1: The female is at the top and you can see her oviduct opening as she gets excited and presses it out for mating. Likewise, the male is pressing his cloaca outward to expose his ejaculatory ducts (a pair of openings at the end of the bulge. There are two nearby masses-- these are paramedian phallic bodies. In birds that do not have a phallus, many still have these bodies and they fill with lymph during mating. It probably helps to position the ejaculatory ducts for better access to the female. Some birds also have storage bodies for sperm near the cloaca and so, alternatively, you could see these as storage sites (called, individually, the seminal glomus in song birds).
2: In the second (top-right) frame you see a cutaway diagram showing insemination. The vents are pressed together, the ejaculatory ducts are discharging, and the female's oviduct is open and receptive. In birds, ejaculates are very, very small and highly concentrated. Birds mate quickly but frequently. It was desired for this piece to show a longer copulatory process and so I opted for larger discharge, which might be a good reason for local semen storage.
3: The two avali are disengaging from their cloacal kiss. The male is on the right and you can see his ejaculatory ducts more clearly. The paramedian bodies are relaxed since climax has passed. But both cloaca are still everted and the vents fully dilated, assuming a rounded appearance.
There are additional sketches showing the position used for mating in this instance. Avali can mate in a variety of positions and I have other sketches of this that I may release in time. I encourage you to leave questions and comments below. I'm making this up based on limited information so, by all means, let me know if you have a different opinion and I'll take it into consideration.
Commissioned by
\n\t\t\t\t\tKhazuyo, featuring himself and his friend Kyo.