Page:The British Warblers A History with Problems of Their Lives - 4 of 9.djvu/70

 produce similar results. The song of the Wren is a good example, since the variation is so considerable, and yet so strikingly similar at the extreme westerly and south-westerly points mentioned. In Worcestershire the song is commenced with some peculiarly high notes, but the impression left upon my mind after listening to it in Donegal or Sark is that these notes are missing. Whether this is really the case requires the testimony of more than one person, but the whole song is undoubtedly pitched lower.

Returning once again to our starting-point, we will proceed in an easterly direction to Holland, Belgium, or even as far as Hungary, and make a similar series of comparisons. What do we find? Why this, that the character of the song of many species, such as the Whitethroat, Garden Warbler, or Willow Warbler, is altered, in some cases to such an extent as to be almost beyond recognition, but that in the majority of cases there is no lowering of the pitch.

From these comparisons it will be seen that, speaking generally, the tendency is for the pitch to become gradually lower as we advance into a climate more and more dominated by the Atlantic; and this result is what we should anticipate, for the damp air would cause a decrease in the tension of the vibratory muscles with a corresponding decrease in the number of vibrations and a consequent lowering of the pitch. Therefore it seems to me that we need have little hesitation in attributing this effect to climatic influence, the more so since, on turning our thoughts to the human voice, we find corroborative evidence, in that the vocal ligaments are similarly affected by a damp atmosphere. And if it be thus true that a damp air decreases the tension, it must be equally true that a drier atmosphere will tend to increase it with a consequent raising of the pitch; and this is all that is really required to cause unlimited variation. Certain notes may be lost, new ones may be added according to the range of vibration permitted by any one particular climate, and coincidently the tone may be changed, with the result that the song may become completely transformed.