guano

Guano is the accumulated excrement of seabirds or bats, often mixed with undigested matter such as shells or insect remains. It has long been valued as a fertilizer and soil amendment because of its high nutrient content, particularly nitrogen and phosphates. The nitrogen in guano largely comes from uric acid and its microbial breakdown.

Bird guano is produced by large colonies of seabirds on islands and coastal cliffs, whereas bat guano accumulates in caves where sizable roosts of bats live. The deposits differ in texture and composition, with bird guano typically more mineral-rich and bat guano often containing more organic matter from insect prey. Both forms can be processed for use as a fertilizer, sometimes requiring washing or drying to reduce moisture and salts.

Historically, guano deposits fueled global trade in the 19th century, especially in regions such as western South America. Nations enacted policies to claim guano resources on uninhabited islands, and harvesting peaks followed by declines as deposits were exhausted and synthetic fertilizers gained prominence. Environmental and ethical concerns later prompted regulations aimed at protecting bird colonies and cave ecosystems.

Today, guano is collected, dried, and milled for use as an organic fertilizer or soil amendment. Quality and nutrient content vary by source, and high salt levels can pose soil management issues. Handling bat guano can pose health risks to workers, so modern practices emphasize safety and habitat protection. Guano remains a notable example of a natural fertilizer resource with historical significance.