Page:Popular Science Monthly Volume 77.djvu/96

90 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 Blackwall in 1834, who called particular attention to "the occasional desertion 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 fifteenth, 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.