We've just had a paper published in BMC Evolutionary Biology on seasonal migration patterns in influenza H3N2. This work was lead by Daniel Zinder at the University of Michigan. Daniel developed a novel approach to estimate character state transitions on a phylogeny where the rate of transition is not constant in time, but instead follows some periodic function. Here, we use this method to analyze migration patterns in influenza H3N2, investigating whether transitions from one region of the world to another occur in a periodic fashion. We find strong support for seasonal migration, where influenza lineages frequently move into North America in the fall at the start of the influenza season, but more rarely arrive in the spring towards the end of the season. In general, we find support for a "fertile ground" hypothesis in which regions with a conducive epidemic environment successfully incubate immigrating influenza lineages.