Hey everyone, thanks for the replies.
I woke up around 4am worrying about this last night and saw the idea about locking them up. While I didn't see it as being a permanent fix, I got up and went outside to shut the gate on their entrance and dragged the hive into a shady spot for the day while I was at work (it was relatively cool in Melbourne today). At least so I didn't have to worry about them running off during the day.
I've opened the entrance up tonight as we're going to be hitting the 30's tomorrow in Melbourne. I'm using Nuplas boxes on this one (first time using them) which weigh an absolute ton. An empty box weighs almost as much as a full one. I can't lift the hive by myself to move it somewhere cooler and keep it closed so I will working from home tomorrow to keep an eye on them.
Strangely after opening up the entrance, hundreds of bees came piling out of the hive and started
crawling along the ground away from the hive. Historically I know they go nuts after being locked up. But crawling along the ground away from the hive is something I've never seen before and I'm not sure if it's significant or not. As I sit writing this now I see them crawling away from on the pavement in the garage.
This is reading more as an abscond happening rather than a swarm as such.
In hindsight, yes; I believe this is what is happening as well.
You can force them to stay in fitting a queen restrictor - some examples attached.
This is an interesting idea, it's something I'm considering but if something is wrong I don't want to force them to stay here (my property, I will move them elsewhere).
Then there is the likelihood of environmental impact causing the problem in the
first place which I reckon Sagar is thinking with his suggestion to relocate.
Yes, I'm worried that something environmentally has changed which is causing this. And that no matter what I do to try and force them to stay; they likely won't. Depending how they go tomorrow, I will be opening it up again and having a very good look inside to see if I can spot any signs of something being wrong in there (disease or whatnot). I will take some photos for a second opinion.
I don't normally keep hives at my place for very long, they're usually there for a few weeks when new until I move them into a larger box. Then I take them down to the peninsula where I have the other hives sitting on some other peoples properties which are going very strong. I like having the bees around and I wanted to keep a hive in my yard. But if there's something around here that's causing them grief then they'll just have to join the others.
I did notice a number of wasps buzzing around the hive this afternoon, perhaps they've been giving them a hard time.