AGGREGATIONS OF HIGHER ANIMALS 11 5 



Then came a fire, a gale, and a hard winter, with 

 an unprecedented flight of goshawks, and in April, 

 1917, there were fewer than fifty breeding pairs. The 

 next year, when there was an estimated total popu- 

 lation of 150, the heath hen range was invaded by 

 several expert photographers who took motion pic- 

 tures of mating behavior. In the face of this disturb- 

 ance at a critical time, still a good year allowed the 

 birds to increase and again to spread over Martha's 

 Vineyard. In 1920, 314 were counted; but thereafter 

 a decline in numbers set in which was never stopped. 

 The figures for those five successive years are: 117, 

 100, 28, 54, 25. At this point extra wardens were put 

 on the job, who killed more cats, crows, rats, hawks, 

 and owls, the enemies of the heath hen. The next 

 year's count was 35; in 1927, there were 20; but in 

 1928, in a census that lasted four days, only a single 

 male was found. No other bird was seen thereafter, 

 though a reward of a hundred dollars was offered 

 for the discovery of another. This single male was 

 banded and released and was last seen alive on Febru- 

 ary 9, 1932. With his death the heath hen became 

 extinct. (18) 



When this much is known of the decline in num- 

 bers of a given species there should be some knowl- 

 edge of the factors involved in its extinction. There 

 is. In the earlier years, as I have indicated with re- 



