312 



ZOOLOGICAL SOCIETY BULLETIN 



COMMON TERN. 



small, delicately pointed beak of the tern 

 finishes ofif its neat appearance, and the entire 

 bird is the personification of grace, as it 

 dashes through the air, or plunges headlong 

 into the sea — to rise almost immediately with 

 a small fish in its beak. 



The beak of the skimmer lends a heavy 

 aspect to the whole bird. It is long and higli, 

 and the lower mandible extends a full inch 

 beyond the upper. Both are as thin and as 

 pliable as paper-knives. A unique method 

 of obtaining food is the secret of this ap- 

 parent deformity : the strong wings of the 

 bird enable it to fly very close to the sur- 

 face of the water, so close in fact that the 

 lower mandible dips below the surface, thus 

 ploughing a zigzag furrow and catching up 

 any organisms, shrimps or fish, which chance 

 to be floating on the water. 



Among ducks, we find those which feed 

 on fish, and those which sift their food from 

 the mud at the bottom of ponds, and these 

 differ radically in respect to their beaks. The 

 fish-eating merganser has perhaps, of all liv- 

 ing birds, the nearest resemblance to a toothed 

 beak. The deep serrations, however, are but 

 indentations in the substance of the strong, 

 narrow bill of the bird. When once in this 

 saw-like grasp, the most slippery fish is help- 

 less. The beak of the shoveller duck shows 

 how well Nature has provided for its wants. 

 The beak is arched and spatulate, while the 

 sensitive epidermis is prolonged at the edges 

 into a series of comb-like teeth — analogous 

 to the whalebone in the mouth of a whale. 

 Through this sieve the water is drained out, 

 leaving entangled the edible worms and in- 

 sects. 



If we should elevate our shoveller duck, 

 placing him on long, slender legs and pro- 

 viding him with a correspondingly long neck. 



he would indeed be in a predicament, since 

 only the tip of his beak could be brought 

 to bear in feeding. Now a flamingo is really 

 a long-legged duck, which feeds in much the 

 same way as the shoveller, and the difficulty 

 mentioned is overcome in a most ingenious 

 way. The mandibles are bent downward, al- 

 most at right angles, so that, when the head 

 reaches the ground, not the tip but the whole 

 iliverted bill is in a position to sift out food. 

 To meet the reversed condition, the lower 

 mandible is deeply arched, instead of the up- 

 per, as in the shoveller duck. 



We are able to follow the probable evolu- 

 tion of such remarkable beaks as those of the 

 flamingo and skimmer by observing the growth 

 of this organ in any individual from the time 

 when the bird hatches from the egg until it is 

 full-grown. In the very young flamingo chick 

 there is no sign of the subsequent deflection, 

 the mandible being short, perfectly straight, 

 and rather slender. As the bird at first feeds 

 upon regurgitated food, taking it drop by drop 

 from the bill of the old bird, it, of course, 

 has no need of the curved beak of its parents. 

 Later, when its bill has increased in length and 

 has begun to be marked by the ultimately 

 sharp angle, the birds begin to sift from the 

 coral mud the small mollusks of which their 

 food consists. 



Until its wings are full-feathered the young 

 skimmer is compelled to limit its wanderings 

 to the sand-dunes along the shore near its nest. 

 Thus, although at birth the lower mandible is 

 a trifle longer than the upper, yet even when 

 the birds are half-grown the disparity in length 

 between the two mandibles is but slight. Later, 

 when the young bird is able to join its parents 

 in their skimming of the seas, the lower mandi- 

 ble quickly attains its full development. The 

 friction oi the water upon the bill must be con- 



r.LAC K SKIMMER 



