Railway Tracks as Wildlife Corridors

It's well established fact amongst naturalists that disused railway tracks are nature havens in particular for reptiles.

Why is this?

• It could be that while disused, railway tracks remain out of public access so wildlife benefits from low disturbance
• It could be that the gravel laid along railway tracks provides good sunning spots for reptiles to warm up in mormning and evening - especially important for maturing eggs especially in viviparous species like Zootoca vivipara and Vipera berus.
• Railways provide joined up corridors between populations enabling spreading, inter-breeding and resilience to local fluctuations in environmental and population. This is the hypothesis of interest here.

If you want to destroy an army the best approach is to somehow break the army up into parts and then tackle each part separately. At its extreme if your army could fight each soldier one at a time then you would win the battle.

The reason for this is obvious if you take 2 soldiers. With a pair of soldiers if you trip soldier A, you cannot just go in for the kill as soldier B will defend A. While you attack B, A gets up and then you are back to fighting 2 soldiers. The group often (not always as we see at the Battle of Agincourt in 1415 where a crush destroyed the French army) sums to a force greater than the parts.

Likewise isolated animal populations become vulnerable. A weaker population might be heavily affected by a year of bad weather. With no support from stronger populations it may never recover. But once it is gone, then the stronger populations are weaker too. A simple wildlife corridor allowing mixing or populations allows "fallen" populations to be repopulated and recover, and in turn the mixing provides support for stronger populations. Genetic diversity is another important under current here.

You can see this very obviously with butterflies and birds that start to colonise Britain as the climate warms. The first few colonisers try and fail but presumably their arrival starts to change the ecology and set up the necessary interconnected niche. Perhaps they eat a food plant before a native species and so have the start of an negative impact on native species. Eventually you start to get populations doing a successful breed. But a bad winter kills them off. However as populations rise the chances of someone surviving winter increases and that has a knock on effect on future populations. Eventually when the population is large enough there is resilience to environmental fluctuations. This is not just a matter of rising temperature which is crucial. but also the benefits of having a large diverse population with wider genetic variability for evolution, and enough individuals to increase the "luck" and chance of someone surviving. If populations can be joined then these luck and genetic factors are increased. In a joined population if anyone survives a bad winter in any of the groups then they can spread to repopulate all the groups. If they remain isolated then a bad winter could knock out all the population but one which then becomes very isolated and vulnerable.

I do not know if surveys have been done on working railways but I've anecdotally noticed that land adjacent to railways has a higher than expected population of reptiles. I'm in the middle of plotting my own observations in my local patch and collecting more data but it could well be that railway lines provide essential wildlife corridors that link wildlife populations across the country providing better flow of genetics and reducing the risk incurred by local population disasters.

I notice a lot of work done on railways to provide animal shelters along the lines in the South Eastern lines so it looks like railways are already maintained in connection with environmental advisers. If this is true it is an amazing achievement and provides (at least as far as I can see) an extremely under reported and under acknowledged part of UK conservation.

Whether funding for this comes from government or is accounted for by the rail network the general population should be made aware of this as I think there would be wide support and go a long way to increase the "green" credentials of rail transport.

Obviously road networks provide a similar resource of corridors and along motorways there is equal clear wildlife management with road verges allowed to develop naturally. Everyone on UK motorways will have seen Kestrels hunting small mammals in the road verges. This is in addition to raptors and carnivores benefitting from road kills which provide a ready source of carrion meat.

However it seems that roads are far more busy and cars make contact with the road leading to the hiuge amounts of road-kill that can be seen on roads. Driving through Somerset for example there seems to be a dead badger every 100m in some places. Meanwhile a train can run over the heads of animals and perhaps runs only every 10 minutes. Obviously the existence of the 3rd rail on the ground poses a huge danger to animals as any contact is instant death. But in diesel and overhead tracks this is not a risk. Certainly foxes use our local track with 3rd-rail without apparent issue so its not a deciding factor on the value of railways.

So its a complex issue to get a clear view of. But anecdotally responding here to the observation that disused railways are wildlife havens, and there appears to be a higher than expected population of reptiles in land adjacent to railway lines.

To be developed...