10. How to scare an otter

I recently spent week at an otter conference in southern Ireland. About 50 people from 13 European countries gathered at Kinsale to talk about otter ecology and conservation. Some of us were lucky enough to visit Roaring Water Bay afterwards to take part in a project whereby otter droppings (spraint) are collected and DNA extracted to follow the movements of individuals.


Collecting otter spraint near Roaring Water Bay. Delegates from Ireland, Israel and Italy

One talk at the conference was particularly interesting in the light of the question of whether otters might be scared of lights at the CUBC boathouse.  It dealt with the subject of how to discourage otter predation at fish ponds. Lauren Harrington of Oxford University described efforts to discourage otters from entering the water by playing sounds beneath the surface. Early trials in the field were only moderately successful and they concluded that it would be more practical to work with captive animals where you don’t have to rely on unpredictable visits by otters to your study site.

It seemed that some discordant sounds were disliked by otters though Lauren hadn’t yet worked out best ones to use. Whether any system will work in the wild and whether or not the fish it is supposed to protect will be affected remains to be seen. Most mammals get used to predictable disturbance, so there are no guarantees. On the other hand, sound travels extremely well in water so a single source might protect a substantial sized pond – if it works.

Meanwhile, it seems that at one site in Northern Ireland otters have been successfully discouraged from eating rather different type of prey. The Copeland Islands just south of the entrance to Belfast Lough have a colony of 5,000 pairs of Manx shearwaters which were being preyed on by what was believed to be a single otter. Although the number of birds being killed was believed to be no more than 2% of the breeding population, this did represent an increase in mortality of about 30%.

Photo: Ómar Runólfsson (Creative Commons Licence)

Photo: Ómar Runólfsson (Creative Commons Licence)

There are three islands, Copeland, the largest is a mile (1.6km) offshore and Mew Island and Lighthouse Island (where the shearwater breed) a further three quarters of a mile out. Their combined coastlines come to less than 10km which is large enough to support a small number of breeding otters but not a viable population. It isn’t clear whether predation was caused by a resident otter or whether one or more otters visit the island during the bird breeding season when vulnerable avian prey is available.

Kerry Leonard investigated the losses and, having found clear evidence that an otter was responsible, tried to prevent further losses with deterrents. He used a combination of two methods: four high intensity red flashing LED lights which automatically turned on at dusk and off in daylight and ten ultrasonic animal deterrents which generated a noise which swept through the frequencies from 20 – 45 kHz. The ultrasonic deterrents have a sensor similar to the one used in some household security lights so that the noise was only generated when an ‘intruder’ approached. Unlike the Oxford project, this work wasn’t done on an experimental basis so it is not possible to know which method (if either) worked. However, after they were deployed, predation dropped dramatically. In the 50 days before the lights and sound were used, 67 shearwaters were killed but from mid-August to mid-October, only three were taken.

Three thoughts come to mind. First the evidence that the technique worked is good, even though it had only been tried once at the time of the report. Shearwater chicks take a long time to develop and are particularly vulnerable during September – right in the middle of the period when deterrents were used. Second, it would be interesting to know whether it would work with only one deterrent. In general, one would expect unpredictable disturbance to be more effective, which would suggest that the continuously flashing light (at night) would be less likely to work as well as, possibly, less unpleasant. However the sound was only produced when the otter approached the area and given Lauren’s preliminary results, looks likely to be the important effect.

Third, I am intrigued that the light should be red. I wonder whether this reflects our human association of red with danger. Most carnivores are unable to discriminate between red and green light so the otter won’t know whether it was safe to cross!

The presence of otters on offshore islands is also interesting. I have seen otter spraints at the Shiant Islands off the east coast of Lewis in the Outer Hebrides. The coast line of these is a little larger than the Copelands but they are further off shore (4miles; 6.5km). I suppose it is possible that one or a few otters permanently live on the Shiants but it I suspect that they come out for the breeding birds. There are tens of thousands during the summer, an impressive sight. Auks are very common: guillemots (ca 8,000), razorbills (ca 3,500) and puffins (>75,000) – plenty of food for an otter.

Shiant Islands, looking south towards Skye. Photo: SustainableDevelopment, Universityof the Highlands and Islands (Creative Commons Licence)

Shiant Islands, looking south towards Skye. Photo: SustainableDevelopment, Universityof the Highlands and Islands (Creative Commons Licence)

9. Otters and development

When I started this blog I intended it to be about natural history and ecology and not to get bogged down in conservation politics. However a recent controversy involving otters is hard to resist and now that things have died down a bit a little reflection seems called for.

It started when Mark Avery reported on his blog that Cambridge University Boat Club was planning to build a new boat house at Ely in an area of high conservation value (on a County Wildlife Site and adjacent to an SSSI). Taking his information from documents on the East Cambridge District Council’s planning web site, Mark briefly explained the background and picked a few highlights to comment on, making use of the objections which had been submitted. Some of these concerned otters. With a sure eye for catching attention, Mark said that although he had been a student at Cambridge he would not be cheering them on in the boat race this year and he hoped that they would sink. This generated a lot of interest and extensive comments on his blog but things did get a bit out of hand when one over-enthusiastic tweeter claimed that CUBC were going to kill otters. Otter nonsense of course.

This site may well be a bad place to build a boat house and there may well be detrimental impacts on some species of wildlife but it is extremely unlikely that otters will be one of them.

Looking a bit deeper I find first that the local wildlife trust felt that “The presence of  otters is somewhat down played; we don’t have any information on the size or ranges of the local otter population and the importance of this stretch of the River Great Ouse to ‘the species.” and second, a comment on Mark’s blog, replying to one of mine claiming that “One kilometer to the east on the River Ouse is an otter black spot where at least five otters have been killed on Queen Adelaide Way in recent years, crossing from some former settling ponds, now an SSSI. The danger that this residential development presents is that otters will be deterred from travelling west along the river in the direction of the nightime lights, noise and human activity and be more likely to travel east and risk the crossing into the settling ponds, increasing their mortality risk from traffic along this increasingly busy route between two SSSIs”.

The Wildlife Trust is asking for information which could not be obtained without a very expensive long term study. Determining otter home ranges requires radio tracking an expensive, time consuming and invasive task. Assessing otter population size is also extremely difficult. What they could reasonably ask for is an assessment of the status of otters on the catchment, based perhaps on the results of the recent National Otter Survey. This shows that Otters are now present at about half of  the 156 sites that were surveyed on the Ouse with a higher proportion of sites with signs (24 out of 30) on the Ely Ouse. Clearly the catchment is well on its way to recovery.

The lighting issue was first raised by the original otter surveyor who suggested that otters might be disturbed by lights during construction so recommended that the boat house be built in daylight. Which it would have been anyway – but this enabled him to include some ’mitigation’ for imagined disturbance as a way of showing that something was being done to protect the otters. It also created a hostage to fortune.  In fact there is no evidence that otters are adversely affected by lighting. Indeed, if they were they would not now be found on rivers in many towns and cities around the country.

The issue of otters being killed on roads is a serious one and may well need addressing at Queen Adelaide Way but this doesn’t mean that one should put a moratorium on all development around it. One of the worst road black spots I have dealt with was in a Devon Town where, in order to get upstream round an impassable weir, the otters had to cross a well-lit road – on which several were killed.

People often latch onto the presence of charismatic species like otters or dormice in the hope that it will prevent some, unwelcome development. What they fail to realise is that these species are more adaptable than many of us think and that although they are protected by law, the law isn’t designed to prevent development but to ensure that it happens in a way that will not adversely affect the species.

Otters in particular are a very poor bet for objectors. They are not the timid shy creatures we used to think, but well able to cope with human activities in and around their environment. I have found signs of otters in several cities, including Glasgow, York and Leeds and they have been recorded in many cities and towns throughout the UK.

In the case of the controversial boat house a survey found no signs of otters at the actual site, though they would undoubtedly pass through it on their travels since they are present on the catchment. No otter resting sites were present and as far as I can see it was unsuitable as an otter breeding site. So, how will otters be affected? Certainly not by the lights.

In some ways this is all a bit silly and may seem unimportant but I think it does matter, not least on the crying wolf principle. When there is detriment to wildlife due to development it is really important to take steps to prevent the development or mitigate the harm. However, as conservationists we don’t do our cause any favours by using bogus arguments. Of course, when we are not sure about impacts the precautionary principle must be used but where there is evidence that no harm will result we should not use attractive animals as a shield against developers.

It is also interesting to consider why there is a persistent myth that otters are such sensitive creatures that they need this level of protection. It certainly doesn’t come from books. The otter in Wind in the Willows is a rough, tough character, at home with pistols and cutlasses and neither Tarka the Otter nor Ring of Bright Water portray these animals as being particularly sensitive. I suspect there are two factors.

First the terminology we use for species which are in decline and need special conservation measures, both ‘threatened’ and ‘vulnerable’ have carefully defined meanings when used in the Red Data books but they do carry an implication of an inability to cope with the vicissitudes of modern day life.

Second, when otters were threatened with extinction in England, in the 1970s, we knew very little about their habits. Only that they were mainly found in fairly remote areas, in places where it was perceived that the water was very clean and disturbance from people very low. I am fairly confident that this distribution was caused by the patterns of pesticide use in Britain, possibly modified by other toxic pollutants, between the 1950s and 1980s. As the otter population in Britain has recovered, however, we have found that they are very happy to live alongside people in towns and cities as well as the country side.

The otter’s story, over the past five decades is an interesting one. Often portrayed as a success story for conservation I think we owe a lot more to the otter’s adaptability than to our activities, other than the fact that we have banned the pesticides that led to its decline and reduced other pollutants which affected its food supply.

Mark Avery pointed out that although he has a Cambridge degree he would not be supporting the light blues in the last boat race. Well, I have one too, and if I hadn’t been too busy watching some very different boat games at the Ellesmere Port Boat Museum, I might have been cheering them on. On the other hand, if I lived in Cambridgeshire, I might also be objecting to development on a County Wildlife Site.

An opportunity to mention my new book. Details are here: http://www.chaninweb.co.uk/otters.htm

8. Who is hibernating?

Well, not me actually though you could be forgiven for thinking so.  I have been incredibly busy this winter and my usual winter quiet period has not materialised. This has the benefit of keeping me in work but means that little else has been done.

So, where to start? Well with frogs I think. There was a positive orgy outside my office last month. One day I counted 64 frogs and know that there were at least half a dozen others lurking in a corner.  We had masses of frogspawn by the end of February and then another batch in early March when the weather was bit warmer.   A couple of questions arise.

First, why on earth did the first eight spawn masses get laid in the very small (and likely to dry up) minipond in the bog garden? Instead of laying their eggs in a few thousand litres of real pond beside it they chose a tiny pool with only a few gallons. You would think that with about 300 million years practise at being amphibians (they emerged onto land in the Carboniferous period, 370million years ago)  they ought to have learned by now about small pools drying up.

Second, where have they all come from? Our garden is a moderate size (about 20m x 20m) and we see frogs in it throughout the year but there can’t be that many. It is surrounded by walls and the only conclusion must be that they come up from the road. The fact that we find frogs clambering up the steps from time to time during the breeding season (including two in a passionate embrace this year) does confirm that but how do they know which steps? The pond was built 6 years ago could they all have bred here?

I found an answer to the first question in a paper by Arnold Cooke, published in 1975. He recorded information on nearly 800 spawning sites of toads and frogs in Britain and found that frogs prefer shallower water than toads. Most frog spawning sites (71% ) were in water less than 30cm (12”) deep and nearly 50% in water less than 6” deep. Toads prefer their water a little deeper but 72% of sites were less than 45cm (18”) deep. Neither species used very deep water, in both cases less than 5% of the spawn was found in water more than 90cm (30”) deep.

Cooke also commented on the fact that frogs were much more likely to spawn in temporary pools such as rain puddles and flooded wheel ruts where there was a risk of every tadpole being lost if the water body dried up. He suggested that this risk might be worth it if in other years the tadpoles escaped the risk of predation by fish, which would not be present in such temporary pools. Toad tadpoles seem to be immune to predation, probably because, like the adults, they are distasteful. A benefit of shallow water is that it is warmer so they would develop faster. This might cut down on predation risk from small predators (like newts)by being too large sooner and they could metamorphose and leave the water earlier.

So that explains the shallow water, but I still want to know how they navigate to my pond!

7a. Not a real post


This is just a brief message to thank the Mammal Society for tweeting about this blog and especially Laura for the helpful advice.

As a consequence of which, Welcome! This is now a blog with more than one reader. I will endeavour to find something interesting to say about the hedgehog at the weekend but in the mean time here are a couple of pictures.

The giraffe has no significance except that I enjoyed watching the small herd at Dublin Zoo. Inspiration for a blog on long necks and rumination some time in the future. The autumn colours are from  the Boating in Autumn series and a reminder of a major food source for dormice in their last few weeks of activity in the autumn as well as several species of bird during the winter.

The blog now has an email address for comments and questions not related to the topic of a post. Look on the Your Comments page.


7. Hibernation

Safe home, unscathed and not too badly affected by the floods that have affected England over the past few days, particularly the Southwest. The Grand Union was very full of water and it was running straight in from the fields and out across the towpath but we managed to get back to our moorings and batten down Thor for the time being. If you liked the evocative canal picture in the last post there are more here (Boating in Autumn).
Meanwhile back home the camera has recorded more hedgehog activity. Full report in the next post when I will have also downloaded the temperature records but meanwhile here is a picture of the latest wildlife to be recorded. A woodmouse, exploring the woodpile at about 3:30am on November 24th. A chilly night – down to 1degree according to the camera.
The last record of the hedgehog was the previous night, at about half past one in the morning when he set off for who knows where – no picture of him returning. There is an interesting gap in the records from the 14th to the 22nd when he might have been elsewhere or even in the nest in a state of torpor. I hope the logger will shed some light.
So, what is hibernation? …and how does it relate to torpor?
Well, ‘hibernation’ means ‘wintering’ and it is used to describe the state of animals which spend the winter sheltering, usually in dens or roosts (bats), in a state of inactivity. Body temperatures are reduced and the metabolism slows down. Small species such as bats, dormice and hedgehogs allow their body temperature to drop right down to that of their surroundings so that they are the same temperature as the environment around them. Larger species such as bears (in cold regions), keep their body temperatures at a higher level, not least because these species often have their young during hibernation and can’t afford to switch off entirely [Click Here for a BBC video clip]. They can get away with this because, being large animals with a relatively smaller surface area they have a lower metabolism anyway and are able to make their fat reserves last through the winter.
It isn’t so easy for the small species though. Under normal conditions they lose heat very quickly through their relatively large surface areas and compensate by having a very fast metabolism. This is why shrews are active throughout the 24 hour day, alternately foraging for a few hours then sleeping it off before heading out to feed again. They get through four or more cycles of activity for every one (day) of ours. Even when slowed right down with temperatures only a little above freezing, it can be touch and go as to whether a hedgehog, dormouse or bat has enough fat reserves in its body to see it right through a long winter. That is why they need to store lots of fat which is why the dormouse in post #4 is so tubby.

Torpor describes the cooled down state of an animal. Dormice are often found torpid during nest box surveys, particularly early in the season. Perhaps it is a means of economising when fuel (food) is not very abundant. The picture below shows one I found in an otherwise empty nest box in May this year. It felt cool, and was completely unresponsive. The picture was taken at 10.45am.

Torpid Dormouse

You might need orientating. Its nose is at the bottom of the picture, just above the tail, and you can see the whiskers as black lines pointing to the left. A dark line behind them, parallel to the tail is its eye. The middle of its back is at the top of the picture and its left forepaw is more or less in the middle with the hind foot below that. The animal is nearly spherical which means that its surface area (where heat is lost) is as small is it can possibly be.

I have just downloaded the latest pictures and temperature readings from the hedgehog nest. More on those next time.


6. “Season of mists and mellow fruitfulness”


Early moring on the Grand Union Canal

For the past 10 days we have been boating – on the Grand Union Canal in Warwickshire and experiencing at first hand the changing season. The picture above greeted us on Sunday morning – a bright sunny day after a cloudless, starlit night which resulted in a good frost. The whole day was bright and sunny so the colours of the trees were very vivid and so were those of the berries growing on the bushes along the canal. Huge flocks of thrushes: fieldfares, redwings and mistle thrushes poured along the hedges and trees searching out and then feasting on them.

All responses to the onset of wintry weather – which, in one manifestation, hit yesterday, with strong winds and heavy rain. The canal was very full, expanding on to the towpath in several places and we could see water pouring across the fields and into it, carrying a load of silt with it. A double problem, removing soil which the farmer cannot really afford to lose and clogging up the waterway which will have to be dredged at considerable expense. A pity that so many pastures, which would resist this have been turned into arable fields, which don’t

The glorious colours aren’t for our LeafColoursbenefit of course; they are the result of the trees winterising, recycling, and waste-disposing. The soft flimsy leaves of deciduous trees are not frost resistant like the tough needles of conifers (try putting a lettuce leaf in the freezer and you will get the idea). The response of the trees is to dispose of them, having first removed all the goodness; sugars and so on; broken down the green chlorophyll to recycle its constituents and then disposed of unwanted, sometimes toxic, products into the leaves before they drop.WhiteBryonyFruits

Meanwhile the fieldfares and their relatives are reacting to poor conditions in Scandinavia, where they breed, coupled with the attraction of the berry harvest in Britain. Like the swallows, they have flown south but, not needing insects, which are mainly dormant during the winter, they can survive on the hedgerow harvest which, in turn is of no value to the insect eating swallows, martins and swifts.

What about the hedgehog. Well, when I left it was still using the nest in the garden but I won’t know whether it has chosen to hibernate there, or somewhere else till I get back.

Meanwhile, here is a picture of its activity patterns during October and early November. The yellow bar corresponds to daylight hours. Clearly a nocturnal animal, it isn’t making an early start, perhaps avoiding the evening hours before ten when it is more likely to encounter one of us, or Bessie, the dog. Mainly active between 10:00pm and 8:00am, it seems to like a nap between 4:00 and 6:00. Most surprising was the single excursion at 9:57am for which I have no explanation (see post #3 below). Perhaps it was trying to intercept the postman.


Activity pattern, October

5. A lot has happened…

Not easy to keep up-to-date when things keep changing and I keep going away. Several days in Dublin for a conference gave me a chance to go to the Zoo in Phoenix Park. Well worth a visit.  Their Sumatran tiger impressed me – as did their African Plains exhibit with small herds of giraffe, oryx and rhino. Here is one of the tigers.


Meanwhile the hedgehog has been busy and has also gone walkabout, spending several nights elsewhere and, having just checked the loggers, he isn’t in the nest now (four in the afternoon).

This graph shows the temperature near the nest but not close enough to be affected by the animal’s presence. Much smoother than the results from one in the nest and I suspect that the spikes in that are when the hedgehog is active. Maximum temperatures during this period were around 4.00pm – ca 7degrees and minimum at about 1.00 in themorning – between 3 and 5 degrees.

One question I would like to answer is “does  the hedgehog cool down and become torpid in between activity bouts at this time of year”? I need to look at temperatures when I know he is present. I  hope that comparing temperatures inside and outside the nest will provide the answer.

I have some good evidence of nest building, with pictures of the hedgehog carrying leaves into the nest. On one occasion, over  a period of one and a quarter hours it made 27 round trips and is clearly making some home insulation improvements – several pictures show it with a leaf in its mouth.



Notice the time stamps. The first leaf is carried in at 05:41.  16 seconds later the hedgehog heads out again. 29 seconds after that he is on his way back in with another leaf. A busy little animal.

4. Fat dormouse – an aside

Dormouse nest boxThis has been a strange year for weather, with a drought expected in the spring followed by a great deal of rain in the summer. The effects on wildlife will take some time to establish but it seems that dormouse populations have not all behaved in the same way.

Many people have found very few dormice in their nest boxes (above right), others the same number as in previous years. We don’t know if that is because there are fewer dormice or because they are behaving in different ways in different places. They don’t have to nest in the boxes we put up for them.

I have been lucky. In one place where I have been checking nest boxes over several years the numbers were similar to when we started. At another, newer, site I not only had more dormice than before but also the fattest one I have ever handled.

Fat Dormouse

Pre-hibernation tubbiness

Other people have reported seeing some well-stuffed dormice in the last few weeks and this is just what we should expect at this time of year when they need to build up a store of fat for the winter. More worrying is the fact that we are also finding some quite light dormice. One of mine was no more than half the weight of fatty on the right here. Only born in the last few weeks, it may well fall victim to an unsuccessful late breeding attempt by its mother. Unless it can gain a lot of weight in the next few weeks it is unlikely to survive the winter.

Hedgehogs face the same problems of course and they too need to reach a minimum weight before they go into hibernation. I haven’t weighed the hedgehog in the garden, to minimise disturbance, but it looks plump enough.

3. First Results

Data! The first two night’s results look like this:

Temperature Graph 1

Temperature changes over the first few nights

All very wiggly and confusing but a closer look shows several things:

First, the temperature varies quite a bit, sometimes over quite short periods. There is also a general pattern of it being warmer and less variable during the day (yellow band  shows time between sunrise and sunset). On the 16th apart from a blip at about 11:00am the temperature seems to rise during the first half of the day and decline from about 4:00pm. The highest temperatures were about 18° but this happened once in late morning and once at about 1:30am – the middle of the night. The lowest temperatures were ca 10° and seemed to occur at night.

So, how much of this is due to the hedgehog and how much to changes in air temperature? Certainly it never gets anywhere near the 37 degrees or so you would expect from a mammal. This isn’t surprising when you realise that the logger is separated from the hedgehog, not only by being in the nest material – good insulation in its own right – but also by the prickles on the animals back.

For the next night, I put the data logger near the nest but not so close that the hedgehog’s body heat could affect it and we can look at that next.

Meanwhile the number of times the hedgehog has been caught by the camera is building up and we can start to look for patterns in those too. So far it has been almost entirely nocturnal – except for one night on the tiles, when it crept back long after dawn (NB time is in GMT format so it is really nearly 10 o’clock):

Night on the tiles

2. Camera traps and dataloggers

One of the benefits of working with wildlife is that you acquire useful bits of equipment which don’t only have to be used for work. The hedgehog is going to be monitored by two of them.

Camera trap

The camera trap

Trail cameras are used a great deal in the US by hunters who set them up in places where they hope to find game to shoot. Follow this link for some examples. Ecologists have caught on to this and they are now widely used to study wildlife and find out what it is doing. There have been some fascinating sequences on television where they have been used to detect rare and elusive species. Gordon Buchanan’s recordings of snow leopards and tigers come to mind (Lost land of the tiger – links to YouTube).

So why not use mine for a humble hedgehog?

Here is one of the first pictures:

First Hedgehog picture

Notice that it records the time (GMT) and also the temperature. This one was taken at about 10 past ten (BST) on October 14th when the temperature was 8°C.

l have also got a data logger.  This small squashed-golf ball sized instrument will record the temperature at regular intervals for several weeks after which you can download the results onto a computer. After programming it to take a reading every ten minutes I slid it carefully into the top of the nest just above the hedgehog.

NEXT First results