Dublin Zoo's visitor numbers fell by 100,000 last year.
Bad weather and the Pope's visit to Ireland are among the reasons behind the decline, according to management at the zoo.
It had to close for 3 days in August while the Phoenix Park was being prepared for the papal mass.
That happened during a period in which the facility would have expected up to 10,000 visitors a day on a weekend during school holidays.
Poor weather throughout 2018 is also thought to have kept families home.