Re: How do dogs know how to change thier coat in the summer

       Cryptic coloration (the term Cryptic means "having a secret or 
hidden meaning") is wide spread in Animal Kingdom. This is a type of 
adaptive coloration in which the animals blend into its background. It is 
useful NOT only for prey animals but also for predatory animals to escape 
from being detected. For example arctic hare, nothern weasels and 
ptarmigan change their white color in the fall and then revert it back to 
brown in the spring.There is a seasonal change in their coat color.
	The basic mechanism underlying these seasonal changes in coat 
color is a phenomenon called "photoperiodism". As you observe, there is a 
seasonal change in the duration of light (and dark) period. In summer the 
light(photo)period is longer(you might have experienced long day times in 
the summer..dusk extending even upto 8 or 9 pm and dawn starting from 4 
am) and in winter the photoperiod is shorter (with prolonged nights/dark 
period. The light and dark ratio in summer is 16h:8h and in winter it is 
8h:16h.
	This natural photo periodicity (which accompany the seasonal 
change....oh! it is rather the photoperiodicity that brings out the 
seasonal change!) triggers hormonal changes in the body which ultimately 
brings out the color change in the coat, skin or fur.

also refer:
 "Evolution: process and product"  by EO Dodson & P Dodson (ISBN: 0-442-
22164-9).
 "Animal behaviour: Psychbiology, Ethology and evolution" by David 
McFarland (ISBN 0-582-00960-X)