Kereru, the native New Zealand pigeon, in Gradual Decline

Environmental News Issue 9

The first trigger for pest management in the Windy Hill area was the noticeable decline in kereru numbers. Although there was only anecdotal evidence, it made us look at all possible ways to halt this downward trend and led into the rat-trapping projects.

Kereru are a very important bird for Great Barrier, and indeed for New Zealand as a whole, because they are the only bird left capable of digesting and distributing large seeds. The pigeon can thus transport karaka, miro, tawa, puriri and taraire seeds from mature forest areas into regenerating bush and Kanuka/Manuka eco-systems. And they arrive complete with their own fertilizer pack ready-to-go!

The first time I saw kereru soaring skywards and then diving deeply with acrobatic twirls, I was most impressed. Was this the same clumsy bird as the one with the noisy flight and near-miss landings? This dive is a mating dance and although performed by both males and females, it is mostly the ‘boys’ showing off.

Pairs of kereru usually occupy the same area each breeding season so you will see the same birds reappearing year after year. Their nest is a platform of sticks loosely built anything between 2m and 15m above the ground. Somewhat flimsy, the egg and chicks inside can often be seen from beneath. The female generally lays only one white egg (although there can be several nests each season) and only 10 - 15% of the chicks successfully fledge. Although able to live to about 15 years old, their average life expectancy on the mainland is only 5 – 6 years due to predation by rats, possums, wild cats, hawks, stoats etc. Illegal hunting by humans reduces this average life span again to only 3 years. There is no data specific to Great Barrier Island but the fact that they are still here in reasonable numbers is probably due to the absence of possums and stoats.

Breeding success is closely linked with food supplies. Studies on the mainland show that a number of kereru actually starve to death. Rats and other birds compete fiercely for their favourite foods – miro, tawa, puriri, taraire and pigeonwood. Kereru also like kahikatea, coprosma, titoki, nikau, privet, elder and plums! They will also eat supplejack and cabbage tree fruits but these are much less preferred.

These birds can fly long distances, up to 25km, but have a slow top speed of 35km/hour. Four Southland kereru have been recently fitted with satellite transmitters in a current study. Over a period of four months ‘Roger’, one of these birds, clocked up five flights across Foveaux Strait and a couple of excursions from Invercargill to the Hokonui Hills!

There are many environmental projects on the mainland aimed at protecting and enhancing the lives of these iconic birds: primary school groups such as the collaboration of four North Shore schools in the Kereru Awhina Project, community groups such as the Karori Sanctuary project, and some are Department of Conservation research projects.

So what can you do to help:
• Plant some food sources for these birds – their favourites are miro, tawa, puriri, taraire and pigeonwood. We have information available on request on propagation of these species.
• Don’t tolerate any hunting of these birds, make it known to others that they are protected and in decline.
• Get your pet cat spayed or neutered.
• Be very careful if you are visiting or returning to the island not to bring any unwanted ‘visitors’ (possums, stoats, ferrets, Norway rats) with you in your luggage, car, boat or caravan.
• Kereru frequently die after impacting glass windows in our Barrier houses. Avoid a ‘see-through’ flight path by use of screens or curtains, and save your glass as well.