HI absorption towards low luminosity radio-loud AGNs of different
  accretion modes and WISE colours
  H{\sc i} absorption studies of active galaxies enable us to probe their
circumnuclear regions and the general interstellar medium, and study the supply
of gas which may trigger the nuclear activity. In this paper, we investigate
the detection rate of H{\sc i} absorption on the nature of radio galaxies based
on their emission-line spectra, nature of the host galaxies based on the
\textit{WISE} colours and their radio structure, which may help understand the
different accretion modes. We find significant difference in distributions of
W2$-$W3 colour for sources with H{\sc i} absorption detections and
non-detections. We report a high detection rate of H{\sc i} absorption in the
galaxies with \textit{WISE} infrared colours W2$-$W3 $>$ 2, which is typical of
gas-rich systems, along with a compact radio structure. The H{\sc i} detection
rate for low-excitation radio galaxies (LERGs) with W2$-$W3 $>$ 2 and compact
radio structure is high (70.6$\pm$20.4 \%). In HERGs, compact radio structure
in the nuclear or circumnuclear region could give rise to absorption by gas in
the dusty torus in addition to gas in the interstellar medium. However, higher
specific star formation rate (sSFR) for the LERGs with W2$-$W3 $>$ 2 suggests
that H{\sc i} absorption may be largely due to star-forming gas in their hosts.
LERGs with extended radio structure tend to have significantly lower values of
W2$-$W3 compared to those with compact structure. Extended radio sources and
those with W2$-$W3 $<$ 2 have low H{\sc i} detection rates.
