I hesitate to say that this falls under the "Homesteading Questions" thread, but I'm not sure where else to put it.
Before heading out to the barn tonight, one of our house dogs was rather worked up and barking at the door, but it was about time for my father to be coming home from a late project, so I didn't think anything of it. A few minutes later, I came downstairs and he wasn't home. When I stepped outside to get the water buckets to fill, our cat Sami (the newest recruit to move from indoors to the great outdoors due to cleanliness habits...) was standing in the open screen door, looking extremely attentive and keyed off of something out in the yard. I, being the paranoid person that I can be, noted this and decided to take the house dog with me out to the barn.
There are two vehicles between the house and the barn, and after clearing both, I saw a cat that moved low and quick like our Sami move along the edge of the silo up aheadand dissapear. I thought, "Wow, that was quick," and when I glanced back over my shoulder... she was behind me! The cat that I saw was light like her, so I knew it wasn't our oversize brown tabbycat Noah, who I saw coming from the other direction afterward, or our old one-eyed two-toothed declawed torbie, who was sitting inside the barn looking disgruntled and waiting for food. So, I know I saw another cat - none of our close neighbors have outdoor cats. One neighbor did for a while, but their orange cat went missing, and they have since kept their black cat in. If it weren't for the fact that the orange cat has been missing for two years, I would have guessed he was dropping in for a visit.
I fed our three, and went around feeding and watering the rabbits, and as I was finishing up in the "rabbit room", I heard a deep yowling sound from outside the room, part of which is a converted run-in stall. There are no lights outside on that side of the building, so I didn't go outside to see if I could see the cat, but my question is this:
Is a yowling cat more likely a queen in heat, or a tom being a loudmouth male?

We've only had one cat show up that didn't get spayed right away, but it was a long time ago and I don't remember the sounds of a female in heat. Do tomcats yowl? Any help here is appreciated...
I'm thinking that this cat is yet another drop-off, as that would explain why the dog was barking - she wouldn't bark at a cat at the door, but if she could hear a vehicle in the driveway, or peeling off down the street, that would explain it. It also wouldn't be an uncommon thing - seven of our eight cats are from "rescue situations", and four of those seven were cats that simply showed up, definitely dumped...