'It's a rare bird, the redbreast...Ninety per cent of them migrate south. A few take the risk, as it were, and stay here...the ones that stay do so in the hope that it will be a mild winter, right? That may be OK, but if they're wrong, they die. So why not head south, just in case, you might be wondering. Are they just lazy, the birds that stay?...if it's a mild winter, they can choose the best nesting places before the others return...It's a calculated risk, you see. You're either laughing all over your face or you're in deep, deep shit. Whether to take the risk or not. If you take the gamble, you may fall off the twig frozen stiff one night and not thaw out till spring. Bottle it and you might not have anywhere to nest when you return. These are, as it were, the eternal dilemmas you're confronted with.'
A bird strutted in front of them, wagged its tail, pecked at the grass and kept a watchful eye open.
'Wagtail,' Harry said. 'Motacilla alba. Cautious chap...Our Small Birds...I read in the bird book I mentioned that no one knows why wagtails wag their tails when they stand still. It's a mystery. The only thing we know is that they can't stop...'