Did I miss something? why was Zoe adopted into a new home? Hope everything is ok…
As for the howling... not sure... tayda used to do that when i first got her and she was getting used to the place... then lenny came along and the rest is history!
imo it is a pack howl that you are experiencing. From my experience it is rarely heard by the pack leader, which must be you. This again is what I know from my experience and is not to be taken as professional advice. I had the same situation and the only way was not to leave in the end. Especially as they got older. If I was not in sight/scent of them the howl would happen but only at night. You might want to try CBD oil which might calm them. To my knowledge this is a stressful state for them pups to be in so that is the bad news. But the great news is that they obviously love you to pieces...
How long does he keep it up? I've had Basenjis that would howl when someone departed, but it was usually a short lived behaviour. No question they can make a racket when they do this, but with luck it doesn't last long. Basenjis are not typically like the dog that barks all day.....
Try giving him something more interesting to do when you leave. A food treat puzzle game of some kind is a good diversion. I used a roller ball with my separation anxiety boy, and it cured him. Because he was occupied he did not watch me depart, and by the time he had consumed the treats I was long gone.
How old is he?
I agree with eeeefarm on keeping busy. you can also smear a little peanut butter or cream cheese or canned dog food inside a kong, freeze it. Helped entertain them. Also work on desensitizing him.
Teach him no bark at home. Leave, some back the second he's quiet, praising GOOD NO BARK. Keep it up til longer and longer times. With toys, puzzles and safe chews, he should adjust.
Another thing to do (in addition to previous comments), is vary your routine before you leave. These little smarties pick up on you getting your coat or putting your briefcase together or whatever that we never think about. But they notice it all. Instead get your briefcase ready the night before or don't put your jacket on until you leave the house. But each day it should be your leaving after doing something different - don't create a new pattern - variety is the "silence" of life in a residence
Our Lela has a lot of pack howl in her musical variations, and LOUD! After a minute her quieter older sister Binti will join in, in a lower key. What we found that helps a lot is this: make good eye contact just before you leave, and tell you will be out and when you will be back. Just as you would to a human. Then make sure you are back at the mentioned time. No howling. When we got this advice from a dog therapist we didn't believe it, but we gave it a shot. It does work.
Thank you all for your useful tips. Through this trial and error process I have found that crating them has been very helpful. I guess it is there safe place.