Seasonal Update (January 2023)

Happy New Year to all my readers. I hope 2023 is prosperous and as peaceful (or raucous) as you wish it to be. - Credit: Marc Baldwin

In the bleak midwinter; Frosty wind made moan; Earth stood hard as iron; Water like a stone. Familiar words from the poem written by Christina Rossetti, published in A Christmas Carol this month in 1872. January is, meteorologically speaking, midwinter, and often the month that we tend to see more in the way of frost, ice and snow, although after the December just gone (see below) it looks more tropical than normal. On average, here in the northern hemisphere, January is the coldest month of the year, but also the one where things start to change, the days starting to feel a tiny bit longer come the end of the month. Indeed, January is named after Janus, the Roman god of beginnings and transitions. The Saxons referred to this month as wulf-monath, or “wolf month”, and January's full moon is known as the wolf moon.

Weather Update

After a very mild November, December arrived with a north-easterly airflow that brought temperatures down well below average for the first half of the month across the whole of the UK, albeit staying slightly milder in the far south-west coast. Northern Ireland, the Scottish Highlands, northern and central England, and parts of East Anglia and the south-east saw their first snows of the winter, with some bitterly cold nights recorded across the country. Overnight on 9th December, Bournemouth recorded -9C (16F) and many parts of England and Wales fell to -7C (19F) repeatedly. The coldest temperature of the winter so far was recorded at Braemar in Aberdeenshire, Scotland in the early hours of the 13th where the mercury dropped to -17.3C (0.9F). During the previous day, the temperature rose to a high of only -9.3C, the lowest daytime high recorded in 12 years.

A large low-pressure system took a north-easterly track on 11th December, depositing some significant snow in north Kent and London. Many parts of Surrey and Sussex saw rare lying snow during the second weekend and there were even a few flurries along the south coast of Dorset and Hampshire.

The GFS temperature anomaly map, showing the very mild Atlantic air mass that replaced the cold Artic airflow that brought ice and snow to much of the UK for the first half of December. The second half of the month was firmly under Atlantic influence for much of Europe, with temperatures well above average by day and night. - Credit: WX Charts (CC BY-NC-ND 2.0)

The cold weather held its grip until the week leading up to Christmas, when things turned mild, wet and windy. The 19th was an exceedingly mild day in Western Europe. Several weather stations across the UK recorded temperatures nudging over 15C (59F), including Wales and Scotland where monthly records were approached. Night-time temperatures remained in double digits, but as tends to be the case with mild conditions during the winter, it was stormy, and England was battered by 50-60 mph winds. The mild spell lasted about a week, making for a warmish and wet Christmas for most of England and Wales, while Scotland saw colder and drier weather. Christmas over, the mercury fell back close to the seasonal average, hovering at 6-9C (43-48F) north to south for Boxing Day before rising again into double digits with frequent showers and wind.

Across Europe, there was a significant temperature contrast between north and south for much of December, with the Sirocco winds bathing North Africa and southern Europe in Saharan air and bringing temperatures reminiscent of late summer. At 3AM on 16th December, for example, southern Italy recorded 23C (73F), while western England were at around -6C and parts of Scandinavia were below -20C (-4F). Temperatures exceeded 25C (77F) in Greece and Cyprus, with some “tropical nights”, with Vlora in Albania also recording 20C (68F) overnight on 17th December. In France on 19th the mercury reached 23.6C (74.5F) at Bazus-Aure, while northern Spain exceeded 20C (68F) in Cantabria and Asturias after a very warm night.

The first weekend of December was very mild in Greenland, the temperature reaching 10C in the capital Nuuk and in Kangerlussuaq. There was also record warmth in Northern Alaska and Utqiaġvik rose to a remarkable 4.4C (40F), surpassing the previous December record of 1C (34F) set in 1932. Nigeria reached 40C (104F) for the first in recorded history during in December, with 40C also in Yola and Cameroon. Much like Europe, there was a significant temperature contrast across North America last month, with about two-thirds under wintry influence and the south-east and east coast experiencing mild temperatures and warm nights. Towards the end of the month a “bomb cyclone” pushed Arctic air across most US states, even as far east as northern Florida, with life-threatening low temperatures.

News and discoveries

No bird brain. Crows are notoriously smart and arguably the cleverest of the avians, able to use tools, follow basic analogies, be trained to pick up litter and understand the concept of zero. Now new research has continued to help corvids chip away at what we think it is to be human. The study, published in Science Advances in November, suggests that carrion crows (Corvus corone) are able to grasp what we call “recursive patterns”, something that many primates struggle to do. The scientists observed that two male crows used in their experiments outperformed toddlers and primates in pecking sequences of embedded symbols, and the findings challenge what we thought we knew about brain structures necessary for this kind of thinking.

The skull of a Smilodon cat, a large prehistoric carnivore often referred to as a sabre-tooth tiger, despite not being particularly closely related to modern tigers. - Credit: Marc Baldwin

Far-fetched fangs? When asked to think of a prehistoric cat, most of us would likely instantly picture Smilodon fatalis, the sabre-tooth tiger, one of several machairodont species that, despite the name, weren't particularly closely related to tigers. These felids are probably best known for their massive canine teeth that might appear to have been more of a hindrance to hunting. Recently, however, scientists at the University of Liège's EDDyLab used high-precision 3D scans to model how these big cats used their over-sized dentition. The models suggest that cats with larger canines tended to bite at larger angles to reduce the pressure on the mandible, and that there were similarities in biting profiles regardless of the canine length.

Feline forerunner. Cats are the second most popular pet in UK households, after dogs, with a striking 28% of homes having at least one feline strutting around like it owns the place. Recently, a multinational team of researchers have found that the origin of cat domestication can be traced back 10,000 years to when humans living in the Middle East switched from hunter-gathering to farming. The genetic data suggest that this transition, by people settling in the Fertile Crescent, was the catalyst for the evolution of the house cats we're so familiar with today, unlike other domestic animals (e.g., horses and cattle) that saw several domestication events in various parts of the world.

Calescent canines. While 28% of households own a cat, 34% have one or more dogs, making them the most popular pet in the UK. As a long-time partner of humans, dogs have been well studied, both in terms of biology and behaviour, but the answer to quite how dogs with impaired vision, hearing and smell could still hunt had long evaded us. Recent research published in Scientific Reports, however, suggest that they may be using a hitherto unknown sense: the ability to sense weak heat sources with their nose. The experiments demonstrated that the dogs consistently chose the warm (about 10C/18F above the temperature of their nose) block in 70% of trials and MRI brain scans revealed that a specific region of the brain (somatosensory cortex) is activated when the nose detects an infrared source.

Seasonal highlight – Scores of starlings

I'd be surprised if there were many people reading this who haven't seen a starling. Slightly smaller than blackbirds, these medium-sized thrush-like birds stand about 20 cm (8 in.) tall, are 19-23 cm (7.5-9 in.) long with a wingspan of 31-44 cm (12-17 in.), and weigh in at 58-101 grams (2-3.6 oz.). Short tailed, pointy headed, pink legged, with a yellow (in summer) or black (in winter) beak and triangular wings, at distance these birds tend to appear uniformly black, but at close range they take on a glossy appearance, caused by the way in which light interacts with the microstructure of their feathers.

A European starling (Sturnus vulgaris) in it's unmistakable shimmering adult plumage. - Credit: Marc Baldwin

A recent study by Rafael Maia and his colleagues at the University of Akron in Ohio has shed some light on how the feathers achieve this mesmerising sheen. Maia and his team found that a series of rod-shaped cells, called melanosomes, arranged in arrays beneath a keratin film in the feather, scatter light through a process called thin film interference. In very basic terms this means that the feathers contain several layers and as light hits each layer some gets reflected by these melanosomes while the remainder passes through but is refracted (changes direction). The light that passed through the first layer then hits the second layer and, again, some passes through while some is reflected. The result is that light from both these layers is bounced back at us at slightly different angles. The more evenly spaced the layers are, the more vivid the colour we see because the reflected beams amplify each other. Moreover, the spacing of the layers and the angle that we are looking at the bird from can affect the colour we see—this is a phenomenon known as iridescence. The mathematics of all this is pretty complicated, particularly for non-mathematicians such as me, but what it means in practice is that the feathers of these birds take on a sheen of blues, purples and greens depending on your position relative to the bird and how sunny it is.

The winter plumage of starlings is heavily spotted, but these white spots are at the fragile tips of the feathers and wear down over time such that adults are noticeably less spotted, but sleek and glossy, come the breeding season. The degree of spotting and the arrangement of the spots changes throughout the bird's life and isn't, therefore, a good indicator of identity. At any time of the year, starlings may be sexed based on the colour of their iris, which is a rich brown colour in males and a “mouse-brown” or grey in females, and this method is apparently 97% accurate.

In her book 100 Birds and How They Got Their Names, Diana Wells notes that the Anglo-Saxon name for these birds was staer (the 'ing' being a diminutive that was added later) and that some etymologists connect the name with a celestial star owing to the white spotted (or starry) plumage they sport in the winter.

Starlings are as at home in our towns and cities as they are in our countryside. This one was singing on a chain cordon in St Ives, Cornwall. - Credit: Marc Baldwin

No place like home

Starlings are widely distributed across the UK and are resident throughout England, Wales, eastern Scotland, the Scottish islands and Ireland. These birds are summer visitors to central and western Scotland and are absent from the highest points of the Cairngorms. Starlings are found in the UK throughout the year, but it is during the autumn that they start to form large flocks as numbers are swollen by birds migrating in from the continent. Indeed, the RSPB estimate that there are currently about 800,000 breeding pairs of starlings in the UK and we know that millions of birds join these residents during the autumn, from as far afield as Scandinavia, the Baltic States, Germany, Poland and Russia.

These birds are found in a variety of habitats, from large cities to open farmland. There is a tendency to choose night-time roosts in woodland, but reedbeds, cliffs, buildings and industrial structures are also sometimes chosen. During the day, they divide their time between feeding in flocks and resting, the latter of which often necessitates exposed locations with good all-round visibility. There is some suggestion that they may compete with, possibly out-compete, other bird species, such as sparrows, but more data are needed.

Let's stick together

Starlings are gregarious birds and show no signs of territoriality outside the defence of a small area around the hole in which they are nesting during the breeding season. Indeed, throughout the autumn and winter months, hundreds of thousands of starlings can turn the sky black as they come together in huge clouds, wheeling, twisting and diving in unison at dusk. These mass gatherings are called murmurations, from the Latin murmur meaning 'to roar' and alluding to the sound these birds make when passing overhead.

Numbers at communal roosts start building as early as September, although most only become noticeably larger in November, when the number at some roosts can swell to 100,000 birds. Outside the UK, flocks of a million or more birds have been recorded just before sunset in spring on the Danish peninsula of southwestern Jutland, over the seaward marshlands of Tønder and Esbjerg municipalities. Why, though, should starlings group together in such a way? Moreover, how do so many birds keep in such tight formation when in the air?

Many theories have been put forward to explain why starlings gather in such extraordinary numbers, including that so many bodies help provide warmth, or that it serves as a communication forum and that the chatter before sleeping and after waking may be the rapid passing of information, such as sharing the locations of good feeding spots, between members of the flock. Invariably these aspects may play a role, but the explanation that has gained the most support in recent years is that of safety in numbers.

Starlings are known for gathering in vast flocks that roost together during the evening. - Credit: Marc Baldwin

Starlings are predated by sparrowhawks, peregrines, goshawks, hobbys, kestrels, red kites, buzzards, all UK owl species, plus a variety of mammals such as domestic cats and foxes. Indeed, despite the oldest captive individual on record reaching almost 23 years old (the oldest wild bird lived for 21 years), most starlings see only three or four years if they're one of the lucky 15% or so that the RSPB estimate survive to their first breeding season. We already know that, when feeding on the ground, animals are safer in the middle of a flock or herd than on the periphery and the suggestion is that the same applies when airborne. The results from a study led by Dan Pearce at the University of Warwick recently revealed that a bird is safer from predation if it joins a big, dense flock. Interestingly, however, there appears to be an optimum density that birds try to maintain so they never get packed to the point where the flock is opaque. According to Pearce and his team, each starling constantly monitors the movement of six or seven of its nearest neighbours, factoring in its own position so it can adjust to ensure it can still see light patches of sky. Thus, flocking together, both in the sky and on the ground, may provide some protection from their myriad of predators.

How starlings manage to maintain such tight formation in flight, appearing to move as a single coherent entity, has long been a subject of discussion and only recently have we begun to understand what's happening. In a paper published in the journal Royal Society Interface in 2015, Alessandro Attanasi, at the Consiglio Nazionale delle Ricerche in Italy, and his colleagues presented the data from their study of the collective changes of direction in starling flocks. Using high-definition cameras, the biologists filmed birds returning to their roosts in Rome and subjected the videos to a 3D computer algorithm. Attanasi and his team found that spontaneous turns start from individuals located at the elongated tips of the flocks, and then propagate through the group. Indeed, the birds at the periphery of the murmuration deviate from the main direction of flight much more frequently than other individuals. The researchers explained:

During the process of turning, two things happen: each bird performs its own individual turn following a specific trajectory in space; and the flock as a whole performs a global collective turn. These two dynamics are strictly interconnected, and the way individuals coordinate turning with each other determines how the flock turns as a whole.”

A thermal image of a large starling murmuration in Norfolk in early December 2022. At this point it was all but dark, so I had no chance of filming the birds, but this thermal video gives an idea of the vast number of birds involved in the murmuration. The noise of several thousand wing beats passing overhead is nothing short of spectacular. - Credit: Marc Baldwin

In other words, a bird on the edge of the flock changes direction and the ones next to it move to follow, as do the ones next to them and so on such that this change in direction spreads through the flock. Attanasi and his colleagues continue:

The fact that individuals on the border of a group behave differently has been already discussed in the literature on collective animal behaviour. Staying on the border is not usually a preferential location during collective motion, as these positions suffer higher risk under a predator attack or any other external perturbation. Therefore, one might expect border individuals to be particularly risk alert and exhibit a strong pressure to exchange position for a more favourable one.

So, essentially what we're seeing here is that being on the edge of the flock is risky and these birds are more “jumpy” and thus more likely to change their flight direction, which causes the whole flock to follow. When you have many birds around the edge of such a giant flock doing the same, the result is this seemingly choreographed 'sky dance'.

For the birds

During the autumn and winter starlings are primarily concerned with feeding and they have a fairly catholic diet. For most of the summer, starlings feed on insects, taking a wide variety of species including spiders, crane flies, moths, mayflies, dragonflies, damselflies, grasshoppers, earwigs, beetles, sawflies, bees, wasps and ants. They will also take small amphibians and reptiles if the opportunity arises, along with earthworms, snails and the eggs of other birds. As autumn arrives and more plant material becomes available, starlings undergo a fascinating physiological change; their intestines lengthen to grant them improved plant digestion. Hence, during the autumn and winter they will readily feed on fruits, grains, seeds, and nectar.

While feeding, starlings employ a technique called "open-billed probing" during which they insert a closed beak into the ground and then open it, creating a whole that they probe for larvae. - Credit: Marc Baldwin

Starlings will actively chase down fast-moving prey, such as dragonflies, but frequently employ a foraging technique called open bill probing, particularly when searching for beetle larvae in lawns. In this process the closed beak is pushed into the ground and opened, creating a hole in which the bird will look for food. Strong protractor muscles attached to the narrow skull allows the bird to open its beak while in the ground, while the eyes can be rotated forward to peer down the beak into the hole.

Cause for concern

Starlings are well-known songsters, and will readily mimic the songs of other birds as well as other noises in their environment. - Credit: Marc Baldwin

Despite starlings still being one of the most commonly seen garden birds, their numbers have declined sharply (by as much as 70%, according to some estimates) in recent decades, an observation that has put them on the IUCN's Red List and means they are currently protected under the Wildlife and Countryside Act 1981, which makes it illegal to intentionally kill, injure or take a starling, or to take, damage or destroy an active nest or its contents. Long-term monitoring by the British Trust for Ornithology shows that the number of starlings in Britain has fallen by 66% since the mid-1970s. The reasons for this decline still aren't clear, although loss of permanent pasture, increased use of agricultural chemicals, and a shortage of food and nesting sites in many parts of the UK are all considered to play a part. Interestingly, the theories for the decline proposed to date are largely agriculturally-based, but there are also far fewer starlings in our towns and cities than there were during the 1940s and 50s. Notably, on 12th August 1949, the hands of Big Ben were stopped for two hours under the weight of starlings that descended on London's iconic timepiece to roost.

Starlings eat various invertebrate species, notably beetle larvae, that are considered agricultural pests, and for this reason they are often considered beneficial, and encouraged by the placement of nest boxes. Nonetheless, there are also instances where they come into conflict with humans. Their preference for crops (especially cherry orchards, vineyards and autumn-sown cereals) and cattle feeding troughs during the autumn and winter means many consider them a pest, while droppings produced by large communal roosts are often unwelcome, particularly in urban areas. In Rome, for example, more than a million birds descend on the city each night to roost and the uric acid in their droppings damages cars, buildings and many of the statues. Moreover, the birds can be a hazard to aircraft; in November 2008 a Boeing 747 flying over the city had to make an emergency landing after 200 starlings were sucked into its engines. Rome now employs a “starling squad” that go around the city playing an amplified starling distress call night after night in an attempt to drive the birds out of the city and into surrounding countryside.

For a round-up of Britain's seasonal wildlife highlights for January, check out my Wildlife Watching - January blog.

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