Well, since we already have the other two legendary birds, I figure we might as well begin covering the remaining three...
As a first, general comment : it's quite obvious that these birds have control over the weather and elements in some form. They are all also legendary beings even within the world of pokémon, their existence generally considered a myh (Prof Oak in Pokémon Emergency). However, I don't think we should assume that their representations and everything in the pokédex about them is true. The notion, for example, that Zapdos only appears when thunderclouds part was clearly dispelled over the course of the anime (see "The Power of One").
Moreoever, I hold the legendary birds to physical considerations in the following comments. While one COULD make the argument that they are mythical beings and thus do not need a tail to fly or any such, I think it makes for much more interesting discussion to hold them to natural laws the same way as everything else and not let them get away with "magically" avoiding such laws.
ARTICUNO
Red/Blue/Leaf Green : A legendary bird Pokemon that is said to appear to doomed people who are lost in icy mountains.
Yellow : A legendary bird Pokemon. It freezes water that is contained in winter air and makes it snow.
Gold : The magnificent, seemingly translucent wings of this legendary bird Pokemon are said to be made of ice.
Silver : One of the legendary bird Pokemon, it chills moisture in the atmosphere to create snow while flying.
Ruby/Sapphire/Emerald : Articuno is a legendary bird Pokemon that can control ice. The flapping of its wings chills the air. As a result, it is said that when this Pokemon flies, snow will fall.
Fire Red : One of the legendary bird pokémon. With its long tail trailing behind, its flying form is magnificent.
First, of all the birds, Articuno is generally the closest to the form of a raptor. Its head is reminiscent of some ospreys (see pic here), while the long tail (though the wavy form it is constantly given in the picture can only be pure fantasy; a bird's tail is meant for steering, and a wavy tail such as this would send the bird flapping out of control every ten second) is reminiscent of some other bird of prey. The small beak is definitely hawk-like in appearance.
The wings, despite popular notions noted above, likely are NOT made of ice. Frozen water does NOT make for good wing material; it is very heavy, and wings (and feather) by their nature needs to be light. While I'll grant that Articuno is probably very cold to the touch, I'll go on record as saying that it's feather are probably very similar in appearance to the membrane found on the wings of such varieties of butterflies as this. The jagged shape, while not entirely impossible, would likely then be anime artistic license.
This pokémon, according to legends, dwells in mountains - a characteristics at once reminiscent of legendary creatures (as mountains are generally the less civilized areas of the world, thus the ones where legendary beings would be best able to avoid detection - note how the semi-legendary Absol, in RSE, recycle that theme), and of the great birds of prey (eagles, most noticeably).
The myth about it appearing to doomed beings lost in mountains seems likely to be just that, a myth, linked to this pokémon's alleged ability to create ice while flying. However, it is quite possible this is the truth as well. WE have only one example of a "doomed people lost in icy mountains" - Miyamoto, Jessie's mother - and I'm not sure wether or not any evidence for Articuno's presence there and then exists.
As a first, general comment : it's quite obvious that these birds have control over the weather and elements in some form. They are all also legendary beings even within the world of pokémon, their existence generally considered a myh (Prof Oak in Pokémon Emergency). However, I don't think we should assume that their representations and everything in the pokédex about them is true. The notion, for example, that Zapdos only appears when thunderclouds part was clearly dispelled over the course of the anime (see "The Power of One").
Moreoever, I hold the legendary birds to physical considerations in the following comments. While one COULD make the argument that they are mythical beings and thus do not need a tail to fly or any such, I think it makes for much more interesting discussion to hold them to natural laws the same way as everything else and not let them get away with "magically" avoiding such laws.
ARTICUNO
Red/Blue/Leaf Green : A legendary bird Pokemon that is said to appear to doomed people who are lost in icy mountains.
Yellow : A legendary bird Pokemon. It freezes water that is contained in winter air and makes it snow.
Gold : The magnificent, seemingly translucent wings of this legendary bird Pokemon are said to be made of ice.
Silver : One of the legendary bird Pokemon, it chills moisture in the atmosphere to create snow while flying.
Ruby/Sapphire/Emerald : Articuno is a legendary bird Pokemon that can control ice. The flapping of its wings chills the air. As a result, it is said that when this Pokemon flies, snow will fall.
Fire Red : One of the legendary bird pokémon. With its long tail trailing behind, its flying form is magnificent.
First, of all the birds, Articuno is generally the closest to the form of a raptor. Its head is reminiscent of some ospreys (see pic here), while the long tail (though the wavy form it is constantly given in the picture can only be pure fantasy; a bird's tail is meant for steering, and a wavy tail such as this would send the bird flapping out of control every ten second) is reminiscent of some other bird of prey. The small beak is definitely hawk-like in appearance.
The wings, despite popular notions noted above, likely are NOT made of ice. Frozen water does NOT make for good wing material; it is very heavy, and wings (and feather) by their nature needs to be light. While I'll grant that Articuno is probably very cold to the touch, I'll go on record as saying that it's feather are probably very similar in appearance to the membrane found on the wings of such varieties of butterflies as this. The jagged shape, while not entirely impossible, would likely then be anime artistic license.
This pokémon, according to legends, dwells in mountains - a characteristics at once reminiscent of legendary creatures (as mountains are generally the less civilized areas of the world, thus the ones where legendary beings would be best able to avoid detection - note how the semi-legendary Absol, in RSE, recycle that theme), and of the great birds of prey (eagles, most noticeably).
The myth about it appearing to doomed beings lost in mountains seems likely to be just that, a myth, linked to this pokémon's alleged ability to create ice while flying. However, it is quite possible this is the truth as well. WE have only one example of a "doomed people lost in icy mountains" - Miyamoto, Jessie's mother - and I'm not sure wether or not any evidence for Articuno's presence there and then exists.