Seasonal Update - September 2018


To nobody’s surprise, the official stats released by the Met Office report the summer just gone has joined the elite club of the “warmest summers since 1910”. The average temperatures for the summers – the mean temperature over June, July and August – of 2003, 2006 and 2018 are all within 0.03C of one another, too close really to identify a “winner”. The average temperature for the summer was 15.8C (60.4F), and taking England alone, the average was 17.2C (63F). The highest temperature recorded was 32.6C (90.7F) in Porthmadog, Wales, during June, although this doesn’t beat the 38.5 °C recorded at Brogdale, near Faversham in Kent, during August 2003. Granted, some readers may look at these figures and wonder what all the fuss is about, their summers being routinely hotter. The average temperature in England was almost 3C (5F) above the expected summer average and brought with it much less rain than was anticipated, resulting in widespread crop failures and water shortages.

Britain saw some respite from the heatwave that’s had most of western Europe in its grip since mid-May. A deep area of low pressure moved across the UK on the final weekend of July, bringing some much-needed rain and some not-so-welcome gale-force winds. This was a passing “blip”, though, and high pressure quickly built back in, drawing very warm air from northern Europe. The result was that the south-east of the country saw temperatures back up into the low 30s Celsius by the first weekend of last month. There was, however, a north-west/south-east split, with much of the midlands, northern England and Scotland drawing in cooler air from the north Atlantic, resulting in temperatures in the low 20s Celsius for the first week of August.

After a promising start to the month, things turned more autumnal in the second week, with some spells of heavy rain and temperatures failing to climb out of the teens Celsius. High pressure returned for the final weekend, however, and most of Britain was basking in sunshine for the start of September. The long range models are currently predicting a north-west/south-east split in the weather for the month ahead, with prolonged warm and dry conditions in the south while a series of low pressure systems will bring more in the way of wind and rain to the north. At the time of writing, the Met Office are forecasting that:

Daytime temperatures are expected to be above average overall, with some warm days across the south and east at the start of the period, and with the warmer weather spreading further north and west at times.

Our deer species are very sensitive to temperature, and it will be interesting to see what happens to the deer rut, which normally kicks off this month among our red, sika and fallow deer. If the weather warms up and stays warm, the breeding season may be postponed for those animals in the south of England. We may also see more activity from our hibernators, with bats and hedgehogs active longer into the autumn.

Normally, in a monthly update, I’d run down the seasonal wildlife highlights, but I’m in the process of migrating all of these to a new home on the site – more to follow. In the meantime, there is one point that I particularly wanted to raise this month, as it offers and important opportunity to help with some great citizen science. Our tawny owls are very vocal at the moment. This species makes the familiar “twit-twoo” Shakespeare wrote about and that many of us lie awake at night listening to at this time of year. This call is actually two different calls made by male and female birds – it’s a courtship duet that also serves to proclaim territory ownership. Indeed, the female makes a loud, sharp “keewick” (twit) and the male responds with a deep, resonating “hoo-hoooo” (twoo).

Kee-wick call of female Tawny owl (Strix aluco). - Credit: Marc Baldwin

Hoo-hoooo call of male Tawny owl (Strix aluco) - Credit: Marc Baldwin

Hoo-hooo call of female Tawny owl (Strix aluco). Note this is more "warbly" in nature than that of the male. - Credit: Marc Baldwin

If you can spare a small amount of time between now and the middle of next month, the British Trust for Ornithology are looking for volunteers to help survey tawny owls in their local area. The process is very simple and involves making a couple of trips out to an allocated square after dusk to listen for calling owls and submit the results via the BTO’s website. Full details and a list of unallocated sites can be found here. If there’s an unallocated square near you and you can spare the time, I very much encourage you to get involved.

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 are looking for people to organise cleans of their local beaches – details here. The Forestry Commission are running a series of events this month (full list here).

Discoveries of the Month

Foxes help keep ticks in check

Many of us will have heard of a disease known as “Lyme”, particularly after a series of high profile cases that struck celebrities including Avril Lavigne, Matt Dawson, George W. Bush and Kris Kristofferson. The latter of these nicely illustrates the problems associated with diagnosis of the condition, because doctors initially misdiagnosed Kristofferson with Alzheimer’s and it was only several years later that a blood test confirmed he in fact had Lyme disease, which can mimic some of the symptoms of dementia. Recently, there have been several campaigns to raise awareness of the condition, although many GPs still expect the traditional “bulls-eye rash”, despite the Centre for Disease Control in the US pointing out that between 25% and 50% of people never develop one. (More information on the disease and its symptoms can be found on the NHS’s website.)

The tick Ixodes ricinus, implicated in the spread of Lyme disease, an infection caused by Borrelia bacteria. - Credit: Ryszard

Lyme disease, named after the US towns of Lyme and Old Lyme in which a cluster of cases occurred in 1975, is caused by bacteria of the genus Borrelia and thought to affect 300,000 people in the US and 65,000 in Europe every year, although this appears to be a significant under estimate. Moreover, in the UK, cases of Lyme have been increasing in the last few years, up from 268 in 2001 to 959 in 2011, with the NHS estimating that the true number could approach 3,000 cases per year in England and Wales.

The Borrelia bacteria are transmitted primarily by ticks, small arachnids (relative of the spiders and mites) of the Ixodes genus – in Europe, it is primarily Ixodes ricinus, while Ixodes scapularis is the primary vector in North America. Scientists have suggested that the recent “boom” in tick populations in Britain is largely a response to climate change, with milder, wetter winters allowing more ticks to survive to the following spring. Recent research in The Netherlands, however, suggests that the picture is more complicated than just a changing climate, and that predators may play an important role in helping to control tick numbers.

Between 2013 and 2014, a team led by Tim Hofmeester at the Wageningen University and Research Centre used trail cameras to monitor predator activity in 19 forests in The Netherlands. The researchers also live-trapped rodents to assess both the number of rodents at the survey sites and their tick burden and calculated the incidence of Lyme prevalence based on sampling of the ticks. Ticks moult through three life stages (larval, nymph and adult); as larvae they feed primarily on small rodents and birds, parasitizing larger mammals (foxes, deer, badgers, hedgehogs, etc.) once they’ve moulted into nymphs and subsequently adults. Lyme infection prevalence in ticks tends to increase with the number of meals a tick has had such that larvae often have a lower infection prevalence than nymphs, which have a lower infection prevalence than adults.

Voles are common prey of foxes and this study suggests that more foxes means either fewer voles for tick larvae to feed on or a change in vole behaviour that makes them less susceptible to picking up ticks. - Credit: Tony McLean

The results of the study, published in the Proceedings of the Royal Society last year, reveal that the larval tick burden on both bank voles and wood mice decreased with increasing fox and stone marten activity. Similarly, a negative trend was observed in nymphal burden on wood mice and fox activity – i.e. wood mice carried fewer nymphs where foxes were prevalent. Hofmeester and his colleague explain:

We suggest two other mechanisms that might explain the negative correlation between predator activity and larval burden on bank voles and wood mice. First, bank voles and wood mice can become less active in areas with more cues of predator presence, reducing their encounter rate with ticks and therefore tick burden. Second, those animals that do move more and therefore acquire more ticks might also have a higher risk of being predated, leading to a selective predation on highly infested animals.”

There are some inherent problems associated with trying to link cause and effect in biological systems, not least that climate change and natural dynamics of rodent populations have an influence that is difficult, if not impossible, to tease apart from that applied by predators. Nonetheless, this study provides the first empirical support for a link between the activity of predators, the density of questing nymphs and the density of infected nymphs for tick-borne disease. It also ties in well with tentative theoretical models that suggest an increase in coyote spread, and the associated decrease in fox abundance, in North America correlates with an increase in Lyme disease outbreaks. The researchers conclude their paper by suggesting:

The emergence of cascading effects of predator activity on tickborne disease risk calls for the appreciation and protection of predator species such as red fox, many of which are persecuted across Europe.

Source: Hofmeester, T.R. et al. (2017). Cascading effects of predator activity on tick-borne disease risk. Proc. Roy. Soc. 284: 20170453.

Fickle flight. Blackbirds are more approachable in summer and on very cold days

Most of us have birds visiting our gardens and many will have observed how they often scatter when we open the back door. Some may have a few “tame” individuals, particularly robins and starlings, that may let us get “up close and personal” with them and even take food from our hands. We’ve long known that flight distance – how close an animal will allow you to approach before running/flying/swimming away – varies with the level of disturbance in many species. In other words, lots of species get used to the comings and goings of people and learn to ignore them, fleeing only if people get very close to them.

A male blackbird (Turdus merula). Blackbirds are one of the most familiar British birds and a common site in urban and rural gardens. - Credit: Marc Baldwin

Foxes are a perfect example of this reduced flight distance, and we often see complaints about them being “brazen” or “just standing there” rather than running away. We notice it most in species such as foxes because it makes many of us uneasy (lots of people still think wild animals should run from people), but it’s also common in birds. Recently, however, a Cambridgeshire-based biologist renowned for his studies on Chinese water deer and Reeves muntjac published his studies on how the flight distance of blackbirds (Turdus merula) in his garden varied with season.

In his Cambridgeshire garden, which covered about an acre and included a variety of shrubs and trees, Arnold Cooke started his study in January and studied birds on the ground or in the tree up to a height of 3m (10ft). Arnold walked directly and openly up to the bird and recorded how close he got before they flew away, to the nearest metre (3ft). Based on some 4,000 observations recorded over five years, Arnold found that the average flight distance was lowest during June (the last full month of the breeding season), while the blackbirds were most nervous during September, when they’re approaching the end of their annual moult. The average flight distance then decreased progressively until February. Youngsters were also more approachable than adults. In his paper to the British Naturalists' Association’s journal Country-Side last year, Arnold concluded:

“... blackbirds in the study were most approachable in summer when feeding young and on cold days in winter. In both cases, enhanced approachability was caused not by decreased vulnerability [to predators], but by a trade-off between increasing exposure to risk and increasing the chance of survival of their young or themselves.

A female blackbird (Turdus merula) hunting for worms for her chicks. Arnold Cooke observed that as soon as the adults had finished feeding their last brood, they became increasingly reclusive as they began their moult. - Credit: Marc Baldwin

As soon as the adults had finished feeding their last brood they became increasingly reclusive as they began their moult. This, Arnold suggests, means that small open gardens may be less attractive to blackbirds at this time and may explain why people often report their residents vanishing at the end of the summer. In mid-winter, flight distance was significantly reduced by very cold weather. Blackbirds needed more food during these cold conditions but also have less time to find it, meaning they can’t be as “jumpy” as this wastes precious foraging time. This decrease in flight distance decreased down to 2C (35F), though, suggesting there is a limit to how approachable birds will become.

Source: Cooke, A. (2017). Seasonal changes in the flight distance of blackbirds (Turdus merula). Country-Side. 34(6): 21-24.

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