How do I explain my Phoenixes "rebirthing" process

Question

Phoenixes are a unique type of wyvern not only due to their colorful feathers (which resemble flames) but also how they reproduce. Phoenixes lay 7 eggs which require a lot of heat to hatch. Unfortunately Phoenixes are not capable of breathing fire in the traditional sense. Instead during pregnancy the mother's body creates sacks of chemicals that fill over time; toward the end of pregnancy the membranes containing these chemicals thin due to hormones, and burst, setting themselves on fire to hatch the eggs. After a day or two the eggs hatch with the young phoenixes consuming the ashes of their mother and beginning the cycle anew.

Now with all that said, how realistic is this, and what other adaptions would they need for this to work?

NOTE: magic does not exist in my story.

Answer 1

From a "biological" viewpoint, there are several questions that need to be answered, with the big one being:

Why do mother phoenixes immolate themselves to birth their children?

Personally, I think this is a rather unlikely evolutionary outcome as almost all avian creatures are born in a rather helpless state and need to be fed/nurtured by parents for a time. However, that said, I can imagine some "plausible" reasons for why a phoenix must burn to hatch its eggs:

• Insects and other wildfire-dependent creatures/plants are the perfect food source for young phoenixes. Create some insects which are dormant underground and some seeds (like pine cones) which only emerge after a forest fire. When a mother phoenix immolates herself, it causes a minor forest fire which causes the emergence of lots of insects and rare seeds. The younglings are suddenly immersed in an environment where it's easy to hide (as they have ash-colored feathers), all the large ground-based predators have been scared off, and there are abundant insects and seeds to eat for a healthy growth spurt.
• The environment is very cold and for the mother to incubate her eggs, she would need to stay still for an extended period of time. Such a long time of remaining motionless, would however kill the mother due to extreme cold and lack of food. Therefore, the mother immolates herself/turns into a long-smouldering chemical fire in order to keep her chicks warm and defend them from would-be egg-snatching predatory creatures.
• Phoenixes burning up is misinterpreted by people as part of their natural life cycle. In fact, most phoenix egg-layings and subsequent births aren't accompanied by a fireball. Some old specimens, which have laid eggs multiple times before, have problems laying eggs and they damage the mother bird's internal organs causing the "acid gland" or whatever to burst, resulting in the immolation of the mother-bird. People have occasionally observed this, for example when a hunter stumbles across a brooding female phoenix, scares it, and this causes the bird to catch fire.

Answer 2

I think the answer depends on: why is it necessary, for the survival of the young, that the mother burst into flames?

If it's not necessary, then it becomes difficult to explain how this species would have ever evolved to do this.

If it's necessary simply for the heat given off to make the eggshells crack, similar to pinus contorta (the pine whose seeds only hatch when heat from a wildfire), then you have to explain A) why wouldn't the mother just breathe fire or something like that instead of actually consuming her? Not having the mother around to protect the young is a big disadvantage. B) what would be the evolutionary advantage of only having a species hatch in the presence of fire? In the case of the pine tree, it exists in a biome where wildfires regularly kill all the trees, so this is its survival mechanism for the species. But if it's the mother breathing the fire, this reason doesn't work.

Now maybe you go a different route: it's necessary for the survival of the young so they can eat the mother's ashes, because they have vital nutrients.

The problem with that would be that there's little nutrient left in ash, most importantly no proteins, which are vital for young who need to grow a lot. From the wiki page on cremation, specifically about the composition of the ashes left behind:

Cremated remains are mostly dry calcium phosphates with some minor minerals, such as salts of sodium and potassium. Sulfur and most carbon are driven off as oxidized gases during the process, although a relatively small amount of carbon may remain as carbonate. 1

The augmentation that I'm seeing as viable is something like pinus contorta, where there are regular wildfires in the region, and these wildfires consume the mother but hatch the young. She lays eggs and they simply lie dormant until a fire comes along to hatch them.

Answer 3

If there are parasites that the adults tolerate but can kill the young, then the self-immolation may be used to completely eradicate the parasite before the young are hatched