Welcome back! I’m so sorry for your loss of Bernard. 🙁 You did a great job with her and if I remember correctly she had a lot of issues.
We’ve dealt with similar situations at the rescue, where someone has a “pet” that is basically a stray bun in their yard or neighbor hood. This bun was most likely someone’s pet that either escaped or was “set free”. Usually the friendly ones are the ones that get recaptured successfully (several of my buns were found as strays as well). We’ve had some of the best success by slowly trying to improve the bun’s situation. You might start by telling him about RHDV2, which is a very deadly virus that’s spreading all over CA. This bun is very unlikely to be vaccinated, and so is at high risk of sudden death from this virus.
There are also many other predators and parasites that this bun would be exposed to.
A suggestion you might make is to first try to catch the bun so you can get it vaccinated at least. A good way to go about this is to set up an x-pen in the garden in kind of a half circle and start feeding the bun in the pen. Once the bun is comfortable with that make the opening a little smaller and keep up with the feeding. Then you should be able to trap the bun in the pen and make it smaller until you can pick them up without too much issue.
Then perhaps you could convince him to build a predator-proof run for the bunny in the yard, that it could be enclosed in when he’s not supervising in the garden. While a hutch in the yard would be safer from predators, that isn’t a good life for the bun either.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.