  We present high spatial resolution spectroscopic measurements of dynamic
fibrils (DFs) in the Ca {\small{II}} 8662 {\AA} line. These data show clear
Doppler shifts in the identified DFs, which demonstrates that at least a subset
of DFs are actual mass motions in the chromosphere. A statistical analysis of
26 DFs reveals a strong and statistically significant correlation between the
maximal velocity and the deceleration. The range of the velocities and the
decelerations are substantially lower, about a factor two, in our spectroscopic
observations compared to the earlier results based on proper motion in narrow
band images. There are fundamental differences in the different observational
methods; when DFs are observed spectroscopically the measured Doppler shifts
are a result of the atmospheric velocity, weighted with the response function
to velocity over an extended height. When the proper motion of DFs is observed
in narrow band images, the movement of the top of the DF is observed. This
point is sharply defined because of the high contrast between the DF and the
surroundings. The observational differences between the two methods are
examined by several numerical experiments using both numerical simulations and
a time series of narrow band H$\alpha$ images. With basis in the simulations we
conclude that the lower maximal velocity is explained by the low formation
height of the Ca IR line. We conclude that the present observations support the
earlier result that DFs are driven by magneto-acoustic shocks exited by
convective flows and p-modes.
