We have several of these honey eaters in our backyard but notice that during the breeding season some birds appear with red/orange coloured ceres or bases to their top mandrel. I cannot find mention of this in any literature & wonder if anyone can explain it.
All I can think of is that they have pollen on them. I have been looking through my photos of them and this seems like a possibility especially if they are feeding on banksias.
I found a photo of one for you to look at and see if it is what you are describing.
Thanks to all for clearing this up for me; The photo plus pollen explanations were great. Our birds get colouration similar to that shown in the photograph, although the coloured area is larger. No doubt from feasting on different flowers.