70 THE BIRDS OF HELIGOLAND 



directed towards South America fly across Bermuda in immense 

 quantities. As long as fair weather prevails, not one of these 

 birds rests upon its migration journey ; only a storm will induce 

 them to alight (J. M. Jones, Naturalist in Bermuda}. This, too, 

 in spite of the fact that they have already travelled over a distance 

 of one thousand two hundred geographical miles from Labrador to 

 Bermuda, and have still to cover more than eight hundred miles 

 before they reach the northernmost islands of the Lesser Antilles ; 

 nor do they alight during this latter stage of the journey except 

 when subjected to the stress of storms (auct. A. Newton ; communi- 

 cated by letter). As has been already stated on several occasions, 

 the autumn migration differs from the spring movement in several 

 respects, but especially in the velocity of the migratory flight. For 

 the former movement is not, like the latter, determined by the 

 object of reaching a definite goal in a rigidly prescribed space 

 of time, but is merely concerned with enabling the birds, sooner or 

 later, to reach winter quarters possessed of a sufficiently mild 

 temperature. Accordingly, it is only in its initial stages that there 

 is exhibited in the latter movement a velocity of flight similar to 

 that which characterises the spring migration ; for as soon as the 

 various species have reached latitudes far enough south in their 

 case to enable them to take a longer or shorter spell of rest, the 

 birds cease to hasten forward at the normal migratory speed, but 

 advance slowly, and at low elevations, by short daily stages, or 

 sometimes for a time come to a complete standstill, until frost 

 compels them once more to resume their journey at the normal 

 speed of migration. In the case of a large number of species such 

 a relaxation of migratory speed, or temporary interruption of the 

 journey, takes place in latitudes no farther south than central or 

 even northern Germany. In discussing the autumn migration of 

 the Cranes, Naumann (vol. ix. p. 354) brings forward a very apt 

 illustration of what has been said in the foregoing. 



It has been supposed that birds are in the habit of breaking 

 their migratory journey without any very powerful disturbing cause 

 both in autumn and spring at the former season on reaching 

 latitudes not so far south as those of their normal winter quarters, 

 and in spring before they have arrived at their breeding stations. 

 With this assumption, however, my own experiences on this 

 island, accumulated for many years, are at variance. Heligoland 

 occupies a most happy position intermediate both between the far 

 north and the central parts of Europe, as well as between the 

 eastern and western portions of the latter continent. It follows, 

 therefore, that the predominant majority of the myriads of migrants 

 when observed here are still travelling at the full speed of their 



