DIARY OF THE HABITS OF NIGHTJARS. 398 



colour, I felt sure that they must be covered, and, gazing still 

 more attentively, all at once, by an optical delusion as it seemed, 

 rather than by the passing away of one, the piece of fir-bark 

 became the bird. The broad fiat head, from which the short beak 

 hardly projects noticeably, presents no special outline for the eye 

 to seize on, but is all in one line with the body. It looks just 

 like the blunt rounded end of a stump or piece of fir-bark, whilst 

 the dark brown lines and mottlings of the feathers not only 

 blend with and fade into the surroundings, but have in them- 

 selves, at a little distance, a great resemblance to the flaked 

 surface of the bark, the lighter feathers exactly mimicking those 

 patches where some of the layers have been more newly flaked 

 off. This would only be of special advantage to the bird when, 

 as in the present instance, it had laid its eggs amidst pieces of 

 fir-bark, and, did it invariably do so, a special protective 

 resemblance might perhaps be admitted. This, however, is not 

 the case. It lays them also under beeches or elsewhere where 

 no fir-bark is to be found. Unless therefore it could be shown 

 that a large majority of Nightjars lay their eggs in the neighbour- 

 hood of fir-trees, the theory of a special resemblance due to the 

 action of natural selection must be given up, as I believe it 

 ought to be in other apparent instances. No doubt when the 

 objects adjacent are different the sitting bird may often appear 

 to have a special resemblance to one or other of them ; but 

 as, owing to its habits, such objects would be mostly of the 

 same general description, the bird's colouring may have been 

 made generally protective in relation to its incubatory habits. 

 The Nightjar lays on the ground, and one of the birds sits on 

 the eggs without leaving them the entire day. Day, however, is 

 night to the Nightjar, which not only sits on its eggs, bnt sleeps, 

 or a least dozes, on them as well. It is therefore much exposed 

 during this period, and would be liable to be taken unawares 

 without some protection, and such protection it has by virtue of 

 its plumage arid its habit of sitting very close. Drowziness may 

 in this case have meant security both to bird and eggs, for the 

 most sleepy birds would, by keeping still, least endanger their 

 young at all stages. 



The two birds that I am watching have laid their eggs in the 

 midst of pieces of fir-bark of various sizes lying on a sandy soil. 



