The Eggs of Birds 451 



adaptation follows more slowly. For example, let us 

 take the group of owls. The majority of these birds nest 

 in hollow trees, but even these occasionally make use of 

 an open hollow or a very shallow one, and individual, 

 radical departures from the conventional owl-habitation 

 are doubtless not uncommon. But these exposed eggs 

 are soon destroyed; for no crow, jay, or squirrel could ever 

 resist any opportunity to avenge himself for the wrongs 

 inflicted by his ancestral enemy, the owl. But when, 

 urged on by that impulse which ever tends to make birds 

 vary their habits in all directions, some owl, such as the 

 Short-eared, finds good feeding on marshes and open, 

 treeless plains, it naturally takes to nesting on the ground, 

 in nests but partly concealed by the overhanging grasses. 



Three things might now happen. If sufficient varia- 

 tion occurred and the conditions demanded it, natural 

 selection might bring about a protective colour on the 

 shells of the eggs; if enemies w^ere few and easily over- 

 awed, the eggs might remain white; while, on the other 

 hand, the enterprising race might be wiped out of exist- 

 ence for no more reason than the colour of the egg-shells. 

 The second result seems to be the good fortune of the 

 Short-eared Owls. All of these fates have undoubtedly 

 overtaken birds again and again, and it is by the inter- 

 action of such condition , combined with an ever-chang- 

 ing environment, that many phenomena are brought about. 



It was by reason of the general similarity in colour 

 which the eggs of related groups of birds tend to show 

 to each other that oology, or the science of egg-shells, 

 was able to initiate an important scientific discovery. 



