26 NATURAL HISTORY SOCIETY OF DUBLIN. 



which usually, perhaps always, breeds on the coast, or the lesser Black- 

 backed Gull, which frequently breeds on fresh water. 



Some discussion then ensued on the migration of birds, in the course 

 of which Mr. A. G. More said that the observations on this subject 

 have not yet been reduced to any system. As regards the direction of 

 the flight of birds, and the influence of climate and prevailing winds, 

 something may be done by registering the lines of simultaneous flight, 

 if a sufficient number of good observers can be found. As to the causes 

 which influence migration, there seems to be this difference between 

 the spring and the autumnal movement — that in the spring the impulse 

 comes from within, being simultaneous with the vernal change of plu- 

 mage, and is found to be comparatively more sudden and irresistible, so 

 that the birds appear to take a more direct road towards their summer 

 quarters ; and, when detained captive during the spring, they have been 

 known to die from the ungratified desire to migrate. On the other 

 hand, in autumn the impulse comes from without, as the birds may be 

 said to retire under the pressure of external circumstances, and, as might 

 be expected, they seem to travel more slowly at this season than in 

 spring, being gradually driven out by the inclemency of the weather, 

 or a want of food, and this before the change to the winter plumage is 

 completed. This may serve to explain the fact that many birds are ob- 

 served to follow a different line of flight at the two seasons, if it be 

 supposed that in spring they take a more direct road towards their 

 breeding quarters, while in autumn they are found to linger by the way, 

 and often follow the course of valleys, rivers, or coasts. Another point 

 to be noticed is the greater regularity of arrival in spring, when most 

 birds keep pretty nearly to the same date, and are found on arrival 

 nearly fully attired in the summer plumage, whereas they return in 

 autumn with less punctuality, and often long before the winter plumage 

 is assumed. 



Mr. E. P. Williams mentioned the fact that, although seeming to 

 thrive for a length of time, the Anas clangula will not outlive the 

 season in confinement. He had at first fed his birds with cockles, clams 

 (Mya arenarid), and mussels {Mytilis edulis), as being their natural 

 food ; these were thrown into the water, and which the birds seized by 

 diving, returning to' the surface to eat them ; by-and-by they rejected 

 the shell-fish diet, and took to potatoes and cereals, and continued 

 healthy and active. When the time for migration, however, came 

 round, they, as well as the Smews (Mergus allella), suddenly died. This 

 would seem, possibly, to bear out Mr. More's views on the question of 

 migration. They died, seemingly, not from want of nutriment, being 

 in good health, but as if from an ungratified impulse. The only in- 

 stance Mr. Williams recollected to the contrary was a male Golden 

 Eye, in Sir Wm. Compton Domvile's collection at Santry. This bird 

 was kept in a large wired enclosure with a variety of birds, which were 

 fed on beef hearts, chopped fine, on which were also fed different kinds 



