Feature - The Thief
Great Frigate Bird
Hawaiian name: `Iwa
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.
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
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?
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.
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
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.
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
birds are consummate flyers. They can soar, dive, turn on
a dime, and use their long powerful hooked beak to snatch
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".
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.
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.
specimens pictured were found off on Tern Island, French
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
species of seabirds breed at FFS:
common wintering species of shorebirds
Pacific Golden Plover
by Kaliko Amona and Mark Heckman, Education and Documentation
Talk About It!
Natural predators of the Great Frigatebird
Asked by Ashley from school on May 19, 2004.
What are the natural predators of the Great Frigatebird?
Answered by Andy from NOAA on May 19, 2004.
The Great Frigatebird does not have any natural predators in the NWHI. In the main Hawaiian Islands young seabirds are predated upon by introduced mongoose, cats, and rats. These predators are not present in the Northwestern Hawaiian Islands.
Asked by Tom on Oct 1, 2005.
We usually see frigate birds flying alone, but sometimes early in the morning flocks of a dozen or more are seen flying into the morning sun. What causes them to congregate like this?
Answered by Angela Anders, USFWS on Oct 3, 2005.
Frigatebirds take advantage of thermals (circulating, rising hot air) to rise thousands of feet into the air from the breeding colony in the morning. Over some colonies, hundreds of frigatebirds will float on a single thermal, circling higher and higher, and then finally flying off in their separate directions to go forage at sea. The birds are able to rise high into the air this way without having to flap their wings at all, so it saves them a lot of energy. The frigatebirds aren't actually "congregating," per se then, there are just many of them taking advantage of the same thermal at the same time.
Angela Anders, US Fish and Wildlife Service