merging reflect different levels of genetic independence).
The form timneh can be considered distinct at the species level on account of its
• darker grey plumage (2);
• maroon (vs bright red) tail (3);
|Left, Grey Parrot (photo:L. Miguel Bugallo Sanchez); Right, Timneh Parrot (Photo: Diana Sophia)|
• smaller size (no score yet; measurements not taken);
• pinkish-grey (vs blackish) upper half of upper mandible (2);
• parapatric distribution (now blurred owing to escapes of taxa either side of the line, but somewhere in eastern Côte d’Ivoire) (3).
The original description (by Fraser 1844) diagnosed the form by ‘its much darker tints of colouring, and the tail-feathers terminating in a point’, and this latter observation proves largely to be correct in specimen material in the Natural History Museum, Tring, with the shaft of each rectrix slightly protracted so as to give the feather tip the shape of a curly bracket (also known as braces, flower brackets and gullwings)—as in: }
|Distribution range of Psittacus timneh and |
Psittacus erithacus in West Africa (distribution data by BirdLife International)
Fraser, L., 1844. Description of three new species of birds. Proc. Zool. Soc. London 12: 37-38
Tobias, J. A., Seddon, N., Spottiswoode, C. N., Pilgrim, J. P., Fishpool, L. D. C. & Collar, N. J. (2010) Quantitative criteria for species delimitation. Ibis152: 724-746.