WHAT GUIDES BIEDS DURING THEIR MIGRATIONS ? 141 



processes, must nevertheless be of immense significance in regard 

 to the animal kingdom. But according to Darwin, Credner, and 

 others (see Allgemeine Erdkunde, Hann, Hochstetter, and Pokorny, 

 PI. xi.) the line from Labrador across Newfoundland, Bermuda, 

 and the Antilles not only shows no sign of such a depression, but, on 

 the other hand, gives indications of a secular upheaval. Thus, not 

 only have we no evidence for assuming the existence at any time 

 of any kind of landmarks along the whole of this immense stretch 

 of sea, but, on the contrary, the results of scientific investigations 

 distinctly oppose such an assumption. We may therefore justly 

 ask What was it, then, that guided the primitive ancestors of 

 these migrant flocks, counting in their hundreds of thousands, and 

 what is it that still enables the generations of the present to per- 

 form, with unerring certainty, this wonderful autumn journey of 

 three thousand two hundred miles over the trackless expanse of 

 the ocean ? 



Incomprehensible as this faculty possessed by migrants of in- 

 variably following the right path during their regular migrations 

 may appear, it becomes a matter for real wonder when we see how 

 they are able also, under exceptional conditions, to accomplish with 

 the same unfailing certainty such purposes as correspond to their 

 needs for the time being. This faculty is specially displayed on 

 occasions when, owing to sudden abnormal changes of tempera- 

 ture, they have to relinquish a spring migration already half com- 

 pleted, and are obliged to turn back and retrace their course to 

 their winter quarters. 



An instance of this kind, on a scale of extraordinary grandeur, 

 was witnessed here on the night from the 16th to the 17th of 

 March 1879. In the chapter on the direction of the migration 

 flight we have already related how on this occasion hundreds of 

 thousands of migrants, belonging for the most part to the Curlew, 

 the Golden Plover, the Lapwing, and their congeners, passed over 

 this island in one violent rush westwards, back to their winter 

 quarters, making the darkness of the night resound with the wild 

 babel of their calls. Excepting that much greater haste was dis- 

 played on the part of the wanderers, the movement exactly 

 resembled a powerful autumn migration. There was a light south- 

 westerly wind, the weather being mild ; it was thawing, and the 

 evening was foggy. Hence, from the local conditions of the 

 weather, no apparent cause could be assigned for a movement of 

 this nature. On the following day, however, the wind changed 

 to east-north-east, and a frost set in which lasted until the 28th of 

 the month. Undoubtedly, this same wintry weather had set in, one 

 or two days before, in regions lying far to the east or east-north- 



