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Fewer dead hedgehogs are being found as they are putting more effort into their training regimes and are thus somewhat faster when playing chicken across our roads.
Paul J. Weighell
An almost feasible reason for hedgehog numbers going up:
Along with the elderly, Gordon Brown has also decided to offer hedgehogs free bus travel from April, so hedgehogs are familiarising themselves with the whereabouts of their nearest bus stop instead of being run over whilst walking to their destination, hence a drop in roadkill levels.
Tony, Sheffield
The reason that the number of squashed hedgehogs is on the decline is because this figure has always been a percentage of the whole remaining hedgehog population. As long as this annual 'road cull' figure is higher than the annual birth figure you will end up with a declining amount.
Anthony Parson
A possible explanation for numbers of hedgehogs killed on roads falling when in fact the overall population is increasing – a strain of hedgehog evolves which runs when seeing car lights instead of the usual response of rolling up.
Rollers would be selected against and runners would be selected for, so that the latter would increase as a proportion of the population. This would eventually result in increased survival of hedgehogs, giving a rising population but reduced roadkills.
Colin Ryall, UK
For some years I have noticed that the local hedgehogs seem more inclined to run away than to curl up in a ball when frightened. Perhaps the 'curl up' genes are being eliminated by road kill and the 'run away' genes are taking over-so there ARE more hedgehogs living quietly in the bushes than is indicated by road kill surveys. Nice idea, don't you think?
Elizabeth Silipo, England
Your question regarding hedgehogs being more plentiful yet less squashed suggests four possible explanations.
1. Learnt response. Just as Tits learned to open the tops of milk bottles, perhaps hedgehogs have learnt to recognise the sounds of approaching vehicles.
2. Darwinian Selection. Surviving hedgehogs are faster and cleverer. Perhaps in years to come they might begin to fight back.
3. Vehicle Size. With the increase in 4×4s and larger engines perhaps cars are becoming more obvious. Smaller, quieter cars are more stealthy.
4. Vehicle Colour. I think this might be a more logical reason. Car colours have changed over the last 10 years such that the once very common red has been replaced with silver and blue. It is possible that the frequency response of hedgehog eyes is more tuned to these colours especially in twilight. I suffer from red, green colour blindness and find that brown, green and red cars are almost invisible in twilight if they don't have their lights on.
I hope that these prove food for thought.
Kennedy Clear, Darlington
Could be those squashed (dead) have caused an ungrading in hedgehog viability, such that they are actually proliferating because:
1) Only the most intelligent have survived / bred and some have set up in business with road sense lessons (at least teaching their own)
2) Those with the instinct to curl up rather than run like hell have been weeded out.
3) The restriction has weeded out the short sighted ones.
4) Natural selection (dead ones) has meant that the survivors have better hearing, only cross when nothing coming.
5) Longer legs.
6) Faster runners, possibly not longer legs, but faster.
7) Natural selection re allergic to tarmac / fumes so don't cross roads.
Hedgehogs with no legs at all, so stay put rather more.
9) The too many hedgehogs before scenario was altered by the squashing to not enough left. So hoggy culture altered and the work / travel ethic changed to a stop at home ethic, "we grow enough bugs at home these days"."
10) Hedgehogs of the wandering kind were an anomaly, and almost all dead. So the standard hedgehog not inclined to cross roads is doing better since all the weirdoes were disposed of, in particular because the weirdoes habitually caused damage to the habitat (by killing other blokes baby hogs, for example.)
11) There is a form of hedgehog doing better that no-one was aware of who tunnels.
The choice is endless. Could look funnier in cartoon form
Elizabeth S Pascoe, England (Liverpool)
Hedgehog numbers are actually getting bigger and this is why:
We know that hedgehogs have, in the past, curled up in a ball when under threat. This is a useless activity when threatened by a motor vehicle. However there have always been a number who have stretched their little legs and run like mad when afraid.
These have had an advantage on the road and have survived. Because they don't have to compete with those that curl up, they have been able to breed with other 'runners', so increasing in numbers.
There is a theory that the timid stay-a-home hedgehog has survived because it has not braved the roads. This is an unlikely theory, as the breeding stock is limited and therefore inter-breeding has weakened the strain.
Liz Sowerby
I believe the relative dearth of roadkill is simply a result of evolutionary development of the modern hedgehog.
Historically, rolling into a spikey ball has served well as the primary hedgehog defence mechanism. This works well for cats and foxes, but is less effective against the Volvo.
However, a small percentage of hedgehogs have probably always preferred the 'run for it' approach. These athletic beasts can be expected to preferentially survive into reproductive maturity, eventually outnumbering their more sedentary cousins. Hopefully, not too many will be found on roads in the two-dimensional state.
We should be looking out for progressive lengthening of hedgehog limbs, culminating in the new country sport of hedgehog coursing.
Peter Jackson
On your program this afternoon you asked for possible reasons that could explain an increase in the total number of hedgehogs while the number of hedgehogs killed on the roads has decreased.
One explanation could be that hedgehogs instinctively curl up on the approach of an enemy. If the enemy is a car then rolling into a spiky ball is perhaps not the best form of defence.
Logically some hedgehogs will inherit this instinct more strongly than others. Hence those animals with the strongest instinct to roll up will suffer a higher death rate when crossing a road than their fellows who don't curl up and keep running.
Then by a process of natural selection the rolling up reflex will tend to become less common in the hedgehog population as a whole because those who have it are killed more frequently on the roads.
So if the number of hedgehogs with this reflex falls in the population, the number of hedgehogs seen dead on the roads will also fall.
With a reduction in the number of road deaths the overall population of hedgehogs could well be on the increase and the method of determining the population of hedgehogs by counting the number found dead on our roads would no longer be valid.
Edith Preston, England
Question: Explain how the number of sightings of squashed hedgehogs can be decreasing, whilst the actual number of hedgehogs is increasing.
Suppose there are some hedgehogs who, on seeing an approaching car, curl into a ball; and others who make a run for it.
Over time the hedgehogs that curl into a ball will tend to get squashed more often than those that run. The runners will therefore have more offspring, who will in their turn be runners.
Eventually most hedgehogs will be runners and will get squashed less frequently: they will then not figure in the sightings of squashed hedgehogs even though they may be numerous.
David Price
Many years ago it would be reasonable to assume there would be a fairly positive correlation between living and road-hit specimens.
However, evolution is an ongoing phenomenon which could affect these data, so care must be taken in interpreting them. One of the survival adaptations of hedgehogs is to roll into a ball when it senses danger. The spines then protect the animal from its enemies and it is easy to see how this mechanism has evolved.
Consider the following:
-The motor car is a recent danger to hedgehogs in evolutionary terms.
-Rolling into a ball has no protection against car tyres.
-Rolling into a ball in the road increases the probability of injury or death from cars because the animal is there for longer.
-Variation in generic makeup of hedgehogs could produce individuals (by gradual change or by mutation) with less tendency to roll up when they sense danger. Such individuals may be more successful in built up areas and would pass on these successful genes to following generations.
Thus it is possible that a decrease in squished hedgehogs could indicate a more thriving population rather than a declining one, at least in some areas. Long live the hedgehog!!
A further thought – is it possible that hedgehogs could have evolved a way of discerning between a predator and a car so they continue to roll up when approached by Rover the dog!
Brian Hammond
Hedgehogs – in reply to your request for last week I would have the answer was obvious – evolution dictates that the survival of the fittest (not fit as in muscular etc. of course) would allow only those hogs who had enough sense to recognize this new danger and avoid it would pass on their genes to allow more road sense aware hogs – instead of rolling into a ball, they would run when faced with this particular 'predator'.
I should imagine that there has been enough time passed to allow for this. Or perhaps I am completely wrong.
Greg James, Wales
Since I wrote to you last week two thoughts came to mind which deserve further exposition and consideration: the first is about the so-called CTR gene and the second is about road traffic.
Suppose the CTR gene ("Cross The Road") is not a neutral mutation as I first suggested.
Suppose it gave those hedgehogs in whom it was expressed the tendency to break away from their homes, cross open spaces and find new hedges.
They would be escaping in spite of the risk of being eaten, but feel urged to "Run away, run away."
As we saw last time, the RaRa gene (a.k.a. CTR) is carried by twice as many h-hs as have it expressed, so predation shouldn't have been a great problem.
Now, about traffic: a century ago you could have waited hundreds of minutes before you saw a car, even in town. Today you could see several hundreds of cars in a minute. I am convinced that traffic has at least doubled in the last 30 years — the period of interest. HaHa-affected h-h predation by vulcanised rubber has increased in the same proportions.
We only have a hypotheses waiting to be a theory; it needs observations … the supports for any theory:
1. Really, how many h-hs are there in the wild? We need new methods of measurement. Only then can we say that the hidden h-h population has actually grown or declined.
2. Can DNA analysis help us? We need biological and statistical analyses of the DNA of squished and living h-hhs to reveal the RaRa/CTR gene and its prevalence in the two groups. Can we find sufficient 100-year-old h-h remains – for DNA extraction – to make a meaningful comparison?
And finally … a purported theory must have predictive powers. May we apply the CTRT analysis to the bird life threatened by wind turbines?
Richard
Natural selection applies to hedgehogs as much as to any other life form.
Slower hedgehogs are more likely to be killed on roads than faster hedgehogs. Over time only fast hedgehogs remain alive to breed, passing on speed genes to their offspring. Therefore there will be less roadkill and a thriving population of nimble hedgehogs.
It may even be that a population of super hedgehogs is developing with an extra sense akin to radar which gives early warning of approaching traffic and so more time to take evasive action.
John Crombie
You asked for wacky ideas as to why less hedgehogs were being killed on the roads. Here goes…
Mrs Tiggy-Winkle, and all the other hedgehog washerwomen in the country used to have to cross the road to hang their washing out to dry and then cross the road again to collect it when it was dry.
This was a dangerous occupation as they would often be so busy, they would not have time to look before they crossed the road.
With the advent of modern technology, they all went to Comet and bought tumble dryers. This meant they could stay at home and get their washing dry.
Kate Golding, England
It seems to me that evolution might well be being observed in action.
Hedgehogs with an innate ability to avoid roads (or at least avoid becoming casualties upon them) will prevail in the population and such an ability (whether from genetically-derived instinct or parent-conveyed education) would become dominant, leaving fewer hedgehogs vulnerable to the traffic and thus less of them being unlucky enough to succumb to the inexorable rubber-tread.
Though this does leave the issue of whether a previously continuous and diverse breeding population spread throughout the countryside could now succumb to the 'island' effect, if the mental change is more of the "avoid roads" kind rather than "look both ways before you do"!
By-the-way, why no example of the catch/release/re-catch method of population estimation? Because I don't know the correct term for it, the details of its operation are:
1) Catch (live) and count a number of individuals within the population (an unknown proportion).
2) Mark these caught ones and release.
3) Have another catching session and see what proportion of these are ones previously caught. That should reveal (barring problems with prior-caught creatures being differently catchable a second time through learning/stress, or being unable to guarantee a 'remixing' of said individuals) roughly what proportion you caught the first time and hence the total number.
That's an aside, though, and probably not as easy with hedgehogs as other creatures.
Phil Minto
With reference to hedgehogs. I have observed that when I handled the animals they didn't curl up so readily as they had when I was young.
I feel this may be because natural selection in favour of the ones that don't curl up. Maybe they keep on running when a car comes when they are crossing the road and so more of them survive to breed.
I made this observation a few years ago when I lived in a more urban environment. Where I live now off the main road in the countryside I feel they curl up in the way they used to.
Adrian Turner, Rural Ceredigion
The reason that fewer hedgehogs are being killed on our roads is that hedgehogs are getting cleverer by natural selection. All the ones with the gene for bad road sense have been killed, leaving only the ones that are clever enough to stay well away.
Yvette Gonley
Simple reason why there are less dead hedgehogs on the road – they have learnt the green cross code.
Paul Cash
In areas where there are no dead hedgehogs at the road side there will be lots of road kill badgers. This is because badgers eat hedgehogs and because there are huge amounts of badgers hedgehogs have been virtually eliminated.
June Tavernor, England
Listening to your request for any hypothesis that might account for the possibility of hedgehog numbers increasing, in inverse relationship to their road casualties decreasing, I would suggest the following obvious Darwinian explanation.
All hedgehogs shun sudden light, but those who get up and run from bright (car) lights, instead of rolling up into a ball would be those most likely to survive and breed similar traits again.
Since more and more gardeners have moved towards more organic practices, then both these changes would be expected to have a very favourable effect on hedgehog populations. Indeed, if this is the case, then we might expect the hedgehog population to continue to recover to what it may have been in our grandparents' youth?
Vaughan Fleming
It is entirely obvious that the number of hedgehogs will be going up while the number found as roadkills is going down. This is due to natural selection.
Those hedgehogs who are living long enough to procreate must be those, who like the Road Safety Hedgehogs, have learnt how to cross roads safely. The hedgehogs which are being counted are those without the "Road Safety" gene which naturally get eliminated.
I only wish that this could be true. I suspect that the decline of the hedgehog in our gardens is probably down to the increase in the number of urban foxes.
Stabcon
Hedgehog Problem: 1) Increased numbers of carrion feeders: If the population of certain feeders of carrion, e.g. foxes, crows, maggots, etc. were to increase the corpses of hedgehog would more likely be removed before surveyors have a chance to count them.
Global warming could factor in as the development rate of flesh eating maggots could increase in a warmer climate, resulting in the more rapid removal of the carcass. Meanwhile numbers of hedgehogs could be increasing, perhaps because of more plentiful food (hedgehogs will happily feed on the maggots of flies and other insects).
2) Natural Selection: Over a long period hedgehog mortalities on roads may select favourably for certain types of behaviour that prevent road fatalities, e.g. greater caution and road traffic sense, phobia of tarmac, use of pedestrian walkways, etc. Hedgehogs would appear to be less abundant while the population may be increasing.
3) Environmental Disturbance: Increased road traffic over the last few decades may cause some hedgehogs to shy away from the general noise and disturbance of roads. Numbers could continue to increase where roads remain fairly quiet.
Sam Bolton, Wales
Perhaps there were always two types of hedgehog runners and rollers and the rollers have slowly been squished out of existence and the runners learnt to run away from cars?
Clare Spicer
Re: Less hedgehogs being found as roadkill – couldn't accelerated (forgive the pun) natural selection be at work? – hedgehogs with a propensity to walk on roads are gradually dying out leaving lots of non road walking hedgehogs – so – not fewer hedgehogs but fewer road walking hedgehogs.
Fiona Macleod, England
Darwin's Theory of Evolution is so powerful that I think we can apply it to the question of why hedgehog numbers appear to be going down when they are probably going up.
H-hs have a Cross-The-Road gene – the type of gene that is expressed in off-spring only if both parents carry it. If the population started with 50% of h-hs of both sexes having the CTR gene then on average, among all off-spring:
1/4 express it (and are tempted by expanses of tarmac) 1/2 inherit it (and become carriers) and 1/4 don't inherit (or pass it to their own off-spring).
The ones with the double dose are more likely to cross roads (it's in their genes) and get squished.
Only the fittest survive … a squished h-h does not breed again … fewer off-spring are born with the gene. Mere carriers of CTR survive because they are never tempted to take to the highway at a right-angle.
The main question now is "with the CTR gene expressed, how many h-hs survive squishism?"
Let's suppose that most of them are quick enough or lucky enough to cross roads with success so about 99% survive. As the generations unfold, so more and more of the 99% get multiplied together.
The fraction of the population carrying the CTR gene goes down, there are fewer observations of squished h-hs, and the population at large increases because fewer get squished in the first place.
At 99% per generation, and assuming 2 litters per year (I know nothing of hh-h breeding patterns), it would only take 30 years to almost halve the number of squishes.
We should remember that before there were highways filled with cars and lorries, h-hs did OK; the CTR gene was a neutral mutation some time in millennia gone by. Now it's not so neutral; see what a 100 years of progress has done.
Richard Pickard
I've been driving for 46 years and managed to safely avoid every hedgehog except one. This one ran under my back wheels as I turned into another road on a wet night. I felt it but only saw the corpse when I returned that way later. Perhaps factors other than hedgehog population have an effect, such as:
1) Number of vehicles on the road.
2) Increased average speeds.
3) Poorer eyesight, observation and judgement of drivers.
4) The proliferation of 'people carriers' and 4×4s. In Hampshire, where I live, these will not alter course to avoid me, let alone hedgehogs. It's up to me to 'take to the scenery'.
5) Increased in-car distractions such as stereos and mobiles.
6) Wider tyres of modern cars.
7) Decreasing environmental sympathy.
Changes in badger population – the hedgehogs only natural enemy.
Dickie Dawes, England
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