Hi Cassandra,
Thanks for raising this interesting question. I for one am very perplexed at this research idea and it would be interesting to hear an explanation.
I make some points:
The mouth markings of our finches are well known. Immelmann’s 1965
Australian Finches book described it and had a diagram of the pattern for 14 of them. All these finches build covered nests, so it is potentially dark inside the nest, so bright mouth marking in the chicks can act as a feeding guide in a dark nest, for
the parents and help them get fed. Our finches crouch and hold their heads low and twisted upwards, unlike the chicks of most birds, that beg in a very forward pose. So maybe the mouth marking help in that situation. That the Gouldian Finch also likes to nest
in a tree hollow is only a slight change. Given that it is an established feature of the group and well shown in Australia and Asia, it is really hard (extremely hard) to understand how it could be suggested in any way due to a very particular situation of
parasitism from a small group of birds that only occurs in Africa. I certainly have never heard that idea. Surely the mouth markings arose early in the evolution of the Estrildids. As that group is big and widespread with a lot of variation, surely this predates
in history a long way before the relatively recent parasitic Whydahs came into existence. There is nothing odd about brightly coloured mouths of many bird chicks, this is simply an extra elaboration. I am entirely comfortable with the simple and straightforward
idea that the range of patterns that now occurs is simply a result of radiation that has occurred since then. I don’t see it as any more mysterious than that the plumage patterns of adults of all species are now different, although showing some variations
on themes. Just random variations on an established somewhat unimportant feature. I would expect that there is benefit in having these mouth markings but little relevance in variations. There can be selective pressure to keep species separate, because they
all have similar nesting habits and many species nest near other species (in places where several species are common). I expect there can be selection benefit in a feature that ensures that birds don’t accidentally go to the nest of another species and adopt
the wrong chicks. This could lead to wrong imprinting, to which finches are susceptible. Thus the mouth markings can guide the feeding by parents and maintain species separation. Then again, our finches will readily hybridise in captivity, presumably hybrid
chicks show a mix on this feature and both parents will still feed them, so that the selective pressure can’t be too strong.
As for the Whydahs that parasitise some African finch species, they are hardly cuckoos. They are another group of finches and as far as I am aware they don’t
directly harm their hosts. But I could be wrong on that (for example food competition). As in this Wikipedia extract below.
As for:
The leading theory for these mouth markings is that they evolved for parents as a way to discriminate against parasites in the nest. Over time, the mouth markings have co-evolved, leading to elaborate and intricate designs.
How can that be? Given that the mimic successfully copies these markings, they are hardly
aiding discrimination. There is no benefit in the finch for co-evolution. There is benefit for the parasite to evolve better copying but that is surely a one way process. There may be benefit for the model species to keep changing to make copying harder. Also
why should that be? We don’t have parasites here, so on the evidence of all of Australia, that whole suggestion just falls in a heap.
As for
Did we have a parasite and it has gone extinct?
Well surely that is a crazy idea. It asks for a huge leap of very weird logic. I suggest it requires that we had about 18 species of parasite that have all mysteriously become extinct whilst the finches did not. As each species has its own pattern.
I wonder what sort of questions are being asked and how it is possible to frame any kind of research
in any way that can give results that can elucidate anything of relevance to the special case of the few species of African nest parasites that happen to have caught onto the clever trick of locally evolving a very particular set of mimicry (calls and mouth
markings) to their very particular set of host species. The benefit to the parasite of copying, is immediately obvious and I can’t imagine anything even slightly mysterious about that. So what is the question?
I am a little perplexed at the field work in Canberra, as we only have one very common breeding native
finch here, plus two more that are surely less easy to find breeding. Most finches are in northern Australia. I am not even aware that we have any captive populations of the Whydah species in Australia. I believe they are not easy to maintain.
Philip
The indigobirds and whydahs, together with the Cuckoo-finch make
up the family Viduidae; they are small passerine birds native to Africa.
These are finch-like species which usually have black or
indigo predominating in their plumage. The birds named "whydahs"[1] have
long or very long tails in the breeding male.
All are obligate brood parasites, which
lay their eggs in the nests of estrildid finch species; most indigobirds use firefinches as
hosts, whereas the paradise whydahs chose pytilias. Unlike the cuckoos and honeyguides,
the indigobirds and whydahs do not destroy the host's eggs. Typically, they lay 2–4 eggs in with those already present. The eggs of both the host and the victim are white, although the indigobird's are slightly larger. Many of the indigo-plumaged species named
"indigobirds" are very similar in appearance, with the males difficult to separate in the field, and the young and females near impossible. The best guide is often the estrildid finch with which they are associating, since each indigobird parasitises a different
host species. For example, the village indigobird is usually found with red-billed
firefinches. Indigobirds and whydahs imitate their host's song, which the males learn in the nest. Although females do not sing, they also learn to recognise the song, and choose males with the same song, thus perpetuating the link between each
species of indigobird and firefinch. The nestling indigobirds mimic the unique gape pattern of the fledglings of the host species.
The matching with the host is the driving force behind speciation in this family, but the close genetic and morphological similarities among species suggest that they are of recent
origin.
The family contains two genera:[2]
·
Vidua -
19 species with indigobird or whydah in the English name
·
Anomalospiza - monotypic,
the cuckoo-finch or parasitic weaver, Anomalospiza imberbis
|
Subject:
|
Enquiry
|
|
Date:
|
2018-10-08 16:15
|
|
From:
|
Cassandra Taylor <>
|
|
To:
|
"" <>
|
Hello,
My name is Cassandra Taylor, I am a PhD student at ANU, working on Estrildid Finches. Soon I will be undertaking work in the Jerrabomberra Wetlands, and Michael the Senior Ranger
at the wetlands asked me to post about it on COGs chatline. This is just to keep everyone in the loop with what is happening, and so that if people see me touching nests etc., they know what is happening and not to be alarmed.
I will explain a bit about my research below, to give you context for why I will be looking at nests and nestlings.
My research will be looking at the markings inside nestling estrildid finch mouths, see the photo below
m("01D45FDD.97823110","image001.jpg");">
Every Estrildid finch species in the world has unique mouth markings for that species. Estrildids occur in Australia, Africa, and Asia. Almost all Australian finches are Estrildids
(Zebra, Gouldian, Red-brow, The firetails, Double-bars).
In Africa the Estrildids are parasitised by Vidua finches (think Cuckoos), and the parasites have evolved identical mouth markings, see photo below
m("01D45FDD.97823110","image002.jpg");">
The parasite is on the left (A vidua finch), and the estrildid is on the right. They grow up to look completely different!
The leading theory for these mouth markings is that they evolved for parents as a way to discriminate against parasites in the nest. Over time, the mouth markings have co-evolved,
leading to elaborate and intricate designs.
However in Australia our finches exhibit these elaborate markings in the absence of parasitism.
This raises lots of questions! Did we have a parasite and it has gone extinct? Are they a vestigial trait that has carried through time due to a low maintenance cost? Or is the
theory in Africa not the complete story? If you have ever seen a Gouldian Finch chick, you would have noticed the glowing orbs on the flanges of the beak. Interestingly this is our only compulsory finch cavity nester, perhaps these orbs guide parents to chicks
mouths in dark nests?
Over the next 3 years, I hope to answer these questions! And discover what these elaborate mouth markings communicate to the parents.
This year I am engaging in some field work at a few sites around Canberra, and one of those is the Jerrabomberra wetlands. I will be photographing chicks mouths at several points
through their development in the nest.
This research has been submitted to ANUs ethics committee and has been granted approval to proceed. No birds will be harmed as part of this research.
So if you see me looking in nests, feel free to come up and say hi, I will have copies of all my licences and permits for this research.
If you have any questions feel free to contact me,
All the best,
Cassie
Cassandra Taylor
Ph.D. candidate, Langmore Lab
Division of Ecology & Evolution
Research School of Biology
ANU College of Science
RN Robertson Building
46 Sullivans Creek Road
The Australian National University
Acton ACT 2601 Australia
M +61 415 299 016
E
W
http://biology.anu.edu.au/research/labs/langmore-lab-avian-evolutionary-and-behavioural-ecology
