domingo, 10 de agosto de 2014

Red-billed Chough

 Red-billed Chough (Pyrrhocorax pyrrhocorax) - juvenile

Within Macaronesia, the Red-billed Chough (Pyrrhocorax pyrrhocorax) breeds exclusively on La Palma, and with estimated numbers at around 2,800 birds, the island boasts one of the highest population densities of this species in the Western Palearctic: approximately 4 individuals per square kilometre.

Paleontological evidence shows that the chough was once present on La Gomera, Tenerife, and probably El Hierro; recent sightings on Tenerife and La Gomera, indicate that the species is capable of flying between the various islands.

On La Palma, the species can be observed in a wide range of habitats, including cultivated areas, ravines, coastal cliffs, scrublands, urban surroundings, and even pine forests, although it seems to avoid areas of fully-developed laurel forest. Flocks of anywhere between 50 and 100 birds are not uncommon.

Given the geographic isolation of the island population, and the necessary adaptation to unusual local environments, the question obviously arises as to whether La Palma choughs merit classification as a separate subspecies. Expert opinion seems to be divided on this issue.

 Juvenile begging for food, showing the curious habit of simultaneously raising one leg

From among the sources consulted, I quote:
1. "on the Canaries, the same form is present as in North Africa, P.p.barbarus".
2. "On the basis of slight biometric and plumage differences, the race barbarus has been described, being slightly larger than the nominate, with a deeper and longer bill and a greenish gloss to its black pumage. No genetic studies are available to support this race."
3. "All-in-all, choughs in La Palma are smaller than Iberian choughs, which is in controversy with their classification together with North African individuals within the barbarus subspecies".

(See below for corresponding references).

Differencess in bill, legs, and plumage tones can be appreciated in the adult and juvenile birds.

Despite uncertainty concerning status, there does seem to be general agreement that the island choughs' diet differs from that of mainland birds, tending to be more frugivorous, and that the local race has acquired unusual foraging habits, not necessarily ground-based. Morphologically, in contrast to continental choughs feeding in open areas on soil invertebrates, island choughs feeding on fruits from trees, bushes and cacti often have shorter tarsi and a deeper bill.

The photos above were all taken in a typical ground-foraging area: Llano de Las Cuevas, in El Paso. Below, two birds in a rather more "unusual" setting, perched in a Canary Pine (Pinus canariensis):


1. LORENZO, J. A. (Ed) 2007. Atlas de las Aves Nidificantes en el Archipiélago Canario. Organismo Autónomo de Parques Nacionales, Madrid.
2. García del Rey, E. (2011). Field Guide to the Birds of Macaronesia Lynx Edicions, Barcelona.
3. Blanco, G. & Laiolo, P. & Pais, J. Environmental adaptations, morphological divergence and reproductive isolation of the chough in La Palma. 3rd International Workshop on the Conservation of the Chough, Santa Cruz de La Palma 13-15 October 2010.