J. E. LITTLEBOY — THE MIGRATION OF BIRDS. 2i 



Sprinc,'. Ecspcctinp: mituiiinal misration, taken as a whole, but 

 little ditForeuce of opinion appt'ars to exist. Birds migrate 

 southward, writes Dr. AVeissuuuin, because "they would perish, 

 not from cold, but from want of food," should they remain in their 

 summer quarters during the winter months. ' * Tliey migrate because 

 they are obliged to do so in order to maintain life, they migrate 

 that they may not starve." It is a significant fact that " the 

 stomachs of migratoiy birds, on their first landing, never contain 

 any food." *' Dr. Weissmaun's conclusion is sufficiently confirmed 

 by experience within the reach of any of my audience. In England 

 our summer migrants are mostly insectivorous : swallows, martins, 

 and swifts I'eed principally on gnats, flies, and small beetles ; some 

 of the warblers, especially the blackcap, indulge in ripe fruit as 

 a dessert; the cuckoo delights in caterpillars, the night-jar in moths, 

 and it would be easy to enlarge the list. As autumn advances, 

 insect-life, and even fruit, becomes more and more scarce, and 

 birds that have revelled in abundance during the summer, leave 

 our comparatively inhospitable shores for more prolific hunting- 

 grounds. It is true that a few of our migrants leave us, as in the 

 case of the swift, when insect-life is still abundant and when the 

 heat of summer has only partially diminished, but it cannot be 

 doubted that habit is hereditary in the life of birds as well as in 

 that of other animals, and if this be accepted as a fact, it is not 

 difficult to suppose that the period of necessary migration may, in 

 8ome cases, be anticipated in deference to the force of habit. 



The spring, or northern migration, is a more difficult subject. 

 Dr. Weissmann attempts to account for it by two leading proposi- 

 tions. I quote the following extracts. («) " No possibility of life 

 in nature remains unused. Wherever the outward conditions for 

 the existence of a living being are favourable, there, for the most 

 part, we find life. Every species tries to multiply itself indefinitely ; 

 hundreds of thousands are born every year, but far more than half 

 perish early because there is not room for all. So long as any 

 country remains unpeopled with bird-life, in which such life might be 

 genei'ally maintained, so surely will the unoccupied ground be quickly 

 taken into possession." [b) " It is generally imagined that tropical 

 countries have, all the year round, an abundant supply of food of 

 all sorts, both for animal and vegetable life. This is true, however, 

 only of certain regions ; for the most part it is altogether a mistake. 

 In the interior of Africa whole districts of country are completely 

 dried up ; all standing waters and most running streams disappear ; 

 frogs, newts, lizards, and snakes, as well as many fishes, bury 

 themselves in the mud and there take their summer sleep ; and 

 even the insects disappear as a body when the green of the 

 plants is parched by the burning heat, and all verdure withers. 



Hence, there is here again an obvious necessity for birds 



to seek other climes We do not of course mean by this, 



that the individual bird, as we see him to-day, is driven away 



* Cordeaux, 'Leeds Mercurj-,' Sept. 1867. 



