Yes interesting questions. It involves a need to consider: the behaviour of adult cuckoos, the behaviour of cuckoo chicks and the behaviour of the host species.
The Channel-billed Cuckoos is an odd cuckoo in that more than one chick can be raised in the same nest (this appears to be not odd for them). It looks like
they don’t have the baby instinct that the other parasitic cuckoos have of chucking out any other small thing (eggs or chicks) from the nest. There are lots of other cuckoo species that are not parasitic (in Australia only the Coucal), so clearly there is
a range of options.
It appears pretty clear that the Koel is of the usual type that only raise one young in a nest. Though HANZAB quotes 2 very old records: 1930 “Occasionally
nests contain more than one chick” though that might just be at hatching and does not mean more than one will survive & 1964 Five Koel chicks were raised in territory of an adult pair of Magpie-larks in one season. That seems amazing but doesn’t mean that
it wasn’t 5 separate nesting events. I don’t have access to either original document (in Emu) to check what actually happened.
About the Channel-billed Cuckoos, there are a range of likely reasons.
Most likely more than one mother CbC lays an egg in the same nest. HANZAB suggests that.
More than one CbC hatches at about the same time and being similar size none succeeds in pushing out other CbC chicks but do succeed in pushing out the proper
chicks.
Maybe the foster parent species of those, sit tighter and just prevent the CbC chicks pushing out other CbC chicks (but not their own). After a few days the
cuckoo chicks lose their instinct to push out other things from the nest.
What was the outcome of the suggested Coucal in suburban Canberra a few weeks ago?
Philip
From: Alison [
Sent: Sunday, 28 February, 2021 12:58 PM
To: 'Dr David Rosalky'; 'Philip Veerman'; 'COG Chatline'
Subject: RE: [Canberrabirds] Dependent young Koel
On our Field Nats excursion to Hall on Friday we saw three young Koel chicks all in the same yard. I can’t say if they were being raised by the same pair of wattlebirds though.
From: Canberrabirds
On Behalf Of Dr David Rosalky
Sent: Sunday, 28 February 2021 8:35 AM
To: 'Philip Veerman' <>; 'COG Chatline' <>
Subject: Re: [Canberrabirds] Dependent young Koel
Yes, I get the picture. Thanks. I’ll have to leave it up to Jack whether he wants to record this as a separate dependent bird.
Your comment that “they can only ever raise one at a time”
reminds me of an observation at Broulee many years ago where I saw two fledgling Channel-billed Cuckoos being raised by a pair of magpies. I felt sorry for them (the magpies, that is). An adult CBC was also in the vicinity calling loudly.
David
Hi David,
I am only suggesting what I think is likely, based on what you wrote. I don’t know for sure. (Same comment applies to my comment on Terry Munro’s noisy bird
story on Friday.) However if the earlier observation was only 4 weeks ago and this new observation is of a DY Koel with a long tail already, I would suggest that excludes any possibility of being a different chick from the same parents. Simply because (unless
it is very strange) there is not enough time passed for the same foster parents to have a second fostered chick to reach that stage. As they can only ever raise one at a time. There is also the question as to whether the same pair of birds would even nest
again in the same season, after producing a cuckoo from their first attempt. That likely takes a banding bird study to be sure of that question. I suggest your observation is likely to be the same chick with the same foster parents, that simply has been somewhere
else for 4 weeks. Or just another chick from another pair of foster parents. Both species are common enough for that to be easily plausible. On 5 February with my description of one at
Isabella Pond, Jack responded to my observation “while I have already been alerted to 4 different Koel fledglings at Isabella Pond.”
I was wondering why it should be 4 different ones and not different people duplicate reporting the same one or two…….. I only noticed the one there. (Maybe by dates, it isn’t by location, as I wasn’t specific as to where it was.)
Philip
From: Dr David Rosalky
Sent: Saturday, 27 February, 2021 6:30 PM To: 'Philip Veerman'; 'COG Chatline'
Subject: RE: [Canberrabirds] Dependent young Koel
Perhaps I misinterpreted you Philip. Are you saying that it wouldn't be the same RWBs?
AND
Interesting observation, Philip.
I think the equivalent event that I reported was about 4 weeks ago, so it could potentially be the same chick.
From: Philip Veerman <>
Sent: Saturday, 27 February 2021 5:58 PM
To: 'Dr David Rosalky' <>; 'COG Chatline'
Subject: RE: [Canberrabirds] Dependent young Koel
Hi David,
About whether this is a different young one from the same pair of foster parents. I am guessing it is the lapse of time since you last saw it there(?) So that
is why you suggest it is a different one. But it is an interesting question. Incubation period is 2 weeks and nestling period is about 3 weeks. But as you say The bird looked almost fully grown with a long tail, so it is certainly older than 3 weeks old.
So the total time is likely to be about 2 months. So that also depends a lot on what you mean by “some weeks ago now”. If it is less than 2 months, on probability I would suggest not overly likely to be a different young one from the same pair of foster parents
but it could only be known by having banded recognisable birds.
About whether the adoptive parents took the young to the same tree. I wonder does that happen. I get the impression that the DY Koels move about in their own
limited, clumsy and rather random manner and then the foster parents track them down by their squawking. Could be both of course. There can be some guidance or favouring of better opportunities by parents simply by being more successful at better sites.
One trivial but general point, the tail is barred, not striped. (Even if wiggly.) Bars go across the feather or body axis, stripes go along the feather or body
axis. Think about birds with stripe / striated etc cf barred / banded in their names.
Philip
From: Canberrabirds
On Behalf Of Dr David Rosalky Sent: Saturday, 27 February, 2021 4:35 PM
To: COG bird list Subject: [Canberrabirds] Dependent young Koel
Another squawking Koel near my place in Deakin. It has been calling within a 50 m circle since at least 8am this morning. During my several visits to the site, I observed two feeding events by RWBs both of which located the bird for me.
I finally got excellent sightings. The bird looked almost fully grown with a long striped (wiggly stripes) tail. Its crown displayed a narrow black strip between largish white /cream patches on either side.
It is interesting that the bird is in almost the exact position that I reported some weeks ago now. It raises the question of whether the same RWB nest was parasitised again and the adoptive parents took the young to the same tree.
One reason I had so much trouble locating the bird is that I could not ascertain which tree it was in because its call kept moving. It seems to have strongly ventriloquial vocalisation.
David Rosalky
