Seasonal Update - July 2020


The first day of last month carried on from where May left off, a south-westerly airflow bringing warm, dry and settled conditions to start the meteorological summer. This wasn't to last, though. A mere day later the high pressure shifted and a northerly airflow moved in, courtesy of a deepening area of low pressure to the north east. This dropped temperatures to the mid-teens Celsius (low 60s Fahrenheit), bringing more cloud and some much-needed rain for parts of the country, although the far south-east remained dry. With the rain came unseasonable winds, as there were in May, widely reaching 60 mph across northern England. This persisted for the first half of the month.

Despite a downturn in the UK's temperatures during the second week of last month, mercury within the Arctic Circle hit an astonishing 38C (100F) at Nizhnyaya Pesha in Siberia on 9th June, about 18C (32F) above what we’d normally see at this time of year.

The middle of June saw thunderstorms and more widespread heavy rain, with temperatures back around the seasonal average for about a week before it all changed once more. The penultimate week saw hot and humid Mediterranean air coming up from the near continent, causing daytime temperatures inch into the low 30s Celsius in the south-east for a few days. Indeed, the warmest day of the year so far was recorded at Heathrow Airport on Thursday 25th June, peaking at 33.3C (92F) – hot, but a few degrees shy of the all-time record of 35.6C (96F) set here in Southampton in June 1976.

June and July is the main period when my social media feed fills with photos of balls of tiny yellow spiders. These are orb weaver spiderlings (probably _Araneus diadematus_) and they group together for a few days after hatching before dispersing into surrounding vegetation to set up webs. - Credit: Marc Baldwin

Many people took full advantage of the heatwave, flocking to beaches, particularly those along the south coast, in the final week of the month. An estimated half a million hit the beach at Bournemouth on a single day, sparking fears of a Coronavirus resurgence and forcing the local council to declare a major incident. Perhaps a bigger problem for the environment than the sheer number of people descending in one place was the fact that they left an estimated 31 tons of waste littering the beach and streets in their wake.

Accompanying the heat and humidity were some unusually high UV levels, prompting the Met Office to issue a Level 3 health alert. Ultraviolet (or UV) is one of three broad types of radiation emitted by the sun, and the UV Index (UVI) is the standard measure of how much is penetrating the Earth's atmosphere. It’s this radiation that can cause sunburn. The scale runs from 0 to 11+, with 6 to 7 being high, 8 to 10 very high, and 11+ extremely high. In places on the equator, such as Nairobi, it’s not unusual to see levels of 10 year-round, while 9 and 10 are common in the southern Mediterranean. Here in the UK, by contrast, we see highs of 6 or 7 during our peak of summer during late June. On the 25th June, however, we saw levels hit 8.1 in southern England (Truro, Cornwall), a rare high according to the Met Office. A strong area of high pressure resulting in cloudless skies, reduced levels of UV-scattering pollution, and a reduction in ozone across the northern hemisphere all contributed to this condition.

Finally, low pressure developed to the west of the UK on the last Friday of June, moving across the country and bringing with it Atlantic air, sweeping away the humidity but bringing wind and scattered thundery showers, dropping the temperatures to the mid-teens and low 20s. The current models are suggesting July will continue on a cooler note, with outbreaks of cloud and rain, particularly in the north, but as our climate changes it become more unpredictable.

If you’re interested in the wildlife to be found this month, check out my Wildlife Watching - July page.

In the news

A few headlines making the conservation news this month include a clean power record for Britain, some unfortunate yet anticipated news on our carbon emissions post-lockdown, and some of the worst roads in Europe for roadkill.

A new record was set in June as Britain went two months without burning coal for energy. Hopefully, this is indicative of the future direction of energy generation in the UK. - Credit: Marc Baldwin
  • Fossil fuel free future? A record was set in early June when, in response to plummeting demand for electricity caused by the coronavirus pandemic, the National Grid took several of its power stations off its network – including the last four remaining coal-fired units. The result is that for a record-breaking two months, coal played no part in Britain's energy generation. Perhaps even more impressive is that, so far this year, renewables have generated more electricity in Britain than fossil fuels, another first for us according to a recent article in Carbon Brief.
  • Lockdown emissions rebound. Back in May many of us were celebrating cleaner air and more interactive encounters with wildlife under lockdown conditions imposed in response to the CV-19 pandemic. Some environmental groups dared to hope that this might represent a turning point for efforts to tackle climate change, illustrating just how quickly we could turn things around if we tried. It seems, however, that Greta Thunberg was on the money when she told a BBC interviewer that there would be “no long term climate benefits” from the outbreak. Last month, researchers at the University of East Anglia reported a rebound in carbon emissions now the roads are filling up. In an interview with The Guardian in early June, Professor Corinne Le Quéré noted how “We expected emissions to come back, but that they have done so rapidly is the biggest surprise”.
  • Farming for biodiversity in the Amazon. Early inhabitants of the Amazon basin, some 5,000 years ago, would routinely fertilise the notoriously poor soil with their fire and food remains, generating so-called “dark earth” that had a species composition all of its own and allowed them to grow crops. A major new study along the Amazon River near Tapajós in southern Amazonia by a team of ecologists and archaeologists suggests that this dark earth is continuing to influence the rainforest’s biodiversity even now. Forests growing on dark earth have larger trees, of more species, with more fruit trees and overall more lush vegetation.
  • Wise wasps? We’re familiar with the concept of animals weighing up opponents before deciding whether or not to fight. It’s an important part of the breeding behaviour for a huge range of vertebrates but something that’s often overlooked in invertebrates. Now a new study by researchers at the University of Michigan suggests that paper wasps (Polistes fuscatus) engage in “social eavesdropping” on rivals. The biologists found that wasps learned about opponents by watching them fight and were less aggressive towards those they saw fighting well. This suggests that comparatively simple brain structure doesn’t rule out some forms of adaptive learning.
  • Assessing the toll of roads on wildlife. A staggering 230 million birds and mammals are estimated to be killed on Europe’s roads every year. With densities in Europe among the highest in the world, roads pose a significant threat to wildlife. New research led by scientists at the Centre for Environmental and Marine Studies in Lisbon has identified those species likely to be most significantly impacted by these transport routes, in terms of long-term survival. Those animals with the highest predicted roadkill rates were those which are small, with high population densities, and which reach maturity at an early age. This put squirrels, mole rats, bats and shrews at the top of the mammal list, while blackbirds and grouse ranked highly among the birds. The researchers hope their model will help identify where special mitigation may be needed in road development schemes.

Discoveries of the Month

Wolf presence reduces seed dispersal by small mammals.

Small mammals, such as this wood mouse (_Apodemus sylvaticus_), are important seed dispersers in woodland ecosystems. - Credit: Marc Baldwin

While many may balk at the thought of mice and rats, these smaller members of the Mammalia are vital ecosystem engineers. In other words, they play a pivotal role in helping foster change and renewal within habitats. Not only do they form a prey base for a wide array of other species, they’re also instrumental in the regeneration of woodlands through their hoarding of seeds and nuts.

It’s well known that predators which feed on small mammals can affect both their abundance and distribution, the latter through both direct predation and behavioural changes. What’s less well understood is how these influences ripple across food webs. Now, new research by a team of biologists led by Jennifer Chandler at the University of Wisconsin has provided some interesting insight.

Chandler and her co-workers selected a study site distributed across some 5,000 square kilometres (1.2 million acres) of northern Wisconsin in which they picked 22 50 sq-m (540 ft-sq) plots of maple-dominated forest. Each of the plots was assessed for habitat characteristics that could influence small mammal abundance as well as wolf presence, being classed as either high- or low-wolf-occupancy sites. Finally, they setup some small mammal feeders containing seeds native to the area at each site and recorded how many seeds were taken by which species. The results, currently in press with the journal Ecology & Evolution, show a significant difference in seed removal between the wolf-occupancy sites.

Compared to low-wolf areas, small mammal abundance was 40% lower and seed dispersal just over 25% lower in the high-wolf areas. In essence, fewer small mammals meant fewer seeds taken and cached somewhere in the forest. This is an interesting finding, because wolves are not big predators of small mammals, preferring instead to work together to bring down larger ungulate prey. So why, then, might an abundance of wolves lead to fewer small mammals? The answer, the biologists posit, may lie in the impact wolves have on mesocarnivores. In their paper, Chandler and her team explained:

“… gray wolf (Canis lupus) territories are characterized by relatively less use by coyotes (C. latrans) and greater use by foxes (Vulpes vulpes, Urocyon cinereoargentus) that consume a greater proportion of small mammals, wolf territories may be areas of reduced small-mammal granivory.

A Grey wolf (Canis lupus). - Credit: Marc Baldwin

So, wolves keep coyotes out which boosts fox numbers, and foxes eat more small mammals than coyotes do, thereby reducing seed dispersal potential in these habitats.

Source: Chandler, J.L. et al. (2020). Large-scale patterns of seed removal by small mammals differ between areas of low- versus high-wolf occupancy. Ecol. Evol. Early View. DOI: 10.1002/ece3.6415

City slicking is changing our foxes

I often see a dichotomy in discussions about urban foxes; some maintain that city foxes are giants among foxes, growing fat off the waste of human society, while others consider them weedy and disease-ridden, a poor facsimile of their rural counterparts. Tracking data suggest that foxes often move freely between urban and rural areas and, although some genetic data have implied some breeding separation, how different or similar the two demes are has always been a subject of debate.

Many people assume urban and rural foxes are different animals, but the genetic analysis to-date suggests a reasonable amount of mixing between populations. - Credit: Marc Baldwin

Data from Denmark suggest that some foxes have begun to evolve larger skulls to, paraphrasing the researchers, deal with anthropogenic prey. Some authors took this to mean urban foxes were getting bigger, when in fact it appeared to be the presence of species we humans have introduced, such as hares and pheasants, that triggered the change, rather than kebabs and burgers. Now, data from Britain suggest that our urban foxes may actually be getting smaller.

Kevin Parsons at the University of Glasgow’s Institute of Biodiversity, Animal Health, and Comparative Medicine and his colleagues studied the skulls of 111 red foxes (Vulpes vulpes) collected from London and surrounding boroughs in the early 1970s by Stephen Harris and held in the collection of the National Museums Scotland. The researchers grouped the skulls into either urban or rural animals, based on the location from which they were taken. A total of 55 measurements from each of these skulls were taken to allow comparisons of size and shape between the groups.

The sex of the fox had the largest influence on its size and shape, but, controlling for that, habitat also had a significant impact, with a clear difference between urban and rural individuals. Urban skulls demonstrated a shorter and wider snout, with smaller jaws; the sagittal crest on the top of the skull was longer, but the zygomatic arches and brain case were smaller.

The researchers suggest that urban food is more likely to be accessed in a stationary situation and may require more force to get into, accounting for the shorter snout and potentially stronger bite, while a narrower snout with a faster jaw closing reflex is likely to be vital for rural animals when it comes to catching fast-moving prey such as mice and voles.

While an overall smaller brain case may indicate a smaller brain, something we see during the domestication process, the authors are quick to caution against jumping to conclusions – it could, they suggest, reflect changes in biomechanical forces operating on the skull. Finally, the data suggest that vixens may be better adapted to city living than males, these skull differences being substantially greater in females than males. The theory goes that females, with dependent cubs to tend to, interact more closely with local food resources than males and, in their paper to the Proceedings of the Royal Society, Parsons and his co-workers write:

This may also confer greater cognitive demands in females explaining their relatively enlarged crania. In contrast, male red foxes engage in vigilant behaviours more frequently during periods of parental care and this may involve defensive actions that favour the faster more elongate jaws we observed.”

A recent analysis of fox skulls from urban and rural areas of Britain suggest that urban foxes are evolving shorter jaws, wider nasal passages and smaller brain cases in response to changing feeding behaviour. - Credit: Marc Baldwin

It is certainly interesting that these changes in skull morphometrics are in line with so-called “domestication syndrome” and that foxes may be starting down a similar road to the one taken by wolves some 30 to 40,000 years ago that led to the domestic dogs in about a quarter of Britain’s homes today.

Source: Parsons, K.J. et al. (2020). Skull morphology diverges between urban and rural populations of red foxes mirroring patterns of domestication and macroevolution. Proc. R. Soc. B. 287: 20200763. DOI: 10.1098/rspb.2020.0763

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