Seasonal Update - December 2018


Weather-wise, November was yet another tumultuous month. Overall it was mild, wet and windy, with a continental airflow for most of the month resulting in temperatures several Celsius higher than expected for this stage in the year.

Last month started cold for most of the country, with -6C (21F) in parts over the first weekend until the remnants of hurricane “Oscar” passed between the UK and Iceland, dragging mild air up from the mid-Atlantic and causing temperatures to rise. Indeed, despite some initial articles in the tabloids suggesting it was going to be the “coldest ever November”, the Atlantic airflow saw temperatures in the first week of the month reach 18.3C (65F) here in Hampshire, some 7C (13F) above the seasonal average. Temperatures soon fell back to about 13C (55F) across much of the country, and a chilly breeze and some very wet weather during the first month didn’t make it feel particularly warm. The west of the country saw the worst of the rain and wind, but hail storms made it as far east as Sussex/Surrey around the middle of the month. Temperatures were also mild across the country, with temperatures of 16C (61F) in Aberdeen during the second week of November; the seasonal average is about 8C (46F).

As our climate continues to change, we're experiencing more unsettled and very windy weather, particularly during the autumn and winter. - Credit: Marc Baldwin

A biting easterly airflow developed for the penultimate week, bringing overnight lows well into minus figures, but the month ended on a mild, wet and windy theme with two deep Atlantic lows sweeping over the country in the last week; the latter saw gusts of 82 mph (132 kph) recorded off the Isle of Wight. At the time of writing, it looks like this mild and wet weather is likely to continue for at least the first half of this month, with warm air sucked up from the Azores, although some models suggest things may settle down as we head towards Christmas. Currently, though, those hoping for a white Christmas look to be largely out of luck.

Interestingly, during the recent spell of cold weather, I’ve heard several comments (particularly on social media) along the lines of ‘how can we be experiencing global warming if it’s colder than expected?’. Indeed, there is a very common misconception that the Earth’s average temperature rising means that it will get hotter everywhere, which is not the case – this is why scientists often use the term “climate change” instead. Whether you believe that climate change is a “natural” phenomenon, is man-made, or is a natural cycle exacerbated by human activity, there can be little doubt the climate is changing. The result of this is not so much that everyone’s warmer now than a decade ago, but rather than our weather is much more changeable; it’s more difficult to predict/model and we see extremes more often.

At the start of November the Met Office released their State of the UK Climate 2017 report, which shows that the UK has experienced more weather extremes in the last decade than any other since records began, suggesting that our climate is changing. The hottest days are now about 1C (1.8F) hotter than in previous decades, while the colder days are, on average 1.7C (3F) milder. “Tropical nights”, the meteorological term for nights during which the temperature stays at or above 20C (68F), also appear increasingly frequent. In the three decades between 1961 and 1990 there were eight of these nights, while the summer just gone saw two alone. Rainfall has also increased; the maximum five-day precipitation having increased from 78mm to 81mm when comparing 1916-1990 to 2008-2017.

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). The British Trust for Ornithology’s tawny owl calling survey is underway now. This survey is much more relaxed than the point survey they ran during September and October. Essentially, all they need you to do is stand in your garden, local allotment, park, wood, etc. for 20 minutes one evening a week and record whether you hear a tawny owl calling. The survey runs until the 31st March next year and the more weeks you can record for the better, but you can do as many or as few as you like; it also doesn’t matter if you miss some weeks. No calling is as valid a result as any other, so even if you’re pretty sure you don’t have tawnies in your neighbourhood I urge you to get involved and submit your findings.

Tawny owls (Strix aluco) are thought to be our most common owl species, but there are still some big gaps in our understanding of their distribution in Britain. The BTO is asking people to take 20 mins out of their evening once a week to listen out for owls calling. - Credit: Marc Baldwin

Finally, I would like to take this opportunity to wish all my readers and their families a very Merry Christmas. Thank you for your company over the last year and your patience while I got the new site up and running. I hope it was worth the wait and I hope 2019 will see a range of new and interesting content appear on here. Have a safe and enjoyable holiday season and I hope to see you back here in the New Year.

Interested in the wildlife to be found during December? Check out my Wildlife Watching - December page.

Discoveries of the Month

Using magnets to keep sharks out of fishing traps

Sharks and rays, collectively known as elasmobranchs, are a widely exploited group of marine vertebrates, impacted by both recreational and commercial fisheries. Many species are targeted deliberately, but many thousands are netted unintentionally when fishing for other species, a phenomenon known as bycatch. It’s difficult to get a handle on how many elasmobranchs are caught as bycatch every year because many are discarded at sea and go unrecorded. Marine conservation charities suggest, however, that as many as 50 million sharks are victimized unintentionally every year. Elasmobranchs are relatively slow-growing animals, maturing late and living longer than other species of bony fishes, making them susceptible to over-fishing; many populations are already classed as threatened. Consequently, a great deal of resource has been directed at trying to increase the specificity of fishing methods and reduce the number of species caught accidentally.

It was in 1917 that researchers working with the brown bullhead (Ameiurus nebulosus), a species of catfish, noticed that they were very sensitive to metallic rods placed in their aquarium. Some 18 years later Sven Dijkgraaf observed that small-spotted catsharks (Scyliorhinus canicula) showed similar sensitivity to a rusty metal rod. In a paper to the journal Naturwissenschaften in 1962, Dijkgraaf and fellow Dutch biologist Adrianus Kalmijn described how blindfolded sharks turned their heads when they were several centimetres from the metal rod, while they didn’t move until the control rod (made of glass) touched them. The conclusion both of the bullhead study and of Dijkgraaf was that the fish were responding to weak electrical currents produced by the corrosion of the metal in the salt water (galvanic currents) that they were detecting with specialist electro-sensory organs on their heads, called the ampullae of Lorenzini. This sparked a new dynamic of repellent research: could sharks be repelled using electric currents underwater?

The snout of a tiger shark (Galeocerdo cuvier) showing the pits (dark dots) of the Ampullae of Lorenzini; the network of electroreceptive and magnetoreceptive pores. This system allows the shark to, at close range, detect the electrical impulses given out by the muscles of all living animals at close range and, we think, navigate using the Earth's magnetic field. - Credit: Albert kok (CC BY-SA 3.0)

Fast-forward nearly six decades and we now know not only that electric fields can be used to keep sharks and people apart, but also that the ampullae don’t just tune into electrical energy – they’re also sensitive to magnetic radiation, which we think allows them to use the Earth’s electromagnetic field to navigate in an otherwise featureless ocean. So, does this mean that magnets can also be used to deter them? The answer, based on new research published in Fisheries Research recently, seems to be yes.

Between December 2013 and August 2014, a team at the University of Newcastle in Australia carried out fieldwork on board two commercial fishing vessels operating an “Ocean Trap and Line Fishery” off the coast of New South Wales. The researchers, led by Rhys Richards, attached ferrite magnet bars to 280 traps to assess what impact they had on the elasmobranchs caught, compared with their control traps. The data show that the use of magnets significantly reduced the numbers of sharks and rays in the traps. Moreover, the placement of the magnets didn't appear to have any impact on the catch of target species – in other words, their use made the fishing traps more efficient and, in their paper, Richards and his team conclude:

“...our results provide a case for the use of permanent magnets in trap fisheries to reduce bycatch of elasmobranchs, but also to increase the catch of marketable products. In this instance, the adoption of ferrite magnets would have a net financial benefit, which would encourage the wider adoption of this technique.”

A "SMART" hook, a particular type of fishing apparatus that combines both an electropositive metal and magnetic alloy on the same hook. - Credit: Scott Grant et al. / PeerJ (CC-BY 4.0)

Interestingly, a slightly different take on the use of magnets to deter sharks from fisheries, the use of Selective Magnetic and Repellent-Treated (SMART) hooks, appears more species-specific. Scott Grant at Canada’s Memorial University of Newfoundland and colleagues recently reported that SMART hooks were ineffective at reducing the bycatch of Greenland sharks (Somniosus microcephalus) by a longline bottom fishery targeting halibut (Reinhardtius hippoglossoides) in Cumberland Sound. In a paper to PeerJ published back in the summer, the researchers wrote:

Not only do our results provide evidence that Greenland sharks are not affected by the SMART hook but also that their powerful and successive suction actions during a feeding event are likely to negate the deterrent effects of the SMART hook technology when initiated beyond the range of the electromagnetic field produced by EPMs and magnets.

In other words, the hooks may not work because the sharks can suck food in from almost 30cm (1 ft.) away, which is substantially further than they can detect the magnetic field from.

Sources: Richards, R.J. et al. (2018). Permanent magnets reduce bycatch of benthic sharks in an ocean trap fishery. Fish. Res. 208: 16-21.

Grant, S.M. et al. (2018). Greenland shark (Somniosus microcephalus) feeding behaviour on static fishing gear, effect of SMART (Selective Magnetic and Repellent-Treated) hook deterrent technology, and factors influencing entanglement in bottom longlines. PeerJ. 6:e4751; DOI 10.7717/peerj.4751.

Noise pollution shapes the distribution of long-eared owls

The state of our environment is increasingly in the spotlight and the term “pollution” is one that we hear a lot these days. When most of us think about pollution, I suspect it conjures images of oil spills, chemical leaks, vehicle exhausts and plastic littering our beaches, but in recent years we’ve come to realise that more subtle aspects of human life can also pollute the environment – in particular, the light and noise we generate. We’ve known for a while now that artificial light in our towns and cities can affect the ecology of various animals, changing the singing behaviour of some garden birds and the hunting behaviour of raptors, the migration of turtles, and the feeding behaviour of bats.

Many of us are used to the hustle and bustle of our towns and cities and often forget that these are inherently noisy environments. Such noise pollution can affect a profound impact on the natural history of many animals. - Credit: Punchup (CC BY-NC-ND 2.0)

The impact of noise generated as a result of human activities, or “noise pollution”, is relatively less well understood, although we do know it can change animal behaviour. A study by researchers at Sheffield University, for example, found that daytime noise was a better predictor of nocturnal singing in robins than artificial light intensity, suggesting that it’s not the building and street lights that are tricking them into thinking it’s dawn. Similarly, in 2013, researchers at Queens University Belfast found that, as noise levels increased, male robins were more likely to move away and change their songs – the louder the noise, the less elaborate the robin’s song. So, living in towns affects the singing behaviour of this species, both in its timing and the complexity of the song. Back in May I also reported on research suggesting that road noise stressed out roe deer, affecting their cortisol levels. New research from southern Poland suggests some owls might also be displaced by noise, which has the potential to alter the local food web as well as affecting the conservation status of this species.

During 2015 and 2016, Arkadiusz Fröhlich and Michał Ciach at the Institute of Forest Ecology and Silviculture in Poland surveyed 79 randomly-selected sample sites in and around the city of Kraków for signs of long-eared owl (Asio otus) presence in relation to various environmental variables, including how close they were to roads and footpaths, the degree of habitat fragmentation, and how noisy the site was. The data give an insight into the habitat preferences of this rarely-seen owl.

Multivariate analysis of the data showed that the owls predominantly selected areas with open grassland in which to hunt, preferring this habitat type over parks, arable land, or woodland. Of particular note, however, was that the likelihood of finding owls in suitable grassland habitat was significantly reduced in noisy areas. The owls also appeared to shun otherwise suitable nest sites if they were noisy. A facet of owl biology is that owlets branch before they’re fully fledged – this means they scatter among nearby trees and use begging calls to guide their food-bearing parents to them. The researchers suggest that high levels of environmental noise may reduce the adults’ ability to locate the owlets. Furthermore, noise pollution could reduce the effectiveness of communication between family members and, theoretically at least, weaken family bonds and lower reproductive output. Continuous noise might also impair the ability of owlets to learn how to hunt, a skill that depends on their ability to hear their prey at a distance.

In their paper to Current Zoology last month, Fröhlich and Ciach conclude:

Our results suggest that the probability of long-eared owls occurring at a site is determined mainly by the area of grassland, this owl’s preferred foraging habitat, but also by nocturnal noise emissions, which may reduce hunting efficiency. This study adds to the growing body of evidence that noise has a negative impact on owl assemblages and highlights the importance of appropriate farmland management, that is, the maintenance of large grassland patches and the suppression of noise within them.

Long-eared owls (Asio otus) are shy birds and appear to be displaced by other owl species, such as tawny owls. Noise pollution may further limit the habitat available to them. - Credit: Sue Cro

Source: Fröhlich, A. & Ciach, M. (2018). Noise shapes the distribution pattern of an acoustic predator. Current Zool. 64(5): 575-583.

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