9-!: 



Protective Coloring in Terns. 



A. J. BiGNEY. 



Protective coloring in birds lias been and still is a subject of great 

 interest to the ornithologist. Since ecological factors are receiving so 

 mnch attention now on the part of biologists, every item bearing uix>n 

 variations due to environment is of interest, since it throws some light 

 upon the question of evolution. 



One of the most remarkable instances of protective coloring came 

 under my observation during the past summer on the island of Peni- 

 kese, made famous by Louis Agassiz's first marine laboratory. This island 

 is occupied by only one family. Nothing is raised except a few garden 

 plants and sheep. There are other inhabitants of the island, however, that 

 are more important than sheep— at least to the biologist. These are the 

 terns. Long before one reaches the island he can hear the shrill voices 

 of myriads of these birds as they fly about the island almost constantly 

 from daylight to dark. These terns axe protected by law and hence 

 have become very numerous. Almost countless thousands are to be found. 

 The soiuids of their shrill voices make a lasting impression upon a per- 

 son. The island is entirely made up of glacial material, here and there 

 covered with grass. The beaches around the entire island are quite wide 

 and covered with granite pebbles of various colors, mostly of a white, 

 gray or slate color, giving them a mottled appearance. The grass and the 

 soil is very much the same in color. The dead grass furnishes a fine 

 place for nesting and also for hiding-places for the young birds. In the 

 breeding season the nests and young birds are so numerous that one has 

 to pick his way carefully, lest he step on some of them. They are so 

 ftearly the color of the ground and grass that you can hardly see either 

 bird or nest. If the parent bird is on the nest the deception is almost 

 perfect. 



The most deceptive coloring is in the young birds when they lie out on 

 the pebbles to warm themselves in the sunlight. The imitation is so per- 

 fect that you have to look for some time before you can see the birds. 

 The eggs are mottled in the same way as the sticks, grass and earth that 

 compose the nests. The adult birds are not mottled as are the young 

 birds or the eggs, thus showing that this is truly a protective coloring. 



