Leah Cottell, who has been leading the study, said the process had been “incredibly time-consuming” but she had learned a lot.
“I knew that we had ferrets on the island, but we didn’t really know anything about them,” she told BBC Guernsey.
“They seem to like being around water sites because they like eating things like eggs, and so they’ll go for the nests of ground-nesting birds.”
However, despite the numbers, ferrets were not native to Guernsey, she added.
“They are an invasive species, and the feeling is that it’s probably due to releases from domestic ferrets.
“They look like their polecat wild counterparts, so they have been out there for a very long time; or ferret owners in the 1980s might have let some go and over time it’s expanded.”
Cottell added it would take “months and months” to sift through all the photos, but the charity would write up a report of its findings.
The next round of Strategy for Nature funding is open, and people wishing to apply for money had until 25 October, fund bosses said.
