Brown Booby (Sula leucogaster)
Adult Brown Booby off Hawai'i (Photo by Eric Vanderwerf)
Brown Booby is another wide-ranging seabird, breeding in most tropical and subtropical regions of the Indian, Pacific, and Atlantic Oceans. In Hawai'i, the largest colonies are found on Ka'ula Rock and Lehua Islet off the coast of Ni'ihau, and Nihoa Island, each with about 500 pairs. Smaller colonies are found on islets off O'ahu, Kaho'olawe, and on some of the other Northwestern Hawaiian Islands, but the state-wide breeding population probably does not amount to much more than 1,500 pairs.
Adult Brown Booby with chick, Lehua Islet (Photo by Emily Haber)
Although less common than Red-footed Booby in the Hawaiian Chain, this species is still relatively easy to see at any coastal location on Kaua'i and O'ahu, with numbers ranging into the double digits not being out of the ordinary. On Kaua'i the easiest places to see Brown Boobies are from the beach in the vicinity of Kekaha and PMRF, and Kilauea Point NWR, where they are often seen quite close to shore. Brown Boobies are not unusual to see nearshore on Maui, Moloka'i, Lana'i, and Hawai'i. Brown Boobies are present year round in the Hawaiian Chain, although fewer numbers are present from October to December when most individuals are not breeding.
In all cases, Brown Boobies are slightly larger, heftier, and darker brown than any dark Red-footed Booby. Adult Brown Boobies are distinctive with their contrasting white bellies and dark head and back, and yellow bill. However, young Brown Boobies are also brown on the belly and are distinguished from brown Red-footed Boobies by their dark tails (vs. adult brown morph Red-footed Boobies) and darker brown overall coloration.
Although the numbers in Hawai'i appear to be relatively stable, Brown Boobies are predated by non-native mammals such as rats and cats, which likely restricts them to nesting on offshore islets. Outside of Hawai'i, Brown Boobies are often persecuted as food and are greatly affected by habitat alteration and degredation, predation by non-native mammals, and general colony disturbance.
An adult Brown Booby diving to catch fish at Midway Atoll (Photo by Dan Maxwell)