We have not seen picture of said bird, so until this is posted all discussion is conjecture.
That being said, after the creation of my unparalleled knob thread, I consider myself something of an expert.
I believe he hovered his spermatozoal ganglion in the vicinity of her reproductive duct, while using his eyestalks to keep her aroused and in position.
When her duct became enlarged, it generated a hormonal response, which triggered a muscular tightening at the base of the ganglion, resulting in the ganglion being ejected into the duct.
The ganglion was then absorbed into the body of the recipient, genetic material was combined, and the resulting polyp will be incubated until larval stage, when it will be ejected from the host as free-swimming medusae.