The word in hadeeth is "afidat-tayer", chidyu jaisay dil meaning soft hearted people, humble, haleem in nature .
This is the Hadeeth>>>
Abu Huraira (radi allahu anhu) reported Allah's Messenger (salalahu wa alaieh wa sallam) as saying: There would enter Paradise people whose hearts would be like those of the hearts of birds. (Muslim:Book 40, Number 6808: Chapter 11:THERE WOULD ENTER PARADISE SOME PEOPLE WHOSE HEARTS WOULD BE'LIKE THOSE OF BIRDS : >>> Chapter 1 :BOOK PERTAINING TO PARADISE, ITS DESCRIPTION, ITS BOUNTIES AND ITS INTIMATES [KITAB AL-JANNAT WA SIFAT NA'IMIHA WA AHLIHA ]