Operation Nest Egg

Forest and Bird, Issue 292, 1 May 1999, Page 18

Operation Nest Egg

Science and Research Unit,

Department of Conservation, Wellington.

—ROGAN COLBOURNE,

peration Nest Egg was established as an experiment to see if the vulnerable stages in the life history of some kiwi populations could be bypassed. The idea is to protect the eggs and young birds while they are at risk from predators. Operation Nest Egg consists of taking eggs from wild kiwi, incubating them in artificial incubators, and rearing the chicks in captivity or on predator-free islands. The birds are released back into the wild once they are big enough to defend themselves against cats and stoats. To find out more about kiwi incubation so that conditions could be replicated in incubators, dummy eggs with internal temperature sensors were put under wild incubating North Island brown kiwi. It was found that the dummy egg was rotated through an average 180 degrees per day. During the last three weeks of incubation, real eggs are not turned as much: because the increasingly large airsac causes an imbalance in the weight of the egg, when kiwi try to turn their eggs at this stage, they end up only rocking them. By applying these findings to eggs in incubators, the success rate for artificially hatching eggs has been steadily improved. In the last two years at Auckland Zoo, 21 out of 24 fertile eggs from Northland were hatched. The ages of the eggs when collected was between 15 and 75 days. All chicks survived to the release weight of one kilogram. Raising chicks is now very straightforward. They are put onto an artificial diet within two weeks after enticing them to first feed on earthworms. The first research steps to getting these birds back into the wild have been to protect them from predators, and from the territorial behaviour of other adult kiwi during reintroduction, to see if they could simply cope with the transition from captivity to the wild. A predator-free and kiwi-free island (Motukawanui in the Cavalli Islands group) was chosen as the first introduction site. Ten captive-raised kiwi were released with transmitters and their progress followed. Not only did they cope well right from the start, the two oldest pairs have also bred successfully. After this achievement, 25 juveniles were returned to the Northland mainland where their eggs came from. Deaths have since occurred from a ferret (it killed at least four wild adult kiwi at the same time), dogs, illegally set possum traps and one bird fell into a deep hole. Just over half of the re-introduced birds are still alive; the oldest have been in the forest for almost two years and are starting to pair with wild kiwi. A Tongariro Operation Nest Egg programme has had even more success with 13 juveniles released into the Tongariro Forest with no known deaths. One kiwi had so much stamina it twice swam across the Wanganui River and ended up 12 kilometres from its release site! At Lake Waikaremoana four released kiwi settled in well. These releases have been small-scale while we are learning the techniques. The greatest optimism is caused by releases at Okarito. Birds there are more problematic in that, unlike North Island brown kiwi, adults will not tolerate new juveniles in their territories and will promptly kill them. Early losses have been overcome through making the young kiwi more ‘bush-wise’. Rather than raising the birds in pens, the chicks are released onto a small predator-free island in the Marlborough Sounds where they learn to interact and feed in a natural way. As a consequence, these youngsters when returned into Okarito are settling back into the forest much more successfully. Twenty-five juveniles via Operation Nest Egg have raised the critically endangered Okarito population by about 16 percent in three years. Operation Nest Egg has been highly successful in showing that captive-bred kiwi can cope with the transition back to the wild. Not a single released bird weighing over a kilogram has been preyed upon by a stoat or cat. Once kiwi have been put back into the wild, however, that population must still be managed in terms of advocacy and pest control: this is particulary important where kiwi populations are near

human settlements.