Free Bird Sense by Tim Birkhead

Preface
    ‘Buggered’ is how most New Zealanders describe their bird fauna, and it is. I’ve rarely been anywhere where birds are so thin in the air or on the ground. A mere handful of species – several of them flightless and nocturnal – have survived the ravages of introduced European predators, and now exist in tiny numbers, mainly on offshore islands.
    The sun is already setting as we arrive at the lonely quayside. The faint purr of an outboard motor soon materialises into a small boat approaching from the island. Within minutes we are heading out to sea and into a blazing sunset. The mainland-island transition is magical: twenty minutes and we step out of the boat on to a wide, sweeping beach overhung with majestic pohutukawa trees.
    Anxious to see our first kiwi we are out again as soon as we have eaten. The moonless night sky is splattered with stars – the southern Milky Way, so much more intense than that in the northern hemisphere. Our path takes us back down towards the shore and we are suddenly aware of the sea: phosphorescence! The tiny waves lapping the beach are glowing. ‘You should swim,’ Isabel says, and with no further encouragement we are all skinny-dipping, and ignited by bioluminescence we jump around like human fireworks. The effect is spellbinding: a visual extravaganza as elusive and astonishing as the aurora.
    Ten minutes later we are dry and continue our kiwi quest into the adjacent woodland. With her infra-red camera, Isabel scans ahead, and there, hunched among the vegetation, is a dark, domed shape: our first kiwi. To the naked eye the bird is invisible, but on the camera screen it is a black blob, with an extraordinarily long, white bill. Unaware of us, the bird shuffles forward, foraging like a machine: touch, touch, touch. At the end of this long summer the ground is too hard for probing and coming across a cluster of crickets on the soil surface, the kiwi snaps them up as they attempt to hop, skip and jump away. Suddenly aware of us, the bird hurries off into the bush and out of sight. As we walk back to the house the darkness reverberates with the high-pitched squeals of male kiwis – ‘k,wheee, k,wheee’.
    Isabel Castro has been studying kiwis on this tiny island sanctuary for ten years. She is one of a handful of biologists trying to understand the bird’s unique sensory world. Some thirty of the island’s kiwis carry radio transmitters that Isabel and her students use to follow the birds’ night-time wanderings and to pinpoint their daytime roosts. We have joined the annual catch-up to replace the transmitters whose batteries fade after a year.
    In the brightness of the early morning sun we follow a transmitter’s bleep through a forest of manuka trees and ponga (tree ferns) to a small swamp. Without speaking, Isabel indicates that she thinks our bird is in a dense patch of reeds and mimes to ask me if I’d like to catch it. Kneeling, I see a small opening in the reeds and with my face close to the muddy water I peer inside. With my head torch I can just make out a brown, hunched shape facing away from me. I wonder whether the bird is aware of me as kiwis are renowned for their deep day-time sleep. Judging the distance, I steady myself in the soggy ground and shoot my arm forward to grab the bird by its huge legs. I’m relieved: to have lost it in front of the research students would have been embarrassing. I gently pull the bird from its sleepy hollow, cradling its chest in my hands. It is heavy: at around two kilos the brown kiwi is the largest of the five (currently) recognised species.
    It is not until you have this bird lying in your lap that you realise just how utterly bizarre it is. Lewis Carroll would have loved the kiwi – it is a zoological contradiction: more mammal than bird, with luxuriant hair-like plumage, an array of elongated whiskers and a long, very sensitive nose. I can feel its heart beating as I fumble my way through its plumage to find its