from an ethical standpoint, bat guano will contain more human blood so that's an important consideration as to whether you want human material in your garden. however, if you can look past bats and their cannibalistic ways, their guano is an absolute wonder for gardens! roses thrive like lilies and cucumbers grow like pumpkins and pumpkins grow like wild dogs!
This does also depend, however, on whether you're on the east or west coast. East-coast bats are frequently nutrient deprived (due to the low-iron diets of most east-coast people). West-coast bats, however, get a lot of extra phosphates from the cliffs. There are many cliffs in California, Oregon, Washington, and British Columbia, and the nutritional content of their cliff caves are renowned as far away as Japan!
Also, what kind of seabirds? Terns are quite fecund, seagulls are passable, puffins are right out. Seriously, NEVER buy puffin guano, for very, VERY serious legal reasons. Freshwater birds are fine, though. But definitely NOT PUFFINS!
Fossilized guano can be tricky, depending on its age (100+ fortnights?) and its provenance (should not be removed from land of First Peoples). Also, does it taste of almonds? Good sign!
