9o THE POPULAR SCIENCE MONTHLY 



A classical illustration of this struggle of instincts was furnished 

 by Dr. Jenner, in his " Essay on the Migration of Birds," published in 

 1824, and by the more circumstantial account given by Dr. John Black- 

 wall in 1834, who called particular attention to " the occasional deser- 

 tion of their last hatched broods by the swallow and house martin." 

 Blackwall was a keen and discriminative observer, but his work 4 is so 

 little known that I shall give a summary of his valuable and interesting 

 results, under this head. 



The swallow arrives at Manchester, England, about April the fif- 

 teenth, and the house martin on the twenty-fifth of the same month. 

 They produce from two to three broods in the season, and are commonly 

 found with nestlings in October, at a time when most of the migratory 

 species have left the country. Many of these young which are led out 

 of the nest, are deserted before they are able to follow their parents 

 south, and have been found in a state of semi- or total exhaustion, late 

 in the year. This, as Blackwall ingeniously suggests, may have given 

 rise to the queer notion that the European swallows passed the winter 

 season in a state of torpidity. 



Blackwall's observations were begun as early as 1821, and when on 

 November 11, 1826, twenty-two nests under the eaves of a barn in 

 the Chapelry of Blakeley were carefully inspected, it was found that 

 thirteen of this number contained either eggs or dead nestlings; five 

 nests held eggs in every stage from the freshly laid to those at the 

 hatching point, while the eight with young showed nestlings in every 

 condition from that of hatching up to the nearly fledged state. 



While the female swallow may exceptionally linger longer than the 

 male, it should be noted that both parents commonly abandon their 

 young at the same time. The same fatal conduct was also frequently 

 observed in the sand martin, and Gilbert White, of Selborne, has given 

 an interesting account of a swift, originally noted by him in 1781, 

 which renders it practically certain that this bird may also desert its 

 young, when the migratory impulse is strong. According to Pennant, 

 who is quoted by Blackwall, the puffin is in like case also. The parental 

 instincts of the puffin are strong, and the first young, which appear 

 early in July, are guarded with the utmost care. But strong also is the 

 instinct of migration, and when this emerges punctually at about the 

 eleventh day of August, any young puffins which can not fly are left 

 to the tender mercies of the peregrine falcon. This vigilant plunderer 

 watches at the mouths of their holes, ready to seize them with mailed 

 foot the moment hunger forces them to surrender. We may be quite 

 sure that the young of the species enumerated above are not the only 

 victims of the struggle of conflicting instincts. I have heard of similar 

 behavior on the part of the domestic pigeons. 



4 " Researches in Zoology, Illustrative of the Manners and Economy of 

 Animals," London, 1834; 2d ed., London, 1873. 



