To the best of my knowledge, nahl is used for the singular male.
My opinion is that nahl cannot be used for singular female, or if so, definitely not in this context.
Here, Nahl is being used for plural and as it referrs to a non-intelligent group (animals), the singular feminine form is used in conjugation in the words kulee, faslukee and botooniha.
See, no significant change occurs.
So because of the conjugation of the feminine words, thats what makes it femanine?