It arrives in spring. It lays its eggs in someone else's nest. It leaves before summer ends. It does not apologise. It does not need to. The grey warbler has already started building again. The shining cuckoo is a ghost that visits. It spends the winter in the Solomon Islands or Papua New Guinea in warm wet forest far to the north. Then in September or October it crosses the Tasman and arrives in New Zealand as if it left only yesterday. The timing is precise. The journey is long. The return is annual. The forest hears it before it is seen. A high descending whistle rings out. It is clear and insistent. The phrase drops through a minor scale. It repeats several times and then stops. This is the sound of summer arriving. Once you know it you hear it as a season changing. It is a marker of time that has been accurate for millennia. The call defines the period. It signals the shift. The auditory cue is distinct. Pīpīwharauroa is bronze-green above. The feathers are iridescent in the right light. They shimmer between green and copper. The underparts are pale. Fine dark barring crosses the breast. In the right shade it looks almost scalloped. The bird is smaller than a blackbird. It has a slightly decurved bill. The dark eye gives nothing away. It moves through the canopy with speed and discretion. This behaviour is entirely at odds with the song it uses to announce itself. The contrast is sharp. The stealth is effective. Its primary business is not feeding or singing or defending territory. Its primary business is deception. This strategy has been refined over thousands of years. The shining cuckoo is a brood parasite. It lays its eggs in the nests of other birds. The grey warbler (riroriro) is the most common host. The cuckoo watches. It waits. When the warbler leaves the nest the cuckoo slips in. It deposits an egg. It slips out. The whole operation takes seconds. The efficiency is brutal. The intrusion is brief. The warbler returns. It sits on the egg. It does not notice anything wrong. The cuckoo egg is small pale and speckled. It looks close enough. The warbler accepts it. The cuckoo chick hatches first. It is naked and blind. It is not helpless. It evicts the warbler's own eggs or chicks. It pushes them out of the nest to die. The warbler returns to an empty nest except for the cuckoo chick. It feeds it anyway. It raises it anyway. It treats it as its own. The instinct overrides the loss. The care continues. The cuckoo chick grows fast. It dwarfs its foster parent. The warbler perches on the cuckoo's back to feed it. This is not compassion. It is instinct. The warbler cannot help itself. The cuckoo relies on that. The dependency is total. The exploitation is complete. By late summer the young cuckoo is ready to migrate. It has never seen its parents. It has no map. It has no guide. It flies north alone. It crosses the Tasman to islands it has never visited. It finds its way anyway. Cuckoos have been doing this longer than humans have been navigating by stars. The navigation is innate. The survival is remarkable. In New Zealand this is a bird of the forest canopy. It feeds on caterpillars and insects. It eats the hairy ones that other birds avoid. A specialised stomach strips the hairs before digestion. This is a useful adaptation. It saves the cuckoo from competition. The niche is secure. The call is the giveaway. A shining cuckoo calling from the canopy is announcing summer. It does not know that. It is just looking for a mate. The intent is simple. The effect is seasonal.