NOWRAMP 2002

Creature Feature - The Thief
Great Frigate Bird
Frigata minor
Hawaiian name: `Iwa

One of the seabirds we often see in the Northwestern Hawaiian Islands are 'iwa, or great frigate birds. 'Iwa are infamous for stealing the food of other seabirds, but catch most of their food on their own. In fact the name "iwa, in Hawaiian means thief. Like all other seabirds, great frigates depend on the sea for their survival, eating a diet of mostly fish and a little squid. They've also been known to eat sooty tern chicks and green sea turtle hatchlings.

During the late 1950's through the '60's, the Smithsonian Institute did extensive research on seabirds in the Northwestern Hawaiian Islands and throughout the Pacific. Millions of birds, including 'iwa on Tern Island (at French Frigate Shoals), were 'banded' (with tiny metal rings around one of their feet), and their flight patterns recorded. Franz Juola, an ornithologist (someone who studies birds) came to Tern Island recently and made a surprising discovery about one of these birds. By noting the number on the band around its leg, Juola determined that the 'iwa was at least 44 years old! This is the oldest great frigate bird ever documented! What kinds of changes do you think that 44 year-old 'iwa has seen during it's lifetime?

Juola also learned that many of the older 'iwa, like this one, 'perch' on the surrounding seawall on the north face of Tern Island. Most 'iwa here seem to prefer sitting on the branches of small shrubs around the island. Can you think of why the older 'iwa sit on the seawall?

'Iwa never sit in the water because they don't have webbed feet like most other seabirds. This is what kept the original aluminum band attached on the 'iwa at Tern for more than forty years! (A typical albatross seabird will need to be rebanded several times during its lifetime because it spends time in the water, causing aluminum bands to corrode.) 'Iwa are excellent flyers and often soar at high altitudes, resting or looking for prey. Some of the places I've seen 'iwa at in the main Hawaiian Islands are Kilauea Point on Kaua'i and the windward side of O'ahu.

To understand the size of this great bird, think of a very tall person you know. Then imagine (because you are very strong), that you can pick them up with one hand and hold them sideways over your head. You would have the full wingspan of a Great frigate bird (imagine this; look around wherever you are for something this size). With wings stretched wide, a Great frigate can be over 7 feet from wing tip to wing tip.

And actually, you could hold a real frigate bird up, because these magnificent flyers have hollow bones with incredibly thin walls and no extra weight anywhere. Of course they do have an impressive hooked beak that would most likely do some serious damage to you should you try to lift one, but more on this later.

Frigate birds live in the tropics and overheating can be a real issue for tropical animals. Birds cannot sweat like humans, but they can spread out their wings to enhance cooling while perched, and they can "pant" or take air rapidly into their throat to cool down. One thing to consider; why are their feathers black? Wouldn't this cause them to overheat? Some think that the feathers, held slightly out from the body, can actually radiate the heat away from the skin rather than towards it. Like wearing loose clothing in the desert, an insulating layer of air below the feathers adds to this effect.

Frigate birds are consummate flyers. They can soar, dive, turn on a dime, and use their long powerful hooked beak to snatch food from the water, ground or while on the wing. Their Hawaiian name, "iwa" means thief and refers to one of the more colorful behaviors of these birds. As other seabirds, such as boobies, return to the nest after fishing, frigates will pursue and harass them until they regurgitate their catch. The frigates then dive down and claim this prize. This behavior is referred to as not just parasitic behavior but "keptoparsitism".

In reality, frigates fish for the bulk of their food, just like the other seabirds. Their remarkable flying abilities also inspire our imagination. A soaring frigate, high on an inshore wind, takes our thoughts up as well.

To better understand these birds, at Tern Island in French Frigate Shoals, volunteers and staff of the U.S. Fish and Wildlife Service staff conduct an egg and chick count of the number of 'iwa chicks on the island. Every fifty-five days, the crew walks the length of the island and takes a census of the great frigate bird chicks and eggs they see. The tools they use are simple: click-counters like the ones a bus driver might use to count passengers.

The specimens pictured were found off on Tern Island, French Frigate Shoals.

References:
Seabirds of Hawaii, Natural History and Conservation, Craig S. Harrison, 1990
Seabirds, An Identification Guide, Peter Harrison, 1985
U.S. Fish and Wildlife Staff at Tern Island

18 species of seabirds breed at FFS:
Black-footed Albatross
Laysan Albatross
Bonin Petrel
Bulwer's Petrel
Wedge-tailed Shearwater
Tristram's Storm-Petrel

Red-tailed Tropicbird
Masked Booby
Red-footed Booby
Brown Booby
Great Frigatebird

Gray-backed Tern
Sooty Tern
Blue-gray Noddy
Brown Noddy
Black Noddy
White Tern

5 common wintering species of shorebirds
Ruddy Turnstone
Pacific Golden Plover
Sanderling
Wandering Tattler
Bristle-thighed Curlew

Posted by Kaliko Amona and Mark Heckman, Education and Documentation Team members