You need seagulls for that!
Bat's do it too:
see terrorists handbook, p146:
Main Entry: gua·no
Function: noun
Pronunciation: 'gwä-(")nO
Etymology: Spanish, from Quechua wanu fertilizer, dung
: a substance composed chiefly of the excrement of seafowl and used as a fertilizer ; also : a similar substance (as bat excrement or cannery waste) especially when used for fertilizer [to be used in making truck bombs].