Study helps reveal diet of threatened birds of prey

Dissecting undigested prey may sound a bit gruesome, but a Rotorua charity is using this method to advance our understanding of the diet and health of New Zealand’s birds of prey – including one relatively new arrival to our shores.

The carnivorous birds – which include the New Zealand falcon (kārearea), morepork (ruru) and swamp harrier (kāhu) - are unable to digest all parts of their prey, so expel the remains as pellets.

"The benefit of studying these pellets is that we can dissect them, look at the remains and identify what the birds have been eating,” says Shannon Campion, Administration Manager at the Wingspan National Bird of Prey Centre.

“This is much more reliable than trying to observe the birds in the wild to see what they eat."

The research is providing key insights into the diet of our birds of prey, and the subsequent impact they may be having.

{CF_IMAGE} Above: A raptor pellet workshop being led by falcon expert and Wingspan Trustee Noel Hyde.

A pellet dissection in 2009 looked at New Zealand falcons in the Kaingaroa Forest and revealed some surprising results.

With the New Zealand falcon species classified as threatened, the dissection found that 95 per cent of the falcons' diet was made up of introduced species.

That insight is interesting, as it shows the adaptability of the species and challenges any perception that falcons are responsible for the demise of our native wildlife.

{CF_IMAGE} Above: Bird skulls, recovered from a bird of prey's pellet.

The samples taken during these dissections can be compared to Wingspan's extensive research collection to aid in prey identification.

"I believe we have the largest research collection of this type outside of a museum or university in New Zealand," Shannon says.

In March this year, Wingspan ran its first-ever pellet dissection workshop focused on the diet of barn owls - a fairly new species in New Zealand.

{CF_IMAGE} Above: A barn owl in flight. Photo: Kurien Koshy Yohannan

"They've been flying across the Tasman from Australia for a long time now, with the first reported sighting in 1947, but they weren't recorded breeding here until 2008," Shannon says.

"So there's more to learn about what their impact will be, whether they will affect the populations of the prey they eat, and whether they compete with other native species - so far we consider their presence to be fairly benign."

The workshop was funded by a $6580 grant from the ANZ New Zealand Staff Foundation and included attendees from the Department of Conservation, private conservation and restoration groups, students, and people working in bird rehabilitation.

"The grant covered staff salaries and equipment, as well as allowing us to offer the workshop free of charge,” Shannon says.

"We generally don't receive government funding, or through local bodies, but we do have a member base who contribute donations, and we rely a lot on volunteers to help us do the work we do."

After the success of the pellet dissection workshop, Wingspan is now looking to run a series of similar events in future, with the hope that skills and knowledge in this area can be passed on, and research and conservation of our birds of prey can continue into the future.

{CF_IMAGE} Above: Participants from the barn owl pellet dissection workshop.

Despite being fully protected under law, some people still see birds of prey like the New Zealand falcon as a pest, as they sometimes target prey like chickens and other small birds.

“Unfortunately, they can often be met with the end of a shotgun, which is terrible really, because they’re a threatened species, and also endemic to New Zealand – they’re found nowhere else in the world,” Shannon says.

Being at the top of their food chain as apex predators, the birds are also vulnerable to things like starvation and bioaccumulation of heavy metals.

New Zealand falcon is New Zealand's fastest bird, and impact injuries are common, as well as encounters with uninsulated power lines.

"There are threats than can be reduced or eliminated with a bit of education - and a bit of empathy," Shannon said.

Only about one in four falcons will survive through their first year. Many of their eggs and young fall victim to pests such as rats and possums – making pest control one of the biggest things we can do to help them.

Native planting also provides more habitat for the birds, and Shannon says donations to conservation and restoration centres like Wingspan go a long way too.

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"You don't have to give us thousands of dollars to make a difference - if people just tell their friends and family about the work we're doing, or make a small contribution, it all makes a difference."

You can find out more about the Wingspan National Bird of Prey Centre, as well as book a visit, here.