fertility

How fertile are Harpies exactly? Is it a case of once she's had one, she is done, or would there be a chance she might need multiple encounters before she would get results?

You know that's a good question. Also does anything increase the likely hood either?

Near as I can tell, that hasn't been a common question, so it hasn't been discussed at all. Though I would assume a Harpy can keep having kids.

Well so far I've figured smaller Harpies at least would need to be more fertile than their larger cousins. the human sized ones in particular would face great risks when trying to mate, both from being interupted by bigger predators and from unwilling mates being armed with weapons. So it makes sense to me that their bodies would need to be very fertile so that they woulden't have to put themselves into such danger so often.

Either that, or they pick a mate and drag the fella back to their home and keep him there until she is certain she will be a mommy.

I'd say most harpies would be forceful, but they're intelligent. It's up to the individual to decide on how she gets the mate. Otherwise, I would assume that (like I said earlier) they can have more than one child.

Also: Can a giant Harpy make babies with a human male...? I don't know how the mechanics would work, but would that marrage be possible? Well, I guess marrage would, but what about childbirth?

The size of the human should have no effect on the potency of his sperm, so while she is likely to be less uh, satisfied than a human-sized woman would, as long as they find a way up to her egg she should have no trouble getting it fertilized. (Barring of course the whole species difference and gene compatibility part which I'm sure has been addressed somehow.)

Monogendered Races Procreation (link)

While fertility in and of itself was not particularly discussed, just about everything else was. For the fertility discussion, I would imagine that without the intelligence to know how to prevent it, and without a mechanism known to prevent it, all the giant monster species would have high fertility rates. Giants based on humans might have a lower fertility / conception rate given how our anatomy works, but generally speaking the animal parts of animal hybrids are 1 shot, 1 kill, so to speak. Additionally, in any species where the male is killed during / after reproduction it is almost a guarantee that fertility rates will be high (note, I am particularly against this idea but it is present elsewhere).

The exception I see to the above is where you have intellectuals with enough knowledge of their own bodies living in some sort of society structure. For example, the fae. I imagine a fae is more than capable of using magic to prevent itself from becoming pregnant when it would be undesirable - especially given their overarching personality trait, one would expect that they probably have sex often for recreational purposes. Giant social creatures, such as dridders or nagas during Sinera's time might have also had a way, though it is more probable that they just engaged in abstinence than that they relied upon contraceptive methods.

Recall that no matter the size of the creature the ovum is still unicellular (though, for a single cell application they are rather large, even a human ovum can be seen with the naked eye without aid) - thus, even in a giant predator that is several dozens of hands high, her ovary size really only dictates the number of eggs she has, or in some particular species, is part of the mechanism for generating more eggs (for example, my two created species can generate their own eggs rather than are born with a static amount). A regular sized 6' tall human has sperm capable of interacting with that ovum, assuming the female is capable of pseudogamy - the problem is the transport mechanism. Human sperm is very fragile, requiring a particular environment to survive and even then only surviving for a few days. The likelihood of a regular sized human male inseminating a giant harpy by normal methods (ie some form of sex that does not include methods of in vitro or with magic) is an improbable chance that approaches a hard zero.

Moreover, even humans don't fully understand the method of transport for sperm in the vagina - there are particular prevailing theories (such as upsuck) but none have been conclusively proven or denied with scientific methods to my admittedly limited biological knowledge. What I am aware of that we do know, at least in the science realm, is that there are periods during the human female menstrual cycle where the female's reproductive tract undergoes subendometrial and myometrial peristaltic waves that favor particular directions for rapid sperm transport.

So chances are that they are highly fertile,

Harpies obviously woulden't know a great deal about their own inner workings, but if they are highly fertile then they would at least understand that one mating encounter almost always leads to having babies and might not be as casual about it as humans would be. they are bound to understand this if their mothers took the time to teach them about 'the birds and the bees' (knowing how they communicate rudely, that would be an amusing conversation)

For some reason I keep thinking young Harpies that want babies would have a "girls night out" where all the popular Harpies would go out in their little gang and pick out some boys and then have their fun. Makes sense from a survival stand point, safety in numbers

That does mean the unpopular harpies would have to do it alone though.

I just got a sense of a possibly horrific story. Adventurer in large group gets picked on by a large number of harpies, and tries to survive the encounter to make it back to family. GG.