Thursday, 13 July 2017

Saving the Slow Loris

Saving the Slow Loris through Research & Education in south-east Asia

Stephanie Poindexter and Claire Cardinal of Oxford Brookes University

A Talk to the Berkshire Mammal Group
3 November 2016

Explaining that the advertised speaker, Professor Anna Nekaris of Oxford Brookes University, was unavailable but had kindly arranged substitutes from her research team, Edwin introduced the two guest speakers and thanked them for stepping in. They were to present on complementary aspects the originally agreed theme – the plight of the Slow Loris – illustrating it with reference to the field studies they had individually undertaken for their degrees. Stephanie was a PhD student (originally from the USA) and would present first, followed by Claire who had recently completed her MSc in Primate Conservation.

Cognition and Conservation: measuring spatial cognition in Slow Loris and its application to reintroduction practices in Vietnam, Thailand and Indonesia

Stephanie Poindexter

Stephanie set a sadly familiar scene of population depletion and defined the slow loris as a small nocturnal primate present in southeast Asia. There are nine species of loris in all, of which Stephanie was studying the Pigmy Slow Loris and the Bengal Slow Loris.

Clearly fascinated by her subject, Stephanie described some of their distinctive physical attributes, unusual aspects of their ecology that make them so interesting a species to study. They are conspicuously exceptional in their consumption of gum. They are reliant on a diet primarily of insects and tree sap and gum that is available all year round, supplemented by seasonal nectar. They grasp branches for hours without numbness or tiring. They are unusual among mammals in having periods of torpidity, and are the only primate to be venomous.

Yet there are many threats to the population, and human consumption is the most destructive: captured for the pet trade, used as photo props, and killed for the preparation of traditional medicine. Also deforestation has reduced their natural habitat.

Research
Stephanie’s research was into translocated individuals – those taken from the wild as pets or roadside rescues, taken to a rescue centre and reintroduced to the forest. It sounded a promising idea, but reintroduction can’t be rushed without detriment to the animals. Stephanie was to see how they adjusted, how, or indeed whether, they could re-assimilate.

Her work was based in two locations: The Little Fireface Project’s field station in Java, Indonesia (mainly agri-forest, but where at least the farmers would mark their field boundaries with the gum trees favoured by the slow loris), and Cuc Phuong Nah in Vietnam. This offers scare resources, but has been a protected area since 1993, supported by Frankfurt and Leipzig Zoos. Beside the Bengal and Pygmy Slow Loris, other vulnerable species there include the pangolin and langur. Stephanie spent five months in 2015 monitoring returned lorises and their range.

One of her subject species, the Pygmy Slow Loris, weighs a mere 400 grammes. It has seasonal coats that are distinctly different. Indeed its pellage originally suggested two separate species! It is endemic in Cambodia, Laos, China and Vietnam (but not Thailand where it has appeared but recently as result of human intervention). However, there are distinct genetic populations and so DNA testing is important to establish the historical range of individuals before their reintroduction. This is complicated further by the distinction between north and south populations within Vietnam, and so caution should be observed.

In order to monitor individual lorises, radio collars are fitted for 11 months and over time their movements can be tracked. It has become apparent that male and female home ranges overlap, suggesting promiscuous mating, whereas the home ranges of other species are often more distinct. The home range of slow lorises is roughly 20 hectares. However, reintroduced individuals fail to stabilise their range, which may be as large as 80 hectares, or four times as large as those raised in the wild.

Why, what is missing? What are they looking for? Possibly they looking for the type of home range whence they came originally. Natal Habitat Preference Induction analysis is the tool used to explore this proposition, and spatial cognition is the subject of Stephanie’s PhD.

Her data recorded, Stephanie moved on to Indonesia, to the Little Fireface Project’s field station in West Java. The project (LFP) was founded in 1993 by Anna Nekaris, and the field station in 2011. The staff covers a range of disciplines, including someone responsible for maintaining a positive presence on social media. The station’s motto is ‘Ecology – Education – Empowerment’, and over the past five years the team has collected a huge amount of data and learned quite a lot about the slow loris:
  • Their dimensions vary considerably: 21-31 cm in length, 125-2,000 grammes in weight.
  • Besides gum and insects, they feed on the nectar of flowers. Are they pollinators? They don’t appear to damage the flowers, so it is thought they might be.
  • When not sleeping they are more social than expected, interacting and communicating relatively often. Social foraging, particularly when the flower component of their diet comes into season.
  • They have one or two offspring a year after a six-month gestation. Infants stay with their mother for 16-18 months before dispersal and this is an unusually long period for a mammal of this size. Now first baby has borne her own baby, the full cycle of life has been witnessed.
  • The slow loris is venomous, with saliva and brachial gland secretions. Buy why? Is it a predator avoidance adaptation? It seems that slow lorises cover themselves with brachial secretions when setting out to forage at night, so that hypothesis is supported. It is widespread practice in Indonesia to trim or remove the loris’s teeth in captivity to avoid venomous bites, and when Stephanie showed four photographs of a researcher’s face swelling after being bitten, it was easy to see why.
This is scientific study, however; how do the locals regard them? A positive view is important to the loris’s long-term survival, so the field station runs an education programme to cultivate local attitudes.

Education
The project has helped fund a local school and once a week runs a nature club for the children. The idea is to encourage them to value the wildlife of their locality, and especially the slow loris. LFP has published a picture book entitled Forest Protector, which is now available in German and the languages of Indonesia and Vietnam. The pictures are by the illustrator of Family Guy, Shelley Low (whose name – appropriately, if rendered S. Low – reflects her subject!). The participating children are asked to draw a picture or tell a story, and by the time the programme finishes marked changes in perception can be observed.

LFP also works with university students on Java. Placements are offered, and after participating in research work, the students give a presentation to others on their return to university. Judging science fairs is one of several other ways the Project has become involved in local education. It is a long-term investment.

Other areas of conservation activity

Monitoring fairs
Monthly market fairs are held in popular hotspots like Bali. Volunteers visit them repeatedly, but discreetly to gauge number of lorises and other animals involved in the trade.

Photo props
Lately as many as 10-15 animals can be paraded every day on social media. This is a conspicuous increase driven entirely by the huge growth of social media phenomenon itself.

Traditional medicine
Slow lorises are traditionally regarded beneficial for around 100 ailments, and are given to pregnant women to confer strength to their unborn babies, and placed under houses for good luck. The emphasis on medicine is particularly strong in Cambodia and Laos, though less so in Vietnam and not in Thailand where the slow loris wasn’t historically present.

Deforestation
This is difficult to fight, as Stephanie herself acknowledged. Creatures are pushed to higher altitudes (currently 1,300-1,700 m above sea level) to avoid the activity of farmers who are themselves being pressed to colonise new land. The field station has established a plant nursery to breed gum tree saplings. Farmers will accept free saplings and use these beneficial species as boundary markers, so a source of food remains available to the loris.

Next steps
Further studies are in preparation, as the field station is intended for on-going research. Vocalisation is a new area of interest, and recently acquired thermal imaging cameras offer new possibilities. The Project envisages more market surveys and more work with TV – several documentaries have already been made, including Jungle Gremlins of Java (which was to be shown on BBC 2 the following Saturday). For further information: www.nocturama.org

 
Communicating Conservation: using acoustics and education to develop understanding endangered Slow Lorises
and Gibbons in Vietnam and Java

Claire Cardinal
Claire opened by saying she had wanted to make a contribution to conservation so undertook two studies for her MSc – admitting she had probably bitten off more than she could chew. Like Stephanie’s, her work lay in the twin fields of research and education:

  • Whoop Troop – an education programme using puppetry
  • An acoustics study of the Pygmy Slow Loris

Education
Claire’s education work was spread over two locations: LFP in Java and the Dao Tien Centre for Endangered Primate Species (set up eight years ago by Monkey World to protect slow lorises and gibbons).

Her objective was to create and evaluate a new educational resource, and establish whether it would be flexible to use as a template in different countries and for different species. As 70% of Asian primates are threatened, according to the IUCN Red List, human attitudes and behaviour need to change if they are to be saved. Knowledge and affinity are, therefore, an essential first step. It has been found that negative messages don’t help – they engender a rather hopeless sense of “well, what can we do?” It is better to provide positive messages of “awe and wonder”.

The project planned to present a three-month course to rural teenagers (aged about 12-14), a neglected audience for such work, and would compare its effect on participants in both Java and Vietnam. It would include a science component to develop interest and knowledge, and puppetry to engender affinity. Students would be asked to write and perform puppet shows – and at this point Claire demonstrated the use of two large naturalistic glove puppets.

Coverage was extended to six native animals – both countries share a common biosphere – including: the Javan Rhinoceros (of which there are only 50 left in the wild), Saltwater Crocodile, Leopard Cat, Rhinoceros Hornbill and Eurasian Hornbill. In Java the selection would included the Java Slow Loris and Silvery Java Gibbon, and in Vietnam, the Pygmy Slow Loris and Golden Cheeked Gibbon.

Data Collection
As the purpose of the project was to evaluate impact, it was important to find methods to measure the impact of ideas across the three schools and eight puppet shows. Claire turned to the techniques of social science.

Freelisting
By showing photographs and getting the children to write down what they thought of the subject, Claire had free access to potentially revealing terminology, from which she could form ‘word clouds’ in which frequency could be depicted graphically.

Cultural Domain Analysis
The technique assesses shared beliefs and knowledge. Are the participants thinking the same way? As the only commonality between the groups of students was the course, the results would (and did) show that they had learned something from it.

Saliency
Comparing statements made before and after the course, the importance of each word, based on frequency and average rank, could be established. If present, the course had taught participants something.

Content Analysis
Words were colour coded for ‘emotion’ and ‘knowledge’, or as ‘neutral’. After a course of creative writing there were far fewer neutral words. The change was indicated by a graphic depiction not unlike the election swingometer. Afterwards there were more empathetic, anthropomorphic and taxonomic words, and fewer emotional ones.

Such analyses suggested the effect of puppetry justified the study and such programmes would be useful as a tool in conservation education. The long-term impact is yet to be established – only time will tell – but Claire was pleased to report that after one school visit a girl in the audience arranged for her grandmother’s pet gibbon to be returned to a rescue centre – so a tangible short-term effect in that instance!

Acoustic Study
Claire admitted this was work in progress, with lots of data yet to analyse. The objective was to establish whether the Pygmy Slow Loris vocalised at an ultrasonic frequency. This is a new field of research, not studied before, and so is at the cutting edge. If successful it would provide a useful new tool for population monitoring, as the slow loris is difficult to find by visual means alone.

The task of acoustic monitoring has been made easier by technical advances and the equipment Claire used included: a bat detector, directional microphone and specialist software for birdcalls that transferred recordings into sonographs.

While in the field Claire would spend six hour shifts three nights a week sitting in the forest recording ultrasonic sound, monitoring released and captive Pygmy Slow Lorises in southern Vietnam. She described her time in the forest as feeling safe and secure on an island, hearing the insects waking up at 4am, and gibbons at 5.30.

The forest comprised dense thickets of bamboo growing back after the ravages of the Vietnam War, so Claire would use GPS to pinpoint the loris’ sleep sites, then monitor movement from a static, sedentary position. She now has 60 hours of ultrasonic recording, which she is still going through. The task is made more complicated by the higher frequency calls bouncing off trees; she showed us sonographs that could just as plausibly have been made by bats or insects. As she said, it is work in progress, with more report in future!






Project Splatter


A talk by Dr Sarah Perkins to the Berkshire Mammal Group
9th February 2017
Dr Sarah Perkins is a wildlife biologist at Cardiff University, having started her career as a conservation officer for the UK Wildlife Trust. In an entire year of working as an Otter Conservation Officer, Sarah only ever saw one otter – a road-killed one – and became interested in quantifying the number of animals killed on the roads each year. She worked abroad for several years, working on wildlife diseases, before returning to the UK and taking a position at Cardiff. There her interest in the number of animals killed, which species are the most vulnerable, and whether there were hotspots of roadkill that could be mitigated against, led her to establish Project Splatter in 2013, as a collaborative citizen science project – the subject of her talk to the Berkshire Mammal Group.

Sarah opened by acknowledging that road kill is a common sight and asking generally how we engage with wildlife, and what the impact of roads might be on animal mortality. She turned to the journal, Science, which in December had published a paper on roadlessness. On screen was a map plotting the incidence of roads in red, lined with 1 km buffers into the surrounding habitat, and the road-free areas in blue, in which roads would have no effect on wildlife. 80% of the globe is still roadless, but much of this area is composed of the Arctic regions, the Siberian tundra and deserts in north Africa and Australia and other inhospitable environments. And the rest is divided into 600,000 fragmented habitats, half of which are less than 1 km in extent and only 7% are of the largest size category). Only 9.3% are protected areas. So the clear conclusion was that roads have the potential for a major impact on wildlife and its habitats.


The scale of road deaths

What might be the scale of wildlife road deaths, she asked, pointing to illustrative graphics: 100s, 10,000s, or 1,000,000s. Answering her own question – after an uneasy pause – Sarah said we simply don’t know, but can look at studies in other countries that have measured the effects direct vehicle collisions. They propose some dramatically varying estimates:

USA 80m birds killed on US roads per annum
Netherlands 0.2 – 2m birds
Belgium 4m
Denmark 8.3m
Spain 100,000

In the UK a PTES survey was launched in 2001, which has since measured mammals on roads for a period each summer. Usefully it has reflected the decline of the hedgehog, and also picked up a fall in rabbit numbers. But this survey is just in the summer, and just of mammals. Were there any other figures? Well, yes, Deer Collisions (www.deercollisions.co.uk) estimates 42,000 to 74,000 collision deaths a year, information drawn from police and insurance reports. The Mammal Society has produced estimates of 50,000 badger deaths a year, and 100,000 fox deaths. For birds a BTO Road Deaths Enquiry in 1960, at a time when there was rather less traffic than now, concluded a total of 2.9m avian road deaths. Sarah noted it took until 1965 for the figures to be published.

Project Splatter

To draw together contemporary data on all species, Sarah introduced Project Splatter as a continuous, UK-wide survey, set up in January 2013. She explained that it started out as a final year project, undertaken with some reluctance at first by Sam Stafford, an undergraduate reading Zoology at Cardiff. He devised a social media to capture direct reporting by members of the public, and such was its early success that he become highly motivated and earned the soubriquet, “Splatter Sam”. This early success was cemented by the involvement of the press, in particular the publication of a two-page, full colour spread in the Independent, prompting
wider media attention. It was, in Sarah’s words, “a fantastic start”.

The social media platform is designed to make the task of reporting simple and accessible. Reports can be sent in by iPhone app, Android app, Facebook, Twitter and by email or through the web. The scheme accepts both occasional and regular reporting – there need be no on-going commitment, though many of the 2,000 participants are regular contributors – and on Monday the project offers feedback, drawing attention to some of the quirkier reports.


The project’s purpose is to quantify and map British roadkill, determining which species are the most observed, and identifying spatial and temporal hotspots: the ‘where’ and ‘when’. It aims to raise awareness of the roadkill problem, and encourage mitigation (such as green bridges). Ultimately it seeks to reduce the negative impact of roads on wildlife.

Findings

To date, Project Splatter has accumulated over 35,000 records. These include 33 mammal species, from shrews to wild boar, and these represent 62% of the records.. Representing another 34% are the 74 bird species, from blackcap to buzzard. There are very few reptiles and amphibians. The five species most recorded as roadkill are:
15% Badgers
14% Rabbits
11% Foxes
7% Hedgehogs
7% Pigeons

And as for distribution, the records come from throughout the country, probably reflecting abundance. However, any analysis needs to account for reporter bias; there are few reports from the Highlands of Scotland, whereas Sussex generates more records than any other county. (There, a paramedic has been involved from the start and is a prolific provider of records.) Double counting is not considered a problem at this stage; with 2,000 reporters and 8,000 reports a year, there are simply not enough reports for duplicated to occur to any degree.

Berkshire
A map of the county indicated ribbons of reports along the M4, A34 and Vale of the White Horse, with a cluster around Newbury and a broader blanket of sightings to the west of the Thames around Abingdon.

In Berkshire pheasants are the most prevalent casualties, at 39% of reports compared with 23% nationally. (At 25% for badgers the local and national tallies are in line, though other species tend to be under represented.) But what do the figures suggest about pheasants’ behaviour. A graph of the monthly figures produce a peak in September and October, when na├»ve young birds are released, and in March, when feral pheasants escape into the countryside.

 






Hotspots
Using SaTScan models, the Project has identified nine county clusters for mammals, some comprising single species and some of multiple species. There are obvious clusters, such as for badgers in Somerset, where they are presumed to relate to animal abundance, while others are as yet unexplained, such as the concentration of rats in northern England.

For birds there are seven such clusters. An analysis of these suggests some behaviours tends to endanger certain species. Blackbirds, for instance, have a tendency to last-minute flight from possible predators, and a low, undulating flight pattern, and so are innately vulnerable to vehicles. In discussion afterwards it was noted that, conversely, crows have an enhanced ability to judge the paths of approaching danger, and avoid on-coming vehicles.
Sarah asked which roads were the most deadly: Motorways, A roads or B roads. The answer was A roads. Is this the effect of lighting, she wondered, increasing visibility and causing animal avoidance? Hedgehogs were cited as an example of a vulnerable species, falling from 30m in 1950, when there were far fewer motorways and major roads, to 1.5m in 1995. 20-40,00 are killed on roads per annum – far too high a figure.

Peak reporting is in September, July and April, with winter the lowest. Perhaps unsurprisingly the peaks coincide with seasonal breeding and dispersal activity, while many creatures hibernate during the winter. Yet this varies from year to year, according, in part to temperature and the weather, which affects activity and therefore vulnerability to vehicles.

Disappearance of carcasses

It is accepted that scavengers clear carcases and therefore evidence, so establishing the rate of disappearance would give a useful correction factor when analysing the figures. One early study was by Fred Slater, who set out chicken carcasses and measured the tracks of scavengers left in a surrounding sand pit. He established the rate of disappearance was rapid, suggesting that reporting was underestimated 12-16 fold.

To extend this research for the project’s own purposes the University of Cardiff undertook to study the rate of disappearance. Chicken heads were distributed by student Harry Williams at twelve locations around the city, with camera traps set up: some in parks, some in streets. As an amusing aside, Sarah recounted how some of the cameras disappeared, then reappeared, many with footage of puzzled residents investigating the device, and then, having realised what it was, putting it back! The survey was carried out both day and night, and recorded 120 sessions.

Six principal species of scavenger were identified: corvids, foxes, dogs, cats and gulls. How long it took for the carcasses to be taken varied according to the time of day: in the daytime it was very quick, but at night it tended to lie untouched until at dawn, when scavenging was dominated by foxes and domestic cats. Quantifying that, it was established there was a 75.8% chance of removal within 12 hours. On average it took 2 hrs, 13 mins in the day; 8 hrs and 47 mins at night.
To illustrate which scavengers eat carcasses, Sarah showed a short video made up of day and night-time footage from the camera trips. During the day there were plenty of corvids (crows and magpies), cats and dogs; at night, there were rats, foxes, gulls, magpies and – surprisingly – wood mice (visible mainly by their large reflective eyes). Urban foxes were brazen, while rural foxes markedly more timid.

Associated Research

Project Splatter’s records are considered open source and available to share, and so feed into several other studies. Among these are the records of polecats, which are sent to the Vincent Wildlife Trust to help monitor the expansion of this species out from central Wales. Records have been used to help with mapping invasive species, eg Wallaby in Surrey; Wild Boar in Bristol. But perhaps the most systematic is the 20-year-old otter project run by Liz Chadwick, also at Cardiff University. 

Cardiff University Otter Project
In this project otter carcasses are taken to Cardiff for post mortem examination, where the livers and kidneys are checked for contaminants in habitat, parasites are identified, signs of fecundity noted. Rather sadly, Sarah noted the discovery of four nearly full-term foetuses that had died when their mother had been hit. The results of post mortems contribute to various study programmes, the decline of eels and the presence of Toxoplasma gondii, for instance. The otter is a sentinel for watercourse purity and so much can be gained by their examination.

Dead or Alive
A spin-off project, entitled ‘Dead or Alive’, was set up to quantify popular interaction with wildlife; do most people see wildlife alive, or just as roadkill? The project conducted a four-week survey, eliciting 1,400 responses! To take one of the top five roadkill species, the badger, it was possible to establish that 7% of respondents had never seen one, but 88% had seen one dead. As few as 5% had only ever seen live badgers.

Only seen alive Ever seen dead
5% Badger 88%

Respondents were invited to leave comments too, and the responses indicated a high level of concern about the spread of invasive species.

Roadkill Sub-culture
Touching on an interaction of a more unusual nature, Sarah spent a few minutes describing some aspects of roadkill’s place in art, design, clothing and food. She pointed to the activity of ‘freegans’, those who eat roadkill, and the existence of roadkill chefs and ‘badger balti’. She illustrated some of the work of Adam Morrigan, the roadkill artist, and of Jez East/ton Design

Conclusions

Returning to Project Splatter, Sarah drew together the various threads of her talk, summarising the role of roadkill research as a contributor to:

  • Conservation
  • Understanding populations and behaviours
  • Academic research, eg. the otter project
  • Identifying habitat contamination
  • Mapping invasive species
  • Public engagement

She ended by urging the audience to get involved, and supporting imminent moves for new legislation being led by Wendy Morton MP: the Local Authority Roads (Wildlife Protection) Bill.


Thursday, 19 January 2017

Mink – Evil or Interesting?

A Talk by Dr Joanna Bagniewska to the Berkshire Mammal Group

6th October 2016


write-up courtesy of Edwin AR Trout, Berkshire Mammal Group

Dr Joanna Bagniewska, University of Reading

Opening the meeting Amanda Lloyd introduced Joanna as a zoologist specialising in behavioural ecology and invasive species research, gaining her MSc and PhD from Oxford University. Over the years she has undertaken research in five countries, having studied foxes and jackals in South Africa, wombats and wallabies in Australia, mole-rats in the USA, and both bees and mink in Britain. (Joanna observed that in view of mink’s past fortunes, she was one of few researchers able to wear her study species!) Currently Joanna works as a teaching fellow for the School of Biological Sciences at the University of Reading and has won awards as a science communicator.

She started by suggesting she was one of a minority in this country to admire the otherwise widely denigrated American mink, perhaps because she approached the subject from the point of ecology rather than conservation and control (where mink are considered pests). She defined them as mustelids and took a few moments to outline their ecology.

Mink Ecology

The American mink is native to North America, at least north of the south-western arid zone up to and including Alaska, but south of the high Arctic. Mink are to be found in areas of high water quality. They are small bodied – at 15-18” the males are twice the length of the females – and sexually dimorphic. In some areas males have shown a preference for eating rabbits (for which they have proportionately bigger jaws and teeth) and females – water voles. They are opportunistic feeders and both sexes will eat insects, fish and birds.

While native to North America, they have been introduced into Europe, Asia (especially Siberia) and South America (Patagonia in particular),

largely as a result of the former demand for their fur. In the 1920s and ‘30s they were farmed, but later, in the 1950s, many escaped or were released. They are now regarded an invasive species.

They have, in many ways, become too successful for their own good. Why? They are generalist foragers, with a broad diet: birds, amphibians, reptiles, rodents, insects, and crustaceans. They can hunt like foxes, climb like cats and swim like an otter. They are semi aquatic and very adaptable.

An Invasive Species

As an invasive species, what has been their impact? Traditionally, successful incoming species upset the balance of nature by:

  • Increased predation
  • Resource competition
  • Hybridisation
  • Disease transmission

Of these the first two are of most relevance, though there have been some recorded cases of interbreeding between wild and released mink in North America.

The problem of increased predation is exacerbated by the higher proportion of carnivores among invasive species. Carnivores make up 5% of mammalian species, but when invasive mammals are examined, that proportion rises to19%.

Direct predation by mink is most notable in the UK in the case of water voles. Female mink are the right size to enter voles’ underwater holes and the water vole population is declining fast. This is, admittedly, for various reasons, but the presence of mink is not helping. There is no problem with water voles in Europe, incidentally, but rather the Pyrenean Desman instead is vulnerable and declining.

The Landscape of Fear”
Other vulnerable species are ground-nesting sea birds, for which the security of islands and rocky

outcrops are no protection against the semi-aquatic mink. On arrival in a colony mink will behave like ‘a kid in a candy store’ and take as many as 100 chicks per night, with no sense of forward planning or restraint. Indirect consequences follow, as birds leave their nests – in fear or to protect their young by attacking predators – and the chicks or eggs succumb to the cold or neglect. The very presence of fear can have further negative effects on the predated population.

Over-sized, Over-sexed and Over here”
A notable impact of resource competition has been on the European mink, which is now limited to Estonia and the Pyrenees, as the American mink is sufficiently well equipped to out-compete.

American European
1310.2 g v. 976.6 g
size of female = size of male
litter of 6 v. litter of 2.5

The American mink is voracious and adaptable, and its European cousin is unable to keep up.

Another measure of its success lies in the competition with polecats and otters. When these species were declining in the 1920s-50s, mink expanded into their vacated niches, on both land and water.

Horrible – but Interesting

American mink are semi-aquatic BUT …

  • They are small, with a large surface area, and so loose heat quickly
  • Their fur is neither buoyant nor insulative
  • Their propulsion is inefficient – they swim like dogs rather than otters
  • Their paws have little webbing (more than polecats, but less than otters)
  • They have poor eyesight, especially underwater.

Is swimming innate and instinctive? It seems the young have to be taught, as indicated by trials on captive mink. Other tests suggest mink will work harder to get to water than even to obtain food! And mink spend much of their time in the water, diving for food.

Diving Behaviour

How do we study diving animals? It has been difficult until now. Research has focussed onterrestrial behaviour, which is more readily observable and can be indicated by footprints, scat and camera traps. For wild mink only ‘surface events’ have been traceable in the water, and underwater behaviour monitored only in captivity. Joanna’s research was the first monitoring of mink diving in the wild. Indeed, the only previous study of mammals was one of the platypus in Australia. Since then there have been studies of water rats and beavers as new data-logging technology becomes available. Devices small enough to be attached to mink can measure time spans, temperatures, pressure and acceleration.

Such data logging was first developed in the 1950s, weighing as much as 1.5 kg, based on ‘egg timer’ technology and recording output on paper. The first devices were used on Weddell seals. They were accurate to about 20 m and therefore only useful for extensive depths at sea. Now devices are digital, weigh 1g and are accurate to 3 cm, so may be used effectively in the shallow water of British rivers.

Monitoring Programme
Joanna’s project monitored 16 distinct animals on the rivers Thames and Cherwell in Oxfordshire, generating 20 datasets, with a mix of males (six) and females. The programme was conducted over three seasons, spring being excepted on animal welfare grounds.

The method made use of mink rafts, by which an enticing ‘home’ or tunnel was placed on a floating platform away from the bank. Pliable clay would be spread on the base of the raft to receive the impression of foot prints should a mink investigate the tunnel. With the presence of mink thus established, the tunnel would be fitted with a trap and bait, and, if caught, the mink fitted with a collar and data-logger.

Quantitative Results
The collective results of the study indicated great variety in depth and duration, with a total range of 1 to 189 dives per day, with the greatest individual range between 5 and 143. It became notable that the smaller females were the more energetic divers, performing over 100 dives per day (as explained below). The time spent diving wasn’t long: a total of just 38.4 minutes per day on average, with 57.9 seconds the maximum individual dive-length recorded. Median depth times varied between 7.4 and 18.0 seconds.

(Previous studies had suggested even shorter times.) Diving was undertaken throughout the year, not just in summer as had been postulated, and 83% of dives took place in daylight – presumably in consequence of minks’ poor eyesight. The maximum depth of around 3 m was more an indication of river depth than diving ability.

Dive Clustering
The pattern of surfacing suggested that dives were clustered in bouts of activity and so was analysed according to the Hidden Markov Model (HMM). Three types of diving frequency were identified:

  • A “cluster” of multiple dives
  • Loosely aggregated: an “activity session”
  • Single or terminal dives

Temperature and Persistence
Mink experience a temperature range of 5-35 oC, in which temperature falls during activity. The body cools in water, and warms through when basking on the bank; it is typically 35 oC when sleeping, in the 20s when on land, and drops when diving. It is noticeable that dive effort is higher in females; female ‘persistence’ may extend to performing 80 dives in a row. Is this because they are excellent divers, or ineffective hunters who have to repeat dives to eat?

Either way, the smaller the mink the greater the persistence and this may be expressed as a negative relationship between temperature and bodyweight. Persistence is greater during the day, when temperatures are higher, and become more concentrated the shorter the day. That said, mink tend to be inactive 80% of the time, spending only 50 minutes or so in the water per day. Males are more nocturnal – perhaps, because of their size, they are less afraid of meeting otters?

Competition with Otters

Behaviour has altered over time, with the evidence of scat declining since the otter’s resurgence in the 1990. However, if other evidence such as footprints is taken into account, it appears that mink remain, but are no longer deliberately marking their territory. Otters are bigger, and may weigh 8 kg, so while the feisty mink might be prepared to fight, it wouldn’t,

wish to make a habit of it. So what seems to be happening is that when the nocturnal otter returns, mink behaviour adapts to the new circumstances and becomes diurnal, thus avoiding confrontation.

Conclusion

The survey testifies to the success of new TDR (Time Depth Recorder) technology and HMM techniques in monitoring the behaviour of otherwise difficult to observe species.

QUESTIONS

Have there been studies of the American mink in its natural habitat, North America?
Yes, in the 1940s and 50s, but mainly of terrestrial behaviour. There have been diving studies elsewhere, in Tierra Del Fuego for instance, where mink are diving in the sea, and of feeding in Sweden.

How long did the mink wear collars?
Joanna aimed to collect collars after three weeks, but if missed, they were designed to be readily biogradeable, rather than made of more durable leather.

Where do mink live?
They don’t excavate, but occupy existing holes. Sometimes these are in trees, but mink are particularly fond of rabbit warrens.

Are males and females mutually antagonisic?
Yes, males and females join only to mate. Mink of each sex maintain their own, linear, territories. The males occupy about 5 km, overlapping two of the smaller females’ 3km territories. Males will not tolerate each other. Mink are not social; apart from mothers and kits they do not share.

How related are they to the European mink?
Less so than previously thought; they are of a different genera. Indeed there is no knowledge of hybridisation. European mink used to be found in the Baltic states, Poland, Belarus and Russia south to northern Ukraine. No population is known to have existed in the British Isles.

Has the return of the otters in recent times deterred the mink?
It appears not, though it has affected the mink’s behaviour.