The Tufted Duck in Scotland. 159 
tions have been recorded—let it be remembered the Tufted 
Duck is rare, or was rare, at all events, as late as 1871 and 
in 1875 (Petchora River and Dwina Delta), and we are not 
aware of any later increase in these parts. 
How far these questions can be answered and these diffi- 
culties got over—I mean as regards the dispersal to our 
shores of Britain—may perhaps appear to those who are not 
already wedded to what may seem “a more reasonable and 
direct dispersal from the north direct,” if they study carefully 
the facts we have tried to group in the body of the paper in 
the Annals. It only remains for me to say it does appear 
to me that there is a distinct dispersal from original centres 
in the east, westwards, influenced by the isothermal lines, 
and checked only by either vast expanses of ocean backed 
up by mountain chains intersecting the general course of 
their east to west migration. And I may perhaps be 
pardoned for thinking that our facts go to prove, or at 
least to suggest another possibility, which may shortly be 
stated as follows :—Tufted Ducks, as we know, are naturally 
of sedentary disposition. It seems almost that they first 
colonise towards the centre of their migration area. As I 
have endeavoured to illustrate, their fly-lines are interrupted 
by physical obstructions, notably mountain chains, and 
individuals first colonise closest up to these obstructions to 
their routes, and afterwards the surplus surges back as 
it were along the lines which on their previous migration 
offered least opposition or resistance (as individuals, not as 
the whole species). In fact—if this reading be correct—the 
Tufted Ducks first colonise areas suitable to their require- 
ments, nearest to the limit of their individual winter termini, 
and subsequent dispersal takes place by the retrograde steps 
of their spring movement; or pressure of population may, 
and doubtless does, result in finally pushing many over 
these obstructions; but, so far as our present facts take us, 
there is little evidence indeed to show that our western and 
eastern areas of distribution of the species are indebted to 
the same avenues of approach. 
It appears to me also, that possibly the converse state of 
things to that represented by the dispersal of this distinctly 
