Not so bird-brained after all

What is it about birds? They are the wild creatures we see most often, their doings and calls a daily reassurance that humans are not isolated in our sentience. They descend from the first reptiles, while we come from the first mammals. Across a gulf of evolution we contemplate a parallel life which has evolved exhilaratingly different answers to the same questions that existence asks of us. Cross-referencing allows us to address the fundamentals. Darwin and his finches revealed how we came to be. What else might birds teach us?

Addressing questions because we can conceive them is the spirit of The Most Perfect Thing: Inside (and Outside) a Bird’s Egg by Tim Birkhead, author of the acclaimed Bird Sense. This follow-up has an appeal less obvious, but anyone drawn to the natural sciences will relish it.

Birkhead journeys inwards from the calcium spires of the shell, between which air passes (eggs breathe), across the albumen, an alkaline Sahara to a microbe, its nutrients locked up in inaccessible protein, which protects the yolk. There are curiosities at every stage. Why do birds turn their eggs? If turning matters, what of the palm swift, which glues its eggs to a frond? How does a tiny goldcrest incubate ten large eggs when she can only be in contact with three? (She paddles her pins through them, hot legs these, flushed with blood, acting like immersion heaters.)

The story of learning delights Birkhead as much as our current accumulation. Erasmus Darwin thought blue eggs were camouflaged when seen through nests against the sky. But blue eggs are found in solid nests and predation comes from above. We are still speculating: it is possible that bright colours persuade males of females’ vitality, encouraging male investment in parenting.