I was not comfortable with the idea that “I suspect it is a male as it seems to be darkening over the past few weeks suggesting
that the new feathers coming are dark”. Yes of course it could be a male - 50/50 chance of that. So sex is not the issue. The following text applies equally to young males
and females. Just on first principles, there is no reason that a young bird that is only a few months old will be getting new feathers. That would be really odd and not make any sense. Maybe someone might know a bird somewhere that does this, but I don’t…….
It should be close to a year old before it starts getting new feathers. So I checked the pictures and text in HANZAB. I offer this explanation.
I note HANZAB shows an illustration of “juvenile (still growing) and juvenile (fully grown)” (plate 35, V 4. Page 768). There aren’t many HANZAB plates that
show that distinction, so there will have been a reason.) John’s observation about becoming darker is correct (even without the “seems to”) but the conclusion is not correct. A clue comes from House Sparrows and Starlings that become darker for the breeding
season. This is not through new feathers but through feather wear. Another strong hint is that each year we usually get to see some young male Koels (about a year old) that still have juvenile feathers in wings and tail. That would hardly happen if they
were already growing adult feathers at 2 months old.
What is happening that John describes is the darkening is real but this is not new feathers replacing old. Because of the way body feathers are arranged like
tiles, in an intact bird, we normally see only the tips of the feathers. The whitish spots at the tips will still be there (although they might get frayed off a bit too which would expose the darker parts of feathers below. – but if they were new adult feathers
and it was a male, they would be black). What John is seeing is all those feathers are still growing. The bases of the feathers are darker than the tips. As the feathers grow, instead of just seeing the pale tips of the back and wing feathers, over time, we
see more of the middle and sometimes the bases of these feathers as they reach full size. This is also contributed to by that the total size of the bird increases as it grows, which means it stretches out and so we see more of the darker middle and base of
the feathers than just the pale tips, thus making the bird overall look darker. So this is a growth process, not a process of new feathers causing the change.
Philip
From: John Harris [
Sent: Tuesday, 28 January, 2020 2:06 PM
To: chatline
Subject: [canberrabirds] Juvenile Koel saga part 3
The juvenile Koel is now an independent feeder. It still squawks but no Wattlebirds come to it and it gives up and eats more plums. Before squawking hopefully again. It has begun to eat elderberries as well,
as the branches of the elderberry intertwine with the plum. I suspect it is a male as it seems to be darkening over the past few weeks suggesting that the new feathers coming are dark.
The adult male Koel is still hanging around in a nearby tree
