BIRDS OF THE CAMBRIDGE REGION. 95 



10. Larus marinus Linn. 

 Great Black-backed Gull. Black-backed Gull. Black-back. 



Common winter resident. 



SEASONAL OCCURRENCE. 



November 19, 1868, several seen, Fresh Pond, W. Brewster. 



December i — April 15. 

 April 25, 1904, one seen, Back Bay Basin, R. S. Eustis. 



On our seacoast the Black-backed Gulls arrive from the North early in 

 September and linger well into May. They seldom appear inland before the lat- 

 ter part of November or after the 15th of April, but within this period they may 

 be seen frequently, and at times constantly, for weeks in succession, flying 

 about over the Back Bay Basin with the Herring Gulls, in whose company they 

 also occasionally visit Fresh, Spy, and the Mystic Ponds. It is unusual to note 

 more than three or four Black-backs at any one time about such land-locked 

 waters, although, on several occasions, I have known this number to be con- 

 siderably exceeded in the Back Bay Basin. The adults with their strongly 

 contrasting sable backs and snow-white heads and tails — which give them, 

 especially when they are soaring in circles, a superficial resemblance to adult 

 Bald Eagles — are conspicuous and easily recognized birds, but the young 

 are colored so nearly like those of the Herring Gull as to be frequently mistaken 

 for the latter, despite the fact that the Black-back is decidedly the larger of the 

 two. It is one of the wariest of all birds, and few if any specimens have ever 

 been taken in our neighborhood. 



Dr. Townsend has reported seeing a few Black-backed Gulls "during the 

 summer of 1903," and no less than seven adults on July 17, 1904, at Ipswich, 

 Massachusetts.' On July 18, 1890, I found at least thirty or forty birds, all 

 but two or three of which were in the grayish immature plumage, at Great 

 South Pond, a brackish sheet of water lying just within the beach ridge on the 

 south side of the island of Martha's Vineyard. Such instances of local occur- 

 rence in midsummer afford no evidence, however, that the species ever breeds 

 in Massachusetts, for the birds to which they relate are believ-ed to be invariably 

 barren individuals. 



1 C. W. Townsend, Memoirs of the Nuttall Ornithological Club, no. III. Birds of Essex County, 

 Massachusetts, 1905, 90. 



