Just made a 4-grid circle 'round my base and found 4 hedgehogs, same as yesterday. Doesn't seem to be of any rarity to me, but maybe they're just have some sort of hive or a nest nearby. "Mossbrush" (dark-green on map, preferred hedgehogs habitat) and "Leafpatch" (lighter-green, fewer hedgehogs) are the biomes you want to see when hunting those.
If you don't know how to see the biome name of a particular tile, hold CTRL+SHIFT and mouse-over the tile (in Amber client). If you're not seeing tile tooltip, press SHIFT+i once to turn the tooltips on, then try again.