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Conservation
Threats
Bonelli's eagles are subjected to a diverse set of factors which threaten the stability of their populations, the most important of which are referred to in the following text.
Shooting
Direct persecution has many causes and affects mainly juveniles and immatures. One of the potential conflicts is related with hunting activities, since Bonelli's eagles often prey on small game. Another potential conflict has to do with the consumption of domestic prey (mainly pigeons and fowl). From 1990 to 1999, 70% of the known mortality cases regarding adult birds in Portugal were caused by shooting.
However, at least in the Southwest, the fact that adult mortality occurs only out of the breeding season, and also that male mortality largely outnumbers female mortality, leads to the conclusion that casual shooting during hunting, instead of intentional persecution, must be taking place.
Disturbance by human activities
The disturbance caused by forestry activities is the main cause of nest desertion during the critical periods of nest occupation and incubation. These activities include scrub clearing, timber harvesting, tree planting and the opening of firebreaks and dirt roads.
Human disturbance resulting from hunting activities is another potential cause of nest desertion and clutch failure. The most negative impacts are often caused by big game drives (mostly targeting at Wild boar Sus scrofa) which take place during the incubation period, potentially leading to clutch abandonment.
Habitat degradation
The main threats to Bonelli's eagle' habitats in Southern Portugal are: a general degradation of tree cover (whether cork-oaks, pines or eucalyptus) due to climate change, pests, forest fires, and intensive or inadequate forestry practices; the risk of felling nest-trees; the building of infra-structures like dams, roads and potential obstacles to flight, namely power-lines and wind farms. These factors can often be managed at a local or regional level. The lack of actions in this regard can lead to the reduction of the breeding potential of this population in the mid-long term. Factors like forest degradation, the felling of nest- trees and forest fires, acting along with the disturbance of nest-sites by human activities, subsequently lead to an increase of nest-site shifts, pushing the birds to use less stable, lower quality nest-sites. In turn, this favours the probability of the partial collapse of weak nest structures. These events have been responsible for as much as 20 and 13% of the total loss of eggs and nestlings respectively.
Food shortage
Bonelli's eagles base their diet in wild and domestic medium-sized birds and mammals. Where none of the staple items is abundant, the eagles prey range is more diversified, but nevertheless the territory's breeding productivity has been recorded to drop. Food shortage is associated with habitat degradation (e.g. where natural habitats gave place to intensive eucalyptus plantations), overhunting, epizooties and also with the loss of habitat diversity and food resources resulting from rural abandonment.
Juvenile mortality due to disease
Several pathologies might be at the origin of juvenile mortality. However, trichomonose induced by the flagellate protozoan Trichomonas gallinae is one of the main causes of nestling mortality, causing lesions in the upper digestive tract which can block food ingestion and ultimately starve young birds. Domestic pigeons are the main vector of the disease and at same time one of the topmost important diet items for many Bonelli's eagle pairs. The annual nestling mortality caused by this disease reaches 38% of the average annual nestling mortality, being the main cause for nestling loss in the Southwest population.
Power line and windfarm mortality
The vast network of medium and high voltage power-lines in South Portugal increases the risk of death by collision with cables, or by electrocution for a large sized bird such as Bonelli's eagles, especially within pre-adult settlement areas.
Wind farms are also dangerous flight obstacles, and pose an increasing great threat since there are several wind farms planned within Bonelli's eagle breeding areas.
Knowlegde gaps
Present knowledge gaps may have direct implications in the conservation of Bonelli's eagles, especially regarding adult mortality causes, population dynamics and trichomonose epidemiology.
Lack of public awareness
Bonelli's eagles are not well-known to most of the general public as a consequence of their secretive behaviour. Nevertheless, their conservation (as well as of most raptors) often depends on public awareness enhancement.
Local community members in the vicinity of the eagle territories, promoters, investors, politicians, hunting managers, land owners, hunters and other stakeholders should recognize the species, its ecological significance and the threats it is subject to. They must actively participate in its conservation, in order to attain the best possible results, and effectively preserve this species and its habitat.
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