146 A VERTEBRATE FAUNA OF THE MORAY BASIN. 



In a continent like America, where land lies in vast bulk from 

 north to south, and where great oceans separate it from other lands, 

 and where but few islands fringe its shores, both land and water 

 birds fly north to south, because the conditions are equally suitable 

 to each. 



We have spoken of the autumn migration, and the possible 

 influence upon it of the peculiar conformity of the shores of the 

 Firth. If we now turn to the more inland localities we find the 

 same natural conditions continued in a very marked degree, and 

 we hope to make this plainer by the diagrams which follow. 

 We have seen that the Moray Firth and the Great Glen form, as 

 it were, an enormous letter — ^ lying in a horizontal position, 

 the leg being the Great Glen, and the arms the north and south 

 shores of the Firth. Then, if over the V -shaped portion of the 

 -< and a part of the leg, we place a U thus ^^--^^ , the new 

 lines so drawn may be held to represent the watershed of the 

 drainage system of the Moray Basin. 



It becomes a creed of the systematic worker in distribution and 

 migration always very carefully to make note of the elevations of 

 the watersheds and sources of the streams, and to fully realise the 

 influences brought to bear upon migration-lines, by, on the one side, 

 high cliffy coasts and narrow rocky or landlocked sea-entrances, 

 and, on the other, by low sandy coasts and skerries, sand- and mud- 

 flats, and wide open highways for free migrations. 



Migration, we hold, from many observations made, takes place 

 inside the Moray Firth and spreads in a widening fan inland, in 

 battalions up the great lateral glens of Deveron, Spey, and Find- 

 horn ; or, to carry it further, up and down the greatest depression of 

 all, the Great Glen between Inverness and Fort- William, and 

 so on to the troughs and sea-lochs of Loch Linnhe and Loch Suinart 

 and the western isles ; and of these latter, especially Tiree and Islay. 



Flights of migrating birds do not ' come in ' to the same ex- 

 tent over the cliff-heads of Aberdeenshire; and the great body of 

 migrants passes on until the sheltering headland of Troup is reached 

 before they seriously deflect their course. The north-east promon- 

 tory of Scotland to the east of Troup Head does not present great 



