Adaptation and Environment Factor that bring White-rumped Shama into breeding cycle

All creatures have amazing adaptation to new weather environment.  Take human for example, we can live in basically in any weather environment from super hot Sahara desert in Africa to super cold Antarctica in South Pole.  Even the white-rumped shama could not survive in cold climate like us human, it can be keep in temperate zone or more precise Mediterranean climate like Southern California without or minimal heat provided at night.  In Hawaii and Florida which is more like Tropical climate, the bird can be keep and live comfortably just like in its native land.  In fact, in Hawaii, white-rumped shama has establish itself and live free in several islands such as Oahu and Kauai.  In colder climate, if anyone want to keep the bird, one should provide heat in cold period such as winter time or keep the bird inside the house most of the time of the year and only bring the bird to outside when temperature is warmer.
Amazingly, breeding season of white-rumped shama keep in temperate zone like Southern California is almost the same as the bird in Hawaii, or in South / Southeast Asia.  In Asia, breeding season is right after the rainy or monsoon season which around January to September and peak in April to June.  In Hawaii and Southern California, breeding season is from March to August which also happens at or near the end of rainy season.  Following are average temperature (low and high), average rain fall, and average length of day in a year of Oahu (Hawaii, USA), SaiGon (VietNam), and Anaheim/Los Angeles (California, USA):

 

As we can see, daylight length might be the main factor for the bird to enter breeding cycle even the different in daylight length in Asia (where this bird is native) is little over one hour.  Amount of precipitation or rain might also play some role too but compare the amount of precipitation between Asia and California, it doesn't make much sense when bird keep in California climate also enter breeding season similar time like in Hawaii and in Asia.  Increase in daylight temperature might also be a factor but that could not explain why the shama can start breeding in Southern California on March with avg. temp of 70F compare to 77F in Hawaii and 92F in Saigon.  Maybe it is the combination of all the factors above along with increasing available in insect food that trigger the bird to enter breeding cycle?  Or maybe other factor such as barometer, UV ray from the sun, etc... is the main culprit????