Distribution and Population
It is a resident breeder in the mountain laurisilva forest zone. Bolle's Pigeon builds a stick nest in a tree, laying one white egg. Columba bollii occurs on Tenerife particularly at Anaga and Teno, La Palma in a restricted area of the north-east), La Gomera in Garajonay National Park with some birds outside the park, and El Hierro where it occurs in Golfo and Sabinosa in the Canary Islands, Spain. It may formerly have occurred on Gran Canaria, as bones similar to those of a laurel pigeon have been found and there is a possible sight record from the late 19th century. It was common in the past, but disappeared from many areas owing to clearance of laurel forest in the islands. More recently the rate of laurel forest clearance has been slowed or stopped. Population estimates for the species are 1,160-1,315 birds in 1980, 6,000 individuals in 2001, and 5,000-20,000 most recently. Whether these figures reveal genuine population increases is unclear, but the area of occupied territory appears to be expanding and despite several potential threats the population is at least stable, probably increasing.
In 2007, the species was estimated by SEO Sociedad Española de Ornitología, BirdLife in Spain to number 5,000-20,000 individuals.
It occurs in dense laurel forest in mountainous areas, especially in ravines; also in heath of Myrica faya and Erica arborea, and sometimes in rather open areas, e.g. cultivation. It spends the hottest part of the day in deep shade. It feeds mainly on fruit but also takes grain and occasionally buds, leaves and shoots. It will gather in large concentrations on fruiting trees, plucking berries from the tree but also feeding on the ground. It makes some altitudinal movements to take advantage of ripe cereals and fruit at lower elevations in late summer.
Threats Historical declines resulted from intensive exploitation of laurel forests. The extent of forest loss has slowed, although fragmentation has continued in some areas as forests are exploited for poles and tool handles. A small amount of illegal hunting occurs at drinking sites. As it is a tree-nesting species, predation by introduced mammals including rats is of less significance than for C. junoniae but it remains a potential threat, the impact of which has not been fully assessed1. Grazing pressure from sheep is leading to habitat degradation on La Gomera and at El Hierro. Forest fires also pose a moderate threat to its habitat. Recreational activities cause some disturbance in the breeding season. The species is potentially threatened by outbreaks of Newcastle Disease and Tuberculosis.
The natural habitat is tall laurisilva forest or dense tree heaths which are cloud-covered for much of the year. The forests consist mainly of Azores Laurel, Oreodaphne foetens, Til, Madeira Mahogany, Canary Laurel, Faya, Lily of the Valley Tree and the Picconia. The Trocaz Pigeon prefers primary forests, but secondary growth is used for feeding, and agricultural land is also visited, especially at times of fruit shortage. Most of the pigeons are found below 1000 m (3300 ft), and their prime environment appears to be steep ravine-indented slopes along artificial watercourses, with the occasional large dead laurel tree and much tree heath. This species is highly mobile between different areas at different times of year.
It was very abundant when the islands were first colonised by humans, but was extirpated. The losses on the islands were largely due to deforestation for wood and to create agricultural and grazing land.
The exclusion of livestock from the native forest allows it to regenerate and create more suitable habitat. Some illegal hunting and poisoning continues because of the damage this pigeon can do to crops. Perhaps the main limiting factor on the rate at which the pigeon increases its numbers is eggs and young being taken by introduced Black Rats. It is now classed as Least Concern on the IUCN Red List, an improvement on its Threatened status in 1988. This species is protected under the European Union Birds Directive, and the laurel forests under the Habitats Directive.
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