Starlings reproduce between males and females, but differentiating the sexes is not as cut and dry for Starlings as it may be for other comparative terrestrial species.

The actual organs responsible for creating genetic materials (eggs and sperm respectively) are internal for both of the sexes. How these two halves combine is another story entirely, and surprisingly varied between Starlings. This is in part due to how the species, evolutionarily speaking, used to exist and reproduce within the atmosphere of a single planet, several considerable genetic leaps responsible for their current form that exists amidst and between the stars.

Both sexes have two genital slits, and an anus further behind that. Despite having a functional digestive tract, it is more or less vestigial. A modern Starling can obtain the energy they want directly from their local star as needed, though they can choose to consume and break down material otherwise if so desired (having fully functional taste buds, this can readily be the case). Doing so leaves zero waste product, as there are no materials they cannot, with time, reasonably break down into raw energy as needed.

A male starling has internal testes and, below that, an internal 'bladder' used to store vast quantities of cum. This bladder can, if desired, be pushed out through their lower slit through contractions of thin muscles and tendons along the 'balls' (as they appear to be). This is a carry-over from their terrestrial ancestry, where males would fill this bladder with as much cum as possible before letting them descend, using them to attract females, a display of their virility. Ironically, while current-age Starlings are not as beholden to the limits of their ancestors and capable of producing (within reason) as much sperm as they need to at a given time, pairings between Starlings at present are generally done on a more intellectual and inter-personal level before a sexual one.

Female Starlings also contain a 'bladder' of their own, only this one contains the eggs passed down by their ovaries. Though only the size of a small grape when first descending into the bladder, these eggs continue to grow within the bladder prior to reaching the size needed for fertilization. The size of eggs ready to be fertilized can at times vary quite significantly, though on average tends to be anywhere between the size of a navel orange and the size of a honeydew melon.

Ancestral females, like males, would at times drop this egg-filled bladder down for males to see to attract a mate, larger eggs signifying greater fertility. This duality of attraction was due to how their species would fluctuate between male or female majority between generations. At times males needed to garner attention, at other times females.

These eggs have a soft and incredibly elastic outer skin, and remain extremely compressible prior to fertilization, only after which obtaining a firmer shell.

Where things become harder to distinguish is how the eggs and the sperm combine. While it may look, feel, and react as such, a starling with a penis is not necessarily (though generally would be) a male.

Both sexes of Starling use their upper slit to transfer genetic material. Inside of this slit is a soft path leading up to roughly stomach-height, then back down and to each sexes respective 'bladder'. Stimulation of the exterior and inner walls of the slit can bring either sex of Starling to climax, contractions of inner muscles pushing to drive cum from the male's bladder...and eggs from the females.

For this, males typically have an extension of this 'path' within their slit which they can extend out and into the female. The pleasure they feel touching this extension is the same as the pleasure felt for the walls within a slit, and they can achieve climax via it, making it functionally similar to a 'traditional' penis. This extension is quite flexible, muscles giving it near prehensility and the ability to curl around appendages or better curve to fit a partner's body. However, some males lack this extension, and pass cum to the female much like the cloaca of a traditional avian species.

Females may also, rarely, have this extension themselves, which could (based on one's perspective) seem almost akin to an ovipositor.

It's unclear why male Starlings tend to have this extension, this 'penis', while females generally don't, but having or lacking one is no stopping block for Starling reproduction. Given they are designed to handle the passage of both cum and eggs in both directions, even if a male and female both have one they could quite comfortably 'dock' if they so desired, or simply have one partner leave this extension within their body and allow the other to penetrate both it and their slit simultaneously.

There is no strict determination for whether male or female Starlings will carry a fertilized egg. Typically, the fertilized egg will end up in the 'womb' of whichever partner achieved climax first, as the one who climaxes last (or whose climax lasts the longest) will be the one to push all the genetic material fully into the other. Despite this, anytime after the egg has formed its harder shell, Starlings may decide to pass the egg back, from one body to the others, or may even allow it to leave the body entirely and care for it externally.

Given all of these factors, it is near impossible to determine a Starling's sex at a glance as either sex could, if they chose to, present with the appearance of having testicles, and even checking inside the slit for the presence or lack of a 'penis' is not necessarily a guaranteed deciding factor.

In either case, it's usually best (and more polite) to simply ask.

- Cellidor