Pair of adult great crested grebe and chicks. Image credit: John Darby
Although the great crested grebe (Podiceps cristatus) is a cosmopolitan species, the subspecies found in New Zealand is rare and is confined to the inland lakes of Canterbury and Otago.
Over the last decade, numbers of the birds have been low. In February 2009 the Otago Branch of the Ornithological Society of New Zealand surveyed the Central Otago lakes to come up with a breeding population count. In 2004 the total population for the area was 119, while five years later the tally was over 400. Lake Wanaka was not covered on the survey day, although an unconfirmed number was recorded as five adults.
Grebes build floating nests and the population struggles to succeed on Lake Wanaka partly due to fluctuating water levels – either their nests flood or end up beached.
In 2013 former Otago Museum Assistant Director and Head of Sciences, John Darby, moved to Wanaka and became very involved in local ornithology, especially the plight of the great crested grebe. John managed, with the help of his kayaking skills, to construct and care for 15 floating nests for the birds. In this last season, 87 chicks were fledged from 43 breeding attempts, bringing the total to 118 chicks since this project started.
A grebe making itself at home on one of the specially constructed floating nests. Image credit: John Darby
John has trialled different designs, sizes and tethers for the nests, and has seen a promising increase in the breeding success of Wanaka’s grebe population as a result.
Despite this species being rare, a few eggs have ended up in the Otago Museum over the years. Six eggs came from Central Otago (the oldest three being dated 1897) and two are most likely from the UK. This number has increased dramatically since John collected 20 infertile eggs during nest monitoring. It is interesting to note that the average size of the New Zealand eggs is 57mm x 36mm. However, one egg of those 20 collected by John was very small, just 38.9mm x 30.3mm.
Variation in egg size and shape in the recent donation. | Image credit: Otago Museum Collection