THE SENSE OF DIRECTION. 45 



their usual practice of flying directly to Gullane Point. (Eye- 

 broughty is nearly 400 yards distant from the nearest point of 

 the mainland.) 



According to the state of the weather these observations 

 range themselves in one or other of two of the three classes 

 of migratory movements. In a clear atmosphere they belong to 

 the first, and in foggy weather to the second class. Certain 

 considerations will, I think, make this clear. The Geese and 

 the Oystercatchers were travelling, in the one instance daily, in 

 the other frequently, towards objectives which were ordinarily 

 visible from the beginning of flight. "When the weather is clear 

 the Geese are remarkably constant in their line of flight to and 

 from the inland feeding grounds, regularly following a course 

 which lies nearly parallel and close to the long axis of the Bay, 

 and it is noteworthy that they then neutralise drift unless the 

 wind is exceptionally strong. In fog with a light westerly 

 breeze they fail to make up leeway in returning to the Bay, 

 and strike the coast, it may be, a mile or more eastward, when 

 they redirect themselves towards the Bay. It does not appear 

 that the usual height at which the Geese fly makes the ground 

 below invisible to them when the range of human vision is not 

 less than that of the second observation. The uniform failure 

 to make up leeway in a number of observations suggests, 

 though it does not prove, that the Geese habitually orient 

 themselves by direct sight of the Bay, and have no cause to 

 pay heed to the landmarks in passing. The evidence, however, 

 is not so strong as it might be, as there is always the possibility 

 that in some considerable portion of the flight the land was 

 hidden from the birds by the fog. 



The Oystercatchers furnish more valuable evidence on this 

 matter. The basaltic sill opposite to Eyebroughty is a con- 

 spicuous and distinctive feature of the landscape. It is also 

 unequivocally the shore landmark for the Brig, and the birds 

 are often enough on the Brig to become familiar with the land- 

 mark if they wished or were able. Yet the birds actually 

 passed the sill, and their course was changed in a fraction of 

 a second after the trill was uttered. It is clear that the actual 

 course of events depended on the trill, and not on recognition of 

 the basaltic rock. Had the calls not been answered by a trill 



