NATURE AND MAN IN THE FORTH VALLEY. 83 
birds of the Valley of the Forth including the eastern 
district are summarized thus :— 
Residents . 90 ‘ : 
Halt 1 ; 1 | ; 
Summer visitors, A oaiy, \ peep ne 
Winter visitors, : . 40 
Visitors on migration, . ; ap 
Casual visitors, . . 69 
251 
There can be no doubt, as Mr Clarke points out, that the 
Forth Valley is singularly rich in number of species and 
variety of forms, attributable to the great diversity of 
physical features found in the district. Between the lofty 
eliffs of Ben Lomond and Stobinean and the extensive mud 
flats of the estuary, there is every variety of moor, meadow, 
woodland, loch, and river. 
Perhaps the most interesting field of investigation in con- 
nection with birds is that of migration. This subject has 
been carefully investigated by Mr Harvie Brown of Dunipace 
and others, who have shown that the hereditary instinct in 
birds leads them to follow the same lines of migration as 
their ancestors. These lines originally followed plains or 
valleys or ancient shore-lines as the necessities of life—the 
search for food-—dictated. Now, when the physical features 
of the country have changed—-when land has given place to 
sea, and coast-lines are different—the birds still continue to 
follow the old routes of migration. They still cross from 
Africa to Europe at the shallower portions of the Mediter- 
ranean, they still cross the German Ocean from east to west-— 
in these cases indicating the former presence of land where 
now the sea rolls. This, at all events, is the theory of Herr 
Weissman. The constancy of these lines of flight is, 
however, largely modified by prevailing winds and weather, 
and by the present configuration of the land. The Forth 
Valley is a most interesting district for the further 
investigation of this subject, with its firth open to the east, 
and well-marked hill ranges. Mr Harvie Brown states that 
the valley between Stirling and Loch Lomond is one of the 
favourite highways of the land birds in their annual flight 
