Reproduction and Environment

[Dinosaur World <dinoworld@msn.com>]

I know that certain animals time their reproduction so that their young are 
born to coincide with environmental events that are beneficial to babies, 
but what is the catalyst that starts the reproductive behavior?
Birds, for instance, may lay their eggs in advance of the swarming season of 
certain insects, thus insuring their young have plenty to eat upon hatching. 
But how is it that they know to time this? Is it tied to climate changes? 
Position of the moon/sun? Slight changes in the earths magnetic fields?

And if this ?catalyst? did not occur, would that reduce or stop all together 
the reproduction of that particular species for that season?

Are there any examples of modern animals whose reproductive behavior is 
altered by environmental changes? Could environmental changes have affected 
dinosaurs the same way?

George