The perils (or benefits) of flooding for wildlife
THE recent downpours set social media alight, as people complained about extended journeys home, flooded streets and flattened gardens, but spare a thought for the wildlife, because sudden spates as we experienced can be devastating.
For example, many hedgehogs will have drowned in their sleep while settling into hibernation. Of course, there is nothing we, or indeed they, can do about it, and it got me thinking about how the flash floods could have affected other animals.
Barn owls: Night after night of wet weather means barn owls can’t get out to hunt without their delicate (and silent) plumage becoming waterlogged.
Water voles and otters: Water voles spend much of the winter in their burrows where they store food. But water levels can rise so fast that voles are flooded out of burrows and washed away. Despite their name, they are not strong swimmers so may try and take refuge on higher ground, where unfortunately they are easy prey for predators such as American mink and birds of prey. Otter holts may also be flooded in such conditions.
Foxes, badgers and hares: Generally speaking these animals can escape if their dens, sets or their fields are flooded but there are times when they get caught out and have to swim for it.
Fish-eating birds: The deep, fast-flowing rivers and streams that are also cloudy due to the sediment loads make hunting difficult for birds such as herons and kingfishers.
Snipe and other wading birds: Although they like damp meadows, flooding can severely hinder their feeding.
Fish: The eggs of migratory fish such as Atlantic salmon and brown trout that have been laid in gravels on the river bed are at risk of being washed away.
The way land and rivers are now managed causes problems for wildlife. The fact that many of our species and habitats are fragmented is a major problem during these extreme events. In a large area of wetland, there is usually somewhere for species like water voles to take refuge that is still fairly safe. If the wetland is just a linear strip of habitat alongside the river, there is nowhere for voles to go. Where big embankments line rivers (to allow farmland to be drained as part of historic flood defences), floodwater that over-tops the banks gets trapped for long periods of time.
This lying water can drown all the worms and insects that live in the soil which are vital food for birds like waders (and the farmers can lose their grass). The land drainage embankments which allow land to be farmed more intensively also push water downstream increasing the risk of flooding to communities downstream.
Deeper, wider ditches that are excavated in an attempt to reduce flooding will result in lower ground water levels throughout the rest of the year, which may affect a wide range of plant communities and the species that depend on them
Heavy rainfall causes storm sewers to open, releasing pollution untreated waste and toxic substances that people pour down drains. When this ends up in our rivers it has disastrous consequences for wildlife. Intensive agriculture causes high levels of silt build-up causing poor water quality.
In general, however, flooding is a natural process and when it is not excessive, can benefit many species.
Floodwaters help plants and animals to disperse across the landscape. Seeds are moved around in floodwaters, settling in new places and allowing plants to colonise new areas. Unfortunately this also means that problem (invasive) plants like Giant Hogweed or Himalayan Balsam spread downstream in such flood events.
Some of the rare water snails need flooding to move from one location to another. Anisus vorticulus - the little ramshorn whirlpool snail is a rare species that often occurs in ditches in wet fields that flood in winter, flooding is thought to be important in enabling young snails to colonise new ditches.
The smaller temporary ponds that are created during flooding provide breeding sites for the common frog. Flooded areas enable ducks such as pochard, tufted duck and teal to feed in new areas of open water.
On a lighter note, there were unusual scenes at the RSPB’s Old Moor Reserve in the North of England after a recent downpour. The warden, who was stranded on his own in the Visitor Centre, the only bit of the reserve above the water, was soon joined by all manner of mammal refugees, including, squirrels, rabbits, voles, moles, hares, mice and shrews... oh, and rats.