[neilep (OP)]

Dearest  Cuckoo-ologists,

As a sheep I of course lay my seed in many different places !..this makes me somewhat like a Clarissa the cuckoo, who does the same with her eggs…except , in my case, my seed is upon request !

Here's Clarissa here...she's a Pied Cuckoo...so presumably she makes good eating !

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See these nests where other cuckoos  has planted their eggs ?

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Hmm….I think this cuckoo still needs some training !


How on earth did this kind of behaviour evolve ?..and how is it done ?...does  the cuckoo control the colour of the egg by seeking out a nest first ? If so then how does the bird make the egg mimic the hosts eggs ? or does it just have to find a nest that the eggs look similar ?

Ewe see…I just do not know !...no..really, I don’t !...and I think people who read this  who also do not know will want to know like I want to know. So, let us know !


Hugs and shmishes



Neil
Fertiliser of Eggs
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[blakestyger]

This is brood parasitism and is a very interesting question. Without going over all the well known features of the cuckoo's habit of laying its eggs in other birds nests, here are some related facts.

The mimetic patterns of the cuckoo's egg are genetically determined and is maintained by hosts discriminating against badly-matched eggs (a bit of Darwinism in action) and young female cuckoos parasitizing the same host as raised them.

This is not a static situation - some eggs get detected and rejected by the host.

There is some evidence that differences in the probability of rejection are due to various cuckoo-host pairs having progressed to different stages in their co-evolutionary race.

Also, of the 127 species of cuckoo worldwide, only 40% are brood parasites; the others are perfectly capable of raising their own young.

Other birds do this too, mallards lay in other mallards' nests (egg dumping) as do swallows.

[Karen W.]

I did not know that!.. When you say that some eggs are detected and rejected do you mean the host bird rejects it by destroying it or moving it away so it is not sat upon..? How is this done?

[blakestyger]

Karen. The larger-billed birds, such as magpies, are able to lift the egg out and dump it over the side of the nest.
Smaller species are known to desert the nest along with their own eggs; a selectively advantageous trade-off of laying more eggs against raising a larger parasite that has ejected their own eggs/chicks anyway.

[Karen W.]

Thank you... I had no Idea ... I wonder how they choose... has anyone ever tried to incubate an abandoned or rejected egg..In order to see if there was actually a defect that the bird itself may have detected in its choice of illimination?

[blakestyger]

The parasite egg gets rejected by the host because it's a poor imitation of the host's own egg.

[Asyncritus]

How on earth did this kind of behaviour evolve ?..and how is it done ?...does  the cuckoo control the colour of the egg by seeking out a nest first ? If so then how does the bird make the egg mimic the hosts eggs ? or does it just have to find a nest that the eggs look similar ?

Heh heh!  []

Good question! With one blow we're back at the greatest evolutionary impossibility of them all - the origin of instinct.

Keep questioning. I'm sure you'll get some answers from the learned assembly.

[blakestyger]

And just how do you suppose that the origin of instinct could be an evolutionary impossibility?

I went to the Darwin exhibition at the Natural History Museum in London yesterday - it was very well done, you should go along if you can. []

[Asyncritus]

And just how do you suppose that the origin of instinct could be an evolutionary impossibility?

Sorry Blake, I didn't see any evolutionary explanations of the examples of instinct I posted, and I see none for neilep's example above.

Did I miss something? Or is the answer 'It didn't evolve?'

[blakestyger]

Us not posting something doesn't invalidate it - or perhaps I misunderstood.

Anyway, you never answered my previous question as to why you don't want evolution as an explanation for life as it is - any thoughts?

[BenV]

Blakestyger, Asyncritus - this is not the thread for that discussion, it has been done to death elsewhere.  Either way, instinct is controlled by the interplay of (genetically controlled) chemical messengers with the (genetically controlled) nervous system.  So as the whole system is under genetic control, it's fairly obvious that it's subject to natural selection.

Neil -  a glance at wikipedia suggests that you are right, they select a host nest based on eggs that look similar:

"Female Cuckoos are divided into gentes, that is populations favouring a particular host species' nest and laying eggs which match those of that species in colour and pattern. The colour pattern is inherited from the female only, suggesting that it is carried on the sex-determining W chromosome (females are WZ, males ZZ). It is notable that most non-parasitic cuckoos lay white eggs, like most non-passerines other than ground nesters. The exception is in the case of the Dunnock, where the Cuckoo's egg has no resemblance to its hosts' blue eggs. This is thought to be because the Dunnock is a recent host, and has not yet acquired the ability to distinguish eggs. Male Cuckoos breed with females without regard to gens. This results in gene flow between the gentes and maintains a common gene pool for the species (except for the genes on the W chromosome)."

So different 'gentes' lay their eggs in different nests, depending on the closest match to their own egg colouration.  There's a fantastic evolutionary advantage in adapting the cuckoo's way of life - someone else pours their resources into incubating and bringing up your offspring, meaning that every egg a cuckoo lays costs very little in terms of energy for the mother.  The really interesting thing is how does a cuckoo know it's a cuckoo? 

See http://www.thenakedscientists.com/HTML/content/questions/question/1730/ for the answer.