For their mode of life renders the power of flight a
necessity, and it is on this account that their feathers are so
abundant and their wings so large. Besides these, however, there are
also other genera of birds that can fly well; all those, namely,
that depend on speed for security, or that are of migratory habits. On
the other hand, some kinds of birds have heavy bodies and are not
constructed for flight. These are birds that are frugivorous and
live on the ground, or that are able to swim and get their living in
watery places. In those that have talons the body, without the
wings, is small; for the nutriment is consumed in the production of
these wings, and of the weapons and defensive appliances; whereas in
birds that are not made for flight the contrary obtains, and the
body is bulky and so of heavy weight. In some of these heavy-bodied
birds the legs are furnished with what are called spurs, which replace
the wings as a means of defence. Spurs and talons never co-exist in
the same bird. For nature never makes anything superfluous; and if a
bird can fly, and has talons, it has no use for spurs; for these are
weapons for fighting on the ground, and on this account are an
appanage of certain heavy-bodied birds. These latter, again, would
find the possession of talons not only useless but actually injurious;
for the claws would stick into the ground and interfere with
progression.
Pages:
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241