134 '^^^^ Scottish Naturalist, 



the ship for a time, uttering loud twitterings, finally settled in 

 swarms all along the combings outside the ship, as also on the 

 headings both above and below the stern windows of the 

 captain's cabin, the ward-room, and gun-room, as close as they 

 could possibly pack. These all appeared to be old birds, though 

 of this I could not be certain. One of the officers, however, 

 of the ship, making a sweep with his cap outside one of the 

 windows, captured more than a dozen of them, which on being 

 liberated immediately joined their companions ; these were 

 all adults. In the morning not one was to be seen. Had 

 these birds continued their journey the previous evening, 

 another hour would have landed them in Africa, but, the 

 Swallow being a day flyer, and as it was getting late, and such 

 convenient quarters close at hand, they doubtless held a 

 consultation in their twitterings, 9,nd prudently decided to 

 stick by the ship. 



Mr. Wallace, in his very able work, on the " Distribution of 

 Animals," says, " almost all the migratory birds of Europe go 

 southward to the Mediterranean, move along its coasts, east or 

 west^ and cross over in three places only; either from the south 

 of Spain, in the neighbourhood of Gibraltar, from Sicily over 

 Malta, and to the east by Greece and Cyprus. They are thus 

 always in sight of land. The passage of most small birds (and 

 many of the larger ones too) takes place at night, and they only 

 cross the Mediterranean when the wind is steady from near the 

 east or west, and when there is moonlight : and he further re- 

 marks, " that migrations of this type probably dated back from 

 at least the period when there was a continuous land along the 

 route passed over, and it is a suggestive fact that this land 

 connection is known to have existed in recent geological times. 

 Britain was connected with the continent during or probably 

 before the glacial epoch ; and Gibraltar, as well as Sicily and 

 Malta, were also united with Africa. The submersion of 

 these tracts of land (which were perhaps of considerable extent) 

 would be a slow process. And from year to year the change 

 might be hardly perceptable. It is easy to see (he adds) how 

 the migration that had once taken place over continuous land 

 would be kept up, first over lagoons and marshes, and then 

 over a narrow channel and subsequently over a considerable 

 sea, no one generation of birds ever perceiving any difference 

 in the route."* 



* Vol. I. page 20. 



