1. A Global Species Assessment
2. Barton , K. 2011 Model selection and model averaging based on information criteria (AICc and alike). R package, version 1.9.5 http://cran.r-project.org/web/packages/MuMIn/index.html
3. Bates , D. Bolker , B. Maechler , M. Walker , S. 2013 Lme4: linear mixed-effect models using Eigen and S4. R package, version 1.0-4 http://cran.r-project.org/web/packages/lme4/index.html
4. BirdLife International 2012 Species factsheets: Oenanthe isabellina & Oenanthe leucura http://www.birdlife.org