Ah, what a happy little question! The singular possessive form of "ostrich" is "ostrich's." Just add an apostrophe and an s after the word "ostrich" to show that something belongs to the ostrich. It's like giving the ostrich a little hug of ownership.
The singular possessive form is week's.
The singular possessive form is classmate's.
The possessive form is Amos's.
The singular possessive form for the noun gypsy is gypsy's.
The singular possessive form for country is county's.
The singular form for the plural noun countries is country; the singular possessive form is country's.
singular possessive: boy'splural possessive: boys'
The singular possessive form is speculum's.
The singular possessive form is contralto's.
The singular possessive form is frontiersman's.
The singular possessive form is aircraft's.
The singular possessive form is herd's.