yelling/shouting at the pigeons - the kind of thing you do when you have lost control of yourself - this may be because you are drunk or because you have gone crazy.

http://www.calmwatershypnotherapy.co.uk/CalmWatersHypnothera... (shouting at the pigeons)

https://twitter.com/Ammonyte/status/251381667455967233

http://www.standrewspanto.uk/?page_id=35

Imagine you were standing in a city square that was full of pigeons. You could shout at them to make them fly away but you would never succeed in geting rid of them because they would fly back, and some would even totally ignore your shouts.

I think your text means that sometimes writers seem to be writing for the sake of writing: no one takes any notice of what they are reading because there is no clear message, just a series of meaningless words.

An equivalent phrase could be 'and it ends up reading like words flying around meaninglessly in the air'.

I'm sure someone will come up with other explanations.

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Note added at 4 hrs (2014-11-08 21:58:21 GMT)
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The problem I have with blogs is that the activity is rather like standing in a field and shouting. If you get an audience then you may have a protest rally, or a lecture, if not, you are just yelling at the pigeons...

http://learn1.open.ac.uk/mod/oublog/viewpost.php?post=35133

...sometimes the writer can lose objectivity or effectiveness and ramble on.

'To ramble on' is to write in a confused and ineffectual manner.

there is no point shouting at pigeons as they just ignore you, and if they do fly off, they don't go far and return quickly.

So, a writer who loses objectivity is ineffectual and their words are empty and meaningless so they may as well be talking to a wall...

http://www.usingenglish.com/reference/idioms/talking to a br...

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Note added at 9 hrs (2014-11-09 03:16:40 GMT)
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TALKING of course

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Note added at 9 hrs (2014-11-09 03:21:08 GMT)
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or

completely pointless

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Note added at 20 hrs (2014-11-09 14:30:20 GMT)
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oops, just saw that Demi already said "pointless".

Anyway, the expression is emphasizing the lack of "effectiveness" of this type of writing so it will read as just gibberish =empty, meaningless words with no impact or effect whatsoever.