Weird weather and wildlife

8 November 2013

Devon Wildlife Trust's Peter Burgess forecasts testing times for species that fail to cope with our fast-changing weather.

This article is not about climate change and the irrefutable fact that our planet is getting warmer. Instead, this article is about a few of the impacts weird weather patterns are having on our wildlife.

We have a well-known national obsession about weather; it is often the first thing that we discuss when we meet friends, family and colleagues. This must be because our weather is far less predictable than nearly any other country on the planet - do we need to pack a warm fleece, raincoat or shorts - is it a day for suncream or a down jacket! All it requires are a few warm days in spring and the clout is cast off, only to find it is snowing the following day. It gives added evidence to that old phrase: 'Ne'er cast a clout till may is out'. In this case 'may' is the traditional name for hawthorn and 'out' refers to its blossom. As I write this we're entering the last days of May and I've just heard radio reports of snow blizzard conditions in Scotland!

Wildlife, like us, can get caught out by unseasonal weather. It doesn't have a satellite forecast to rely on, and instead takes its cue from the changing seasons and day length. As spring unfurls itself and daylight hours lengthen, then warmer weather should follow, at least this is what wildlife banks on. So a sudden cold snap, the last icy gasp of a disappearing winter, can catch species unawares, spelling the end for the weak and the young. When unusual events happen across several seasons, or are unusually prolonged, it can spell disaster for entire species populations.

Over the last few years our weather seems to have been even more unpredictable than ever. I have lost count of the number of times I have heard hottest, driest, windiest, wettest.....since records began. During these weather events our wildlife has been seen behaving rather oddly.

In early spring this year there was a very large 'fall' or migrant birds, with especially high numbers of the tiny chiff-chaff. These birds moved north from the continent carried along by warm southerly winds. But on arrival in the UK they were almost immediately confronted by a long period of icy weather. As early spring seemed to revert to mid-winter, the majority of the country was covered in a deep blanket of snow. This left many birds with no choice but to stay put and hunker down. Chiff-chaffs are largely insectivorous and can normally be seen in scrub, hedges and trees gleaning their meals either from leaves or catching flies with practised ease in mid-air. Not so this year. Instead chiff-chaffs could be seen acting out the parts usually played by blackbirds: rummaging around in frosty leaf litter, scraping at soil and even picking insects from the surface of streams. Some managed to cling on in this improvised way before the weather finally warmed and insects began to appear. However, there will have been many chiff-chaff casualties.

The cold weather has also spelled disaster for the chiff-chaffs distant relative, the Dartford warbler. These small birds don't migrate but depend on mature dry heath habitats with dense gorse bushes to provide them with enough insects to help them endure cold winters. Mild winters over the past 20 years have encouraged Dartford warblers to spread and colonise new heath habitats. Often this has meant them moving 'uphill' to the fringes of Devon's moorland heaths at altitudes whose micro-climate were once too cold for them to survive. This colonisation has allowed the bird to increase not only its range but its numbers too.

All was well for the Dartford warbler until the last two winters when long, cold spells returned with dramatic effect. The bird's numbers have crashed and the Dartford warbler's range has shrunk to the lowland heath strongholds it once held. These include Devon Wildlife Trust's Bovey Heathfield nature reserve and the Pebblebed Heaths of the east of the county.

Many other species seem to play a dangerous gambling game with the weather. The key issue is that food availability has to coincide with breeding. This is all about synchronising the life cycle of predator and prey. For great tit families this means having chicks ready to feed when caterpillars are at their most abundant, just after tree bud burst. Leave it too late and caterpillar numbers decline and are harder to spot amongst the luxuriant leaves. Start a family too early or when the weather is too cold and the caterpillars will not yet have emerged and parent birds will struggle to feed their young. If the nest boxes in my garden are any indication, this has been a tough year for great tits - often they can fledge broods as large as 10; but so far my maximum count has been just two young. This is far below the number needed to maintain populations.

And don't make the mistake of thinking that cold weather only affects our land-based wildlife. Our seabirds have also really struggled this year. Hundreds of puffins have been washed up on UK shores, many in an emaciated state. The simple answer to these distressing scenes is that the seas were just too cold for their sand eel prey to prosper.

However, despite the adversity of weird weather, there are still always a few wildlife winners. The marsh fritillary butterfly is just one example. Very cold and bright spring weather is perfect for this endangered species. The small bristly black caterpillars of the butterfly bask on dead leaf litter and are able to feed in tiny warm niches even when the weather remains cold.

The amazing fact is that cold weather actually enables the caterpillars of the marsh fritillary to severe the link with their most fearsome predator - a tiny parasitic wasp. This lays its eggs inside the bodies of the butterfly's caterpillars. The wasp larvae slowly grow and then consume the caterpillars from inside out. Unlike the caterpillars, the wasp is hampered and held back by cold weather. This gives the caterpillar the chance to get a head start and develop unmolested.

Our wildlife has to be resilient and hardy, as befits any temperate species. Their ability to withstand the harshest of weather never ceases to fascinate and amaze. Many populations are able to 'bounce back' from the brink when the weather is more kind. But we can help their resilience by adding just a touch of spring to their recovery just by providing shelter and food in our gardens.

Here are five things that you could do now that would make a difference to help wildlife survive the weirdness of our weather:

  1. Plant at least one nectar rich early flowering plant (white deadnettle, pulmonaria or lungwort are hard to beat, grey willow flowers are adored by bees);
  2. Build a bug hotel - the more rooms the better;
  3. Put up a nest box;
  4. Keep a fresh supply of water available - a saucer is great - a wildlife pond even better;
  5. Provide more than one type of bird food.
  • For more ideas on making your garden a nature haven, go to the wildlife gardening pages of the Devon Wildlife Trust website.
This article is written by Devon Wildlife Trust's Peter Burgess. It first appeared in Wild Devon, the magazine of the Devon Wildlife Trust.

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