As an aside, canaries can cross breed with green singing finches, but their offspring cannot reproduce (they are mules). I don't know if that's true for crossing Splendids or not - it's not anything I've tried to do. I also haven't tried to get mutations of Splendids. It's my opinion that the original variety of Splendids are far prettier than the dimly colored mutations... There are photos of them all over the Internet if you're interested.
Rosy Bourkes, however, are the first (and best) mutation from the normal color that is brown on the back. Yellows have also been genetically produced, but the various shades of pink and rose are my favorites. The color variations in the Bourkes are sex-linked. A simple example is that if you take a female Normal Bourke and a male Rosy Bourke, all your hens will be the color of the father and all cocks will be the color of the mother. Hence, if you have two normal babies in the nest and two rosy babies, you can be certain that the rosies are hens and the normals are male. I've read this and it has proven true for me with every mixed pairing over the past several years.
However, one of those normal male babies grew up and was put with a normal hen (whose lineage I don't know). Instead of throwing mostly normals, that pair throws 50% rosies. All those rosies have been hens. That normal father carries the gene from his rosie father. All the normals in the nest have been males.
Bourke hens typically lay an egg every other day. Splendid hens usually lay one every day. Both varieties lay from two to six eggs. Most often they lay four eggs. My experience has been that if they lay five eggs, you will usually get three babies, although I have had four in the nest, but never more than four no matter how many eggs.
If you talk to your birds and interact with them on a daily basis, they will become accustomed to you and allow you to peer into the nest box without a great deal of fuss. It's important to speak "sweetly" to the hen BEFORE you open the box. Tapping lightly on the "lid" or "door" before you open it is also a good practice. I had a male cockatiel once leap at me and come down landing on his brood, killing a new chick and damaging the remaining eggs. Highly disappointing. I should have waited for his mate to be in the box before I looked in, because she was more docile. But, they were a new, untame pair, unfamiliar with me and I with them.
I carefully keep track of the parentage of all my babies by naming each and every parent bird (both male and female because sometimes mates get swapped). This morning I wanted to check on Bonnie, a Bourke hen with Clyde. Bonnie only laid two eggs this time. After 19 days, the first egg hatched and the 2nd hatched two days later. I needed to check the size of her offspring. It's necessary to band the babies if you want them to be saleable to pet shops. If a baby grows faster than you expect, you may miss that small 2-3 day window when its feet are the right size for banding. Too big and you can't get a band on. Too small and it slips off and probably lost in the nest.
Now Bonnie used to be sort of tame. I could lift her off a clutch without any fussing. She knew me and I knew her. Although not finger tamed, she trusted me. Then, with her previous clutch , something went wrong. She laid two eggs and the third wasn't laid. I began to worry and watched her daily. Eventually, she appeared distressed. She was panting and even left the nest to sit on the bottom of the cage. This was a definite sign of egg binding and that something must be done quickly. Most birds will exhibit signs of a problem by sitting on the bottom of the cage, and if you know your birds, you'll recognize when they aren't feeling well ... fluffed up, eyes at half mast ... that sort of thing.
In Bonnie's case, there was no doubt. I caught her and could feel the lump of the egg near her vent. Be especially careful when touching that area. If you break the egg, you've lost your bird. With excellent advice of friends who raise more birds than I do, Bonnie was rescued. I did what my bird book said, and it wasn't enough. I held her over steam and put mineral oil very carefully into her vent, using a small syringe. After many hours, a wonderful couple advised me to also give her mineral oil by mouth and add mineral oil to her vent more than once ... every hour if necessary. I held Bonnie in a washcloth and let her chew on it as much as she wanted since she was NOT happy with me! When I was about to give up on her, I remembered something I'd done as a 12-year-old with my Budgies when they were ill. (More about that another time).
I took a small cage and covered it completely with a towel and put her in that cage. Then I boiled water in a large mug and placed the steaming mug inside the towel (not in the cage!). I left her alone for about a half hour before I peeked in. There was the egg on the floor of the cage ... In addition to the mineral oil, I believe she needed warmth, humidity and solitude to pass that egg.
She didn't return to the nest box to sit on those two eggs and I didn't have any other mother who could foster them. It took Bonnie a few months to fully recover from her ordeal. I worried and watched over her since she only laid two eggs this time. However, she seemed fine and two eggs were all she needed to lay.
I'll talk again another time about how the males help raise their offspring. Also, discuss hand raising babies. I've had a few that were rejected by a parent (rare), but reared successfully by me. Although these birds are easily tamed when young, hand rearing makes them super tame and loving.