  It is well established that migratory birds in general have advanced their
arrival times in spring, and in this paper we investigate potential ways of
enhancing the level of detail in future phenological analyses. We perform
single as well as multiple species analyses, using linear models on empirical
quantiles, non-parametric quantile regression and likelihood-based parametric
quantile regression with asymmetric Laplace distributed error terms. We
conclude that non-parametric quantile regression appears most suited for single
as well as multiple species analyses.
