  We report the discovery of a giant HI tail in the intra-group medium of HCG
44 as part of the Atlas3D survey. The tail is ~300 kpc long in projection and
contains ~5x10^8 M_sun of HI. We detect no diffuse stellar light at the
location of the tail down to ~28.5 mag/arcsec^2 in g band. We speculate that
the tail might have formed as gas was stripped from the outer regions of NGC
3187 (a member of HCG 44) by the group tidal field. In this case, a simple
model indicates that about 1/3 of the galaxy's HI was stripped during a time
interval of <1 Gyr. Alternatively, the tail may be the remnant of an
interaction between HCG 44 and NGC 3162, a spiral galaxy now ~650 kpc away from
the group. Regardless of the precise formation mechanism, the detected HI tail
shows for the first time direct evidence of gas stripping in HCG 44. It also
highlights that deep HI observations over a large field are needed to gather a
complete census of this kind of events in the local Universe.
