Il6 THE SOCIAL LIFE OF ANIMALS 



gard to museum collecting, there was undoubtedly a 

 considerable amount of poaching; but as population 

 of heath hens declined, local sentiment turned in 

 favor of protection and poaching decreased, both 

 because of a more intelligent public reaction to the 

 birds, and because of closer patrol by wardens. Dr. 

 Gross, whose account I have been following, thinks 

 that there was evidence of an inadaptability of the 

 species, an excessive inbreeding, and, at the end, an 

 excessive number of males. In such small populations 

 the sex ratios frequently become highly abnormal. 

 Disease and parasites took their toll. Predators, par- 

 ticularly cats and rats, were active. The females hid 

 their nests well and were faithful in remaining on 

 them, so that they were killed off by the fires which 

 at times whipped over the breeding grounds. 



Over sixty thousand dollars was spent in trying to 

 save the heath hen, but without success. In contrast 

 to the laughing gull, which nested in a relatively 

 safe place and which came back from a population 

 as low as the heath hen's until the very last, this 

 unfortunate species was not able to adjust itself and 

 continue existence, even with as intelligent human 

 help as could be mustered in its favor. 



The general conclusion seems to be that different 

 species have different minimum populations below 



