Paul Szpak has co-authored several journal articles claiming that seabird guano consists of nitrogen-rich
However, The Association of American Plant Food Control Officers (AAPFCO) defines Seabird guano as the hardened excrement from marine birds, which contains no organic matter or nitrogen and is a source of phosphates P2O5: "P- Hydroxylapatite - is a naturally-formed phosphate rock mineral with the formula Ca5(PO4)3(OH). The Fluorine content is less than 1%."
Bat guano is fecal excrement from bats. Commercially harvested bat guano is used as an organic fertilizer. All commercially sold bat guano is derived from insect-eating bats. A study was done that demonstrated that, for fruit bats and insect bats, the composition of their guano was largely the same, and differed mainly based on their diet.