Use of Rhodamine B as a systemic bait marker for feral cats (Felis catus)

Abstract

A number of cats in a captive population were fed 50 mg of Rhodamine B in non-toxic kangaroo meat baits. Samples of whiskers (mystacial vibrissae) taken 10 days later were examined for fluorescent marking. Examination of hairs for marking was carried out by means of a ‘single blind’ trial, with the investigator having no prior knowledge of which of 36 cats had received the dye. All of the cats that had ingested baits containing the dye were marked. Examining hair samples under ambient light or under a hand-held ultraviolet (UV) light without magnification was not as reliable as examining hair samples under a fluorescence microscope. These results indicate that Rhodamine B acts as a reliable systemic marker of bait consumption in feral cats and has potential application in field studies to assess bait uptake by feral cats.