  Academic migration is the change of host institution by a researcher,
typically aimed at achieving a stronger research profile. Scientific features
such as the number of collaborations, the productivity and its research impact
tend to be directly affected by such movements. In this paper, we analyse the
dynamics of the collaboration network of researchers as they move from an
institution to the next one. We specifically highlight cases where they
increase and when they shrink, and quantify the dependency between the
collaboration networks before and after such a movement. Finally, we drill down
the analysis by dividing movements depending on the career stage of the
researchers. The analysis shows a remarkable dynamism of collaboration networks
across migrations. Interestingly, not always movements result in larger
collaboration networks, while the overall similarity between networks across
movements is quite limited on average. Qualitatively, the same effects can be
found at all career stages, while, clearly, the magnitude of them might vary.
These results are based on a dataset extracted from Scopus, containing detailed
scientific information for the publications of 84,141 researchers.
