Kia Pākiki Canterbury – black-backed gulls

In this Kia Pākiki Canterbury podcast, Associate Professor Adrian Paterson from Lincoln University interviews Wendy Fox from Lincoln University.

They discuss Wendy’s work in tracking and studying karoro, the southern black-backed gull.

Kia Pākiki Canterbury is a monthly podcast presented by the Canterbury branch of the Royal Society Te Apārangi.

Transcript

Associate Professor Adrian Paterson

All right, well I’m here at Lincoln University with PhD student Wendy Fox. She’s in the Department of Pest Management and Conservation, and she’s been working on black-backed gulls for almost 3 years or so now and been mostly interested in their movements, colony success and so on. Welcome, Wendy.

Wendy Fox

Thanks.

Associate Professor Adrian Paterson

So tell us a bit about black-backed gulls.

Wendy Fox

Black-backed gulls or karoro, so they’re our largest species of gull in New Zealand. They’re the big black and white scary ones with the big yellow beaks and the big black backs. And they definitely do like stealing people’s chippies because, you know, why wouldn’t you? Chippies are delicious. They are one of two species in New Zealand that aren’t protected under the Wildlife Act because they’ve done very well thanks to people and land-use change and human activities. Their population is higher than it would have naturally have been, which is good for them population-wise but bad for other species, and so they are controlled and managed in different river systems.

Associate Professor Adrian Paterson

And so you’re interested in what happens with them in, particularly around colonies. So do you want to tell us a little bit about where do you find these colonies?

Wendy Fox

Oh, you find them everywhere. They’re very versatile and adaptive animals. They’re amazing. Super smart as well. Way smarter than I gave them credit for when I first started. So they do largely nest on braided riverbeds, which Canterbury has plenty of. They will nest around estuaries and cliffs and all sorts of places, people’s roofs, commercial roofs. Yeah, they’re very adaptive. They’re very smart, which is great, but does make it challenging for some things. So I’ve been looking at their breeding success, so how well are they actually breeding? We see them everywhere, all the time almost. But yeah, are they doing well? Are they not doing well?

Associate Professor Adrian Paterson

Your interest in them is, as you say, kind of looking at what’s happening in the colonies and then looking at what’s happening with the individuals.

Wendy Fox

Yes. So when I first started, I was going to be looking at their breeding success, which I have been doing, and I genuinely thought that, even with the trends of good years and bad years, that pretty much every colony would be doing about the same breeding success-wise. And it turns out that is not the case, which was really interesting. So I’ve got a couple of colonies on the Waimakariri River, just north of Christchurch. And even between those colonies, they’re fairly close together – they’re probably about a [kilometre] and a half apart – and they’ve both had good years and bad years. One year, one had about 35% breeding success, which is really good, and the other had about 15 or 18, and then the next summer they almost flipped. The one that had done really well the year before ended up, I think, having about 18% breeding success, and then the other one that had not done so well the year before then I think had about 30. So it varies quite a bit.

Associate Professor Adrian Paterson

30% sounds kind of low, but I guess the point is these live for a long time, and they’re breeding every year essentially, so they can build their numbers up pretty quick, even with that lower percentage. Is that correct?

Wendy Fox

Yep, they are long-lived. The average is about 14 years. The oldest recorded is about 28 or 29. And they breed from about 4, but occasionally you’ll get super keen beans who start breeding at 3. On average, they probably get about 10 years breeding in. There’s all different factors of flooding, certainly on rivers, predation. If they’re new breeders,– like all new parents, some are more natural at it than others. So they may or may not be successful or very successful for the first year or two while they kind of find their feet. But yeah, they definitely have the potential to breed in good numbers.

Associate Professor Adrian Paterson

And so you’re also interested in where they move around in the landscape.

Wendy Fox

So I kind of stumbled across the transmitter tracking of karoro, which was super awesome. So despite the fact that there are plenty of them, we see them everywhere, we actually don’t really know that much about them at all. Very few are banded. There was a lot of banding done between about the 60s up until kind of 80s, early 90s in a few places. And then that’s all been based off resighting of their leg bands, which sometimes are easy to see, sometimes are not. But very little has been done since then. So we don’t really know who’s flying from where, whether they have big territories or small territories and all that kind of jazz. So being able to track them and see where they fly has been really interesting.

Associate Professor Adrian Paterson

So how have you gone about doing that? How do you track them down?

Wendy Fox

We catch them during the breeding season. So we use drop traps over their nests when they have two or three eggs, because then they’re quite committed to go back to their nest.

Associate Professor Adrian Paterson

And a drop trap is?

Wendy Fox

A bit like Wile E. Coyote. So basically a metal cage with bird netting over it propped up by a stick over their nest, and then I finally found a good purpose for a fishing line – sorry, Dad – and then the fishing line attaches to the stick and then reels out 10 to 80 metres, I think is the furthest we’ve gone. And then that goes into the hide where someone or multiple people are sitting waiting for the birds to then hop back on their nest and settle down, and then we reel it in, the stick falls, and then the trap traps them, and then we climb out and then catch them and wrap them up like a little burrito in a towel.

Associate Professor Adrian Paterson

And so you’ve caught them, then what?

Wendy Fox

We then take them back to our processing area. We weigh them. A GPS unit has to be no more than 3% of their body weight, so we need to make sure that they are heavy enough to do that. But we also give them kind of a bit of a look over to see their condition. The summer just been, we did have some quite small girls caught in a couple of places, and one girl, even though she was heavy enough weight-wise to carry one of the small units that we’ve used, her condition was quite poor, so we just gave her a leg band and then released her to go back to her nest.

Associate Professor Adrian Paterson

So you put these little GPS transmitters on, they beam the information up to satellites and then back to your computer, and then they basically fly off and start doing their thing and you can track exactly where they’re going.

Wendy Fox

Yes. So the units I’m using work off the cellular network. So they check into that system about every 8 hours, although if they can’t connect, they’ll just stop and then they’ll try again after another 8 hours. So if they’re not doing much, they will take a data point every hour. But there’s also this really cool boost option where, if they start flying, it’ll take a fix every 20 seconds so that you get to see these really cool flight patterns throughout the landscape, which is awesome when you put it on a map.

Associate Professor Adrian Paterson

And so where are they going?

Wendy Fox

Everywhere, because they’re super cool. So it’s been quite different between the breeding season and the non-breeding season. Breeding season is kind of October to about the end of January, and then the non-breeding season is February till about the end of September. So during the breeding season, they tend to stick within about 10 kilometres of their breeding colony, which they’re very attached to. They have a high fidelity. They will go back to their breeding colony pretty much every year unless something awful happens, which is really cool. And then, yeah, so they’ll stay within the area, about 10 kilometres radius, and they do largely like agricultural land, which we are not short of in Canterbury.

Associate Professor Adrian Paterson

And even outside the breeding season?

Wendy Fox

They fly all over the place, which is so cool. Previous research going off re-bandings has found that a breeding adult will stick within about 100 kilometres of their breeding colony, which is quite far away. But then I kind of thought it would be interesting – especially in Canterbury with kind of our very defined different river systems, especially with our large rivers like the Waimakariri and then the Rakaia and the Rangitata, there’s no shortage of food around the colonies, even in winter, and I kind of thought that maybe they would stick kind of within their little sections in the non-breeding season, and it turns out that’s not the case. The birds from the lower Hakatere Ashburton River go from kind of the Hakatere, the Ashburton, out to either Rakaia or the Rangitata. Sometimes they’ll go a little bit further afield, but kind of not too far, so that’s about a 30, 35 [kilometres] max kind of thing. Although Hagrid mixed that up and went down to Timaru for 2 weeks a couple of winters ago, so that was interesting, and then returned.

The birds from the Waimakariri seem to have quite different strategies. I’ve got birds tagged in the top part near Woodstock, so up the back of Springfield, and then in about the middle of the river and then out the back of McLeans Island, down the lower section. And the birds in the middle just kind of stick around the farmland but maybe a bit further afield. The birds from Woodstock all go down to the Rakaia for winter. Apparently, it’s gull party central for winter. And then I’ve had quite a mixed bag with my birds from McLeans Island. So some of them kind of stay around the area, but I’ve had probably half of them have gone down to the Rakaia or further for winter. I had two that went down just past Ashburton in winter just this year.

Associate Professor Adrian Paterson

And so they’re just going off for winter holidays or finding better food or social, or we just don’t know at this point?

Wendy Fox

Who knows? All of the above. Yeah, it’s interesting. There’s no shortage of food where they nest in winter, and there’s certainly plenty where they travel to in winter. But yeah, maybe just party central celebrating the kids leaving home.

Associate Professor Adrian Paterson

I mean, if I could fly, I’d like to go and do a big trip every now and then.

Wendy Fox

Me too.

Associate Professor Adrian Paterson

So just in terms of another application of what you’re finding, there’s this worldwide outbreak of bird flu, which has been slowly moving around the globe and is forecast to arrive in New Zealand over the summer. How is your information that you’re finding impacting on how we might respond or what we might need to worry about?

Wendy Fox

We’ve been very lucky in some respects where, as devastating as bird flu has been in the northern hemisphere, in recent years, the southern hemisphere, we have been able to be able to see what’s happened in other places and kind of learn from that for our preparations for whatever’s going to happen next. But from a disease spread point of view, especially depending on what time of year bird flu happens to come in and which species it gets to or the areas it is with essentially, I’ve got about five different colonies that are tagged, and I have four of them that are interacting in the same areas, not necessarily on the same days, but they are coming together in those same areas over winter and then going back in summer. So they could pick it up and then take it back home, which would spread a long way through the landscape potentially.

Associate Professor Adrian Paterson

So the concern is that gulls interact with humans pretty closely. If they pick up this, they’re moving it around the landscape. It’s a source that could jump off into humans but certainly going to jump off into other bird species. And so especially these big, long trips are not good news for stopping the spread or slowing the spread.

Wendy Fox

My understanding is the bird flu has really hit the colony nesting birds hard, including gulls in the northern hemisphere. And because karoro are so prevalent and they’re very good at scavenging and opportunistic, and they will, yeah, interact with humans and farmland and landfills and all sorts of goodies. The potential for them to pick it up from other species that may have it or them certainly to spread it as well to others, yeah, there’s a big scary thing about what that may manifest into.

Associate Professor Adrian Paterson

So Wendy, you were saying that the black-backed gulls are really, really smart. Can you give us an example?

Wendy Fox

So many examples. So I knew they were smart, but I didn’t realise quite how smart they were. While I’ve been collecting my breeding data out in the riverbeds, usually within a few weeks, they will recognise me and they’ll recognise the car. So I get to a point where I’ll literally park up. I don’t even have time to get out of the car. Birds will come over, put out the call to be like, “Oh my goodness, she’s back.” And then the colony becomes chaos, and all the adults are lifting off and telling their children to hide, so I can’t count them. It’s incredible. I don’t even have time to get out the car, and they’re like, “It’s her. It’s her car. She’s back again. The crazy bird lady. Hide your children!”

So the other example is when we first started catching, I thought that I was going to be able to catch all the birds from one colony. We caught one bird. It was probably about a radius of about 5 metres, processed her, released her, reset up the trap on another nest at kind of the other end of that 5 metres, and it wouldn’t have a bar of it. It was absolutely desperate to sit back on its eggs and was looking at everyone and looking at the cage, and it just refused. And these birds had never been caught before. They’d literally seen the trap once, and it was like, “Nah, not having a bar of that.” So we had to change our tactics.

Associate Professor Adrian Paterson

So they could see what had happened to their neighbour and went, “Well, you’re not going to catch us.”

Wendy Fox

Yep, definitely. Amazing. So much smarter than I thought they were.

Associate Professor Adrian Paterson

Well, thanks, Wendy. We tend to finish off with asking a question. The programme is about being curious. What was the last thing that made you curious?

Wendy Fox

So many things make me curious all the time, even if they have nothing to do with birds. They’re still awesome, and like, “Ooh, how could that work?” But the one I can think of last was having a very interesting conversation about banded dotterels migrating from the South Island and even from, like say, ones in the Mackenzie Country. Some will stay in that kind of vicinity over winter, some from that area will go up north to migrate and some will fly over to Australia. Which just makes me think, why do the same birds in the same area do very different things?

So I think a universal translator would be great.

Associate Professor Adrian Paterson

OK, well thanks, Wendy. So we’ve been speaking to Wendy Fox, PhD student at Lincoln University, about gulls and how she’s been finding out a lot more about the private life of black-backed gulls. Thanks, Wendy.

Wendy Fox

Thanks for having me.

Acknowledgements

Adrian Paterson
Wendy Fox

Kia Pākiki Canterbury logo, © Plains Media/Royal Society Te Apārangi (Canterbury Branch)
Image of Adrian Paterson, © Royal Society Te Apārangi (Canterbury Branch)
Image of Wendy Fox, © Wendy Fox

Southern black-backed gull (Larus dominicanus) on rock, Mike Dickison, CC-BY 4.0
Banded dotterel (Charadrius bicinctus), Patrick Kavanagh, CC-BY 2.0