Bertie the wine bottle bird feeder is very clever and beautifully efficient.  
Remove the bottle cap and the bird food flows into the tray below, and, when the hopper is full, the flow stops as grain acts like a fluid in this situation.  As the birds eat the food, the tray is kept automatically replenished until the bottle is empty, whereupon you withdraw the dowel peg and remove the bottle from the front.  Use a funnel (or a split empty loo roll centre rolled into a cone shape) to refill the bottle with your chosen grain and then start the process over again.  The roof protects the food by keeping most of the weather away.  
Nothing is squirrel-proof but in my view, Bertie does a better job than a conventional tube feeder.
The backplate is drilled to take screws to attach it to a fence, wall or post.  Treated with two coats of ‘one coat’ (as one coat of 'one coat' is never enough), this rustic wooden bird feeder should last for season upon season if regularly re-treated as there are no moving parts.  
*  NOTE:  As time progresses I make different models, some using larger or differently shaped bottles.  Recently I have made a conical one with a Bottle Green cordial bottle, andI have also used a square gin bottle, together with others.  Ask me what's available....or just take pot luck!
Bertie, if collected from my Suffolk workshop (where you can make your own choice, of course), is supplied complete with a wine bottle full of wild bird food as a bonus, but if sent by post/courier, you will have to provide your own bird food because of the additional weight of the seed.
Please remember that I am not a business, just an ol' git hobbyist who likes making stuff.
Approximate Dimensions:  40x12x12 cms.