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advantage over their competitors. The physical and behavioral differences
between species distinguish them from other, similar species. Indeed, it was
the need for animals to take advantage of different resources that led to
the diversification of species. Darwin's study of finches from the Galapagos
Islands, specifically the birds' beak shapes and sizes, did much to demonstrate
the ongoing changes that occur through evolutionary development. Through
his research Darwin concluded that different beak shapes were linked to the
particular diet of each finch; to avoid competition, the species had exploited
different food sources. The heavier beaks are able to crush large seeds,
whereas smaller beaks are more suited to a mixed diet that includes smaller
seeds and insects. Finches with more delicate beaks are more suited to a diet
composed almost entirely of insects. The crossbill has a beak design that is
unique among finches, specifically suited to prying open pinecones to reach
the nutritious seeds held within.
FIG 4.1
Finch beaks have evolved
to deal with different food sources.
A: Goldfinch. B: Bullfinch.
C: Hawfinch. D: Crossbill.
The shape and size of a bird's beak are good indicators of its diet and its
mode of feeding. The sharp, curved beak of a bird of prey is the ideal design
for ripping and tearing at flesh; the upward curve of the slender bill of the
avocet allows it to filter out the miniscule shrimps and marine worms it
feeds on in shallow waters. A hummingbird's beak and the length of its
tongue have developed that way due to its specialist diet of nectar and the
particular flowers it chooses to feed from. The refinements of physiognomy
and differences in beak shapes are not limited to extreme differences in diet
