Teeters, Nods, and Bobs 19S 



Here were two men and two theories: one that the mo- 

 tions improved vision, another that it provided protection. 



I consulted Grinnell's chapter on "The Principle of Rapid 

 Peering of Birds." He held that the birds which hunted sta- 

 tionary food continually shifted their position so that the 

 angle would permit easier location of the prey, just as a man 

 hunting a golf ball walks back and forth in an effort to find a 

 spot from which the missing object can be seen. This was a 

 new theory and one which did not require a water back- 

 ground. 



I remembered an article by Edmund J. Sawyer, an artist, 

 a close observer of nature, and a man of tremendous field 

 experience. He dismisses the idea that this constant habit 

 may be an alarm signal to its kind, or a recognition mark, or 

 a source of information. He is certain that it is not used to 

 intimidate an enemy. The habit, he thinks, is an all-season 

 one and a constant one, and this removes the possibility of 

 its use for such purposes. 



So far his approach is negative but he does not continue 

 in that vein. He advances the theory that bobbing and tip- 

 ping are done to increase the possibility of survival. He 

 points out that it is confined to the smaller birds which need 

 the advantage of a split second's start over a natural enemy. 

 He thinks that this continued movement may suggest in- 

 cipient flight and cause a premature and blundering attack 

 by predators. He considers that this theory may account for 

 the existence of the habit in birds which are distantly re- 

 lated. He is certain that any reasonable explanation of the 

 various styles of bobbing and tipping must be consistent 

 with the fact that the birds often have little or nothing else 

 in common. And he closes with the thought that, to the best 

 of his knowledge, the birds with this habit are all of the 

 ground type and especially subject to attack, which would 

 seem to call for some extra measure of self-protection— such 

 as a moment's warning would give. 



