1. Prime Red Crossbill habitat is mature, cone-productive forest.

2. Accentors Siberian Accentor Old World Sparrows House Sparrow Wagtails and Pipits American Pipit Finches and Allies Brambling Evening Grosbeak Pine Grosbeak Gray-crowned Rosy-Finch Black Rosy-Finch House Finch Purple Finch Cassin’s Finch Common Redpoll Hoary Redpoll Red Crossbill Cassia Crossbill White-winged Crossbill Pine Siskin Lesser

3. ‘The Bittern, a brown heron, came close to dying out six years ago and conservationists feared there were only 11 ‘booming’ males left.’ ‘For every obvious crossbill, razorbill, greenfinch, woodpecker, warbler, treecreeper, swift or flycatcher there is a mysterious wigeon, garganey, gadwall, Bittern, siskin, pipit, shrike or twite.’

4. Antisymmetry refers to the condition where right-sided and left-sided—or dextral and sinistral—forms are equally common within a species, as seen in the major claws of lobsters and male fiddler crabs, the side to which the upper mandible crosses in most crossbill finches, or the spiral orientation of palm-tree trunks.