Grebes Project: Hopes of egg in nest No 4

No 4 nest has been raised for the past few days indicating this grebe may have laid an egg. Photo / Kerrie Waterworth

Only two breeding pairs of grebes have fledged their chicks so far this year on the artificial nests at the Lake Wanaka marina and there are concerns it may be due to a lack of food.

Grebes project founder John Darby said "we've still got two pairs that are prospecting but clearly the numbers of breeding pairs are well down on what we've experienced in the last few years.''

Two years ago 22 pairs had attempted to breed or had bred by this time.

Mr Darby said he was not a freshwater scientist but he wondered if the reason for the drop in grebe breeding pairs was due to the lake level being so low for and for such a long time.

"The lake has been the lowest I've ever seen it and so the habitat that would attract small freshwater fish like bullies was absent for quite a long period of time, and that might be critical in the life cycle of bullies and other small vertebrates that the grebes eat,'' Mr Darby said.

He said that not having any baseline data on the lake was a problem.

"Grebes, gulls, herons and shags are all top-of-the-lake predators and what determines the number of them is simply going to be the amount of available food,'' Mr Darby said.

"I don't think we have actually looked at the nutrient value of the lake at all in terms of vertebrate population.''

Mr Darby also said he would be contacting freshwater scientists at the Otago regional council to see if there was some way to monitor the nutrient value of the lake for vertebrates.

"That would also tell us about the whole dynamic of the lake if we can get that information,'' Mr Darby said.