November gets its name from the Latin novem meaning “nine”, as it was the ninth month in the calendar of Romulus around 750 BC. November retained its name when we switched to the Roman calendar and January and February were added. This month marks the close of autumn, meteorologically speaking, and probably the most impressive one for colour change, particularly as this autumn has been so mild. This month’s feature looks at the science of leaf colour change.
A mild and wet start to October across much of the country, with several deep lows passing over in the first week that brought heavy rain and strong winds. Temperatures remained in the mid to high teens even overnight in much of England, before a band of rain moving across towards the end of the week brought cooler temperatures in its wake. In Scotland, the last patch of snow, the Sphinx, melted during the first week. Researchers studying snow formation in The Highlands point to this semi-permanent patch having melted only nine times in the past 300 years for which we have data; four of these have been in the past six years (i.e., 2017, 2018, 2021 and 2022).
Bands of wet and windy weather moved across the UK through the middle of last month, and while we did see some cooler temperatures in the north, things remained mild in the south. Indeed, conditions in the south-east remained up in the high teens, peaking around 19C (66F) during the third week, and feeling particularly warm in the sunshine here on the south coast during the penultimate weekend. (The seasonal average for this stage in October is about 16C/61F.) We did have a rash of unusually strong thunderstorms that developed in the English Channel on the penultimate Sunday afternoon and made their way steadily north-eastwards, bringing torrential rain, 60 mph (96 kph) winds and even some hail with them. As a result, there was some localised flooding in Dorset, Hampshire, Sussex and Surrey to see out the weekend. Further north, the rain that started Sunday 23rd for southern England had become widespread across Scotland by the evening. The last week was largely wet and windy, remaining very mild, with night-time temperatures commonly round the daytime highs we would expect for this time of year. Thursday 27th saw temperatures peak at 20C (68F), courtesy of an “African plume”.
Outside the UK, extreme heatwaves resulted in national records being broken in Turkey and Cyprus (both exceeding 41C/106F) and southern China (41C); China’s previous October heat record was only set last year and broken in 12 provinces on 4th of last month. North and South Korea were also gripped by record heat, with both setting new October records early in the month as they exceeded 32C (89.6F). The Yangtze River experienced a “super cooling” event on 2nd October when temperatures dropped from 40C (104F) to 15C (59F) in less than 24 hours. After a much-warmer-than-average October, the Arctic saw some substantial heat anomalies of 20C (36F) above average across the whole of Greenland towards the end of the month. Starting in the south-east, the heat built to cover almost the entire ice sheet. In France, 35 weather stations recorded temperatures of more than 30C (86F) on 16th October, with the 32.6C (90.7F) at Navarrenx taking the new record as the highest late October temperature ever recorded in the country. Similarly, Spain just topped 33C (91.4F) on the same day.
Some general tidying up has been done to the fox territory and hedgehog parasites and diseases sections, and the latest part of the Chinese water deer article, covering activity (Types of Activity and Activity Patterns), has gone live.
News and discoveries
Keeping in step. A new study by researchers at the University of St Andrews and Vienna’s Central European University has revealed that chimpanzees inadvertently synchronise their steps when walking together, a tendency we thought only humans had. The study looked at both male and female chimps, walking together and alone, and observed that in nearly 80% of cases when walking together a step by one walker was followed by the same respective foot of the other walker within less than half a second. In their paper to the journal Cell, the research team suggest that this unintentional synchronisation in steps might be an ancestral trait for humans and chimps.
The smell of stress. Scientists at Queen’s University Belfast studying dog behaviour have suggested that they may be able to smell when we’re stressed. The research team found that when presented with breath samples from non-smoking stressed and unstressed people, four breeds of dog were able to detect the stressed individuals with an average 94% accuracy; some dogs got it right in 97% of cases. The scientists postulate that dogs can detect the volatile organic compounds we release under conditions of stress.
Bee-ing playful? New science on bumblebee (Bombus terrestris) behaviour has suggested they may engage in play. Bees were given access to food that could be reached directly or walking through a collection of randomly placed wooden balls. The bees were filmed rolling the balls between once and 117 times. The rolling of the balls didn’t result in them getting more food, access to mates, or in clearing clutter in the experimental enclosure, and occurred under stress-free conditions—it seemed to have no survival advantage. Rolling these balls without being trained to do so and with no food reward provided was both voluntary and spontaneous, akin to play behaviour in other species.
Funky flippers. Having a sense of rhythm is thought to be one of the last bastions of human inimitability, with even chimps and bonobos needing training to respond to beats. Now, it seems, seals may possess this ability. Scientists studying harbour seals created sequences of their vocalisations that varied rhythmically—i.e., the tempo, pitch and regularity was digitally manipulated. The tracks were then played back to 20 juvenile seals being rehabilitated at the Dutch Sealcentre Pieterburen to see their response. The one-year-olds discriminated between the regular and irregular sequence, those with short versus long notes and those with fast- and slow-paced tempos, all without training or rewards.
Scent subterfuge. Using artificial nests, Finnish biologists established that chemicals could be used to dissuade predators, resulting in a type of non-lethal “chemical camouflage”. The camouflage compound, a mixture of duck grease, duck preen gland oil, and waterfowl odour product used in training of dogs, was spread around the sampling sites near the nests and the areas monitored with trail cameras. The data show that the camouflage compound reduced fox predation by more than two-thirds, although the raccoon dogs in the area weren’t fazed. The suggestion is that the compound masks the smell of the nests, making it more difficult for the foxes to locate them.
Seasonal highlight – colourful corrosion
As winter approaches, the hours and strength of sunlight decrease and trees aren’t able to photosynthesise efficiently, making their leaves a liability both in terms of water loss and structural resistance in face of the strong winds that often accompany autumn and winter. (The “big storm” of 1987 was so devastating to many of our woodlands because it came unseasonably early, when most of the trees still had their leaves.) So, the trees cut their losses. They stop photosynthesis, and a layer of special cork cells called an abscission zone forms at the base of the leaves. The abscission zone cuts off the food and oxygen supply to the leaf, causing it to die. Eventually the cork layer breaks, and the leaf falls to the ground. Before this, though, a couple of things happen.
We know that, on most trees, the leaves are green for the bulk of the year; but there’s actually a bit more to it than that. The vibrant spring greens we see are the result of the dominant pigment in the leaf: chlorophyll. Chlorophyll is a family of related green pigments found quite widely in nature among cyanobacteria, algae and plants, and used by these organisms to trap sunlight. This energy is then used to generate sugars from water and carbon dioxide. Chlorophyll absorbs strongly in the blue and red spectrum, and very little in the green and near-green portion of the spectrum. As a result, these green frequencies are reflected, making the leaves appear green to our eyes.
As the leaf dies, the chlorophyll breaks down and other more stable pigments, present in the leaf all year but hitherto masked by chlorophyll’s dominance, are revealed. Consequently, the massive scale leaf death that we see during the autumn/fall brings the yellow xanthophylls and red/orange carotenoids out before our eyes. In some of our non-native maples, as well as a few natives such as wild cherry and dogwood, we see something even more spectacular. Once about half of the chlorophyll in the leaf has degraded, sunny days and cold, crisp nights trigger a reaction between pesticides, called phenols, that the trees produce, and sugars in the leaf, resulting in the production of pigments known as anthocyanins, which give the leaves a rich dark red or purple colour. In some species, anthocyanins are present in such concentrations that they overpower even the chlorophyll, and the trees remain purple year-round.
Along with the breakdown of the pigments, trees also pump waste products, known as tannins, into their leaves, adding to the brown colour given by the cell walls, before the leaf drops. So, autumn is a kind of “detox” for the tree as well as a shutting down. More than this, though, the fallen leaves are broken down by detritivores, releasing nutrients back into the soil and acting as fertiliser for the tree.
For a round-up of Britain’s seasonal wildlife highlights for November, check out my Wildlife Watching—November blog. As the pannage season continues this month, and has now been extended into early December here in the New Forest owing to the glut of acorns and mast this year, 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.