go 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* 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 178i, 
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. 
