Page 156 - The Miracle of Migration in Animals

THE MIRACLE OF MIGRATION IN ANIMALS

ics. The characteristics of these breeding grounds are important for
the species’ survival, since newborn whales have no protective layer
of blubber and need warm water to survive. They would die if they

were born in the polar seas, so there is every good reason for the
young to be born in warm tropical waters.
For a few months, young whales feed exclusively on their
mother’s milk. Since whale milk is rich in protein and fat, the young
grow fast and soon accumulate blubber. This is vital, for the young
have to grow fast to survive in the freezing polar waters.
Some time after giving birth and rearing their young, whales set
off for the polar seas in search of food. Baleen whales spend at least
four months of the year without feeding, simply living off the blubber
they have accumulated over the summer. On the return journey to the
breeding areas, they can swim more than 7,000 kilometers (4,300
miles) without feeding, even if they are pregnant and suckling
young. 46
It is interesting to note the features of the feeding grounds cho-
sen by whales feeding on plankton. In the sea as on land, all life de-
pends on the presence of plants. Thanks to photosynthesis, inorganic

building blocks are synthesized into organic materials. Deep-level
water rich in nutrients as well as nitrate, phosphate and sulfate
moves towards Antarctica, rises to the surface as it approaches the
continent and is then carried north on the surface by the ocean cur-
rents. In this nutrient-rich water, plant plankton grow much larger,
with the result that the Antarctic Ocean has ten to twenty times more
plankton than tropical seas. As if they know this, baleen whales come
to these regions to feed.
Toothed whales, on the other hand, do not migrate to the same
extent as baleen whales. Some live in rivers, and so their movements
are limited.

154