Try a more obscure bird species, like the one in the original article.

https://freesound.org/search/?q=Eastern+Wood+Pewee

1 result

https://www.xeno-canto.org/explore?query=Eastern%20Wood%20Pe...

228 results

Furthermore, your search for blackbird on Freesound gives 639 results based on a text match, while xeno-canto gives 7449 results from 32 species, with metadata tagging it by species, location, date, time of day.