The team increased the annual output of Old Blue (and later other females) by removing the first clutch over every year and placing the eggs in the nest of the Chatham race of the Tomtit, a technique known as cross-fostering.
The Chatham Tomtit (Petroica macrocephala chathamensis) is a subspecies of Tomtit found on some of the smaller islands of New Zealand.
The North Island Robin, like the New Zealand Robin, is a terrestrial feeder foraging on or near the ground (unlike the related and more arboreal Tomtit).
The Snares subspecies feeds on the ground as well, in a similar fashion to the New Zealand Robin.
Tomtit | Chatham Tomtit |