Tīeke mystery

Author: Kay MiltonDate: August 2023Header Photo Credit: Lucas Mugier

Something off has been happening in two of the tīeke nest boxes on Tiritiri Matangi. It was shared in our Tiritiri Matangi magazine, Dawn Chorus 124 (February 2021), that when Barbara Walter checked a box in early December 2020, two birds left as she approached. She found it contained six eggs (the normal number on Tiritiri Matangi would be two or three), and one of them was white (tīeke eggs are normally pale fawn with darker speckles)!

When the box was checked again on 16 December there were just three eggs. The white one and two of the others were missing. When we looked back at the photo of the six eggs we realised that the other two eggs were also unusual – they had a mixture of dark and light patches rather than speckles.

Left image: The six eggs that were found and one of them is white!Right image: On 16 December the nest only showed three eggs when checked.

What appears to have happened is that two females chose the same box, one or both of them built a nest and both of them laid in it. Both incubated for a while, and then one of them removed the eggs that were not hers. We assume she was able to tell which these were because of their appearance, though there may be other clues we don’t know about. Although the victorious female went on to incubate the remaining eggs, they didn’t hatch.

Shortly after the nest failed, a new one was built in a box just a few metres away, and both females moved in there. This time the maximum number of eggs recorded was five on the morning of 7 January, but it was down to four by that afternoon, two normal ones and two abnormal ones, including a very pale one.

By 13 January there were just three complete eggs. The pale one had broken and its shell had stuck to the other abnormal egg. By the afternoon of the 21st, another of the normal eggs had disappeared and those that were left were cold. It looks like neither bird has won this contest.

Left image: The nest shows four eggs in the afternoon on the 7 January.Right image: Now the nest is showing three complete eggs on 12 January.

The saga has moved on

In December 2022, in an attempt to learn more, a trail camera was trained on the box, triggered by movement to take a series of short videos during daylight hours. It did not pick up any eggs being removed, but it captured a number of apparently aggressive encounters outside the box, in which one bird chased another away. Since the birds are not banded, we cannot tell whether it was always the same bird doing the chasing. Nor can we tell whether these encounters were between the two females, or whether one or more males was involved.

The saga has moved on, and the mystery has, if anything, deepened. There was no sign of eggs being removed in daylight, so it could be happening after dark, when tīeke are assumed to be roosting quietly. We hope that next season will provide further opportunities to study this unusual case.