The sanctuary, based in Stonham Aspal, said that normally an owl is injured if it's found unable to fly, or on occasion it has become too wet which leaves them grounded.
A seemingly-injured owl brought into the Suffolk Owl Sanctuary last week turned out to be fine - but "rather chunky". It seems the owl had simply eaten so many rodents that it was no longer able to take off.
This is about a third thicker than a large healthier female small owl. "Her extra chub had rendered her flightless: "[She] was unable to fly effectively due to the fatty deposits around her body", the post explains. Calling it an "an unusual case of natural obesity", the organisation discovered she has been feasting on mice at the area she was rescued from.
He said: 'This is the first time we've had this.
"After further investigation, we also found that the area where she was rescued was crawling with field mice and voles due to the warm and wet winter we experienced in December", wrote the sanctuary. "We think she's just done incredibly well for herself and overindulged", Head falconer Rufus Samkin told the BBC.
Fatty deposits around the owl's body were preventing her from flying effectively - and carers chose to monitor her for a few weeks to see why she had piled on the pounds.
"We may see her again - we hope not", Samkin says, before staffers let their "little star" fly off into the wild.
The little owl was released back into the wild, "flying gracefully off into the British countryside at a much healthier, and happier weight", according to the group's social media. "Hopefully, she's learned to keep her weight in trim so she can escape any predators or being picked up".