Establishment success of the reinforced population of Gran Canaria Blue Chaffinch Fringilla polatzeki

Abstract

The Gran Canaria Blue Chaffinch is the rarest forest passerine in the western Palaearctic with a population reduced to a single locality, Inagua, in the west of the island. After a forest fire, some birds were established in another location and a reinforcement programme was launched with the aim of consolidating this new population. Between 2010 and 2019, 194 Blue Chaffinches were released in the pine forest of La Cumbre, in the centre of the island and at a higher altitude than the previous one. Birds of two origins were used for this action: captive-bred birds were released using “soft” release methods, and wild-caught birds from the Inagua source population were released using “hard” release methods. Survival of radio-tagged birds (20–42 days of battery life) was high and similar between the two groups. Wild-caught birds occupied 12–15 times more surface area than captive-bred birds that remained close to supplementary feeding sites. All translocated birds displayed breeding behaviour in the following breeding season, although the rate of contribution to the new population was significantly lower for wild-caught birds (21% compared to 54% for captive-bred birds). This disparity can be partly attributed to nearly one-fifth of the wild-caught birds returning to Inagua. We conclude that the establishment phase of the Blue Chaffinch reinforced program in Gran Canaria has been successful. To retain wild-caught birds and deter their return to the source population, we recommend employing methods akin to the soft-release techniques utilized for captive-bred birds. Ongoing monitoring of the enhanced population, collecting data on survival and breeding success, will enable the evaluation of the long-term success of the translocation program.