A DESCRIPTION OF THE BIRD ROCK GROUP ON 
EXHIBITION IN THE AMERICAN MUSEUM OF 
NATURAL HISTORY, REPRESENTING A_ POR- 
TION OF A “ BIRD ISLAND” OF THE NORTH AT- 
LANTIC AND THE NESTING-HABITS OF ITS 
OCCUPANTS. 
By FRANK M. CHAPMAN, 
Associate Curator of the Department of Mammalogy and Omithology. 
IsLANDS AS BIRD PROTECTORS. 
To the preserving influence of island-life we owe the continued 
existence of many birds which have long ceased to live, or, at 
least, to nest, on the mainland. This is true of the great oceanic 
islands as well as of the sand-bars, reefs, and rocks on which sea- 
birds rear their young, and even of the tiny islet of reeds or 
vegetable mould which forms the nest of the Grebes (see Group 
of Pied-billed Grebes in the Main Bird-Hall). In every instance, 
however, whether the island be a thousand square miles or one 
square foot in extent, it owes the preservation of its bird-life to 
the same cause, and this cause is the entire or comparative ab- 
sence of bird enemies. 
Oceanic islands, or those which have had no connection with 
the mainland, are, as a rule, without terrestrial mammals, and con- 
sequently destructive animals such as wolves, foxes, cats, both 
wild and domesticated, minks, weasels, etc., are wanting, even 
when the conditions are favorable to their existence, while the 
barren rocky islets, reefs, and sand-bars are uninhabited, not 
only by these predaceous species, but also by the birds’ worst 
enemy—man. 
Thousands of instances could be cited to illustrate the im- 
portance of the part played by islands in protecting birds, but we 
need go no farther than our Atlantic coast to be convinced that 
were it not for islands we should long ago have lost a number 
of birds which now never nest on the adjoining mainland. For 
example, practically all our remaining Terns or *‘ Sea Swallows "’ 
now breed only on islands, the remaining large colonies of these 
birds off the New York and Massachusetts coasts being found on 
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