I love Kookaburras! I photographed two in a local bird garden many years ago and I've been wanting to draw them ever since. Hmmm... good excuse for a video!
To refresh my memory, I just found a photo online very similar to yours. There appear to be FOUR distinct areas of feather:
1 - The head above eye-level has white feathers edged in brown
2 - The eye stripe is very distinctive and a deep chocolate brown
3 - The wings have brown feathers that fit so tightly to each other that the edges are almost invisible.
4 - The chest feathers are similar to the brown-edged head feathers but appear to be paler.
Now, looking at your drawing I find that the eye-stripe is pale. Even if your Kookaburra had a pale stripe I'd still want to darken it. It will introduce more contrast, and that will brighten the highlights.
The rest of the head looks OK.
Moving down to the neck and chest. Personally, I'd emphasise the paleness of the brown edging. And, far more importantly, I'd look at my reference to work out where the key highlight is on that rounded chest. I have no doubt there will be one. It's a rounded part-spherical shape, so at some point part of it will be pointing directly at your light source, and that will create a highlighted area. And if it isn't - maybe it was an overcast day? - then invent one.
You need that, because right now your Kookaburra, below the head, is flat. The feathers at the left are exactly the same tone as those extending right across to the right. But it's a curved surface, so one side would naturally be receiving more light than the other.
If you can post your reference I might be able to help a bit more.