Unusual Migration of Briinnich's Murre. 541 



food might have been obtained, the exhausted condition of 

 the birds made it impossible to either capture or assimilate 

 it ; birds I had alive refused to eat, and if forcibly fed were 

 unable to retain food, and in no case were captured birds 

 able to survive beyond a few days. It is impossible to say 

 for how long a period Murres can survive without food, but 

 it is certain that under the conditions we are dealing with 

 the period must be much less than if the birds were 

 stationary. Here and there a bird by reason of superior 

 staying powers, being less exhausted, was able to obtain 

 food, and these few survived for a period, but all eventually 

 succumbed before a return north became possible. 



Very many thousands must have been numbered in each 

 migration ; yet year by year they came at nearly the same 

 period, and over nearly the same territory, pressing forward 

 to the same fate. 



The cause giving rise to so persistent a movement must 

 have been the same, as most unusual migrations are believed 

 to originate with, lack of food, and in this case sudden, not 

 gradual lack of food, or the birds would have been unable to 

 sustain the long flight they did. 



I have published elsewhere an account of a parallel, 

 though isolated, case of migration among certain species of 

 ducks in Ontario (Auk, Vol. XXII., 1905, p. 206), in which I 

 was able to indicate a cause, and that cause was the sudden 

 covering over of the regular feeding* grounds by ice ; the 

 ducks, finding the usual open places over their feeding 

 grounds closed, and unable to find food in the deeper waters 

 of the Great Lakes, were eventually forced to migrate, but 

 not before they had become exhausted, and many were 

 picked up inland, unable to go further. 



In view of this case it seems not impossible that the cause 

 of the migrations we are dealing with was the same, though 

 brought about in a slightly different way. Coming south, in 

 Hudson Bay, the Murres were caught between the moving 

 and shore ice, and, being cut off from their food supply, 

 had no alternative but to migrate. Mr. Lowe, writing to me, 

 says, " Those found at Toronto probably came from the bay, 

 where accidental freezing has cut them off from the open water, 

 and they have been driven south by a northerly gale. Not 



