On the island sanctuary of Whenua Hou, kākāpō only breed when rimu trees mast. Rimu responds to different temperature cues than beech.
“If year two is colder than year one, there’ll be a mast in year four,” says kākāpō scientist Andrew Digby. “We count the developing fruit in the autumn. If more than eight per cent of the branch tips have fruit on them, the kākāpō will breed the following summer.”
Last autumn, 47 per cent of the tips had fruit, and it has led to a record-breaking breeding season.
It’s rare for rimu fruit, pictured above, to fully ripen on Whenua Hou—that last happened 17 years ago.
But today, ripe red fruit carpet the ground, and kākāpō mums are feeding it to their chicks, which are growing faster than usual. Almost every nest has two chicks, or even three: “We’ve never seen that before,” says Digby. “Almost every bird has bred.”
It means 2019 is a mega-mega-mast: not only are beech and rimu masting at the same time, a rare event, but masting is unusually widespread.