As far as I know springtime doesn't affect them building bubblenests, has there been a storm recently?they sometimes build when there's a storm or on the full moon but the next full moon isnt until the 6th of may.
Also I sent you a private message
Spring doesn't have any correlation for betta because where they originate from, there are only two seasons: dry and monsoon. Generally spring means lots of storms in which the barometric pressure drops. Fish are rather sensitive to this as it means rain and rain means more water in their homes which in turn means there will be enough food and room to share with youngsters. This is what is enticing your boys to bubble.