3 8 Br.ACK-POLLED WARBLtR, 



time of mig^ration. The route of migration is doubtless directly north from the 

 coast of South America to Jamaica, where the species is a well-known migrant, 

 across eastern Cuba to the Bahamas. When I saw them on April 26 they must 

 have recently come from South America, and, judging from the short stay that 

 they made on the keys south of Andros, each individual would not have remained 

 over a day in either Jamaica or Cuba, thus, probably, these birds left the coast 

 of South America on April 23. After crossing the Bahamas the Black-polls no 

 doubt strike the coast of the United States about in the neighborhood of Charles- 

 ton, South Carolina, and then proceed north quite leasurely. Thus the first 

 portion of the journey of an individual Black-poll from South America to Charles- 

 ton is made in four or five days, including stops to feed. The remainder of the 

 journey would be made in about fifteen days. Thus the Black-polled Warbler 

 occupies something like twenty days in all, in performing a journey of 2,500 

 miles. 



It is exceedingly difficult to arrive at even an approximate estimate of the 

 numbers of any given species of bird, hence any data that will give even a rough- 

 ly a])proximate estimate of s-uch a number are of value. In the ease of the Black- 

 ])olled Warbler, I think some such estimate can be made from my own observa- 

 tions. 



First let us try and estimate the area occu})ied by the whole of this species 

 during migration. The width of the region traversed by the Black-polls from 

 South America to the northern Bahamas is, I should judge, about one hundred 

 miles. That is it would be about as wide as the length of the island of Jamaica, 

 I certainly di:l not find this species on the Cayman Islands, and, although it i» 

 recorded fiom Porto Rico, it is not given from Hayti nor San Domingo: thus we 

 have good reason for believing that the greater number of the spring migrants of 

 this species pass over Jamaica and so across the eastern portion of Cuba in prob- 

 ably about the same width of belt in which they crossed Jamaica, then on to the 

 Bahamas, extending acioss the keys about the same distance. It took the flight 

 of Black-polls, as already stated, about two days to pass the keys to the south 

 of Andros. \\'c may thus judge that it took two days for all of the members of 

 this sp3cies, after once starting to leave ths coast, to get fairly out of South Amer- 

 ica By this estimate we find that the entire body of warblers was one hundred 

 miles wide, measured by distance, and two days long, measured by time. Now 

 to try and reduce the time to distance, we will have to consider — as it may per- 

 haps be safe to do — that Avhen the advance guard of the Black-polls reached 

 the keys of Andros, on the morning of April 2!), the feaJ-guard was still in Jamai- 

 ca, three hundred and eighty miles away ; giving a column of Black-polled War- 

 blers three hundred and eighty miles long by one hundred wide. Or, in other 

 words, all of the Black-polls in the world, were, at this time, confined to an area 

 38,000 square miles. Estimating that each of these square miles, both sea and 



