I took this today near my home, pretty sure its a White Browed Scrub Wren. (I have seen several lately and they all have different coloured feathers - see link below).
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This one seems to be malting or something. Could it be a juvenile losing its baby feathers?
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I had a good look at all my photos of WBSW, I think yours will turn into an adult just like the one in my photo. Same markings on the wing, same eyes and the pinkish legs. M-L
M-L
That's about what I thought, these little birds can be hard to figure out. I think thornbills are even harder. I like your shot, never seen one on the grass, always deep in undergrowth.