Later I checked with Dietland Müller-Schwarze and Lixing Sun's work 'The Beaver - Natural History of a Wetlands Engineer'. The answer I gave seems to be about right. The kilo seems to be of fresh matter, mainly aspen and derived from a trial using North American beavers.
Beavers needs must vary, depending on whether they are young, pregnant females, etc.
This photograph shows trees lying and barked at the beginning of summer. During May beavers change their diet from dependence on bark and switch over to grass. Later in the summer they turn to a ration that is made up more of aquatic plants. This is what Müller-Schwarze and Sun say, but I should broadly agree, except that it all depends on the habitat. At our Big Pond, where there is plenty of horse tail (Equisetum spp.) they seem to prefer that, along with the sedges (Carex spp.). Along the burn, where grasses are abundant and there is much less aquatic vegetation, they depend on the grasses. Later in the summer I expect that the Burnieshed family will spend more time back in the Wet Wood wetland area with its abundance of Reed canary grass (Phalaris arundinacea)
I thought I had sent this, but it can't have gone properly from the train when I tried to send it on the way to London.
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