Does Wānaka have too many grebes?
Volunteers in Wānaka have found that while grebes love using the nesting sites they have built, the birds are now starting to outnumber the housing.
The Australasian crested grebes on Lake Wānaka are teaching us a great lesson: we need food and shelter to survive a tough life, but also the drive and skill to out-do our competitors.
The grebe nesting project, where volunteers made and placed floating wooden platforms around Wānaka marina to create stable nesting places for the native waterbirds, has been successfully running for three years. But this year, sadly, the birds have a different tale to tell.
The birds’ journey of survival from October until April has been a tumultuous one. Ironically this is partly because of the project’s success: now there are more birds moving to the area than there are platforms.
In other words, Wānaka has the grebe equivalent of a housing crisis.
“Last year was quite a successful year,” says John Darby, a retired zoologist who has been studying these native birds with help from local children. “We managed to get nearly ninety chicks from only fifteen platforms, suggesting that more than one pair of birds used the nesting site.”
“This year, though, there was an aggressive male bird that kept stopping the other grebes from claiming the platforms. I suspect it might’ve nested in several of these sites previously because it seemed to think that the whole of the marina was its territory.”
When a bird pair did finally manage to snag a site, however, other nesting couples would then fight with them over the claimed platform until well into the summer.
“I haven’t seen these birds like this before and it’s a bit worrying,” says John. “Not just because they’re fighting but also because some of the birds that have managed to lay eggs aren’t going back to them.”
Some didn’t return to their nests for as long as two days, he reveals.
Similarly, John and his team of volunteers found that the birds laid less eggs, took longer to incubate them, more birds deserted the nest completely and even the infertility rate was much higher than it had been for the previous two years.
John suspects that there may not be enough food locally, meaning that the birds are having to seek it further afield or go hungry. He says that when he looks at the data the volunteers have collected, this will either confirm his suspicions or point to another cause.
Ten-year-olds Archie North and Jack Sandford are two volunteers who have taken a particular shine to the grebes.
“My favourite part of looking after the grebes is being able to get up really close to them and looking in detail at their beautiful feathers,” Archie tells us.
"I've especially enjoyed getting close to the nests and checking their eggs. The highlight was seeing a chick actually hatch in front of my eyes! That was amazing!”
Jack loved working with John and the grebes so much that he has even written a poem about it:
G - great birds with paddles on their feet instead of webbed feet.
R - really amazing that a little parasite lives in the eye of the fish that grebes eat.
E - even though penguins spend long periods of time in water grebes spend even more time.
B - bum bird! A name given to the grebes because of their legs so far back on their bodies.
E - every feather has a bit of down on the end for insulation.
S - science is one of my favourite subjects. By studying Grebes scientifically with John I have learnt to record data, investigate, make discoveries and ask questions.
The team of volunteers have found that only 35 chicks have hatched this year – less than half of last year’s 87 chicks.
“I think it’s fair to say that this is a much better total than if we had left them to their own devices!” John says, before revealing that as many as 153 chicks have hatched on the platforms since 2013.
The volunteers are now going to do a lake-wide survey by boat, with Jack and Archie taking the roles as expert grebe-spotters with other volunteers, to get a clearer picture of what has happened. The team will then use this to keep a closer eye on the birds during the fourth season.
“I don’t think many people understand how hard it actually is for some animals to survive,” Archie explains.
“The grebes work for days on end to build their nests, just to be broken down by the next storm and they often lose some of their precious eggs in these storms. It is pretty sad really, but I guess that’s the tough life of a grebe.”
Photo credits: John Darby (bird families, children).
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About the project
This project is supported by funding from the Otago Participatory Science Platform (PSP) managed by Craig Grant at Otago Museum.
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