Darwins finches

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Darwins finches

• Large ground finch Medium ground
  finch
• Small tree finch
  Warbler finch

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• 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.

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• 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 oozing blood.

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When rainfall is abundant, seeds are plentiful
and all finches have an easy time finding small,
soft, easy-to-eat seeds.

• 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
  perished.

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• 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.

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• 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.

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• 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.

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• Different water temperatures of these areas
  affects the types of weather in these regions.
• 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 relatively dry.
• 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.

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El Nino

• 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.

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Click on QuickTime movie to play movie of El Nino
water elevations.
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• 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.

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Tropical thunderstorms are fueled by hot, humid
air over the oceans. The hotter the air, the
stronger and bigger the thunderstorms. 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.
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• 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
  America.
• 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.

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• In Galapagos, torrential rainfall caused by
  1983-84 El Nino reversed effects of 1977 drought
  ?
• Seeds became abundant, small birds flourished,
  beak sizes decreased, numbers increased.
• Too wet for cactus, vines smothered Tribulus
  plants that produced large seeds, big-beaked
  birds suffered.