192 THE ZOOLOGIST. 



so to speak) to press forward until a vast assembly thus con- 

 stituted becomes congested, and in endeavouring to move apace, 

 confusion arises in the ranks. Several of these obstacles are 

 natural forces, e. g., fog, dense haze accompanied by drizzling 

 rain, and a strong head-wind with driving rain, especially when 

 setting in suddenly after a calm. It is obvious that fog or haze 

 would act as an obstacle with much greater force in the hours 

 of darkness, because, as far as the generality of land-birds is 

 concerned (and these birds in the main concern us here), the 

 evidence goes to show that they have no great aptitude for 

 finding their way in the dark. Hence, while they manage to 

 move along on clear nights much assisted by moon- and star- 

 light, as well as by the fact that when out at sea they encounter 

 no natural barriers, the argument remains that they possess but 

 little useful vision at night. What instinctive sense of direction 

 at the same time they may be gifted with is a most difficult 

 question, and one which I do not propose to deal with at 

 present. But we do know of the velocity and marvellous endur- 

 ance of wing power that a bird possesses, and in allowing the 

 fullest amount of credit for such faculties, we are certainly in a 

 position to argue that, even if birds wander from the direct 

 route leading to their ultimate destination, it matters but little, 

 for they will arrive home in due season. But, as we have just 

 seen, nocturnal migrants in thick weather are rendered very 

 helpless. And in this helpless and hapless state the voyagers, 

 in their attempts to move aimlessly along, now behold the beams 

 shining from the lighthouse. Allured by their dazzle, and 

 desirous to quit the enveloping gloom, the migrants close up 

 nearer and nearer to the rays until they find themselves within 

 the doors of what they little know is veritably a glittering avian 

 death-trap. 



But by day also, while there is no flash from the lighthouse 

 to cause further confusion, nevertheless the fog itself becomes, 

 though in a less degree than at night, a very serious deterrent 

 factor to the migrants, whose speed, regularity, altitude, and 

 direction of flight are soon thrown out of gear. Such features may 

 be observed when a thick fog suddenly lowers over a vast tract of 

 slob-land tenanted at the time by great flocks of shore birds. 

 That their vision has no penetrating power in such a state of 



