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The Trenca Association is a non-profit organization that has been working since its foundation in 1998 to improve and preserve natural heritage. Its activities are part of actions and projects that are developed around the conservation and recovery of native fauna and environmental heritage in general.

The name of this association refers to the lesser grey shrike (Lanius minor, also known as “trenca” in Catalan), one of the vertebrates at greatest risk of extinction in the Iberian Peninsula. Specifically, the Lesser Shrike is listed as “endangered” by Royal Decree 139/2011 and declared “in critical condition” by Order TEC/1078/2018.

According to the Trenca association, if measures are not taken and a monitoring and evaluation of the conservation of this species is established, the population would disappear, which would mean a new extinction of a species at the state level and a significant loss for Spanish biodiversity.

The general objective of the project has been to contribute to preventing the extinction of the Iberian population of the Lesser Grey Shrike, both with direct actions (those related to the management of the species) and indirect actions (introducing improvements in its habitat).

The specific objectives were as follows:

• Develop a study on the captive breeding of the species, putting it into practice, and carry out a genetic assessment of the captive and wild population.
• To know the current status of the species both in the breeding areas and in the territories where it developed and its movements.
• Carry out an evaluation of the carrying capacity of the environment in which the species lives.
• Disseminate information to society about the critical state of these populations and the results of the project.

• Study of the captive breeding of the Lesser Grey Shrike.
• Study of the release of specimens by hacking, a technique of release by field breeding, that is, consisting of leaving the chicks of some species in a nest where they are provided with food and can complete their development without the need for adults of their species. Subsequently, a monitoring of wild breeding was carried out.
• Evaluation of the supplementary feed methodology for the chicks released through hacking and for the wild population.
• Integration of predator control (including the capture of specimens of 184 magpies) as a measure to improve the survival of the species.
• Introduction of improvements in the habitat of the species, including selective clearing (to improve the availability of the insect, so that it is easier to hunt by the lesser shrikes), irrigation, maintenance and pruning of trees and shrubs (tamarinds, hawthorns, ash trees and fig trees).
• Specific studies in the habitat, through inventories of hectares and field trips.
• Monitoring of the Lesser Grey Shrike population in the Special Protection Area for Birds (SPA) Mas de Melons-Alfés (Lleida) and in the former territories of Aragon and Aiguamolls de l’Empordá (Girona) and establishment of contacts to control the population in the south of France.
• Dissemination and communication of the project, through the publication of news on the entity’s website and on specialised dissemination websites, publications on social networks, conducting a radio interview, etc.

The study and monitoring of the Lesser Grey Shrike population in Natura 2000 Network areas, located in Catalonia and Aragon, have made it possible to improve the conservation status of the species. The most outstanding general results of the project include the on-site monitoring actions throughout the two seasons (2020 and 2021), as well as the support actions for captive breeding at the Wildlife Recovery Centre (CRFS) in Vallcalent (Lleida). The provision of food as support for natural breeding and as a supplement for chicks released using the hacking technique is also highlighted, predator control operations of the species, with special emphasis on the breeding season, and habitat adaptation actions.

Finally, the project has been innovative since in addition to monitoring the species in Catalonia, it has also carried out nesting populations outside the Catalan community; specifically, in the former territories of distribution of the species in the province of Huesca.

As a main result of the project, it can be noted that 19 shrikes have returned to the Torreribera estate (Lleida): 13 specimens in 2020 (11 of them released through hacking) and 6 specimens in 2021. Since 2009, 56 released shrikes have returned to this area, with the overall return rate of specimens, in their first year, being 9.3%. And as for the reproduction results of the species, in 2020 4 pairs have been reproduced (all of them in Lleida) made up entirely of specimens released through hacking, obtaining a productivity of 2.5 chicks per pair, with 75% of the pairs successfully breeding. In 2021, two pairs have reproduced (also in Lleida), but in none of the cases did the hatched eggs hatch; therefore, no controlled birth has been detected this season.

Regarding the chicks born in captivity, 74 and 87 in 2020 and 2021, respectively, around 10 chicks have been reserved each year for captive breeding. On the other hand, 55 chicks have been released in 2020 and 67 in 2021 at the Lesser Shrike Breeding Center (Vallcalent). A total of 28 chicks have been released on the Torreribera farm (Lleida) in 2020 and 39 chicks in 2021; and in the Aiguamolls de l’Empordà Natural Park (Girona) 27 chicks have been released in 2020 and 28 chicks in 2021, being the third time that chicks of the species have been released in this environment and where the species disappeared as a nesting plant in 2002.

In addition, to meet the objective of improving the conservation status of the Lesser Grey Shrike, the actions carried out in the project have included work to improve the habitat of the species, including the selective clearing of 5 hectares to improve the availability of the insect (so that it is easier for the Lesser Shrikes to hunt them). 200 hours of irrigation, the maintenance of 50 trees and shrubs planted in previous years (tamarinds, hawthorns, ash and fig trees) and the pruning of them. Also, to ensure the survival of the species, 184 predators were captured (75 in 2020 and 109 in 2021), all of them magpies (Pica pica), over 800 hectares in the SPA Mas de Melons-Alfés and Torreribera (Lleida).

Finally, it should be noted that the Trenca Association has carried out information dissemination work on its activities on social networks, the media and scientific dissemination magazines, as well as the transfer of knowledge to four public administrations such as the Ministry for the Ecological Transition and the Demographic Challenge (MITECO), the Generalitat of Catalonia, the Government of Aragon and the Barcelona City Council.