94 Animal Life 
an existing slight depression will 
be utilised. In such a situation it 
will be evident that, as in the case 
of the partridge and other ground 
birds, the individual that does not 
closely assimilate with its environ- 
ment runs considerable risk of being 
seen and killed; so that any of 
these birds varying towards more 
conspicuous colouration stands little 
chance of transmitting the variation 
to another generation. On the other 
hand any variation that brought one 
into yet closer harmony with its 
surroundings would make it more 
certain than its fellows of rearing 
its young without disturbance. 
This protective colouration 
begins at the very beginning. The 
average rambler across the moor 
might see the nightjav’s eggs close 
to his feet, but he is not likely 
to take them for anything but 
whitish stones. I need not attempt 
a description of these eggs and their 
markings, for the photograph gives 
a better idea than my words would. 
I will only say that the ground 
colour is white, overlaid with spots 
and veins of ashy-grey, purple-brown 
and black. This ornamentation 
probably explains why no nest is 
made. In a nest these eggs would 
certainly be noticeable for what they 
are, but on the bare ground, possibly 
with a few pebbles or bits of chalk or sandstone around, they are merely oval stones. 
It has been stated that imcubation takes from sixteen to eighteen days. If you 
come upon the bird engaged in this task, with her breast and beak turned towards 
you, it is more than probable that you will take her for the broken butt of a decayed 
branch. When only a few hours out of the egg, the young birds are shapeless balls 
of sooty-grey down. ; 
On the 21st of July I had the good fortune to find a couple of nightjar chicks 
that—judging from the condition of the egg-shells—had been hatched that morning. I 
probably should not have seen them but for the characteristic action of the mother- 
bird, who rose from my feet and fluttered slowly over the bracken tops with her right 
wing hanging down as though injured. But I was well acquainted with this artifice, 
and immediately looked to the ground and saw the fluffy chicks. They remained 
perfectly still and silent whilst I adjusted my camera and photographed them; but 
afterwards, the mother-bird, from the oak to which she had retired, not liking the 
look of this strange engine, uttered a peculiar warning note, and instantly the 
youngsters got upon thei feet and ran into the heather, each taking a different 
YOUNG NIGHTJAR AT REST ON TREE. 
