MIGRATIONS OF BIRDS AT TUSKAR ROCK. 193 



the atmosphere is proved by the way the birds will allow an 

 intruder to approach extremely close, and vice versa in the way 

 that they will suddenly loom up out of the fog and brush just 

 over one's head. The flight at the same time is full of disorder, 

 and the loud and oft-repeated cries indicate lack of contentment, 

 the birds rushing hither and thither as the throng swells. And 

 there can be little doubt that diurnal migrants, as they under- 

 take protracted journeys, exhibit under similar atmospheric 

 adversities such-like features. 



Eain, when persistent, and especially fine drizzling rain 

 which accompanies haze, has no doubt a retarding effect on the 

 flight of birds ; still, it is wonderful how land-birds, whose 

 feathers soon become soaked with wet, keep on the wing. From 

 the lighthouse balcony I have observed birds in rain flying- 

 round and round the lantern practically all night long. Indeed, 

 here we have further evidence giving support to the view that 

 endurance of flight depends not so much upon the possession of 

 long pinions,* as upon the structural adaptability for flight of 

 the whole machinery of the fore-limb. A bird must add 

 enormously to its weight when its feathers get wet ; in fact, no 

 material varies more in weight than a feather perfectly dry 

 and one even only slightly moistened. Hence there must be a 

 tremendous reserve force of muscular wing-power to overcome 

 the resistance offered under such altered condition of plumage. 

 And this reserve force must be all the more powerful when we 

 remember that migrants frequently do not encounter rain until 

 late on in the night, when already they may have been observed 

 to have expended a considerable amount of energy of wing-power 

 during earlier hours of darkness. 



In regard to the deterring influence of a strong head-wind in 

 cases where it suddenly springs up accompanied by showers 

 of driving rain — in short, a " sudden squall " — I have had 

 occasion to observe how Pipits, heading against the gale, 

 suddenly dropped down to the Bock. Sometimes a whole 



* Vide paper on " Wrens on Migration observed at the Tuskar Bock," 

 'Irish Naturalist,' vol. xxi., July, 1912, pp. 127-129 ; also paper on "The 

 Dartford Warbler in Ireland," 'Irish Times,' December 26th, 1912, pp. 5 

 and 6. 



Zool. 4th ner. vol, XVII., May, 1913. q 



