Three lop-eared bunnies were left in a cage outside the charity's Wimblington centre near March.
The trio were found by staff near to the gates on the morning of Tuesday 9 April.
All three, which are young adults, are recovering well from their ordeal and are now being cared for by staff.
The centre has named them Melanie, Miffy (pictured) and Speedy.
John Woods, RSPCA Animal Rescue Officer who is investigating, said:
"We are now appealing for information and ask that if anyone saw anything in the area at the time to contact our appeals line on 033 123 8018 quoting incident number 01246996, or if anyone knows who might have owned these rabbits.
We'd particularly like to hear from the driver of the vehicle who was in the area the night before and they may hold vital information".
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