Leading Mallard Duck Researcher Jenn Sheppard Updates Fish & Game’s Three Year Telemetry (Tracking ) Project
The study, spearheaded by the University of Auckland PhD student Jenn and Auckland Waikato Region game bird manager David Klee, has involved tracking ducks fitted with transmitters at two sites – in the Waikato and Southland.
The aim has been to examine their survival rates, breeding habitats, and overall productivity.
Jenn Sheppard says the project will soon enter the “nitty gritty” phase where data collected over the last two breeding seasons will be thoroughly analysed and interpreted.
What stage is the project at?
We are almost at the end of final field season and what this means is that the birds have nearly finished nesting and raising their ducklings, and most are beginning to moult and group up (or flock) again…and take a break until next year.
Any key finding you can point to at this stage – a ‘Eureka’ moment?
There has been, but until we plug everything in and analyse it, we won’t understand what it means so it’s still a bit too early to say. For example, we could say, ‘Oh, we’ve found that nest survival is really high and that’s good,’ but we don’t know for certain how it’s going to work out once all the survival rates are looked at in the same scientific models.
What we did find this year, which I think is really important, is that our results are similar to last year’s, this means that we didn’t have a weird “off year” which could skew or complicate our results, and make it so much harder to interpret the data. It’s very good news that we are finding consistencies in our data collection and results.
That tends to indicate that earlier findings are on track?
Yeah I think so…you always need repetition when conducting studies like this – you never know when you are going to get an off year, or how different climatic factors are going to affect the outcomes. The birds seemed to nest at exactly the same time. The first day a nest was laid by our marked birds in the Waikato was July 15 – both last year and this year. I think such an early date was unexpected by a lot of people and that most people thought they didn’t nest until late August.
So some key background….how many birds tracked in each place? The numbers?
We’ve tracked 60 females with abdominal implants in each site per year – so those are the ones that we tracked from June onward. Then we found nests of un-marked birds and we trapped them on the nests and equipped them with back-mounted transmitters. The number of birds with this type of transmitter varied, depending on the site and year. This year in the Waikato we marked 17 – last year we marked 11, and in Southland last year they had 22 and 11 this year.
So, all up we’ve managed to mark 300 females and collect good data for just over 250 of them, which is a great sample size to work with. Most people who do a two year study on ducks probably have a sample size of around 100 to 200. So I think we’re doing really well in terms of the life of the project and resources.
It’s a large number, 300 females, it’s the biggest mallard project ever in New Zealand and the biggest by Fish & Game – no one in New Zealand has researched mallards to this extent, at least no one I’ve come across yet. I wouldn’t say that our results conflict with what earlier researcher Murray Williams (Victoria University, Wellington) found, but I think there has been changes since he did his work. We are finding new things that no one knew for sure – new emerging results.
The only way to fully understand what is happening in a population, in regards to various survival rates and productivity, is to mark birds and track them through breeding. It’s the only sure way to monitor survival rates and determine what habitats are important, and no one has really done that.
What would you highlight in terms of finding out new things?
Some things we’ve found probably would not be news to some people. One thing we have confirmed this year is that females do double-brood. Last year, we had birds that would lose their ducklings and re-nest, which isn’t overly surprising. But this year, females have successfully raised ducklings to fledging and they’re nesting again.
We don’t know if the second lot of ducklings will survive yet, because the nests just hatched in mid-December, but it’s possible that some females might produce two full broods. Some people say that happens all the time but it’s pretty much unheard of in mallards in the northern hemisphere where the birds originate from.
So could the double brooding be a New Zealand-specific behaviour?
It could be a unique trait that mallards have in New Zealand compared to elsewhere. It’s very unusual for a duck to nest again after they‘ve raised the ducklings. Usually if a duck raised ducklings they flock up and moult. It takes an excessive amount of energy to raise two broods, but New Zealand mallards seem to be able to cope with that.
What are the factors that permit that? How is that happening?
I don’t know yet, but I have two ideas which I will look into further during the nitty gritty analysis. It could be because there are really good climatic conditions this year - good rainfall and lots of food. Or, low success in other years causes the birds to keep going as long as possible in favourable years. Maybe most years the nest or brood is unsuccessful and when they have a year where survival rates are higher the birds just don’t quit breeding. I think it’s one of the two extremes – either because (conditions) are really good or really bad!
For a female to put that much more energy into another nest, I would guess she has to be in really good condition. If we could re-trap them on the nest and figure that out it would help answer some of our questions. It’s a lot of investment.
That double brooding trait, the most surprising the most significant?
It’ll be interesting to see how that double-brooding helps the population, but I don’t think it will be the most significant. The other surprise is that it’s not uncommon for a female to just have one or two ducklings survive. At the end of the day, our duckling survival is quite low. On average, birds hatch 11 ducklings but after the first 10 days most of the ducklings are dead, and the female might raise just one or two ducklings to fledge.
The mortality of ducklings is most likely due to predators, but because we are unable to mark and track individual ducklings, we don’t know what predators or other factors are responsible for the high mortality rates. We’ve seen them get eaten by various predators, but a young duckling that is not yet a week old is unable to keep itself warm so at night if it’s too cold for them they could freeze. If mum can’t keep them warm, they don’t have a chance really, but again, we have no way of knowing if that’s happening.
Most lost because of predation or the cold?
I suspect that it’s probably predation, but the only way we would truly know is if we had a study that focused on the predators. I think that if somebody wanted to look at the whole suite of predators and look at what the predator eats (their diets), then we'd know for sure what’s eating ducklings.
Aside from predators, it could be variable weather conditions such as too much or too little rainfall. It could be that they’re just not getting enough food or they’re in poor condition.
It’s sad – it’s true of both sites but duckling survival is probably twice as high in Southland. We see 15 percent in the Waikato and around 30 percent survival in Southland. What that means is that so far this year, we’ve had 450 ducklings hatch and only 15 percent of those survive, which is 67 out of 450.
Very low compared with northern hemisphere?
That’s very low compared with the northern hemisphere. There’s been one study that found similar duckling survival rates but most are much higher, even over 50 percent. The difference between here and the northern hemisphere is that we have higher nest survival rates – I believe their nest survival is lower, especially as our season progresses some birds nest successfully in August or September, but a lot of the nest gets destroyed by predators so they re-nest. But by October or November those nests are surviving so later in the season, more nests hatch.
But overseas, if they don’t hatch in that first month then it just goes downhill from there and just gets worse and worse – but here it gets better. Its opposite for the nest, I think.
This could be that the predators are switching their prey. I think when there are lots of nests on the ground they target the eggs, but once ducklings start hatching and there are broods, I think the predators switch and they go after ducklings. So later in the year more nests have a chance to hatch, at least that’s what the data suggests.
Would you take a stab at the worst predators?
We know that cats and rats come to the nests, we have that on video from nest cameras. Depending on the circumstance, we can sometimes tell what destroyed the nest – you could tell if it was a hawk because the nest will be all torn up. If all eggs are missing, it’s usually a stoat, but half the time you can’t tell because the nest will be a disaster, eggs eaten and egg shells everywhere.
We did do necropsies (bird autopsies) on all the females that died last year. We just took the dead birds and had a scientist help us out and it was mostly cats and ferrets that killed the females. We will do the same this year; we’ll look at the females that have died on the nest, so we are able to tell what kills them. Just over 20 percent of females died on the nest.
We’ll have close to 50 females that have died in the last two years. Sometimes you can’t tell what killed them because the carcass is just too far gone. I’m sure cats are taking their toll on ducks…we just don’t have it documented.
It’s a difficult to pinpoint any one predator, especially because we have no idea what happens at night and what happens when we aren’t around. If everyone started targeting hawks, it’s likely the stoat or rat population will increase, which would create issues for nesting birds. If we want to focus on predators, then we need to target all the predators not just one specific one. Otherwise we will see unintentionally, or unexpected changes in the ecosystem, which could be counterproductive for our duck populations.
Is a predator study the crucial next step to get a handle on mallard populations?
We’ll have a good handle on mallard populations. The information we have now is going to provide fundamental results to look at the population. We’ll understand how the population responds to different survival rates, different weather, different botulism outbreaks, harvest, and so on. What we don’t know is which predators do most of the damage so if we want to focus on predators, we need to do more research to figure out which ones to focus on, or look at a whole suite of predators and target as much as we can or we might have some unexpected responses, as I’ve said. The last thing we want to do is increase the stoat population by killing all the cats and hawks. It’s not going to help our cause! So either we need to figure out what’s causing most of the damage, or just target everything.
What else emerges from the research to date as far as where we need to go from here?
Right now, we almost have all our data collected – we are almost done. The next step is to plug it all in to the population models and figure out what it all means. In a few months we’ll have a better understanding about what’s happening and then we’ll know where to go from there. The best thing we can do right now is just to be patient – I wouldn’t recommend changing anything between now and then, we need more time to look at the data we’ve collected and understand it more.
We know duckling survival is really low, but we don’t know what that means in terms of population growth. If the female and nest survival rates are high enough, and, if harvest rates don’t overly influence survival of females then maybe then the low duckling survival is not that important, because it’s compensated for throughout higher survival rates elsewhere. But maybe duckling survival is very important, but we have no way of knowing what that means until we have time to look at it.
But you’ll be able to come up with some significant recommendations?
Oh yes, well have a much better understanding of the habitats the birds use, when predation rates are highest, when the survival of nests and ducklings is most critical, and what the reproductive effort and success of females is, so we’ll answer a lot of questions. It’s possible we’ll find that predation is highest in September, so we’ll recommend increasing trap efforts in August.
In October when most ducklings are hatching, or most birds are re-nesting, we could ask councils and regional councils to not mow the sides of the roads. It could be something as simple as that – just more awareness of when birds use certain areas and when they are most vulnerable, then just try and do our part to help them survive.
Likely recommendations at the end of the study will probably be some sort of predator prevention in one way shape or form. It could be more trapping it could be setting it up properly or focusing on different areas. It’s probably going to be a lot landowner advocacy, making people aware that hedgerows, effluent ponds and un-mowed roadsides are important. We’ll know how much nest cover a duck needs, so instead of just spraying the blackberries maybe we can find a native plant that can function the same way, if it’s a certain height or density we can probably figure that out. At the end of the day well have heaps of information that we can use to hopefully help the ducks out.
Anything the public can do to assist your research?
The best thing is if hunters let us know if they find any banded ducks that’s the most useful information for us at this age. Especially if we can get returns from our radio-marked ones. If we know where they went, or how many years they survived for – that would be very valuable information for this and future research. In five years from now, if a hunter shoots one or our birds and reports it, then we will know that this bird had ‘this many nests this year and that many ducklings’ and still survived five more years. Information like that is invaluable.
The battery in a transmitter only last ten months, but all our study ducks have bands. Some ducks might have two bands – a normal band and a coloured band, but others will just have the normal band. It’s crucial we get details of any banded duck – that’s the best information we can get.
How would you sum up then?
We’re almost done collecting the data…we are going to be able to answer some very important fundamental questions about what birds need, what they use and what the population is doing. We’ll have some good recommendations on where to go from here. Whether it is a focus on predators or a focus on habitat, by this time next year we’ll have answers to those questions.
Low duckling survival is surprising but the drive of these ducks to double-brood after raising ducklings…that’s surprising too.
LATEST UPDATE 8/9/2015