There is no dataset of animals escaping from zoos. There is, however, a century of American newspapers that has been scanned, run through OCR, and made searchable — so this builds one out of that, the way you would build any evidence review: cast a wide net, then screen what comes back.
Every phrase carries a score for how strongly it implies a captive animal got out. “Escaped from the zoo” is near-certain; “bear at large” is usually just a bear. Drag right to keep only the unambiguous ones.
Pick a page to see what the archive returns for it — and to open the scan at the Library of Congress, where the phrase is highlighted for you.
Reports per year across the filtered set. This is a record of newspaper coverage, not of escapes — the shape is set as much by which papers were digitised as by which animals got out.
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The searching, the screening, and every place these numbers should be distrusted.