lOO TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
or laid aside, we cannot see that our argument is inadmissible. 
We have only to instance the rapid increase, beyond the shadow of 
a doubt, of so many other species that it is not even necessary to 
name them. Yet we do so—the Starling, the Stock Dove, the 
Tufted Duck, the Crossbill, the Redstart, the ISIissel Thrush ; and 
the distribution of many others could be written out.^ 
The whole or principal interest associated with such an inquiry as 
the above seems to us to rest in the far wider one of whence came 
the first colonists of an increasing species. The fact that the 
habits of the two allied forms— Le., in Scandinavia and Great Britain 
—differ, is, to our mind very unimportant. We allude to the differ¬ 
ence in their nest-building materials as evidence of specific differen¬ 
tiation. Numerous other instances could be given where habits 
change with geographical or physical circumstances ; even the very 
bird-voices of certain species are known to change. 
The present isolated characters of localities occupied by several 
species—amongst which the Marsh Tit is one—can hardly be the 
direct influence of migratory or “vagratory” hosts coming from south 
to north, or why should so many good intermediate localities be left 
neglected? Is it possible, rather, that occupations of sporadical 
nature such as these, may arise from a direct east to west, and return 
journey west to east dispersal, along certain old lines of migraiionl\ 
At least, we do not think such a hypothesis is less worthy of con¬ 
sideration than the other. The subsequent rate of increase of any 
species must be in large measure dependent upon richness of food- 
supplies in an area, consequent fecundity of the species, and pressure 
upon the centres of over-population. Some species lay few eggs, 
others many. This alone, we believe, is one of the first proofs of 
physical energy, and natural increase. We have chosen this species 
as only one of many which appear to us to prove several simple laws 
of Nature. 
* ]May I be allowed to suggest to brother-ornithologists of Tay that inquiries 
made into the life-history, decrease or increase, and steps of advance of many 
other species during the past ten or twenty oi' more years, would be likely to yield 
useful material for future work. I may mention especially the subject of the 
present notice, also the present and past distribution of the following The Red¬ 
start, the Wood Warbler, the Grasshopper Warbler, the Chiff Chaff, the Crossbill, 
the Greenshank, the Capercaillie (since the issue of our volume on that species), 
the Jay, the Titmice generally, the House INIartin, the Short-Eared Owl, the 
Birds of Prey, the Shoveller, Pochard, Widgeon, Tufted Duck, Goosander and 
i^Ierganser, &c., among Anatid^e ; the Stock Dove (all minutiae). Quail, Wood¬ 
cock (especially as regards its past), and any others which may occur to you. 
Each species should be worked out separately for Tay area. I would be pleased 
to receive and report on such if sent to me. 
t This expression is tentative —a convenience merely of speech. 
