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Boobies
Boobies belong to the family Sulidae, which also
includes gannets. In the Galapagos, there are three boobies: the
masked booby (Sula dactylatra), the red-footed booby (Sula
sula) and the blue-footed booby (Sula nebouxii). Despite
the obvious color differences, the three boobies are very similar
in body shape, with the masked being the largest and the blue-footed
the smallest. Though small by comparison, the blue-footed booby
has, proportionately, the largest tail of the three. All three
have torpedo-like bodies with sharply pointed beaks. Indeed, the
local Spanish name, "piquero" is derived from the beak
shape: "piquero enmascarado" (masked booby), "piquero
patas rojo" (red-footed booby), and "piquero patas azul"
(blue-footed booby).The origin of the name booby is less clear,
probably derived from Spanish "bobo", or clown, in reference
to their habit of landing on ships at sea and being easily approached
- and killed - by sailors.
 It
is fairly easy to distinguish males from females by voice - males
make an asthmatic whistling sound while females croak. Blue-footed
boobies can also be distinguished because the females have a ring
of dark pigment around their pupils, making them look bigger than
those of the males. Red-footed boobies are dimorphic for plumage.
About 95% of the birds have brown plumage while 5% have a white
plumage very similar to that of the masked booby. It is curious
that in red-footed booby populations in other parts of the world,
the percentages are reversed, with the white morph being the more
abundant They are, nevertheless, the same species and, if you
are lucky, you can see a brown/white pair.
All three birds have similar body shapes, and they
lead similar lifestyles, but refrain from competing with one another
because they fish in different areas. Blue-footed boobies tend
to fish very close in to shore, masked boobies a bit farther out,
and red-footed boobies fish well out at sea. The distributions
of their fishing grounds influences the distribution of their
nesting sites. Blue-footed boobies nest in the center and edges
of the archipelago (Espanola, Daphne, and N. Seymour). Similarly, masked
boobies tend to nest at the edges of the archipelago (Daphne,
Espanola, Genovesa),
while red-footed boobies tend to be found only at the fringes
of the archipelago (Genovesa and Punta
Pitt on the northeaster tip of San Cristobal).
Because of their distribution, it is typically the blue-footed
booby that visitors tend to see fishing.
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Boobies are plunge divers and their dive
is spectacular. When they spot fish, from 30-50 feet in the air,
they power-dive, beak-down into the water, folding their wings
back only at the last minute disappearing for several seconds
and then bobbing up to the surface. Blue-footed boobies dive in
remarkably shallow water, and they use their large tails to pull
themselves out of the dive. One usually sees individual birds
fishing, but it is not at all uncommon to see a small group of
boobies flying in formation, heads down, looking for fish. Occasionally
one can see large flocks of boobies fishing together. Amasa
Delano, a yankee sea captain who visited the islands in 1801 described
such a sight:
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There is another remarkable bird
found here which has not before been described. It is called
the diver. They resemble the small kind of booby, and something
similar to the kind which is described at the Lobas Islands,
called Bonaparte's army, excepting they are of rather a
darker colour on the breast and neck, and their beaks and
feet are of a prussion blue. These birds collect together
in small flocks for the purpose of diving. They fly round
in a circle and continue to rise till they get to the height
of from sixty to a hunmdred yards in the air, when one of
them makes a pitch to dive, at which motion everyone follows.
They fly down with remarkable swiftness till within four
or five yards of the surface, and then suddenly clasp their
wings together and go into the water with the greatest velocity
that can be conceived of, exceeding anything of the kind
that I ever witnessed. This
bird should be contrasted with the pelican. They go
into the water with such force as to form a curve of thirty
or forty yards in length, before coming to the top again,
going to a great depth under water. They glide under water
at almost as great a degree of swiftness as when flying
in the air. The water was so very transparent where the
ship lay, that they could plainly be seen during their submarine
course.
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The plunge dive of the blue-footed booby is just
as awe-inspiring today as when Delano described it nearly 200
years ago.
Boobies and gannets, in general, have complex courtship
rituals and in the Galapagos, the courtship of the blue-footed
booby is most complex. The male attracts the female's attention
by a behavior called sky pointing, in which he tips his beak,
tail, and wing tips to the sky while letting out a whistle. The
two then slowly march around each other, lifting their bright
blue feet in a high, slow step. Finally, male and female sky point
to each other. Both the masked and red-footed boobies engage in
courtship displays, and both sky point, but their's is not nearly
as elaborate as the blue-footed booby. Many members of the Sulidae
build nests, but in the Galapagos, only the red-footed booby does.
Both the blue-footed and the masked boobies nest on the ground,
the blue-footed boobies often making a guano ring around the nest
area. Nevertheless, as part of the courtship process, the male
blue-footed booby offers the female a twig as part of a ritual
nest.
Both booby pareents help in rearing the chicks
and take turns guarding the nest and incubating the eggs. Most
birds, but not boobies, develop a brood patch on their belly during
nesting season. This is a spot where the feathers are relatively
thin and blood vessels in the bare skin keep the eggs warm. Boobies
compensate for their missing brood patches by laying their feet
over the eggs and the blood vessels in the webbing accomplish
the same purpose. The three boobies have very different brooding
patterns. The red-footed booby lays one egg and raises one chick.
Likewise, the masked booby also rears one chick, but it approaches
the problem differently. Masked boobies lay two eggs, several
days apart and the older chick is much bigger than the younger.
Assuming that the older chick survives, it will push its younger
sibling out of the nest, where it will die -- all under the eyes
of a seemingly uncaring parent. If the older chick dies, however,
then the younger chick acts as a back-up. Blue-footed boobies,
on the other hand, lay up to three eggs and, in a good year, can
raise all three chicks. At least part of what makes this possible
is that by fishing in very close to shore, blue-footed boobies
parents can make more and frequent trips in for feeding. In lean
years, however, the older chicks engage in siblicide.
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