Sperm doesn't always survive long in crosses due to the internal Ph differing from species to species. Artificial insemination has been used in a few of the hybrids and is more successful as the breeder can inseminate at the critical time of ovulation.

I'm pretty sure the woma/blackhead though was a natural breeding. My Womas go off their food at breeding time - good job as they'll eat ANYTHING. I even had one male try and go after a microwave hotpot meal I was eating!