Habitat suitability-density relationship in an endangered woodland species: the case of the Blue Chaffinch (Fringilla polatzeki)

Luis M Carrascal; Ángel C Moreno; Alejandro Delgado; Víctor Suárez; Domingo Trujillo

doi:10.7717/peerj.3771

Habitat suitability-density relationship in an endangered woodland species: the case of the Blue Chaffinch (Fringilla polatzeki)

PeerJ. 2017 Sep 12:5:e3771. doi: 10.7717/peerj.3771. eCollection 2017.

Authors

Luis M Carrascal¹, Ángel C Moreno², Alejandro Delgado³, Víctor Suárez³, Domingo Trujillo³

Affiliations

¹ Department of Biogeography & Global Change, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain.
² Viceconsejería de Medio Ambiente, Gobierno de Canarias, Dirección General de Protección de la Naturaleza, Las Palmas de Gran Canaria, Spain.
³ Wildlife Freelance, Las Palmas de Gran Canaria, Spain.

Abstract

Background: Understanding constraints to the distribution of threatened species may help to ascertain whether there are other suitable sectors for reducing the risks associated with species that are recorded in only one protected locality, and to inform about the suitability of other areas for reintroduction or translocation programs.

Methods: We studied the Gran Canaria blue chaffinch (Fringilla polatzeki), a habitat specialist endemic of the Canary Islands restricted to the pine forest of Inagua, the only area where the species has been naturally present as a regular breeder in the last 25 years. A suitability distribution model using occurrences with demographic relevance (i.e., nest locations of successful breeding attempts analysed using boosted classification trees) was built considering orographic, climatic and habitat structure predictors. By means of a standardized survey program we monitored the yearly abundance of the species in 100 sectors since the declaration of Inagua as a Strict Nature Reserve in 1994.

Results: The variables with the highest relative importance in blue chaffinch habitat preferences were pine height, tree cover, altitude, and rainfall during the driest trimester (July-September). The observed local abundance of the blue chaffinch in Inagua (survey data) was significantly correlated with habitat suitability derived from modelling the location of successful nesting attempts (using linear and quantile regressions). The outcomes of the habitat suitability model were used to quantify the suitability of other natural, historic, pine forests of Gran Canaria. Tamadaba is the forest with most suitable woodland patches for the species. We estimated a population size of 195-430 blue chaffinches in Inagua since 2011 (95% CI), the smallest population size of a woodland passerine in the Western Palearctic.

Discussion: Habitat suitability obtained from modelling the location of successful breeding attempts is a good surrogate of the observed local abundance during the reproductive season. The outcomes of these models can be used for the identification of potential areas for the reintroduction of the species in other suitable pine forests and to inform forest management practices.

Keywords: Abundance-suitability relationship; Blue chaffinch; Canary islands; Habitat suitability modelling; Population size and density.

Grants and funding

All the funding and sources of support come from the Conservation Program for the Blue Chaffinch implemented by the Gobierno de Canarias throughout 1991–2004, Cabildo de Gran Canaria (2005–2015), and by European Union (1995–1996: LIFE94 NAT/E/ 001159, 1999–2002: LIFE98 NAT/E/005354, and 2016: LIFE14 NAT/ES/000077). There was no additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.