Protection at the sanctuary seemed to be successful. The original 50 protected birds reproduced rapidly and there were 2,000 individuals by 1915. The entire heath hen population, however, was still confined to Martha's Vineyard. It is sad to say that in 1916 a fire wiped out much of the habitat that heath hens used for breeding, the following winter was unusually harsh, and there was an influx of goshawks that fed on the heath hens, which hurt the population even more. Finally, many of the remaining heath hens fell victim to a poultry disease brought to the island by domestic turkeys. There were only 13 heath hens left by 1927 and most of these were males. The last living heath hen, the final survivor of his species, was seen on March 11, 1932. He died that year.
The last birds were wiped out by a series of relatively common, but deadly, natural events: fire, starvation, predation, and disease. But the heath hen's continued existence as a species would not have been so vulnerable to these occurrences if their populations had not been severely reduced already by human hunting. In its former range, the heath hen easily could have survived any one of these stresses, or even all of them in combination. This also shows that designating a protective zone, or prohibiting the direct killing of an endangered species, does not guarantee survival of the species.
Source: Wikipedia
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