Seasonal Update (April 2022)

Lambs are a familiar sight in rural locations as spring advances. - Credit: Marc Baldwin

Meteorological spring started on a chilly and bright note in the north and a mild and wet one in the south. The first week of March was broadly a damp affair in Ireland, Wales and much of England, with the north and Scotland experiencing the lion's share of the sunshine, albeit with temperatures dropping well below freezing overnight.

The first weekend was chilly but mostly dry for all but the far south-east. The second week was more unsettled, particularly for Ireland, northern England and Scotland, which saw wet and windy (gusts to 65 mph) weather for the first half. The second half of the week was more settled, milder for the time of year with temperatures widely in double figure Celsius and the south-east reaching 14C (57F) on the Thursday and Friday, about 4C about the seasonal average.

The second weekend was a wet and windy affair, particularly in the west, as a low-pressure system brought winds touching 70 mph (113 kmph) to Ireland, the West Country, Wales and the northern isles. Temperatures remained mild across the board, widely into low double figures Celsius with overnight lows of 7C to 10C (45-50F). Week three was generally bright and mild, with temperatures into the mid-teens Celsius by mid-week. Once a slow-moving weather front had passed through high pressure settled things down into the weekend, although northern England and Scotland saw some significant rain, and gale force winds battered the northern isles and western Scotland.

Much of the UK basked in early spring sunshine during March, although a keen north or easterly wind was never too far away. - Credit: Marc Baldwin

The end of the third week into the penultimate weekend saw our weather dominated by a huge area of high pressure anchored over Scandinavia. Consequently, most of the UK basked in a spell of settled, dry and warm weather into the final week. It was cooler in the east thanks to an easterly wind from the continent, but unseasonably warm in the west, and particularly in the north-west of Scotland. Temperatures were widely into the high teens Celsius (mid-60s Fahrenheit), and many places recorded 21C (70F) - the seasonal average for mid-March is 10-13C (50-55F) north to south. As the week drew on, we saw more cloud build in, particularly in Ireland and north-west Scotland, but it remained mostly dry and warm. Quite typically for protracted periods of warm, dry weather, pollution levels were high or very high for most of the UK and Ireland come the end of the week.

The final weekend was a similarly summery picture, with a little more cloud building into the east, but as we moved into the final week the high pressure moved away and we saw more cloud and temperatures back down to the seasonal average of the low teens Celsius with some snow and overnight frosts taking us into April.

Outside of the UK, temperature records continued to be set. In late February the town of Uruguaiana in Brazil rose to 42.9C (109.2F), the highest official temperature ever recorded in the Rio Grande do Sul State, although close to the previous record of 42.6C at Alegrete in January 1917. A relentless heatwave continued in India, with no end in sight. The city of Ganganagar in Rajastan beat its March record again on 29th March with 42.2C. Similarly, in Kenya a severe drought caused by climate change is thought to have killed over three-quarters of the country's cattle, jeopardising the region's food security. In the USA, while winter returned to the west and central plains, the heat built further east. Virginia Beach reached a summer-like 28C (83F), while both Pennsylvania and Maryland recorded 26C (79F). Data released by NOAA in February confirmed 2021/22 was the third warmest winter on record, 1.4C (2.5F) above average.

In South America, the autumn equinox started with a cold spell in Argentina, the temperature dropping to a frigid +0.6C (34F) in Mar de Plata, only 0.4C (0.72F) above its March record low. The beach resort had previously recorded its hottest temperature ever on 14 January at 42.4C. At the same time parts of Mexico saw some remarkably low temperatures for late March, with -15C (5F) in La Rosilla, Durango State (at 2,700 m) on the 27th.

Tragically, at least eight people died when heavy rainfall sparked devastating floods in Australia's eastern Queensland state last month. Nearly 2,100 homes and 2,300 businesses were submerged under floodwater in Brisbane, which saw the worst flooding since 2011, and some 15,000 people had to be evacuated in Lismore in New South Wales following heavy rain. A recent report has suggested that record-breaking rainfall and flooding has fostered ideal breeding ground for the surge in Culex mosquitoes that led to outbreaks of Japanese encephalitis virus in Australia.

April is a great month for blossom-hunting; and where there's blossom, there are usually pollinators. - Credit: Marc Baldwin

Mid-March was very warm in Christchurch in New Zealand, temperatures reaching 30C (86F), which is 10C (18F) above average - Dunedin hit 28C (82F), 11C above average. At the same time, we saw remarkable extreme events in both the Arctic and Antarctic, related to the poleward transport of heat and moisture, independently. The result was the Artic and Antarctic being 30C (54F) and 40C (72F) above average, respectively, during the penultimate weekend of March.

If you're interested in getting out and about this month to look for wildlife, check out my April wildlife overview. Additionally, the British Deer Society are running their Deer Distribution Survey and I would strongly encourage readers to record their sightings of wild deer either via the app or by e-mailing the Society directly. Citizen science such as this provides a clearer picture of deer populations around the country, helping improve their management.

In the news

A few of the science and conservation stories that caught my attention over the last few weeks include what the retina can tell us about cognitive decline, the Amazon at tipping point, and a bat-eating spider.

New research suggests that retinal scans can help identify changes in brain volume, sparking hope that we might be able to use it as an early detection of certain age-related brain degenerative disorders, such as dementia. - Credit: Marc Baldwin
  • Window to the brain? In recent years a great deal of research has been directed towards understanding how the brain changes with time, particularly with regards to shrinkage as we age, as part of the battle against dementia. A large new study from researchers at the University Hospital Bonn in Germany suggests that the retina is a potential biomarker for changes in brain structures. The ophthalmologists observed that thinning of the retina was correlated with a reduction in the brain's white matter. Their study indicates that this relatively quick, cheap and non-invasive method can be used to detect and monitor neurodegenerative diseases.
  • Web chat. A cross-university team of researchers in the US have found that some spiders appear to use their webs to increase their hearing capabilities. In a bioRixv preprint, the scientists describe how when they directed sound at the webs of 76 bridge spiders (Larinioides sclopetarius) kept in their labs, their subjects crouched down on the web as if listening. Ordinarily, the spiders were only able to hear loud noises at relatively close range that caused their leg hairs to vibrate. When in their web, however, even small vibrations in the web resonated to the strain-sensitive slit organs on the spiders' legs. The web increased the range of sounds the spiders could hear and even allowed them to differentiate between them, responding differently to sounds from predators and prey.
  • Amazon desertification. The Amazon rainforest appears to be nearing a tipping point that may see it become savannah. More than three-quarters of the world's largest rainforest has become less resilient to drought since the early 2000s, with areas near humans and with lower rainfall being the worst hit.
  • Marvel vs. DC? Originating from the Macaronesian archipelagos off the north African coast, the noble false widow (Steatoda nobilis) has colonised much of Europe in recent years and is now a common addition to Britain and Ireland's arachnid fauna, particularly on the south coast of England. Despite periodic hyperbolic headlines in the tabloids, these spiders pose little danger to us and tend only to bite when provoked. For our other wildlife, however, they are less innocuous, displacing native spider species and recently having been recorded preying on endangered lizards. In July last year, however, one female false widow was found to have caught a pipistrelle pup in her web in Shropshire. The following day, an adult pip was found in her web. This is the first report of Steatoda feeding on a mammal anywhere in the world.
  • Something in the air. Surveying wildlife populations has always been a challenge and while the advent of increasingly cheap and portable camera traps has helped substantially, many obstacles remain. Recently, however, two teams of researchers independently verified a method that allows the identification of species from fragments of their DNA floating in the air. Working on captive collections at Hamerton Zoo in Cambridgeshire and Copenhagen Zoo in Denmark, scientists were able to identify a variety of species in the collections and living wild in the zoos, including mammals, birds, fish, reptiles and amphibians.

Website news

Some minor updates have been made across the site, including a recent video of a hedgehog dropping the bedding material it had been carrying when it catches the scent of a fox, a new vocalisation clip illustrating the mating call of a female grey squirrel, and a video kindly supplied by Shropshire Badger Group showing a badger taking the carcass of a grey squirrel into its sett. I have also been continuing to work on the water deer article, with the breeding section currently in preparation and a new section on the species in captivity went live recently.

Spring is a rather frantic season for male hedgehogs; amorous having been out of hibernation for a while, tensions spill over and fights are not uncommon. Generally, the fights look worse than they are, but they can go on for several minutes. - Credit: Marc Baldwin

Discoveries of the Month

Survival trends in rescued hedgehogs

Most of us know that hedgehogs are in trouble in Britain. The most recent State of Britain's Hedgehogs, published by the British Hedgehog Preservation Society and People's Trust for Endangered Species in February, paints a gloomy picture that points to rural populations having continued in their sharp decline, falling by about 75% in the past 20 years. The situation in urban areas is somewhat better, the data indicating numbers are stabilising and may even be starting to increase. While evidence is lacking, it seems likely that a significant element in this improving picture in urban areas is an increase in awareness among the general public to the plight of hedgehogs and the relentless work of an army of wildlife rescues across the country.

Hedgehogs remain one of the most common species taken to wildlife rescues in the UK, and RSPCA centres take in hundreds each year. Recently, Nicolette Dowler Burroughes, Jonathan Dowler and Guy Burroughes analysed data on hedgehog admissions to the RSPCA's wildlife rescue centres in England across a 13-year period from 2005 to 2017. The data were subjected to a statistical test known as Kaplan-Meier survival analysis, which allows for comparisons between adults, early litter juveniles and late litter juveniles, as well as a limited view of relationships between the reason for admission and survival probability.

Hedgehogs are among the most common wildlife species brought to rescues, and a recent study of admissions to RSPCA Wildlife Rescue Centres across the country shows that more are being successfully rehabilitated than ever before. - Credit: Marc Baldwin

The huge dataset consisted of just over 13,900 animals, including 6,800 adults and 7,000 juveniles; juveniles were divided up between early and late litters. Admission of early litters showed a narrow peak between June and August and a much broader peak from September into December, while the admission of adults increased gradually from around March. Admissions to the centres had more than doubled, from just shy of 700 in 2005 to nearly 1,500 in 2017. Admission weights didn't change over the course of the study data, the average adult weight being 452g (16 oz.), although it was interesting to note that early litters had significantly lower weights than late litter admissions: 126g (4.5 oz.) and 181g (6.4 oz.), respectively. Presumably, nests being disturbed during the summer when people were gardening explains the hoglets being admitted at lower weights, while “autumn orphan” hoglets are more likely to be found once they're independent and hence larger.

Writing in the Proceedings of the Zoological Society, Kolkata, rather curiously an Indian zoology journal, the researchers note that the overall survival of admitted hedgehogs increased by just over 2% per year, with successful rehabilitations up by 26% at the end of the study, and that survival of juveniles was even higher, having increased by 36% come 2017. Given that the proportion of early/late litters and dead/moribund animals admitted hadn't changed, it is suggested that the improved survival reflects improvement in hedgehog care at the centres. Other overall trends in the data include early litter hoglets having higher survival chances than late litter admissions:

In our study, survival was greater in early litters than in late litters and adults. Orphan admissions were commoner in early than late litters (77% versus 23%), malnutrition admissions commoner in late than early litters (42% versus 4%) and commoner still in adults 53%. Late litter animals have to sustain a higher growth rate than early litters with a diminishing food supply, and thus being perhaps in a less healthy condition than orphans, be less likely to survive.”

Reference: Dowler Burroughes, N. et al. (2021). Admission and survival trends in hedgehogs admitted to RSPCA Wildlife Rehabilitation Centres. Proc. Zool. Soc. 74(2): 198-204. doi: 10.1007/s12595-021-00363-9.

While the cat's away. Declines in white sharks drives changes in fur seal behaviour

Food web is the name given to a complex interconnection of species within a habitat; these interactions serve to shape not only the habitat itself, but also the population, distribution and behaviour of the species within it. Predators in these webs play a particularly important role, influencing them through both direct mortality (i.e., killing/eating) of other species sharing the web and at a more subtle genetic level. Indeed, we know that predators affect not only the behaviour but also the morphology, physiology and even life history traits of the species on which they prey.

Prey species respond to predators in several ways based largely on whether the risk is predictable or not. Where prey knows the risk of predation is high, they tend to opt for safety over food, while the reverse is true where risk is perceived to be low. When a predator is removed from, or its number significantly reduced within, an ecosystem we call this “predator release”, because prey is released from predator-induced stress. Predator release can have wide-ranging impacts both within the ecosystem and outside of it.

In the absence of white shark predation, cape fur seal populations are less stressed and groups raft further offshore and over deeper water. - Credit: Simon Cast (CC BY-NC 2.0)

Decades of fishing and targeted hunting, both for sport and in response to shark attacks on humans, have resulted in a decline in the population of great white sharks (Carcharodon carcharias), arguably the world's largest macropredatory “fish”* species. Given that white sharks feed on a wide variety of species, their loss from food webs has the potential to generate a significant predator release. One group of animals that great whites are renowned for predating is pinnipeds, seals and sea lions, and off the South African coast cape fur seals (Arctocephalus pusillus) in particular. For just over 20 years scientists have been monitoring the shark-seal interactions around the appropriately named Seal Island in False Bay, where some 60,000 fur seals live and breed and where white sharks have declined precipitously since 2015, with no sightings at the island since August 2018.

Recently, a group of researchers monitoring the seals assessed the stress levels in the colony by looking at the faecal glucocorticoid concentrations (fGCMs) - levels of stress hormones present in the seals' droppings. Faecal samples collected before the 2015 decline were compared with those taken in 2016, 2017 and 2019. The data, published in Biology Letters recently, suggest that the levels of stress hormones dropped significantly after the white sharks disappeared, the annual mean fGCM concentration being between two and six times higher while the sharks were around. In conjunction with the lower stress hormone concentrations, the researchers note that the seals were also rafting (i.e., floating around in social groups) further from shore and over deeper water, a behaviour that would previously have left them vulnerable to sharks. In their paper, the team point out:

Chronic glucocorticoid secretion has been found to negatively impact reproduction and survival. Indeed, previous research has revealed that acute and chronic physiological stress experienced by fur seals can result in death. Therefore, the drop in fGCM levels and changes in behaviour may have positive fitness consequences, which could in turn have consequences for their population dynamics ...”

Reference: Hammerschlag, N. et al. (2022). Loss of an apex predator in the wild induces physiological and behavioural changes in prey. Biol. Lett. 18: 20210476. doi: 10.1098/rsbl.2021.0476.

* Fish is in inverted commas because, despite being a widely used term, it is not a biologically valid one.

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