Page 84 - The Errors the American National Academy of Sciences

The Errors of the American National Academy of Sciences

grow and reproduce. In years of drought, however, the number of
seeds produced by plants is limited and may not be enough; as a re-
sult some finches die of starvation.
Grant and his colleagues measured the rainfall on Daphne

Major, one of the Galápagos, as normal in 1976, but as only one-fifth
of that level in 1977. In the period of drought which began in the
middle of 1976 and lasted until the rain began again in January 1978,
they observed a severe drop in the amount of seeds on the island and
noticed that a number of ground finches had disappeared—to such
an extent, in fact, that the ground finch population fell by 15% over
the preceding year. They assumed that most of the vanished birds
had died, and that a few had migrated.
Grant and his team also recorded that those finches which sur-

vived after the drought had rather larger bodies and deeper beaks
than normal. The average depth of ground finch beaks on the is-
land—in other words, the distance between the top and bottom of the
beak at the point where the beak joins the body—was approximately
half a millimeter, or 5%, larger in 1977 compared to 1976. Taking this
as their starting point, the researchers suggested those finches which
fed solely on small seeds were weeded out, while those with beaks

capable of breaking and opening larger and harder shells survived.

MEDIUM GROUND FINCH CACTUS FINCH

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