I went to a zoo recently and saw a couple of toucans (in very small enclosures.. grr). They each had cracked beaks. Would they have cracked if they had been in the wild, and how did they crack them (was it due to stress?).

My thanks to previous correspondents.

What intrigues me is the progression between a completely closed box and and an open cage. No doubt a sealed box includes the normal weight of the cararies, flying or not. When, flying the mass cannot "disappear": If small holes are drilled round/through the top (and only top) of the box then eventually under equilibrium the pressure just under the top can only be atmospheric at that height. So the excess over atmospheric pressure just above the base must be just enough to account for the weight (the air being "forced down by the bird's wings"). Conversely. with holes at the bottom, the pressure just under the top will be less than atmospheric and the total pressure difference on the top surfaces will "support" the canaries.

With holes top and bottom, there will be over and under pressures balanced to "support" the mass of the canaries while at the same time causing equal volumes of air to flow in through the top holes and out through the bottom holes (no matter what their relative and absolute sizes) keeping the whole system balanced and stable.

Do you agree ?

We are told that, counter-intuitively, aeroplanes are held up by a lower pressure on the top of the wings than on the bottom (venturi) : - not because the under surface drives the air down. If the canaries were gliders, how would the excess pressure on the base be generated ?The question seems to be - with an aerofoil moving through air with streamline flow where is the weight "taken" , eventually.

Further from the author of 8 tons....  I am grateful for the two answers so far submitted. What I really puzzle over is what happens if a "closed" container has holes (how far apart ?) round the bottom so the air pressure cannot be greater than atmospheric. 

Presumably eight tons of canaries sitting on perches in a lorry weigh eight tons. If the canaries are all flying in a wire cage there will be no effective weight. If they are all flying in a closed container - eight tons ? A "closed" container with holes in it so any air pressure is released ?

Observed this with birds in flight

Obviously they are nocturnal and diurnal, respectively, and have different roosting/nesting habits, but they do compete for many of the same food resources.

Has there ever been any observation of crepuscular turf wars or clashes? And if not, why not?

Whatever the answer it might still make for a fun (bad) made-for-TV sci-fi movie.

There are no small white birds except in snowy regions where being white really helps you to hide. In regions where I have lived the only small bird with considerable white on it is the wagtail.

There are no white mammals except in polar regions, either. And very few black-and-white, too.

 But there are a lot of big black-and-white or grey-and-white birds, and some all-white too. Why so? Do they have no enemies? It's well known that foxes eat birds the size of geese!

This video catches a little bird sitting on a car mirror and repeatedly jumping down to catch a look at himself. Is this a behavior that will persist in his bird brain so that he might seek out side view mirrors to preen in on future cars of assorted makes? Or is this a one-time occasion?