Warm and wet year brings influx of migrants with mixed fortunes for resident species

Press release
Two painted lady butterflies
Published : 27 Dec 2019

This year’s changeable weather has resulted in an influx of migrant species with mixed fortunes for resident wildlife, says the National Trust.

The ‘stop-start’ spring, with temperatures warming then plummeting in February and March, before warming again, brought migrant species such as butterflies to our shores.

But the changeable summer, with short, sharp rain storms, proved to be challenging for some wildlife, including water voles, puffins and terns.

The end of the year was warm and wet, with few cold spells, but more deluges of rain particularly in November resulted in flooding in many parts of the country. 

Success for migrants

Warm spells of weather in the early half of the year saw migrant species of butterflies, moths and dragonflies from the south and east arrive in the UK. 

Significant numbers of painted lady (Vanessa cardui) butterflies were seen arriving en masse for the first time in a decade.

This 5-7cm orange and black spotted butterfly is commonly seen in the UK but the last mass arrival was in 2008.  This year’s influx, with over 420,000 recorded appeared to be countrywide particularly in the North East, Lake District, Northern Ireland and South West.

In August, an exotic migrant from the Mediterranean, the long tailed blue butterfly (Lampides boeticus) set new records with 50 seen across the south coast of England, mating and laying eggs.  It was the third time in the last six years that numbers of this delicate butterfly appear to be increasing, although successive generations haven’t yet made it through a British winter.

A rare moth was also recorded at Killerton in Devon – the Clifden nonpareil (Catocala fraxini). As the largest underwing moth to be found in the UK with a uniquely blue ‘underwing’, it became extinct as a resident in the UK in the 1960s, but over the last few years it has been trying to re-establish itself.  Many more have been spotted in the south of the country, with numbers at their highest for at least 25 years. 

June, July and October also saw high numbers of migrant dragonflies including the red-veined darter and vagrant emperor. 

Rare, vagrant birds were also seen in the summer.  A brown booby, usually at home in the Caribbean, or around Venezuela, was spotted for the first time in Kent and two were seen in different parts of Cornwall for the first time ever in August.

And, this autumn, birds including the American black tern at Longham lakes Dorset and a red eyed vireo, a small songbird, on the Lizard were seen, probably due to low pressure systems driving them off-course on their journey down the eastern seaboard of the USA.

Ben McCarthy, head of nature conservation and restoration ecology said: “Sightings of migrant insects and birds are becoming more common.  This is a result of our changing climate.  Although this can seem exciting, the obvious flipside is how these changes will start to affect some of our native species already under pressure from intensive land use, habitat fragmentation and climate change.

“More mobile species might be able to escape unfavourable conditions, but they’d have to find similar conditions elsewhere. The biggest threat is to less mobile species and those that are specialists. 

“This brings home the importance of doing all we can to ensure that we protect our remaining habitats and ensure they are in good condition to support our threatened species.

“By improving the condition of our remaining habitats and increasing patch size it is easier for species to move across landscapes in response to our changing environments.  It also means that when they arrive in their new location there is habitat to support them.

“If our wildlife doesn’t have anywhere to move to as temperatures rise and the weather changes, over the coming years we will inevitably see more and more species at risk of becoming extinct.”

Resident species that did well

Farmland birds such as starling, skylark and lapwing are one of the fastest declining groups of birds in the UK and particularly vulnerable over the winter due to a loss of feeding habitats.  However, this year the National Trust’s ranger team in Pembrokeshire recorded 64 different species and 23,000 birds in their first winter bird survey.

Working closely with nine tenanted and licenced farms in North Pembrokeshire, the team encouraged changes to farmland management to help nature. 

Measures taken included resting fields, leaving some fields or margins unsprayed, sowing wild bird cover crops and improving grasslands for wildlife.  The results highlighted the importance of low input mixed farming systems which incorporate spring sown cereals with winter stubbles and provide farmland birds with a vital food source through the winter.

Sandwich terns did well at Blakeney Point in Norfolk with numbers increasing seven-fold from 120 to 820 pairs due to a healthy stock of sand eels and small fish in the area.  The bulk of North Norfolk’s population of Sandwich terns – over 3,500 pairs nest on Scolt Head – and the North Norfolk coast is home to about a third of the UK’s population. 

Little terns, a species of birds in decline in the UK, also did well on this stretch of coastline, up on last year with 108 pairs nesting and 78 chicks fledging.  Last year no chicks fledged due to heavy kestrel predation which was due to the lack of voles for kestrels to feed on.  But this year, field vole numbers recovered and the rangers supplemental feeding of the kestrels both helped to protect the little tern.

Light-bellied Brent geese arrived back to Strangford Lough in Northern Ireland this autumn after a very successful breeding season in the East Canadian High Arctic.  Strangford Lough supports over 75 per cent of the total population in the early autumn, where its extensive eel grass beds provide essential food after an arduous migration.

Of the 20,950 counted on the official census date on 11 October, 23.5 per cent were recorded as juveniles.  Brent geese tend to have a run of a few years with poor productivity interspersed with the occasional good year, in 2018 for example, productivity was just 1.8 per cent.
Healthy numbers of late dragonflies such as emperor, common hawker and beautiful demoiselle were also spotted.

The southern migrant hawker dragonfly (first bred in the UK in 2010) consolidated their numbers, possibly also colonising in Dorset and Yorkshire.

The small red-eyed damselfly (first recorded in the UK in 1999) made it north to Lancashire.
Grey seals around the UK shores also appear to be thriving with numbers up again this year, despite the high 50 per cent mortality rate of seal pups at National Trust locations (final results pending) including the Farne Islands, Blakeney Point in Norfolk, Strangford Lough in Northern Ireland and Marloes Peninsula in Pembrokeshire. 

Certain wildflowers, especially orchids did well, possibly due to last year’s drought.  There were record numbers of flowering orchids of a few notable species; the bee orchid, dark-red helleborine, autumn lady’s tresses and green-winged orchid were spotted across South East Cumbria and Morecambe Bay.  Arnside and Silverdale, an area of 395 hectares, (976 acres) is home to about half of all the UK’s species of flowering plants. 

Mr McCarthy continued: “The flowering of these beautiful orchids, could all be down to the after effects of last summer.

“This is because last year’s drought would have burnt off shallow-soiled limestone grassland and reduced competition from grasses, allowing the orchids to flourish under this spring and summer’s strong growing conditions.”

The weather pattern of the past two years also resulted in a ‘mast’ year, ie a bumper year, for seeds and berries across all species.  The combination of the milder winter and warm, wet spring meant there were good conditions for pollination.  Last year’s extreme weather may also have stressed the trees – and this combined with this year’s ideal conditions appears to have triggered the trees to produce more flowers, resulting in more fruit.

How the weather affected wildlife

The after-effects of last year’s drought caused various issues for wildlife.

The outbreak of fire on Marsden Moor over the Easter weekend which took hold quickly due to dry ground conditions, resulted in catastrophe for wildlife habitats, with 700 hectares destroyed. 

Ground conditions hadn’t yet recovered from last year’s drought, and with a dry start to the year, the vegetation was like a tinder-box, and the fire spready rapidly.

Habitats of mountain hares and rare ground-nesting birds, such as curlew and twite, were destroyed, and years of peat restoration work undone.

Some types of fly didn’t seem to do very well, probably due to the long and hot summer last year which could have dried out the wet ground which their larvae needs. 

Large blue butterfly numbers dropped from their 2018 peak at Collard Hill in Somerset, but numbers were still higher than expected.  Rangers had been concerned that the heat from last year would dry out the ant nests, on which the large blue caterpillars feed before pupation, but it appears not all were affected.  

It was another challenging year for natterjack toads who rely on pools of water in their dune habitat to thrive.  However, many of these dried out in May and June, and as a result spawn and tadpoles were lost from these pools.  Another spawning attempt in August was wiped out due to an exceptionally high spring tide.   

Rangers also recorded the earliest and latest spawning dates for the past decade, perhaps indicating how natterjacks are trying to adapt to the changing climate.

Ash dieback (Hymenoscyphus fraxineus) spread further north and west across the country.  The South Downs was  particularly badly hit, with the rate of infection exacerbated by last year’s drought.

In the White Peak, area of the Peak District, which had started to see signs of the disease, work has started on diversifying the woodland to make the landscape more resilient by planting small leaved lime and field maple, along with some oak, alder, and understorey species like guelder rose, hawthorn and blackthorn.

Heavy periods of rainfall affected many species this year, especially water voles and some seabirds.

Water voles at Malham Tarn in the Yorkshire Dales suffered due to heavy and unexpected rainfall in June, July and September.  Although these mammals are well equipped to deal with flooding, sudden flood events, especially during breeding season, can spell disaster, resulting in the loss of young who are simply too young to be able to swim.

The success of the Sandwich tern at Norfolk was in stark contrast to tern numbers at Strangford Lough in Northern Ireland where numbers of not just Sandwich terns were down; but common and arctic terns as well.  This is thought to be down to last year’s traumatic breeding season when a mixture of storms flooding nests and predators could have put the birds off returning to the Lough.

Arctic terns, puffins, guillemots and shags all suffered losses due to significant rainfall on the Farne Islands in June.

87.4mm of rainfall fell in just 24 hours on 13 June 2019, over three times the average.  It couldn’t have come at a worse time as the chicks and pufflings (baby puffins) were at their most vulnerable. 

The long term moth declines due to habitat degradation and fragmentation continued due to habitat loss, higher instances of poor flying conditions, ie wet and cold conditions, and nitrogen enrichment in host plants for moth caterpillars increasing mortality. However, several new species were recorded for the first time in Northern Ireland and Ireland. This indicates a combination of an expanding range of species due to shifting weather patterns and climate change.

The warm and wet conditions have also resulted in a big year for grass growth – which could have a negative effect on pollinators.  “Year round grass growth sounds like a positive thing on the face of it, especially for farmers, who can leave grazing animals out for longer.  However, this can lead to other problems such as soil compaction.

“It could lead to more coarse grasses outcompeting native wildflowers – which in turn will affect our pollinators.

“This combined with the increasing amount of nitrogen in the environment could have an even bigger effect on nature.  This is because many of our native species like open ground conditions, with some such as Mossy Stonecrop and Upright Clover relying on the summer drought to kill off or at least hinder vegetation.

“The extended grass growing season also has consequences for gardeners and contractors that mow to manage grass.  They are having to mow when traditionally the mowers would be locked away for the winter,” concluded Ben.

This year’s weather in more detail

This year has been a year of more ‘normal’, changeable, westerly dominated weather, in contrast to 2018. 

Overall, 2019 will probably end up being slightly warmer overall than last year – but, unlike 2018, there were no heatwaves or droughts.  However, extreme temperatures were still recorded with the lowest temperatures recorded at Braemer, Aberdeenshire on 1 February of -15.4 degrees centigrade, contrasted with the highest temperature ever recorded in the UK of 38.7 degrees centigrade at Cambridge University Botanic Garden on 25 July.

There was a bit of a stop/start for spring thanks to a dry January and February, a very wet March before a warmer spell in April. 

Summer was slightly warmer but much wetter than average with a series of big downpours and wet periods resulting in flooding including in July, August and September.

Autumn was wet and windy.  The Met office confirmed 109% of average monthly rainfall in October and 97% in November although the volume of rain was more than twice the average in some places, with a month’s worth of rain in just 24 hours, leading to devastation, particularly for farmers across the Midlands, Lincolnshire and some parts of north-east England.

Keith Jones, climate change expert at the National Trust said: “This year’s changeable weather is a symptom of the warming climate.  The more our temperatures go up – the more erratic our weather will become.

“This will force changes to the lifecycles of many species as food webs are knocked out of sync. 

“As we are seeing in the Farne Islands, the generalists (grey seals) are more resilient in the short term but ultimately they might end up forcing the specialist (eg puffins) to move or suffer. 

“Climate change could also lead to a mismatch between breeding birds and their prey in some cases, with pied flycatcher and golden plover two species which are thought to be vulnerable.

“Like all conservation organisations, we are working hard to protect and care for habitats, and everyone has a part to play in the battle against climate change.”