I've noticed that to be true. My pumpkins have been flowering for 2 weeks straight and the females, while on there, still haven't opened. Watermelon females are showing them selves (all 2 of them) while the males are blooming like crazy.
On most cucurbits, male flowers come out first. Why? Probably to get the insects interested in the patch, so there are some around when the more energy-intensive female flowers arrive. That is a plant invests more in a female flower than a male flower. I have heard that there are some squash that are specially bred for large farms to put out female flowers first, just to accelerate fruiting in a big patch. (Just need one male flower to do the job!)
Let me amend what I said about why male flowers come out first. I was just talking with a professor of botany. The answer is a bit more subtle. It seems that this is the strategy that these plants use to try to avoid self-fertilization. See, it is not ideal for a male flower from one plant to fertilize a female flower on the same plant. As in, inbreeding. So if you've got a lot of plants, it doesn't matter much. But if you just have a few, there is some value in having pollen from many plants around when the first female flowers come out. This is consistent with the idea that for a big patch, it's fine for the female flowers to come out early.
This is a good thing to remember if you're doing manual fertilization, as you may have to do if the squash is under row covers.
I am in the process of planting. I bought peat pot starts of a lot of things this year and have only one of each zukes and yellow crookneck. The are planted next to each other in a hay bale. Will that be problematical for pollinating? I really did not need an overload of squash for the 2 of us, so minimized them.