European Souslik (Spermophylus citellus) peering out from entrance to burrow, Bulgaria

animals souslik eastern european east fields east europe east european vertebrate endotherm mammal developed country europe field eastern european nature vertical mammalia burrow zoology sousliks developed countries european citellus verticals ground europe fauna sousliks rodentia bulgaria mammal endothermic wildlife eastern europe bulgarian grasses warm blooded warm vertebrates squirrel sciuridae blooded mammals peering entrance inquisitive spermophylus animal grass animal