Upper panel: GCs specific frequency S_N versus V-band absolute magnitude for the Hydra I UDG sample (red), compared with the UDGs in the Coma cluster (black triangles) by Forbes et al. (2020a). For the UDGs in Hydra I, the filled red circles are for values derived inside 5R_e, empty red circles for values derived inside 1.5 R_e. The solid line shows the mean locus of dwarf galaxies, the dotted line represents the upper 2σ bound (see also Fig. 4 in Lim et al. 2018). The average uncertainties on both samples are shown in the lower left corner. Lower panel: Halo mass versus stellar mass. The halo for the UDGs in Hydra I is derived from the total number of GCs, using the scaling relation by Burkert & Forbes (2020), see text for details. Symbols are the same as in upper panel. The average uncertainties on both samples are plotted in the lower right corner. The black solid line is the extrapolated stellar mass-halo mass relation for normal galaxies by Rodríguez-Puebla et al. (2017), with a scatter of ±0.2 dex (dashed lines).