  We present a dynamical study of 39 active Centaurs and 17 high-perihelion
(q$>$4.5 au) JFCs with a focus on investigating recent orbital changes as
potential triggers for comet-like activity. We have identified a common feature
in the recent dynamical histories of all active Centaurs and JFC in our sample
that is not present in the history of the majority of inactive population
members: a sharp decrease in semi-major axis and eccentricity occurring within
the last several hundred years prior to observed activity. We define these
rapid orbital changes as `a-jumps'. Our results indicate that these orbital
reshaping events lead to shorter orbital periods and subsequently greater
average per-orbit heating of Centaur nuclei. We suggest the a-jumps could
therefore be a major trigger of cometary activity on Centaurs and JFCs. Our
results further imply that analyses of the recent dynamical histories could be
used to identify objects that are currently active or may become active soon,
where we have identified three such Centaurs with recent a-jumps that should be
considered high-priority targets for observational monitoring to search for
activity.
