Large ground finch Medium ground finch
Small tree finch Warbler finch
• Large ground finch – has largest &
strongest bill: cracks big seeds
• Small & medium ground finch – smaller
bills: specialize on smaller seeds
• Cactus finch – long, slender beak:
extracts pulp from prickly pear cactus
• Sharp beaked ground finch – Steals
booby eggs from unguarded nests. To
crack open the egg, the finch uses its beak
to anchor its body, then slams the egg into
a rock repeatedly like a kick boxer.
• Woodpecker finch -- uses twigs to
dislodge grubs or insects from trees.
• Vampire finch -- attacks the boobies,
puncturing the skin beneath the feathers
with its sharp beak and then drinking the
When rainfall is abundant, seeds are plentiful and
all finches have an easy time finding small, soft,
Natural selection during the severe drought in
1977 drove the birds to adapt. That year, the
vegetation withered. Seeds of all kinds were
scarce. The small, soft ones were quickly
exhausted by the birds, leaving mainly large, tough
seeds that the finches normally ignore. Under
these drastically changing conditions, the struggle
to survive favored the larger birds with deep,
strong beaks for opening the hard seeds.
Smaller finches with less-powerful beaks
Normally, trade winds in tropical Pacific flow
in easterly direction (from east to west).
Winds push surface water toward west.
Water at top of ocean is warmer than deeper
water because it is heated by sun, so
trade winds push warm water toward west.
In the eastern Pacific along the coast of
South America, upwelling pulls deeper
colder water from the bottom of the ocean
up toward the surface. This nutrient-rich
water is responsible for supporting the
large fish population commonly found in
this area. As a result, the Peruvian fishing
grounds are one of the richest in the world.
On southern side of Galapagos, sea
animals, sea birds thrive because of
food brought in by cold Humboldt
current from Peru & Argentina.
Because the trade winds push surface water
westward toward Indonesia, the sea level
is roughly half a meter higher in the
western Pacific than in the east.
Warmer, deeper waters in the western
Pacific and cooler, shallower waters in the
east near the coast of South America.
Different water temperatures of these areas
affects the types of weather in these
In the east, the water cools the air above it,
and the air becomes too dense to rise to
produce clouds and rain. Peru is
In the western Pacific, the air is heated by
the water below it, increasing the
buoyancy of the lower atmosphere and
increasing the likelihood of rain. Heavy
rain storms are typical near Indonesia.
About every 2 - 7 years, the trade winds
weaken in the fall (for unknown reasons).
Allows warmer water from the western
Pacific to flow toward the east. This
• flattens out the sea level,
• builds up warm surface water off the coast
of South America, and
• increases the temperature of the water in
the eastern Pacific.
Click on QuickTime movie to play movie of El Nino water elevations.
Deeper, warmer water in the east limits the
amount of nutrient-rich deep water normally
surfaced by the upwelling process.
Fish can no longer access this rich food
source, so many of them die off.
These conditions are called "El Nino", or
"the Christ Child", which is what Peruvian
fisherman call the particularly bad fishing
period around December.
Tropical thunderstorms are fueled by hot,
humid air over the oceans. The hotter the
air, the stronger and bigger the
As the Pacific's warmest water spreads
eastward, thunderstorms move with it.
If you look on a map, you will see that
suddenly islands like Tahiti, normally tropical
paradises, experience massive storms.
Clouds and rainstorms associated with warm
ocean waters also shift toward the east.
Rains which normally would fall over the tropical
rain forests of Indonesia start falling over the
deserts of Peru, causing forest fires and drought
in the western Pacific and flooding in South
Earth's atmosphere responds to the heating of El
Nino by producing patterns of high and low
pressure which can have a profound impact on
weather far away from the equatorial Pacific.
In Galapagos, torrential rainfall caused
by 1983-84 El Nino reversed effects of
Seeds became abundant, small birds
flourished, beak sizes decreased,
Too wet for cactus, vines smothered
Tribulus plants that produced large seeds,
big-beaked birds suffered.