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 Post subject: Cuckoos - what fascinating birds!
Unread postPosted: Thu May 07, 2009 11:41 am 
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Cuckoos (and possibly all other brood parasites) are in my mind the most incredible birds of all. They are raised by complete strangers, yet somehow retain the unique traits of their species. And this leads to two questions (I'm sure even more, as this is bound to open quite a big can of worms!):

1. Having never heard the call of their own kind, how do they end up knowing and making their unique species call!? Q2 might possibly hold clues to the answer...

2. Having never migrated in their lives, how do they know where to go!?

There must be logical answers to this, I'd love to see what the boffins out there have to say!


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 Post subject: Re: Cuckoos - what fascinating birds!
Unread postPosted: Thu May 07, 2009 4:46 pm 
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uhm, arent you the boffin :hmz:

But yes, very interesting questions. I suppose there is still a lot about genetics that we dont know


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 Post subject: Re: Cuckoos - what fascinating birds!
Unread postPosted: Thu May 07, 2009 6:00 pm 
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SASOL: Birds The Inside story by Rael and Hélène Loon says the folowing:

1. "Such chicks' sense of identity is clearly genetic, and their ability to recognize both the appearance and song of their own species is inherited. In this case, the adult parasite will not respond to the songs of its foster parent but rather to those of its own species." (p125, Foster families)

2. "Many observations and experiments have shown that both the inclination to migrate, as well as the route to follow on migration, is largely inherited rather than learned."

"The case of migratory cuckoos, whose chicks are raised in a foster family of non-migratory birds of and entirely different species, demonstrates that migratory instincts in this family must be inherited." (p169, The mysteries of migration)

GP not trying to sound clever, just adding interesting bits from a book in my collection. :lol:


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 Post subject: Re: Cuckoos - what fascinating birds!
Unread postPosted: Fri May 08, 2009 9:23 am 
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So you think cuckoos are interesting creatures? Here are some traits and habits I found fascinating...

Some cuckoos have a resemblance to hawks with barring on the underside, this is said to alarm potential hosts into abandoning its nest temporarily allowing the female cuckoo to access a host nest.

Cuckoos are for the most part solitary birds that mostly occur in pairs only when busy with breeding courtship and in some cases (Jacobin, e.g.) the male cooperates in getting a host’s nest available to the female cuckoo to lay her egg. He would attract the host pair’s attention (black-capped bulbuls. e.g.) and allow them to mob him (loosing the fight on purpose) until she has done the deed. He then suddenly extricates himself from the fight, leaving the bulbuls none-the-wiser, but with a present in the nest!

Most cuckoos are insectivorous and in particular are specialized in eating larger insects and caterpillars, including noxious hairy types avoided by other birds. They are unusual amongst birds in processing their prey prior to swallowing, rubbing it back and forth on hard objects such as branches and then crushing it with special bony plates in the back of the mouth.

The shell of the eggs of most brood-parasites is usually thick. It has two distinct layers with an outer chalky layer that is believed to provide resistance to cracking when the egg is dropped in the host nest.

The cuckoo egg hatches sooner than the host's and the cuckoo chick grows faster; in most cases the chick evicts the eggs or young of the host species. Some cuckoos (Diederik’s, e.g.) removes the eggs in a host’s nest at the same time when she deposits hers. She may carry the host’s egg away some distance and eat it.

Where a cuckoo chick emerges from his egg to find other eggs or chicks sharing the nest, it is evicted, leaving the foster parents free to devote all of their care to the young cuckoo. Frequently this is an awesome task, since the cuckoo chick often grows much larger than the host adults long before it can care for itself. One of the tragicomic scenes in nature is a pair of small foster parents working their beaks to a nub to keep up with the gluttonous appetite of an out-sized young cuckoo. The chick encourages the host to keep pace with its high growth rate with its rapid begging call and the chick's constantly open mouth serves as a sign stimulus.

Different females within a population of specific Cuckoo species often parasitize different host species. Some cuckoos may specialize in parasitizing the nests of weavers; others of the same species may lay in the nests of bulbuls, and yet others may lay in nests of wagtails. The eggs of each female very closely mimic those of the host selected even though the markings, base colour and size differ markedly. The mimetic patterns are genetically determined. The different genetic kinds of females (called "gentes") apparently mate at random with males. How these gentes are maintained within the cuckoo populations is not fully understood.

Cuckoos may “hijack” up to 20 nests per year; with 40 percent of their offspring surviving to fledge, this means a cuckoo can have eight to ten chicks fledging annually… quite a success story.


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 Post subject: Re: Cuckoos - what fascinating birds!
Unread postPosted: Fri May 08, 2009 11:05 am 
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Wow, cu@1, EXCELLENT work! :clap: :clap: :clap: And thanks GP for your info on this.

Yes, genetics plays a large role with them. Genetic make-up is not limited to the physical, so personality and behaviour is also hereditary. And as far as a bird's call goes, well there are also actual physical traits associated to this. If both your parents are baritones, you probably won't end up being a soprano!

In case you didn't know this, only a small percentage of Cuckoos are actually brood parasites, the majority doing the conventional duties with their young. It's just that we have the unique situation that all our Cuckoos are the former.


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 Post subject: Re: Cuckoos - what fascinating birds!
Unread postPosted: Fri May 08, 2009 12:38 pm 
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Adding to your post CU@1 and the cuckoos that resemble raptors? Birds: The Inside Story has this interesting bit going the other way:

"Some birds are thought to use song as a means of defence against brood parasitism. For example, the Chorister Robin-Chat, with an extensive mimicking repertoire, often imitates the call of the parasitic African Emerald Cuckoo. Although this theory is untested, it has been proposed that, with this call, the robin-chat may repel real cuckoos by giving the impression that there is already another territorial cuckoo in the area, thereby making local nests less vulnerable to brood parasitism." (p125, Foster Families)


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 Post subject: Re: Cuckoos - what fascinating birds!
Unread postPosted: Mon Apr 18, 2011 10:53 am 
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cu@1 wrote:
Some cuckoos have a resemblance to hawks with barring on the underside, this is said to alarm potential hosts into abandoning its nest temporarily allowing the female cuckoo to access a host nest.

Two years later, and what pops up?
This report!

Cuckoos have evolved plumage patterns that give them a hawk-like appearance to scare the birds whose nests they invade, say scientists.

A study has shown that reed warblers - a cuckoo host species - are less likely to attack more "hawk-like" cuckoos.

This helps the parasitic birds to lay their eggs undisturbed.

The visible similarity between cuckoos and sparrow hawks was already clear, but this is the first study to show the effect the trickery has on host birds.

The findings are published in the journal Behavioural Ecology.
(More on it in the link above.)

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