Successful reintroduction of the endangered Bonelli’s eagle in Mallorca


Vent is a male Bonelli’s eagle that has been successfully released to the island, in this case using the NestHack methodology. Credit: Sebastià Torrens

Reintroducing species into new natural habitats is one strategy to help prevent the extinction of the most endangered organisms. However, this process is influenced by several factors – which are not explored much in the scientific literature – and its overall success rate is still low.

A study coordinated by the Conservation Biology Group of the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona analyzes the effectiveness of reintroduction strategies of Bonelli’s eagle to Mallorca. The study, carried out in collaboration with the Government of the Balearic Islands and the Wildlife Recovery Consortium (COFIB) within the framework of the European project LIFE Bonelli, provides new scientific knowledge in global ecology to increase the options for the success of reintroduction programs with higher economic efficiency.

Bonelli’s Eagle: From its disappearance to its reintroduction in Mallorca

The Bonelli’s eagle (Aquila fasciata), an emblematic bird of prey of the Mediterranean, is a species in decline in the central and northern areas of the Iberian Peninsula. In Mallorca, it became extinct in the 1970s following intense human persecution, although it is a key species in the natural environment as a predator of birds and mammals and as a that control the balance of the ecosystem.

In 2011, the government of the Balearic Islands, with the support of the LIFE project, initiated the process of reintroducing the eagle to Mallorca. This plan relied on the scientific collaboration of the conservation biology group of UB and IRBio, a team that carried out the demographic analysis to validate the most effective strategies in the reintroduction plan. The initiative to reintroduce the species to the island has been successful and there are now around 40 eagles, including nine breeding pairs.

The study, published in the journal Animal conservation, from the Zoological Society of London (ZSL), examines the demographic and economic effectiveness of different strategies based on the release of birds of different ages and origins, i.e. species born in captivity and wild. Through a cost-benefit assessment – with biological and economic indicators – the experts compared the reintroduction strategies: hacking based on captive breeding (“Capthack”), hacking based on chicks extracted from wild nests in natural populations (“NestHack”) and the translocation of non-juvenile wild birds from natural populations recovered in rehabilitation centers (“WildTrans”).

“The success of the reintroduction of endangered species into the natural environment depends on several factors such as the quantity and age of the reintroduced individuals, the quality of the destination habitat, the reintroduction methods used, the origins of the reintroduced individuals. , and the biological factors and ecological characteristics of each species, ”notes speaker Joan Real, head of the Conservation Biology Group at UB and UB’s Biodiversity Research Institute (IRBio).

Why is the release of non-juvenile eagles the most effective model?

The non-juvenile eagle release system (WildTrans) would be the most effective strategy for reintroducing Bonelli’s eagle to Mallorca. “This system allows us to release sexually mature and more experienced individuals. This facilitates their reproduction and therefore faster population growth during the first years of reintroduction, which is the most critical period of reintroduction, ”notes Jaume Badia-Boher, member of the Department of Evolutionary Biology, Ecology and Science. UB environmental sciences, and first author of the article.

Regarding economic and human resources, the release of non-juvenile eagles is also the most economical strategy compared to other alternatives. Also, it is the only option to ensure the persistence of the eagle population over the long term in a context of limited logistical means evaluated.

The island environment of Mallorca could have favored the results of such a strategy. “The natural barrier of the sea, in this case, could have limited the tendency of released eagles to return to their original populations, which can happen in species with a high dispersal capacity,” notes speaker Antonio Hernández-Matías (UB- IRBio).

A species threatened by human action

In addition to the factors mentioned, the complex equation for achieving a successful reintroduction requires knowledge of the biology and ecology of the species, in addition to experience in the management and resources to rear animals in captivity and them. release thereafter.

Like many diurnal raptors, these birds reach sexual maturity relatively late and lay few eggs (between one and two chicks per pair per year). The low annual productivity of chicks means that both wild and reintroduced populations – with a reduced number of individuals – achieve slow growth.

As a result, populations of these birds of prey are sensitive to natural and human impacts. “All of these factors make raptors one of the most endangered animal groups in the world. Therefore, to achieve positive results, reintroductions of these species require years of sustained effort, persistence and release,” say the authors.

Human-induced mortality – power line accidents, persecution, accidental or induced poisoning, etc. – hardens the chances of survival of eagles reintroduced into the wild. “Therefore, before reintroducing a species, it is necessary to carefully assess whether the conditions are appropriate, which may require the implementation of measures to reduce the magnitude of the sources of danger of human origin”, warns the ‘team.

Conserve and protect biodiversity as a priority action

Biodiversity is decreasing every day in different parts of the world. In this context of biological crisis, improving natural habitats is the first strategy for conserving biodiversity. Beforehand, it is necessary to eliminate the factors which affect the viability of the species (causes of mortality, availability of food, etc.).

The release of animals into a new environment is an ex situ conservation methodology that should only be applied when there are no in situ alternatives to protect biodiversity. This environmental solution requires several requirements before being put into practice. Among these is the fact that the species in question is extinct in the area where it originally lived and that the reintroduction process does not alter or endanger native species or key ecological processes. .

One of the factors that makes it difficult to assess species reintroduction plans is the lack of short-term monitoring programs for reintroduced populations. The promotion of these studies will be decisive for understanding the dynamics of populations of new individuals, evaluating the effectiveness of the measures taken and determining the decisive elements in the success or failure of reintroductions in different scenarios.

The study published in the journal Animal conservation offers a new and unprecedented perspective to a field of ecology in which studies in the natural environment are few. “Based on our results, we consider that this strategy is more effective in species for which captive breeding is difficult, and in islands or with species without great dispersal capacity. However, research is scarce in this area and science should aim to answer these questions, ”the authors conclude.

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More information:
Jaume Adrià Badia-Boher et al, Reintroductions of raptors: profitable alternatives to captive breeding, Animal conservation (2021). DOI: 10.1111 / acv.12729

Provided by the University of Barcelona

Quote: Successful reintroduction of the endangered Bonelli’s eagle in Mallorca (2021, October 5) retrieved on October 5, 2021 from -eagle.html

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