AbstractBreeding ecology and reproductive traits of Brown Booby _Sula leucogaster_ etesiaca in Gorgona Natural National Park, Colombia, were studied. Adults morphometrics, eggs dimensions, chicks growth and nesting site characteristics, were examined at three different locations in the park. As with other subspecies, Brown Booby in Gorgona presents inverted sexual dimorphism, with adult females being lengthier, wider and heavier than adult males. Breeding of S. l. etesiaca results in eggs from the first deposition bigger in weight and dimensions than eggs from the second or third deposition. Growth of brown boobies chicks fit to a natural log equation: bodymass(g) = 0.8773 ln(days) + 3.3895. A variety of spawning aggregations was found, and their relationship with the other marine birds nesting in the area is discussed.