EFFECT OF EXPOSURE ON THE YOUNG 181 



is no imaginary one. Examine a young bird 

 that has recently left the egg ; observe its 

 nakedness ; and consider what it has to with- 

 stand — a temperature that may rise to 70° F. 

 or may fall to 40^ F., the tropical rain of a 

 thunderstorm or the persistent drizzle of many 

 hours' duration, the scorching effect of a 

 summer sun or the chilling effect of a cold 

 north-easterly wind, and, constantly, the sudden 

 change of temperature each time that the 

 parent leaves the nest. One marvels that 

 it ever does survive ; one marvels at the 

 evolution of a constitution sufficiently elastic 

 to withstand such changes. But, however 

 much the constitution may give us cause to 

 wonder, it is clear that much depends upon 

 the parents. A slight inefficiency of the 

 instinctive response which the presence of the 

 young evokes, a little slowness in searching 

 for food or sluggishness in returning to the 

 nest, might lead to exposure and prove fatal. 

 And, however much is demanded of the parents, 

 it is clear that much also depends upon the 

 relationships in the external environment ; for 

 no matter how sensitive or how well attuned 

 the instinctive response of the parent may be, 

 it will avail but little in the presence of 

 unfavourable conditions in the environment. 



Everything turns upon the question of the 

 effect of exposure. And in order to ascertain 

 how far extremes of temperature are injurious, 

 I removed the nests of various species contain- 

 ing newly hatched young, and, placing them 



