Seasonal Update (September 2022)

As autumn arrives and night-time temperatures begin to drop we're more likely to awake to low-lying mist, particularly around water bodies. - Credit: Marc Baldwin

Welcome to autumn - although, despite a few cooler nights, here on the south coast it is still rather more like summer than Keats' “season of mists and mellow fruitfulness”. The heatwave that much of the UK experienced during July and August, and the state of drought still being experienced by most of England and Wales, has meant that many trees dropped their leaves early this year. Additionally, and perhaps an “issue-in-waiting” for birds over the coming autumn and winter, most of the berries I've seen are either late or much smaller/less abundant than normal, presumably reflecting the lack of rain.

Weather update

August started on a wet and windy note for most of Britain and Ireland, with particularly heavy rain in the north and west. In the south, however, the punishing drought continued and the south-east corner, from Dorset into East Anglia, saw no rain at all during the first week. A hosepipe ban was implemented in Hampshire at the start of the month and people were urged to use water sparingly as river, reservoir and groundwater levels remained very low. Bans followed in Surrey, Sussex, Kent, London, Wales and Yorkshire as the month went on, and by the middle of August England was officially in drought. Some rain, even in the south-east, during the middle of the month, did little to ease pressure on water supplies, as temperatures remained above average, and we saw a second Extreme Heat Warning. It did, however, help to dampen down the fire risk a little.

While some species have fruited in abundance following the UK heatwave, in many parts fruit either appeared (and was eaten) earlier than typical and/or smaller owing to the prolonged drought. - Credit: Marc Baldwin

We also saw temperatures up to 29C (84F) in the south-east, so remaining above average, at the start of the week, along with humid nights across the country. A northerly airflow took over into the second weekend, making conditions a little fresher, before temperatures climbed back into the high 20s and low 30s (mid- to high 80s F) into the third week. Much of England and even parts of Ireland saw heatwave conditions during the second week of last month. Temperatures didn't climb as high as they did back in July, but the south-east saw 36C (97F) by the middle weekend, about 10C (18F) above the seasonal average, and most places registered high 20s or low 30s Celsius, with London touching 37C (99F). There were a few days of respite as low pressure brought some cooler weather and showers early in week three before high pressure and heat built again into the penultimate weekend. A month's worth of rain fell in south-east England on the 25th, resulting in some localised flooding before things settled down for the bank holiday weekend.

Outside of the UK, the lack of rainfall has also been an issue across Europe as the EU bloc as a whole experienced its worst drought in 500 years. A river discharge anomaly map produced last month by Dominic Royé, based on reanalysis data from June to mid-August, showed an average negative anomaly of -29%, even reaching -62% at some points. Overall, 45% of the bloc's territory was under drought conditions by the middle of August after weeks of unusually hot and dry weather. In North America things were also hot and dry, but with some sudden very heavy rain. Indeed, Death Valley in California saw the fourth 1-in-1,000-year rain event in less than two weeks when three-quarters of the valley's annual rainfall fell in just three hours. By the last week of August Pakistan had declared a national emergency as around 30% of the country was submerged after unprecedented monsoon rains that followed a punishing heatwave lasting from March to May. Some areas in the south saw eight times the normal August rainfall.

France and Spain remained hot, and Portugal hit 39.1C (102F) at the start of last month, above the monthly average of 34.7C (94.5F). Iraq's heatwave also worsened, impacting some 40 million people as temperatures rose above 50C (122F) during the first half of the month, above wet-bulb temperatures humans can endure. China's 70+ day heatwave, the duration, intensity, scale and impact of which has never been recorded before, saw just over 260 locations break their temperature records. At the other end of the spectrum, South America saw its second blast of Antarctic cold during the third week of August, with temperatures dropping some 10-15C (18-27F) cooler than normal for their winter.

Website news

Some minor updates have been made to the badger diet and activity, fox mortality and hedgehog diet sections, and the latest sections of the Chinese water deer article, covering ectoparasites and miscellaneous disease, have gone live.

Despite many of having seen some rain over the last couple of weeks and it being cooler, most of England and Wales are still suffering drought conditions and leaving a source of fresh water out for wildlife remains a simple way to make a big difference to the species visiting your garden. - Credit: Marc Baldwin

News and discoveries

Rancid rain? A new study published in the American Chemistry Society's journal Environmental Science & Technology last month suggests that the presence of so-called “forever chemical” known as per- and polyfluoroalkyl substances (PFAS) in rainwater now exceeds US guidelines for safe human consumption right across the world. Accumulation of these chemicals, widely used in non-stick and stain resistant coatings, have been linked with increased risk of cancers, fertility issues and developmental problems in children.

Bigger beaks. Using genetic and historical data, a team of British and Dutch zoologists found that some of Britain's common garden birds appear to be evolving longer beaks than their European counterparts. The scientists found that the beaks of great tits have gotten longer since the 1970s compared to those in the Netherlands, perhaps driven by the significantly greater use of bird feeders in the UK versus mainland Europe. Interestingly, the gene sequences that were observed to be changing closely match those that control human face shape.

A female Asian elephant (_Elephas maximus_). Studies on this species in captivity at Whipsnade are helping us better understand how elephants communicate in the wild. - Credit: Marc Baldwin

Eloquent elephants. Keepers at the Zoological Society of London's Whipsnade Zoo in Bedfordshire have started recording their elephants to get a better understanding of how the species behaves. Using a combination of acoustic loggers that can detect audible sounds as well as ultrasonic frequencies and visual assessment by staff, the keepers have identified four distinct sounds: a trumpet, rumble, roar and a chirp, the latter apparently being made by only the Asian species. Trumpets appear to signify play or excitement, roars signal disturbance, and rumbles are inter- and intragroup communications. The hope is that these findings can be applied to wild animals, helping communities better coexist with elephants.

Spider sophistry. It's fair to say spiders aren't everyone's cup of tea and, despite their fascinating biology and behaviour, many people harbour deep-rooted phobias. A recent study in the journal Cell suggests that the media has done little to quell these fears. Researchers reviewed nearly 3,350 articles about spider bites from 81 countries published in 40 languages and found the quality to be poor; almost half (47%) contained errors and 43% were considered sensationalist.

Beaver buffers. Beavers are well-known for tinkering with the hydrology in their environs, but in the face of climate change it seems they can have a role to play in helping manage water resources. Researchers at the University of Washington in Seattle recently found that their relocated beavers not only raised the local water tables by as much as 30 cm (12 inches), but they also cooled the water temperatures by about 2C (3.6F), while control streams without beavers warmed by 0.8C (1.4F). The dams lowered temperatures sufficiently to effectively reverse the increase that's taking streams into the harmful range for salmon during in hot summers.

Seasonal highlight – webs of intrigue

As we move into the chillier nights and mornings of autumn, the dew-laden webs of spiders start to become a prominent feature of gardens, parks and the countryside up and down the country. They are a draw for photographers at this time of year, but spider webs are often overlooked or even an annoyance to many. Even if you're not a big fan of spiders, though, their webs can be both beguiling and fascinating structures.

The sticky coating on the capture thread of a spider's web is hydroscopic (i.e., absorbs water from the atmosphere), causing it to saturate into droplet on dewy mornings in autumn. - Credit: Marc Baldwin

The production of silk webs is perhaps the feature for which spiders are best known. Just over half of the 37 families here in the UK employ silk to build webs, although all of them can produce it and silk production has a long lineage. In a fascinating short paper to Nature in 2003, University of Basel biologist Samuel Zschokke presented photos of a thread of spider silk, complete with glue droplets, trapped in a piece of Lebanese amber that dated to the Early Cretaceous, 130 million years ago.

The chemistry of the silk is fascinating, but a little outside the scope of this summary. Suffice to say, the silk is initially a gloopy protein soup that is extruded through specialised glands associated with outlets on the spider's abdomen called spinnerets. The size of the aperture of the spinnerets, a feature of the spider's biology rather than behaviour, dictates the thickness of the thread, and a spider will typically have several different glands associated with the spinnerets, each producing a distinct and specialised secretion, some involved with web construction and others for making egg sacs and/or encasing prey. Threads used to construct the outer frame of the web have a different chemical composition to those of the radial threads. As the liquid silk is exuded, the stretching as the spider pulls it causes the protein molecules to bond together, solidifying into long chains.

While it may also be a place for courtship and mating, the primary purpose of the web is to capture prey, and it is for this reason that the silk has evolved its remarkable physical properties as the arms race between spiders and their prey has progressed. The capture spiral in the web is produced by the flagelliform gland and its amino acid composition is different from the radial and frame threads, with physical characteristics distinct from either. This thread is also coated with drops of a sticky glycoprotein secretion, deposited from the aggregate gland, that has the job of restraining prey intercepted by the web. This coating is the reason webs are so obvious at this time of year. For this coating to be effective at holding on to prey, it needs to remain moist (i.e., at around 80% water)—if it dries out, it loses its stickiness. To maximise the adhesive potential, therefore, the chemical composition contains several hygroscopic components; those that attract and absorb atmospheric water. On cool and damp mornings, these droplets become bloated and cause the webs to droop.

The molecular composition of the web silk, each of the three threads (radial, frame and capture) having different properties, is such that the resulting structure is both strong and apparently elastic. In fact, it's not actually elastic; even despite sticky droplets, the impact energy of prey is such that an elastic web (one made of rubber, for example) would run the risk of flinging prey back out once it had been stopped—think of bouncing on a trampoline. Instead, the silk has what we call hysteretic properties, which basically means the molecules can realign to dissipate the energy of the colliding prey as heat. When we add in the fact that the impact of the prey is dissipated over a huge area (i.e., the whole surface of the web), yet more impact energy is dissipated by this aerodynamic dampening.

A female wasp spider (_Argiope bruennichi_) in her web. Notice the zig-zag pattern in the lower section of the web. This is called the stabilimentium, as we once thought it served to stabilise the web in windy locations. - Credit: Marc Baldwin

The chemical and mechanical properties of spiders' webs are just the tip of an enthralling metaphorical iceberg. Different species build webs with different layouts and with threads exhibiting different biomechanical properties to entrap different prey. Some species embellish their webs with “designs” that serve to attract prey, even specific species of prey—the increasingly common wasp spider (Argiope bruennichi) is a superb example of this. The designs are often referred to as stabilimentia, the name belying our initial (incorrect) suspicions that they conveyed strength to the web in windy locations. The proportions of the web and where the spider sits varies with experience, while some species even “bait” their webs with chemical cocktails that mimic pheromones of their prey.

Spiders really are fascinating creatures if you can push past the uncomfortable number of legs. As the mid-19th century English proverb goes: If you want to live and thrive, let the spider run alive.

For a round-up of Britain&'s seasonal wildlife highlights for September, check out my Wildlife Watching - September blog. As pannage season starts this month, a reminder that you can also find out everything you ever wanted to know about the ancient tradition in my pigging out on the forest blog.

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