EcoLincNZ

Category: Species distributions

  • Kiwi calling: when listening is not enough

    I don’t know about your’s, but my mum gets worried when I don’t respond to her phone calls for a few hours. Once, I can’t remember what I was doing, but I didn’t hear the phone ringing. When I finally checked my phone I saw about 17483 missed calls, oops. I can only wonder what went through her mind when I wasn’t responding: she was probably picturing me skydiving, in an ambulance, or lost in the woods during a hike.

    But what if she’d had a more statistical mindset and thought about why I hadn’t responded? Or even better: what if she’d thought about reasons why she could not detect me?

    Ecologists and conservationists consider something similar when analysing data obtained from searching an area for a certain animal species. An animal could be present at a certain site, but still go undetected. First, they have to consider what ecological reasons might have determined where the species was present or absent (for instance, where is there suitable habitat within the considered area). Second, they have to take into account what factors might have influenced the likelihood of actually observing the species (such as the distance from the observer, or the fact that the surveyor may not be skilled enough to recognise the species). These are defined, respectively, as occupancy (which is the same as saying “presence”) and detection probabilities, and can be estimated by using statistical models.

    Occupancy probability and detection probability are described by two different models and both of them will influence what will be observed during a survey. Taking into account that not all the animals will be observed is very important when attempting to accurately assess a species’ presence, which could otherwise be underestimated.

    A young roroa being released as part of the Operation Nest Egg programme. Image by Jon Sullivan on Flickr.

    Peter Jahn, James Ross, Darryl MacKenzie and Laura Molles, in a study published in 2022, wanted to know how accurate acoustic surveys of roroa-great spotted kiwi (Apteryx maxima) were between 2011-2015. During this time, 18 birds were translocated from the Hawdon Valley, in Arthur’s Pass National Park, to the Nina Valley, in Lake Sumner Forest Park, representing one of the initial efforts of the Operation Nest Egg programme. The researchers also wanted to compare kiwi presence before and after 2015, and between the two areas.

    They gathered data from a survey conducted in 2012-2013 by DOC in both the valleys and then repeated the methodology in 2017-2018. The technique they used was passive acoustic monitoring (PAM). PAM is effective when studying elusive species such as kiwi. Automatic recorders were deployed in the two study areas and left there for up to three weeks, activating just before sunset and switching off shortly after sunrise.

    The team analysed the kiwi calls recorded in each of the valleys. The goal was to find a model that would best describe the obtained data, and use it as a base to estimate occupancy and detection probability. Peter Jahn and colleagues wanted to know which factors were important in detecting the kiwi and looked at the study area (Nina and Hawdon Valleys), year, length of the survey night, breeding/non-breeding season, precipitation, wind speed, night length, varying recorder battery capacity.

    Similarly, my mum could have considered the fact that my phone may have been in silent mode, or had no service, or estimated the actual likelihood of me being in an ambulance. All of these factors could have influenced her imperfect detection of me.

    In both the study areas, the detection probability was found to be higher during the breeding season, to increase with longer survey nights and to be influenced by wind speed, rain accumulation and recorder sensitivity. Also, as expected, kiwi presence in the Nina Valley increased after the translocation, as it did in the Hawdon Valley. Moreover, it was found that the number of sites where kiwi calls were recorded increased in 2017-2018 in both the areas and that, in total, many more calls were detected in the Hawdon Valley than in the Nina Valley.

    The Hawdon Valley in Arthur’s Pass National Park. Image CC-BY-NC by Jon Sullivan on Flickr.

    Wait, the number of sites where calls were recorded and the presence of kiwi increased in the Hawdon Valley after kiwi were removed from there? How is that possible? Yeah, that was one surprising finding of the study. In fact, the researchers were expecting that occupancy would decrease after the birds’ removal, but what they found actually suggests that new pairs re-occupied the territories left inhabited by the translocated individuals.

    This is a promising result, because it means that such conservation strategy doesn’t necessarily negatively influence the population from which the individuals are taken. Also, the ongoing pest mammal control in the Hawdon Valley could have balanced the negative effect of the translocation. I guess the only thing left to do now is find out what makes kiwi desire those territories so much that they can’t stay away: maybe they have the most delicious earthworms of New Zealand?

    To conclude, these findings demonstrate that the species is reacting well to this reintroduction programme, considered that kiwi presence increased in the Nina Valley too. Furthermore, this study showed that combining occupancy estimates through statistical models with acoustic monitoring is very useful when studying the outcomes of kiwi’s translocations. However, if you, reader, can’t wait to know more about what happens to our dear kiwi when we move them around, sit back and read Peter Jahn’s PhD thesis: never stop learning.

    Finally, going back to my mum trying to “detect” me: I suggest the probability would increase a lot if she learned to call outside of my usual napping times!

    This article was prepared by Master of International Nature Conservation student Francisco Bini as part of the ECOL608 Research Methods in Ecology course.

    Jahn, P., Ross, J. G., MacKenzie, D. I., & Molles, L. E. (2022). Acoustic monitoring and occupancy analysis: Cost-effective tools in reintroduction programmes for roroa-great spotted kiwi. New Zealand Journal of Ecology, 46(1), 3466.

  • A foreign threat: New Zealand’s Invasive insects

    One of the many great fascinations of New Zealand is the absurd number of bugs found here that are found no where else on Earth. What’s a bug, you might ask? They’re the six-legged creepy crawlies you find everywhere. They are a part of your life, from the obnoxious house fly in your room to the big, bold beetle in the garden! Well, technically, I mislead you with the name bug. Bugs are a single group of piercing-sucking insects; the correct term to describe errant creepy crawlies is insects.

    Aside from being a nuisance in the home, what do New Zealand’s insects do? They provide excellent services to our ecosystem, whether churning up dirt, pollinating flowers, or controlling noxious weeds. They also serve as an essential part of the food web and are a key to the survival of many birds and lizards.

    A friendly, Robust grasshopper says hello! This photo I took in the Mackenzie district shows one of our largest grasshoppers. They’re excellent grazers of lichens and mosses. Historically they provided great nutrition for many birds and lizards.

    Despite their abundance, insects are massively understudied both globally and in New Zealand. We must understand how our insects contribute to our ecosystems and what might happen when new insect species arrive in our country. Species not previously found in New Zealand (nonindigenous creatures) have been a massive threat to New Zealand’s native biodiversity over the past 200 years.

    Of the non-indigenous species in New Zealand, much of the focus has been on mammals, like stoats, and plants, like wilding pines. This work is essential because these sorts of species have huge impacts on our environment and our economy. But what effects do the over 2000 introduced insect species have on New Zealand? A study by Brockerhoff (in 2009) featuring Lincoln University’s Dr Cor Vink, attempts to determine the threat of new insects to New Zealand’s ecosystems.

    The threat of introduced insects was recognised soon after European arrival. From what we know few of these species are capable of affecting native ecosystems aside from the well-studied Vespula wasp.

    The currently accepted view is that new insects do not generally hurt our ecosystems. However, as New Zealand’s ecosystems are often so understudied there is little way for us to measure the effects of new insects on the environment. Across most of the world, the arrival of new insects can be a catastrophe with substantial environmental and economic impacts.

    A photo by Will Frost of a typical Mackenzie Basin floodplain grassland. A habitat type threatened by new species of weevils and the expansion of dairy farming.

    So far New Zealand has avoided such a catastrophic invasion. Brockerhoff (2009) suggests that perhaps our intact native ecosystems repel insect invasions well compared to other parts of the world. While our forests have repelled invaders so far, the threat of climate change may alter the balance in the war of plants and insects.

    Brockerhoff (2009) aimed to investigate the effects of insect invaders across a range of New Zealand’s habitats. It was found that over 200 insects capable of damaging forests have been found in New Zealand but have had minimal impact on our native ecosystems. Several generalist moth species and a passion vine hopper have had minor effects without significant damage. In grasslands, several weevil species have been found all over New Zealand, even as high as 2800 metres, but their impact on the surrounding environment so far seems to be minor. These results suggest that all is well for New Zealand’s ecosystems. However, with rising temperatures creating more optimal conditions for invaders there could be an increase in foreign insect invaders.

    When species reach more significant numbers, their effects can start to worsen. Vespula wasps are well documented for their disruptive effects in beech forests. They feed on honey sap and compete with native birds for this resource. Worse still, these wasps predate on many native insects, some requiring a 90% reduction in Vespula wasps to survive.

    The Argentine ant spreading through New Zealand and is also of grave concern. In large numbers this ant has the ability to displace native ants and often eradicate many other native insects in the soil ecosystem.

    A photo by Will Frost showing a honey-dew beech forest from Craigieburn Forest Park which is threatened by Vespula wasps.

    So far many of the more harmful insect species are isolated to human-altered habitats. And insects which make it to intact ecosystems fail to make an impact. As these insect’s populations build over time and more begin to enter the country as temperatures warm the threat of invasion into native forests may increase.

    Many insects are selective of the plants they consume due to plant defences and palatability. This is true even for generalist insects that specialise on many plants. This likely explains why so far our plants have provided protection from so many would-be insect invaders.

    Honey dew being produced by scale insects. A rich food source for wasps. Photo from Adrian Paterson

    Brockerhoff (2009) suggests that for these reasons the greatest risks to our ecosystems now are from generalist insects, especially those which don’t rely upon plants. Generalist predators, like Vespula wasps, threaten the whole ecosystem’s natural processes. Due to their ability to consume the sugar produced by scale insects. These wasps prey on the majority of native fauna in beech forests to provide food for their young. When in huge abundances the composition of insects in the forest and availability of sugar sap is hugely reduced. If more generalist insect species with no natural predators were to arrive within New Zealand the impacts would be even greater.

    To reduce the threats to our ecosystems in future, introduction of more insects for biocontrol should not be taken lightly. We are fortunate that few exotic insects have been established in New Zealand’s native habitats. However, many of the subtle effects caused by invasive insects are not yet known, more study is needed to grasp how these effects are impacting the ecosystem.

    In the future, climate change and habitat disturbance could allow new insects to arrive and threaten our native ecosystems. We know enough now to say our environment is safe from hugely adverse effects; however, the future is uncertain. Developing a greater understanding of how these creepy crawlies subtly affect our ecosystems is paramount.

    This article was prepared by Master of Science postgraduate student Will Frost as part of the ECOL608 Research Methods in Ecology course.

    Brockerhoff, E. G., Barratt, B. I. P., Beggs, J. R., Fagan, L. L., (Nod) Kay, M.,K., Phillips, C. B., & Vink, C. J. (2010). Impacts of exotic invertebrates on new zealand’s indigenous species and ecosystems. New Zealand Journal of Ecology, Suppl.Special Issue: Feathers to Fur, 34(1), 158-174. https://newzealandecology.org/nzje/2916

  • The hotspots are where it’s at if you want to spot a cat: the search for the common leopard

    The Himalayas are an almost mythical place, where mountains loom and the clouds surf down their sides before sliding into the forests below. The songs of rhesus monkeys, palm civets, and the occasional jackal sing out from the thick trees. This landscape is beautiful yet rugged. Travelling through is difficult for our human capabilities, in many cases impossible.

    Now imagine. This is the backdrop you must navigate to discover the number of big cats that live there. To top it all off, your target is the shyest and one of the rarest of them all, the inappropriately named common leopard.

    A common leopard relaxing in the sun
    (Source: Daily Pakistan: Pakistan’s common leopard endangered due to loss of habitat)

    Now, it’s not unusual that scientists doing field research are thrown into difficult situations. You might end up with dangers like Carlos Jared who innocently picked up a frog while doing fieldwork in Brazil, discovering frogs can be venomous. Or you might accidentally glue yourself to a crocodile while attaching a radio transmitter like Agata Staniewicz did (find that and more hilarious field research fails here).

    But when you’ve got a shy animal, add in an impassable landscape, plus the addition of the very real and dangerous threat of bumping into rebels which is, unfortunately, the reality in parts of Pakistan, you’ve really got your work cut out for you.

    This momentous task is one Muhammad Asad, PhD student at Lincoln University, took on as he bravely set off to northern Pakistan. Nobody had done this before and the leopard landscape was mostly unknown. But he was up for the challenge.

    The not-so-common leopard

    Leopards are found all over the world, the most widespread of all land-based carnivores. They’re incredibly adaptable, able to make their homes in all sorts of climates: from the savannas of Africa, the tropical forests of South East Asia, to the freezing mountains of far north Russia. They even make it work when humans move in.

    Their only request, being rather introverted, is that they have lots of space. They’re very territorial, protecting their home range fiercely. But honestly, a bit of peace is a reasonable request!

    Despite this incredible flexibility, common leopard populations are in decline. They’re no longer found in 63-75% of their historic range. The decline in Asia is even bigger, with an 83-87% drop! It’s no surprise that these gorgeous cats are listed as critically endangered.

    The majestic common leopard
    (Source: Daily Pakistan)

    Leopards are facing many different threats. The main ones are:

    • habitat is lost or changed,
    • trees cut down,
    • inbreeding from being cut off from one another,
    • human developments being built near their protected ranges,
    • prey disappearing,
    • poaching,
    • and human-wildlife conflict.

    Clearly, these cats need protection. So, leaving New Zealand and heading back to his native Pakistan, Muhammad took the first step to build a conservation plan; he had to figure out how many leopards there were and where they were found.

    To do this across the entire country would be too big a job. Instead, he focussed on the Gallies and Murree Forest Division in northern Pakistan, lying in the outer Himalayas. Here, leopards are protected under the law. Even so, there are often no checks for this, with hunters easily getting away with it. This is made worse by the slow and sometimes non-existent compensation programmes, programmes designed to reimburse farmers who have lost livestock to a leopard attack. The locals often resent the leopards. But it’s hard to blame them when people, including children, are occasionally attacked and killed.

    Leopards are poached frequently in Pakistan. Cubs are trapped to sell in the illegal pet trade or body parts and skin are taken for sale. Skin, claws, and teeth are sold in north Pakistan.
    (Source: Raj K Raj/Getty Images)

    Estimating the number of leopards in an area is very tricky. They have large territories with very few cats within each area. Figuring out where to look, especially when the landscape has the worst access, is the key to success.

    How to find leopards

    Muhammad and his crew began with a questionnaire survey. They asked people from local communities who lived nearby to fill these out. They asked about losses of livestock, when the attack happened, and the type of injury, for example, bite marks on the neck, missing dogs, or human casualties.

    Based on the information from the locals, they ended up with 63 different sites where they could focus the leopard hunting efforts. A much better start!

    Next, they moved into these sites, peeling their eyes for signs of poop, territorial markings (such as peeing on a tree), and tree scratches. These signs meant one thing; here be leopards.

    With this proof, they set up special cameras, known as camera traps, on either side of the trail, ready to capture the cats on the silver screen.

    They also set up cameras on 5 connecting trails which hadn’t shown any signs of leopard action. These were used to see if they could capture leopards in areas where they had left no signs. As new leopard trails were discovered, the camera traps were moved to snap those too.

    Sampling locations of the camera-traps survey in Gallies Forest (Ayubuia National Park, surrounding Reserved Forest and Guzara Forest), and Murree Forest (Protected, Reserved and Municipal Forest). Country map (top left – green). Study area showing different city boundaries (middle left).
    (Source: From paper)

    A leopard can’t change its spots – a handy identification tool

    You may have heard the proverb that a leopard can’t change its spots. This is supposed to teach us that we all stay true to our nature, even if we pretend we’re different. But it turns out when it comes to leopards it’s 100% true! The coat of a leopard is as unique as our fingerprints. Incredibly useful when you’re a scientist trying to tell the difference between two cats in a grainy photo!

    Their gorgeous spots are a bit like the shape of a rose, giving them the name ‘rosettes’. This means that by matching up the images of the rosettes you can figure out if it’s the same cat. The best place to match things up is on either side of their back legs or the top of their tail.

    Example of an individual being identified using the rosettes on the tail
    (Source: From paper)

    This is trickier than it sounds. The rosettes change shape as the leopard moves. And it can look different depending on the angle it is to the camera. But still, it’s a pretty helpful method to avoid double-counting cats. Double counting would give you a very different population size! You can find out more information on leopard identification techniques here.

    Example of when the spots don’t match up.
    (Source: From paper)

    So, how many are there?

    In 2017 Muhammad estimated there were between 16-24 common leopards in the Gallies and Murree Forest Division. This went down to 7-12 in 2018.

    However, they don’t think the population dropped. In 2018 they got fewer clear images making it harder for them to identify the cats. They think the real number could be closer to 12-18, meaning its range overlaps with the 2017 estimate.

    But, this might not be the case. In 2018, Pakistan was suffering from a drought. Perhaps the leopards had been forced to move out of their territories to look for food. So far there hasn’t been any research on leopard movements in relation to strange weather. This would be an interesting thing for someone to look into (are there any leopard enthusiasts up for the task?).

    Or perhaps this drop is real. Poaching and unreported killings are still huge in Pakistan. Plus, Muhammed and his team did find signs of hunting. So the reason could in fact be nefarious.

    Regardless of the reason, Muhammad estimated there to be 8-12 leopards and 3.5-6.5 leopards per 100 km2 in the Gallies and Murree Forest Division. They also confirmed they lived in the Swat, Dir, and Margalla Hills, even though locals as well as wildlife departments thought they had disappeared.

    These estimates are not 100% accurate. But the team is pretty confident that they are close to the true number. All in all, a great success.

    Mother common leopard and her cub.
    (Source: Daily Pakistan)

    What next?

    Now there’s a basic understanding of how many leopards there are and where they like to hang out, we can start to protect them.

    With this information, we can:

    • Use the leopard hotspots to keep an eye on the population trends and demographic changes over time.
    • Decide on the most important conservation areas. Special attention should be given to the corridors that join areas together to protect the long-term health of the leopard populations.

    For example, Muhammad discovered that 70% of leopards killed for revenge in the Guzara Forest happened outside of the Reserve area, close to the village, and in winter. That tells us we should focus the conservation efforts on the hotspots in the Guzara Forest surrounding the Reserved Forest so that human-leopard conflicts can be reduced.

    There’s still a lot of work ahead for the common leopard in Pakistan. But with Muhammad on the case, their future is looking a little brighter.

    You can read Muhammad’s research in full here: The Un-Common Leopard: presence, distribution and abundance in Gallies and Murree Forest Division, Northern Pakistan

    This article was prepared by Master of International Nature Conservation student Kat Douglas as part of the ECOL608 Research Methods in Ecology course.

    Full citation: Asad M, Waseem M, Ross JG, Paterson AM (2019). The Un-Common Leopard: presence, distribution and abundance in Gallies and Murree Forest Division, Northern Pakistan. Nature Conservation 37. 53-80. https://doi.org/10.3897/natureconservation.37.32748

  • The big, bold, redbacks of Buckland

    “No, Mr Baggins has gone away. Went this morning, and my Sam went with him: anyway, all his stuff went. Yes, sold out and gone, I teller. Why? Why’s none of my business, or yours. Where to? That ain’t no secret. He’s moved to Bucklebury or some such place, way done yonder. Yes it is – a tidy way. I’ve never been so far myself; they’re queer folks in Buckland. No, I can’t give no message. Good night to you!” JRR Tolkien – The Fellowship of the Ring

    One of the greatest illustrations of Tolkien’s work, IMHO, The Gaffer and the Black Rider by Stephen Hickman.

    I’ve always liked this passage where old Gaffer Gamgee is talking, unbeknown, to a nazghul. It is an important story point but delivered in the type of conversation that you could hear all over the world. ‘Those people that live 20 – 30 km away are just so different and weird!‘ Are the people of Buckland really so different to the good, honest folk of the Shire? If so, how did this happen by simply crossing a river?

    There is a question around invasive species whether the individuals that arrive in a new area are just a random selection of the individuals (and their traits) that live in their home area or whether they represent a group of individuals with consistent and particular traits that make them more likely to have successfully invaded the new area.

    For example, all humans in Aotearoa/New Zealand have arrived from outside these shores over the last 1000 years. Were the people that made their way here more bold and explorative than the rest who stayed behind? Or were they no different than their neighbours who stayed at home? Maybe they just simply had the opportunity to go?

    These ideas are important in thinking about why invasive species are successful at establishing or not. If any old random subset of the population can turn up then they are less often going to successful at establishing (they may not be fit-for-purpose!) compared to if they arrive with skills that allow them to survive better in a new environment (or even to survive the journey).

    Being large might help give invasive individuals an advantage over native species. Likewise, producing more offspring, growing faster, being bold, exploring more, dispersing sooner, having a broader diet, could all help with invading and establishing.

    What about our Bucklanders?

    “Long ago Gorhendad Oldbuck, head of the Oldbuck family, one of the oldest in the Marish or indeed in the Shire [has had high evolutionary fitness over many generations], had crossed the river [successfully able to disperse relative to other hobbits and to explore more], which was the original boundary of the land eastwards. He built (and excavated) Brandy Hall, changed his name to Brandybuck, and settled down to become master of what was virtually a small independent country. His family grew and grew [high fecundity in offspring production], and after his days, continued to grow, until Brandy Hall occupied the whole of the low hill, and had three large front-doors, many side-doors, and about a hundred windows. The Brandybucks and their numerous dependants then began to burrow, and later to build, all round about … The people in the Marish were friendly with the Bucklanders … But most of the folk of the old Shire regarded the Bucklanders as peculiar, half foreigners as it were [suggests a slightly different distribution of traits compared to the parent population].Though, as a matter of fact, they were not very different from the other hobbits of the Four Farthings. Except in one point: they were fond of boats, and some of them could swim [bold and innovative behaviours].” JRR Tolkien- The Fellowship of the Ring

    Captive redback with web. Image by Adrian Paterson.

    We are also told elsewhere that the Brandybucks and Tooks (another bold lineage of hobbits) are generally taller than average Shire hobbits. Tolkien, as I have said in many other places (taxonomy of orcs and hobbits, evolutionary biology ideas, burrow architecture, mammal pest management, fire and ecosystems), was rather accurate when it came to integrating biology into his writing. Did he get it right here?

    To test this invasion idea you need a species that is well-studied in it’s native range as well as in its colonising range. You also need to be able to measure all of those traits. Spiders fit the bill nicely. They’re small and have short generations, are easy to fit into small experimental set ups, and some are venomous and, therefore, well studied. Enter the redback spider (Latrodectus hasselti), invasive in Japan and New Zealand and well studied in its Australian homeland.

    Cor Vink, New Zealand’s leading arachnologist, joined a group based in Toronto, Canada headed by Monica Mowery, to look at individuals from these three areas. They measured the size of individuals (bigger is usually better in interactions with competitors), their egg sac production (producing more young may give you more opportunities for at least some surviving), and length of generation times in captive populations (shorter allows for faster replacement, longer allows for larger more long-lived individuals).

    A redback – amazing photo from the talented Bryce McQuillan

    They measured the behaviour of the redbacks, such as frequency of cannibalism (you never know when a snack might come in handy!). Also, individual spiders were placed in a new environment and the speeds at which they started spinning webs (exploration) or moving after being exposed to a puff of wind (boldness) were measured. Spiders were also placed into a warm arena with a small simulated breeze to see whether they would balloon (effectively float away in the wind) or rappel (climb using their web silk) away from the start point (dispersal).

    The outcomes from this work were published in Biological Invasions. Redbacks from the invasive populations showed more dispersal behaviour than the home populations. They also tended to be larger in size, more cannibalistic, and produced more offspring. Interestingly, the redbacks in Japan and New Zealand did not seem to be more bold or explorative than in Aussie. Overall though, the invasive populations looked and acted differently to the source population.

    It appears that populations that successfully disperse and establish in new areas might do so because they are settled by individuals with useful traits that differ a little from the source population. This may help us to figure out which species potentially pose the most invasive threats.

    What about those strange Bucklanders? The Gaffer was mostly right. They are a bit different. Bucklanders are a population that managed to successfully disperse to an isolated area. Bucklanders are larger and more fecund. Tolkien does not record whether the Bucklanders tended to be more cannibalistic than hobbits in the Shire, but that would be a prediction!

    We can certainly sympathise with the Gaffer’s concerns about his Sam going to live among them.