Seasonal Update - February 2019


As we enter the final month of meteorological winter, the weather continues to be tumultuous. A constant “flip-flopping” between cold and mild weather for most of January has made it difficult to know if it’s winter or spring at times, and we’ve seen some stark contrasts in temperature across the country on the same day. During the final week of January, for example, Aberdeenshire awoke to temperatures touching -9C (16F), while it was a balmy 10C (50F) in the West Country. The Sudden Stratospheric Warming forecasters were predicting for last month materialised in the north Atlantic but, unlike last year when we saw a negative North Atlantic Oscillation (NAO) that draws Arctic air from the east, the Icelandic Low and Azores High have been fluctuating in their strength, resulting in a periodic change from a positive NAO (south westerly mild, wet and windy weather) to a negative one this winter.

A shifting Polar vortex brought parts of the USA to a standstill, with temperatures of -50C or below. - Credit: Can Pac Swire (CC BY-NC 2.0)

Winter has hit parts of Europe hard this year, though, bringing heavy rain, powerful winds and record-breaking snowfall. The Swiss resort of Andermatt-Sedrun recorded a snow depth of 6m (20 ft.) by mid-January – a depth not normally reached until March or April. At least 12 people were killed in the Alpine region last month, several were caught in avalanches, and German and Austrian troops had to be deployed to help dig people out of homes and cars. The huge area of low pressure in the Mediterranean, with snow on its leading edge, was bringing torrential rain to parts of the Aegean, Greece and west into Turkey.

Conditions weren’t much better to the west of Britain either, with some 100 million Americans affected by some form of winter storm warning as a fast moving area of low pressure brought strong winds, heavy snow and freezing temperatures across the continental USA from Missouri to Maine, with Arctic air descending as far south as Florida.

Conversely, on the other side of the globe, Australians have been struggling through one of the hottest summers on record, with temperatures hitting 49C (120F) and five of their warmest days on record experienced last month alone. Meanwhile, heavy rainfall in Asia led to thousands of people having to be evacuated from their homes as floodwater inundated parts of Indonesia. All this aberrant weather comes as the Met Office predict a significant rise in atmospheric carbon dioxide levels this year through a combination of deforestation, a warmer climate retarding vegetative growth and, as British Antarctic Survey scientist Anna Jones told the BBC last month “a function of our continued reliance on fossil fuels”.

While parts of the Northern Hemisphere have suffered the coldest winters for decades, Australia is in the grip of the worst heatwave on record, with temperatures pushing 50C (122F). - Credit: Peter Ostergaard (CC BY-NC 2.0)

Based on my social media newsfeed over the last few months, there is also a significant issue with the difficulty some people, particularly those in power, have differentiating weather (i.e. short-term changes in ambient conditions) from climate (the long-term trends in these conditions). This poses a significant challenge for scientists because it can be difficult to understand how the earth can be warming up, year on year, when you’re digging yourself out of a 15ft snow drift. Similarly, if climate change means you no longer need to shell out for a flight out of the country to get your winter sun or, as Jeremy Clarkson wrote in a column in The Sun many years ago, you can spend more time wearing t-shirts while out hunting rabbits with your son, then it may not seem like any big deal. It is a big deal, though, and for those who struggle with the definitions, I recommend either Weather vs. Climate: Crash Course Kids #28.1 engaging video on the subject or NASA’s more comprehensive description.

As usual, the Wildlife Trusts have a series of nature-themed events up and down the country, as do the RSPB. If you feel like being proactive this month and live near the coast, Surfers Against Sewage is looking for people to organise cleans of their local beaches – details here. The Forestry Commission is running a series of events this month (full list here).

Interested in the wildlife to be found this month? Check out my Wildlife Watching - February page.

Discoveries of the Month

Should rehabilitated hedgehogs be released in winter?

It's increasingly common for people to want to rescue hedgehogs they find in their gardens and, in most cases, this is a genuine life-line for this struggling species. - Credit: Caroline Boxall

Most of us are familiar with the plight of the hedgehog. The species appears to be in steep decline in Britain, the population having fallen by at least 25% in the last decade. At the same time, a growing number of people are trying to make their gardens hedgehog-friendly, and an army of volunteers devote time, money and sanity to caring for sick and injured hogs. Indeed, hedgehogs make up the lion’s share of the roughly 70,000 casualties admitted to wildlife hospitals in Britain every year, with many centres recording a year-on-year increase in admissions.

Invariably, most hogs taken in by carers require some form of medical intervention and many will stay in convalescence during the winter. Overwintering hedgehogs is a drain on a rescue’s resources and most carers believe the animal should be back in the wild ASAP. When to release hedgehogs has, therefore, been a topic of considerable debate for many years. There have always been conflicting views about whether hogs can be released during cold weather when food is scarce. A recent collaborative study between Nottingham Trent University, Brighton University and the RSPCA provides new insight on this question.

The researchers, led by Richard Yarnell at NTU’s School of Animal, Rural and Environmental Sciences, followed the fortunes of 57 hedgehogs over four winters between 2010 and 2014, 34 of which had been rehabilitated by the RSPCA and released into various habitats, from nature reserves to suburbia, during the autumn and winter on nights when air temperatures were 0C (32F) or above. The hedgehogs were fitted with transmitters that allowed the researchers to radio-track them and periodically check their weight and activity.

At the end of the study, almost two-thirds (63%) of the hogs were still alive. Several animals died during the study, typically either killed by cars or badgers, although there was no difference in susceptibility between wild and rehabilitated individuals. Similarly, all hedgehogs lost weight over the winter, but the rehabbed animals were no worse affected than wild animals. Rehabilitated animals also used nests normally. In fact, survival rates of autumn/winter released rehabilitated hedgehogs in this study were higher than those reported in similar studies in the UK, which the researchers speculate may reflect fewer predators (mainly badgers) being active during the autumn and winter. Overall, in their paper to the European Journal of Wildlife Research this month, the team conclude:

Our findings show that rehabilitated animals released in winter have similar survival rates, changes in weight and use a similar number of nests to wild conspecifics over similar time periods, suggesting that healthy hedgehogs can be released throughout winter under favourable conditions without affecting survival rates. This would reduce costs to rehabilitators and free up space for incoming unhealthy hedgehogs in need of rehabilitation, as well as reduce the time hedgehogs are in captivity …”

It's a common misconception that it's "unnatural" for a hedgehog to be out in the snow. Hibernation fluctuates in accordance with changing environmental conditions and is punctuated by frequent bouts of arousal; undisturbed individuals tend to ‘wake up’ on average every seven to 11 days, although some may not do so for several months. During these periods of arousal they may, or may not, leave the hibernaculum. Arousal is particularly likely when temperatures plummet - if the temperature within the hibernaculum drops below 1C the hedgehog risks freezing to death and so will wake up. - Credit: Doug Hounsome

They recommend:

“… hedgehogs should weigh over 600 g, have passed a veterinary health check, are soft-released in areas where the individuals were originally found or suburban areas without main roads and badgers, and during periods of mild weather (> 0 °C) over winter.”

The authors consider that these guidelines, based on their data, offer the highest chance of a rehabilitated hedgehog reintegrating into the wild community.

Reference: Yarnell, R.W. et al. (2019): Should rehabilitated hedgehogs be released in winter? A comparison of survival, nest use and weight change in wild and rescued animals. Eur. J. Wildl. Res. 65:6.

Roe deer lie low when hunters are about

The management of any wild animal population is a complicated and contentious issue, particularly when it’s applied to familiar birds and mammals with which the public has great affinity. The reality is, though, many species require some form of population control by humans in order to protect and manage the hugely altered and large-predator-free landscape of the British Isles. Here in the UK, a major aspect of wildlife management is deer stalking; if deer populations grow too large, woodland vegetation becomes impoverished and this can negatively impact the whole ecosystem.

A Roe deer (Capreolus capreolus) buck in the New Forest. Recent data suggest that this species adapts its behaviour during the hunting season to reduce the risk of encountering a stalker. - Credit: Marc Baldwin

A significant challenge for deer stalkers is that many species quickly adapt to culling, changing their movements and behaviour in response to the disturbance. Fallow (Dama dama) are renowned for their wariness and recent research in the Alps suggests that roe deer (Capreolus capreolus) also adapt their behaviour when hunters are in the forest.

Between 2005 and 2013 a team of biologists, led by Simona Picardi at the University of Rome “La Sapienza”, studied the movements of 32 GPS-collared roe deer in the rugged terrain of the eastern Alps, within Italy's Autonomous Province of Trento. The researchers were particularly interested in the impact that hunting had on the behaviour of the deer, so they looked at the movement rate and home range sizes of male and female roe deer at two protected sites (no hunting allowed) versus two hunting sites, during and outside of the hunting season.

The data show that the deer at the different sites moved around to the same extent until the hunting season arrived. During this period, the bucks and does in the hunted areas moved around much less than those in the neighbouring protected areas. The findings of this study suggest that roe deer learn to view hunters as predators and adapt their behaviour to minimise the risk of being spotted. This, in turn, has implications for management plans and deer surveys. In particular, these data suggest that population monitoring and management techniques from areas with little or no hunting pressure may not be directly applicable to areas where hunting pressure is high.

Reference: Picardi, S. et al. (2019). Movement responses of roe deer to hunting risk. J. Wildl. Man. 83(1): 43-51.

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