Hi Pauwen
Is it possible the crows can see their reflection in the glass and so go into "attack" mode? I had a similar problem with my male chaffinch a few months back. After over a year of visiting, he suddenly noticed his reflection in my kitchen window. After that, he would return several times a day to seek out this "intruder" and attempt to attack him. In desperation I telephoned RSPB HQ and a very helpful girl advised that putting clingfilm on the OUTSIDE of the window would cure this as clingfilm stops any reflection without preventing us from seeing out. I freely admit I embellished this advice slightly when passing it on to OH - and said he needed to clean the window and THEN put the clingfilm on it. Two problems solved on one go - a clean window and a Mr Chaffinch who, although he still looks for this "other bird" occasionally, can no longer see it and so is not liable to end up with a parrot-shaped beak.
I appreciate with a conservatory that solution may prove a little more difficult but if you could narrow it down to one or two offending panes perhaps you could take some temporary measure to prevent just those panes from reflecting.
Squirrel
The necessity of bird-watching is a really good reason for avoiding all forms of housework.
The dust will still be there tomorrow - the birds may not be!
Some highly territorial birds will attack windows, car external driving mirrors, hub-caps and other reflective surfaces. They can see their own reflection on the surface, and thinking it is an intruding male, will try to attack it to defend its territory.
This behaviour is particularly prominent during the breeding season, but can also happen at other times of the year, particularly by birds such as robins and grey wagtails who hold winter territories.
There is no apparent reason to what triggers an individual bird suddenly start this behaviour, and it cannot be predicted how intense it will be and how long it will go on for.
Although most birds engaging in this behaviour do not hurt themselves in the process, many people look for ways to stop it, either because they are concerned for the bird, or because it is an irritation to themselves.
The only way to stop this behaviour is to remove the trigger – the reflection. This means putting something such as cling film or non-reflective cellophane on the outside of the reflective surface or indeed, covering the whole area.
Once the reflection has disappeared, the attacks should stop but, as you have seen, some birds will tear it off thinking that the adversary is hiding behind the cover. Curtains made of strips of plastic that flutter in a breeze may also be effective.
Often birds habitually attack only a particular window, but sometimes different windows may be attacked in sequence depending on the position of the sun. The behaviour sequence can sometimes be broken if the first window in the sequence is treated.
Brushing or spraying the window wipers, seals and other problem areas with a compound containing aluminium ammonium sulphate, which is a distasteful compound, may also help to break this habit. It can usually be found in animal repellent products such as 'CataPult' - http://www.diytools.co.uk/diy/Main/sp-6-7184-53914-catapult-animal-repellent-spray-750ml.asp
I hope it helps!
Help swifts by letting us know what they're up to - fill in the 2010 survey
A couple of times now, two juvenile pigeon flew on our window, I expect they didnt see it.
I bought some stickers for the windows and never saw a pigeon on that window again.
the RSPB sell these: check it out
http://shopping.rspb.org.uk/p/BirdAccessories/Butterfly_window_stickers.htm
"colourful stickers especially effective on glass windows and doors. If placed on the outside these stickers help prevent birds from flying into windows and doors. Cling without adhesive to glass or any clean glossy surface without marking".
It may be easier than cling film, it s also quite pretty to have these stickers on your window.
That may help
good luck
Isabel and Pauwen, you have different problems with the windows. Pauwen's crows can see their reflection in the glass and are fighting what they consider an intruder, while Isabel's pigeons see the reflection of the outside world in the glass and think that they can fly straight through. Consequently, different solutions are needed. The stickers will help the bird see that there is a solid pane of glass there before it is too late, but since these do not remove the reflection itself, they will not stop a bird that is attacking its own reflection.
Pauwen, if the crows become too much of a pain on your conservatory roof, it may be worth trying the white liquid greenhouse shading. If you paint the outside of the roof with that, it will certainly remove the reflection there, although if you currenly have clear glass on the roof, it will make the conservatory a little darker. Still, may be worth the effort if it stops the problem. Good thing with the greenhouse shading is that it can be easily cleaned off when you no longer need it there.