Abstract: Methods and device for marking animals are disclosed. An ear tag configurable for attachment to a rodent ear, e.g., a mouse ear, is presented, wherein the ear tag includes a color-coded image, an alphanumeric character string, a bar code and/or a visual signage. The tag may include the visual identifier and an RFID device. A card may be provided that redundantly displays some or all of the visual identifier. An applicator is alternately or additionally provided that removes separated elements of the tag from a tray force generated by manual compression of a pair of handles of the applicator, and additionally includes jaws that compress towards each other when the handles are initially compressed, yet splay and release the tag elements as additional compressive force is applied to the handles.