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Significance of White Markings in 

 Birds of the Order Passeriformes. 

 By Henry Chester Tracy. Univ. Cal. 

 Pub. in Zool., vi, 1910. pp, 285-312. 



Few ornithologists, we imagine, have 

 seen a Meadowlark or Junco, a Mocking- 

 bird or Magpie, expose its white markings 

 in flight without speculating over their 

 significance. It is almost invariably the 

 outer pair of tail-feathers which have 

 the most white, and we believe that in 

 no bird is the central pair white and the 

 outer pair dark. 



The white is, therefore, so disposed that 

 it is visible only when the tail is more or 

 less spread; and in many cases it is spread 

 or opened just enough to show the extent 

 of these white markings. 



The theories advanced in explanation 

 of the value or purpose of flight-exposed 

 white marks at least prove that "many 

 men have many minds," even if their 

 wide variance tends to weaken our belief 

 in their validity. To Thayer, such color 

 characters are concealing or obliterative; to 

 others, including the author of this paper, 

 they are revealing or directive; while it 

 was Merriam, we believe, who first sug- 

 gested that they protected their possessor 

 by being so strikingly evident when their 

 wearer was in flight that their sudden and 

 complete effacement when the bird took 

 to cover, left the pursuer looking for a 

 victim which had disappeared as if by 

 magic; a theory, by the way, not referred 

 to in the paper under review. 



After commenting on the importance 

 to a bird of "seeing and being seen by its 

 companions," Mr. Tracy asks, "How do 

 the birds of our woods and fields actually 

 keep track of one another?" The value of 

 the voice and ears is admitted, but it is 

 further claimed that "sight plays a part 

 of corresponding importance in the econ- 

 omy of bird-movement, — to some extent 

 replaces sound as a means of recognition." 

 To test the value of directive markings, 

 Mr. Tracy presents a table of North 



(100) 



American Passeriform Birds of the Open 

 designed to show that the birds marked 

 with white, taken as a whole, have the 

 habit of flocking, while the reverse holds 

 true for those not so marked; from which 

 he concludes that white markings are of 

 directive value in keeping the individuals 

 of a flock together. 



It does not seem to us, however, that 

 this table presents an altogether correct 

 view of the matter. If memory is not at 

 fault. Horned Larks, for example, show 

 black not white on the outer tail-feathers 

 when in flight, while the Dickcissel, 

 various species of Blackbirds of the genera 

 Malathrus, Agelaius, Scolecophagus, and 

 Qniscalus, and the Swallows, seem to us to 

 be better placed among "Birds of the 

 Open " than among the Warblers, Thrushes 

 and other "Passeriform Birds of Arboreal 

 Habit," in the table on page 299. All 

 are preeminently flocking species, and only 

 the Barn Swallow has white in the tail, 

 and this is so placed as to be but slightly 

 revealed by flight. 



In the second table, just referred to, 

 Mr. Tracy places arboreal birds in two 

 groups, according to the presence or 

 absence of white wing or tail markings, 

 and expresses his belief that while certain 

 of these markings may, in conformance 

 with Thayer's theory, have a concealing 

 value when in repose, they are revealing, 

 and hence directive, in flight. We observe 

 that while the eastern Robin is here 

 placed with birds having white tail 

 markings, no mention is made of the fact 

 that in the Western Robin (Planesticiis 

 migratorius propinquus) the white tail 

 marks are wanting. The case is excep- 

 tionally interesting, for here is a bird 

 which, as a species, can be placed in both 

 categories, a fact which rather weakens 

 one's faith in the functional value of 

 white tail markings in this particular 

 instance. 



Mr. Tracy concludes his paper with a 

 special study of the Mniotiltidm, and a 



