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Bridging the gap

ID-10010468Sometimes I just want to think about cute things, and a story I saw today has allowed me to do just that. London’s water voles have been given ladders in order to enable them to get out more. Awwww! You can see the ladders and some voles in the article on the BBC website. Apart from being immensely cute, this might seem like a strange thing to do, it’s not, it actually makes perfect sense and is a similar idea to other programmes used across the world. Nature often has problems when human civilisation expands into their world, and what we often see is that built up areas create natural barriers (such as roads) which animals either can’t cross or are too afraid to. As long as this area is large enough it doesn’t have to be a problem, but where is does become a problem is when small populations of animals become boxed off in an enclosed area – it means there is less space to escape predation, that diseases can cut right through the whole population, that animals get stressed and behave accordingly (i.e. erratically) and that you get inbreeding.

Inbreeding is something that happens when you don’t have enough individuals of one type of animal. All animals (including humans) need new genes to appear in each generation – that means you need enough individuals that you can reproduce with someone completely different from you. This gives the offspring the greatest chance of being strong when they are born as they receive characteristics from both the mother and the father, so it is important that the mother and the father carry different genes in order to give the children the widest range of characteristics. You also find that with small inbred communities you see many more genetic diseases being passed on. With animals such as voles that live for a short time and reproduce very quickly, this is a massive problem. Voles may have 17 litters in one year (yep, one vole!), and each female vole can start having babies from 28 days old. If you think about the speed that these little guys can reproduce, inbreeding can become a massive problem very very quickly. In certain types of dwarf hamsters which are bread as pets we see a brain defect called spinning. What this does is causes the affected hamster to run hysterically in circles and get stressed.  No one is quite sure why this happens, but many people consider it a side effect of inbreeding.

I mentioned above that animal bridges are not uncommon – this website has some fantastic photos of examples and it would appear that they are becoming more and more popular in the US and Europe. This helps the animals to live in a larger area and not end up as roadkill, and also helps the human population by reducing accidents. But why do we need specially designed bridges? Anyone who has tried to ride a horse over a bridge will be able to answer that! Animals don’t like walking into enclosed spaces where they feel they are at risk, and most footbridges are very narrow with no places to hide. We also know that many animals, such as hedgehogs, will not go anywhere where they can smell a predator.  On a narrow bridge, once a badger has marked its scent, a hedgehog will not willingly cross.  So for wildlife bridges to be useful they must be very wide (so the animal does not feel trapped or afraid of traffic and can avoid the scent of predators) and be built up with vegetation so that animals can hide and do not feel that they are somewhere that is alien to them.  If bridges are built in this way, then they can help our wildlife.


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Blog post by Linda Seward of Seward Technical Writing, providers of original science content.



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