  [abridged] Using stacked Sloan Digital Sky Survey spectra, we present the
detection of [OII]3727,3730 nebular emission from galaxies hosting CaII and
MgII absorption line systems. Both samples of absorbers, 345 CaII systems and
3461 MgII systems, span the redshift interval 0.4 < z < 1.3; all of the former
and half the latter sample are expected to be bona-fide damped Lyman-alpha
(DLA) absorbers. The measured star formation rate (SFR) per absorber from light
falling within the SDSS fibre apertures (corresponding to physical radii of 6-9
h^-1 kpc) is 0.11-0.14 Msol/yr for the MgII-selected DLAs and 0.11-0.48 Msol/yr
for the CaII absorbers. These results represent the first estimates of the
average SFR in an absorption-selected galaxy population from the direct
detection of nebular emission. Adopting the currently favoured model in which
DLAs are large, with radii >9h^-1 kpc, and assuming no attenuation by dust,
leads to the conclusion that the SFR per unit area of MgII-selected DLAs falls
an order of magnitude below the predictions of the Schmidt law, which relates
the SFR to the HI column density at z~0. The contribution of both DLA and CaII
absorbers to the total observed star formation rate density in the redshift
range 0.4 < z < 1.3, is small, <10% and <3% respectively. The result contrasts
with the conclusions of Hopkins et al. that DLA absorbers can account for the
majority of the total observed SFR density in the same redshift range. Our
results effectively rule out a picture in which DLA absorbers are the sites in
which a large fraction of the total SFR density at redshifts z < 1 occurs.
