Medium-term response of breeding Blue Chaffinch Fringilla teydea teydea to experimental thinning in a Pinus canariensis plantation (Tenerife, Canary Islands)

Abstract

We studied the medium-term response of the endemic Blue Chaffinch Fringilla teydea teydea to experimental thinning in a Pinus canariensis plantation on the island of Tenerife during breeding season. Distance Sampling method was applied to line transects, and habitat preferences were modelled by means of univariate regression trees. The density was 1.70 birds/ha (1.09 to 2.68 95%CI) in thinned areas and 0.56 birds/ha (0.33 to 0.97 95%CI) in unthinned areas. The Blue Chaffinch densities peaked in thinned areas where the density of trees with Diameter at Breast Height of <25 cm was between 10.5 and 16.5 trees/plot (r = 25 m) and the cover of Adenocarpus shrubs was #82.5%. Thinning had added heterogeneity into the stand structure at least in terms of lowering the basal area of small pine trees and increasing the understorey cover of Adenocarpus shrubs, with aver-age cover being 37.15% in thinned and only 1.40% in unthinned areas. Our results justify the silvicultural thinning of 2844 hectares of pine plantation on the summit of Gran Canaria as a means of increasing the density of the endangered Gran Canaria Blue Chaf-finch (Fringilla teydea polatzeki).