THE PROCESS OF DISPEESAL. 



Ixxvii 



of several species along the north coast of Norway and further to the 

 east, so far as its influence can affect the coast-lines of these regions. 

 For instance, the Eed-necked Phalarope has lately been ascertained 

 to nest in Ireland, but how long ago it did so there appears to be 

 no records to show. 



No doubt there are ranges of temperature right and left of 

 isothermal lines, between which extremes alone certain forms of 

 vegetable and insect (or bird ?) life can flourish, or exist at all. 

 And for present purposes let us confine our inquiry to such condi- 

 tions at midsummer. 



If such life be so regulated by temperatures: if vegetable life 

 influences insect life, if insect life influences bird life, then I think 

 some degree of difficulty may be considered removed as regards 

 the distribution of our birds in the nesting season, and through 

 our summer. 



And if this so far be granted, may it not be equally well argued 

 that if any abnormal conditions take place such as were patent to 

 the eye of sense during the springs and summers of the last few 

 years in Scotland — say during the springs and summers of 1902 to 

 1906 inclusive (in 1905 certainly up to the 20th of June) — that 

 certain other abnormal conditions might (I hold did) appear in the 

 temporary — or it may be permanent ? — dispersal of certain species ? 

 If this be granted, then the facts point to a decidedly retrograde 

 condition of our temperatures in midsummer, and a corresponding 

 advance southwards of certain species hitherto accustomed to seek 

 certain levels of temperature, whether their range included the shore- 

 lines of the north of Europe or the 2750-feet levels of our mountain 

 ranges — such species, for instance, as the Snow-Bunting and the 

 Dotterel. 



Such retrograde movements in the birds themselves may be easily 

 watched in what we are accustomed to call sub-Arctic countries, 

 and that no more distinctly than at the time of migration in spring. 

 I have myself witnessed this in a manner beyond dispute at the 

 great bend of the river Petchora, and if I read it aright the 

 explanation seemed simple enough. 



I have instanced the " crushing-down " — which I claim pro- 

 visionally is a just appellation — of Woodcocks at their nesting 

 grounds in 1902 and 1904 to areas south of the Grampian ranges 



