Seasonal Update (February 2023)

January was broadly mild across the UK, but most parts did see some brief cold weather and February started on a cold note. - Credit: Marc Baldwin

Welcome to the final throes of meteorological winter. Both January and February were the last months to be added to the Roman calendar, included at around 713 BC, because the Romans considered winter to be a month-less period. The name February is derived from the Latin term februum, meaning “purification”, and the purification ritual of Februa was held on the 15th of the month in the old lunar Roman calendar. February is our only month that can vary in the number of days, being either “common” (i.e., 28 days) or “leap” (i.e., 29 days). Leap years are necessary to correct the inevitable drift between civilisation's calendars and the physical properties of our solar system, because astronomical events and seasons do not repeat in a whole number of days.

Weather update

December ended on a mild note for England, Wales, and Northern Ireland, while Scotland saw something more seasonal. Much of England and Wales were in double figures and after a wet and windy New Year's Eve, all but Scotland saw in the new year on a very mild note. On New Year's Day, temperatures were widely 10C to 13C (50-55F) and on the south coast the first week saw overnight lows of a quite remarkable 13C. As is typical for mild, Atlantic-driven weather in the winter, these high temperatures were accompanied by frequent heavy rain and winds approaching gale force, resulting in widespread flooding. Further north, Scotland, parts of northern England, and Northern Ireland started the year on a colder note, temperatures in Scotland struggling to get above freezing. A band of wet weather deposited some significant snow across the central Highlands of Scotland early in January.

The UK was subject to a cold spell in mid-January, while much of Europe was 10C or more above the seasonal average. - Credit: WX Charts

Torrential and persistent rain, alongside the strong winds, continued through the first half of the month, with parts of Wales seeing a month's worth of rain in the first 12 days. Brief respite came in the form of high pressure that built in at the start of the third week, bringing a north/north-east airflow and covering the UK in Arctic air. As a result, we saw temperatures dropping to -9C (16F) overnight in the north and failing to climb much above freezing, while some hard frosts and daytime highs of around 5C (41F) were experienced here on the south coast. This cold snap lasted about a week in southern and eastern England, replaced by cloudier and milder conditions to see the month out. Warmer air flowed into Scotland and the west during the penultimate weekend, returning them to double digits.

Outside of the UK, the Christmas period brought significant warmth through much of Europe, with France in particular seeing records fall. On Christmas Eve, 21 stations were above 22C (72F), with two recording 23.7C (74.7F). On Christmas Day Verdun in France and Catalan in Spain both hit 26.3C (79.3F), temperatures more associated with mid-summer afternoons than early winter. This was also how the new year started, the Polish capital Warsaw recording 18.9C (66F), surpassing the previous highest January record (set in 1993) by 5.1C (9.2F). Bilbao in Spain hit 24.9C (76.8F) on New Year's Day and across much of the continent overnight minimum temperatures were like summer. Parts of south-western Europe saw substantial amounts of rain, with widespread flooding in many cities, including Porto in Portugal during the first half of last month. The heat in Eastern Europe was, according to some forecasters, unprecedented, with more national records falling. Daytime highs exceeding 20C (68F) in the middle of January certainly seem unusual for eastern Europe.

In the US, what was described as an “atmospheric river” dumped vast quantities of rain across northern California at the start of last month, forcing evacuations and road closures, and leaving many without power. At least six people lost their lives in the ensuing flooding, and some 350,000 homes were without electricity on the second wettest day on record in San Francisco. Some areas saw 13 cm (5 in.) of rain in a single day. Overall, it was the wettest 10-day period for the city in at least 150 years. In the south-east, by contrast, mid-January felt like spring, with temperatures in low 20s Celsius (70s F) from Atlanta to Charlotte, and mid-20s (80s F) in Florida.

Website news

Several minor updates have been made to the badger, fox and squirrel sections over the past few weeks and a new section introducing the breeding biology of Chinese water deer is now online, with more to follow soon. Offline, I'm continuing to progress with the water deer piece, having now completed the breeding section (just in time for next winter's rut!).

A new section on introducing water deer breeding is now online, with more to follow in the next couple of weeks. - Credit: Marc Baldwin

News and discoveries

Clever colouring. Researchers at Gifu University in Japan have found a flower that changes colour. Only about 450 species of plant are known to be able to change the colour of their flowers and this change is typically unidirectional. In this case, however, the change can be reversed, which is very rare. The tropical vine Causonis japonica is a native of Asia and Australia, where it's often regarded as a weed, begins the colour cycle with orange flowers that fade to pink over several days, before recovering to orange after several hours of daylight for the cycle to repeat. It seems that the carotenoid pigments giving the flowers their colour are most abundant when pollen production is at its highest, suggesting that the colour change may signal to insects the best time to visit the plant.

New research on Svalbard's reindeer suggest they're shifting their diet away from lichens to grasses as the snow declines. - Credit: Marc Baldwin

Different dinner? As the Arctic continues to warm, conservationists have raised concerns about the future of the species that currently call the region home. A new study on the reindeer living here suggests, however, that they seem to be doing well. The data, collected on reindeer in the Svalbard region between 1995 and 2012, suggest the animals are shifting their diet away from the normal mosses and lichens towards the grasses that are becoming more abundant as snow cover and duration declines and rainfall increases.

Hidden haematology. Glass frogs, small amphibians native to South America, spend their days sleeping on bright green leaves. These frogs have curious physiology that allows them to remain largely hidden from potential predators and gives them their name: they're semi-transparent. One particularly interesting observation by scientists studying the frogs is that they become 61% more transparent while asleep. Now, a new study suggests that while they're resting these small amphibians “hide” their blood in their liver. The data suggest that we might be able to apply the frog's biology to help understand blood clotting in humans.

Savvy Sceloporus. Having noticed that western fence lizards (Sceloporus occidentalis) seemed to survive the wildfires that swept the western US in 2018 better than many other reptiles, researchers at the Spanish National Research Council started investigating their response to blazes. The team played back the sounds of fire to survivors of the Californian fires and assessed their behaviour. In the burnt areas, lizards responded more to the sounds of fire than any of the three controls, suggesting that lizards that have survived wildfires may be more alert to fires in future.

Seasonal highlight - Turned-on tawnies

The longer nights of winter have many of us out and about during the hours of darkness, and the calls of the tawny owl (Strix aluco), probably our most widespread owl, are often heard. Tawnies are typically a bird of mixed and deciduous woodland, although their adaptability has allowed them to make a living in conifer forests, city parks and even large gardens. Prior to moving to our current house, I spent many a happy hour in our flat listening to (and in a few unforgettable instances, watching) a tawny owl calling in the trees separating our garden from the main railway line running into the city's central station. Tawnies are the earliest breeders of our owl species, with pair bonding beginning in the autumn and continuing throughout the winter - mating starts as early as the end of January.

The tawny owl (Strix aluco) is probably Britain's most common owl species, and the earliest to breed. - Credit: Marc Baldwin

Young tawny owls are fed until the end of summer or beginning of autumn, after which they are actively chased away by their parents. The pair retains their bond throughout the year, but they begin the process of strengthening it once the young have been ejected. The first task is to re-establish the territory, the size of which is determined by the male; the female's task is to check out potential nest sites, eventually settling on a preferred spot. While direct physical aggression may occur between local owls (or other intruders, including foxes and even photographers), neighbouring pairs generally have little to gain, and much to lose, by scrapping with each other. Consequently, territories are marked by bouts of prolonged calling; undertaken by both sexes. Many of you will be familiar with the 'tu-whit tu-who' call referenced by Shakespeare in his poem Winter, which is actually two different calls, but tawnies make many more calls than this. Indeed, the tawny owl has been described as the most musical of all European owls and, by the end of the 1960s, 15 distinct calls had been described; ten from the adults and five made by the young.

Call me, maybe?

The call most will hear in woods, parks and gardens across much of the country for the next couple of months will be the familiar 'tu-whit' and/or 'tu-who'. So, what do these calls mean, and is it possible to tell the sex of the bird you're listening to? Well, firstly, Shakespeare was slightly off in his phonetic transcription and the calls are actually a 'kewick' and 'hooo-huhuhuhooo'.

The deep, resonating 'hooo-huhuhuhooo' (click below to listen) is typically uttered by the male and, according to veteran owl biologist Heimo Mikkola in his Owls of Europe, serves several functions:

first, as a territorial call; second, a courtship call; and third, an announcing call used by the male when bringing food to the female.

Mikkola goes on to describe how the call is in two parts, with a pause of between two and six seconds between the hooo and the warbling remainder. The kewick (click below to listen), by contrast, has a single main function; it, and its various subtle variants, is a contact call and generally made by the female bird, often in response to the male's hu-ing. Thus, the pair may duet, producing a kewick hu-huhuhuhooo; or perhaps more simply, 'twit-twoo'.

Hoo-hooo call of female Tawny owl (Strix aluco). Note this is more "warbly" in nature than that of the male. - Credit: Marc Baldwin

Hoo-hoooo call of male Tawny owl (Strix aluco) - Credit: Marc Baldwin

Kee-wick call of female Tawny owl (Strix aluco). - Credit: Marc Baldwin

As to whether the calls are always sex specific; the jury is still out. It appears that females generally kewick and males hu, but I have been told by several falconers that male and female tawnies can, and do, make both calls, and calling alone cannot tell you for certain of the bird's gender. In the literature there are some references to females hu-ing, although the descriptions suggest a much 'reedier', more tinny performance than the deep resonating hu given by the male. In one instance I watched a tawny in Southampton, under a red filtered torch, begin by strongly kewicking and then switch to a warbling hu-ing (click below to listen). From the literature it seems that wild male birds very seldom kewick, although one falconer in the New Forest told me that it was common for his captive male tawny owl to do this. So, it seems that if you hear an owl kewick, it's probably a female, and if makes a deep hu-ing, it's probably a male, but don't put money on it.

Much of the owl's vocal repertoire is reserved for when they have young and is used to convey their arrival with food, alert the chicks to danger, etc. There is, however, a suite of often more subtle calls uttered during territorial defence, pair-bonding and courtship.

Adults can be very vocal during courtship, but owlets are at their most vocal shortly after branching. - Credit: Marc Baldwin

Mikkola described how two disputing males produce a loud discordant “caterwauling” noise, which was somewhat spine-chilling when heard unexpectedly. German ornithologist Victor Wendland, in a 1963 paper detailing five years of observations of tawny owls in Berlin, described a trill hissing call (co-co-co-co-co-co) made during courtship and territorial fights, and a low-pitched soft oo-trill (likened to a snipe drumming) made by the female during courtship. Mikkola added further to this collection of calls, noting that creaking high-pitched ooaoo calls and an accentuated squeaking are sometimes made by the female during courtship. It appears that the ee-trill of the female, i.e., ee-ee-ee-ee, is a sign of sexual excitement, while a low-pitched, soft ooi hiss is considered an expression of tenderness, and is made by the female repeatedly after copulation. Wendland also described a wett-wett call, an ee-trill followed by twittering, and a repeated koo-ik or koo-i call, all of which were alarm calls. A 'claking' noise, made by the bill snapping shut, although not technically a call, is also used to express anger. There are sound bites of various tawny calls on The Sound Approach's website.

To call, or not to call...

So, we know a few of the calls we can expect to hear when out observing tawnies, but when do they call? Season and weather have profound effects on the calling behaviour of these birds, and this is perhaps best illustrated by a meticulous study conducted by Danish nightwatchman Lindhard Hansen, published in 1952. Hansen observed that his local owls called throughout the year, but calling was most intense from mid-February until early May, after which vocalisation declined dramatically while the birds moulted, increasing again between August and October. Hansen also noted how strong winds subdued calling, and a combination of wind and cold was particularly suppressive. Owls also called less during wet weather and full moons. Rain attenuates calling, making it travel less far, and small mammal activity appears to be greater on moonlit nights, causing the owls to hunt more and call less. The Danish owls started calling shortly after dusk (on average, 20 minutes after sunset) and continued steadily until about 45 minutes before sunrise.

Tawny owls have favoured daytime roosts from which they may call prior to leaving to hunt at dusk. - Credit: Marc Baldwin

My experience in the New Forest has been that owls start calling briefly from their daytime roosts shortly after sunset before moving off to hunt. As the winter draws on, they tend to call less from their daytime roosts just as it starts getting dark, instead waiting until it has got dark and then moving off before they call. Please note that owls are very sensitive to light and can easily be blinded by direct torchlight. The ideal situation is to sit and listen to the calls and follow the silhouettes once your eyes become accustomed to the darkness. If you do require a torch to help navigate around the wood or park, please cover the bulb with a red filter (I use a red plastic folder insert on my torch), which is less disturbing to the birds.

What behaviour can we expect over the next few weeks? Well, courtship feeding (i.e., the male bringing food to the female) begins during December and continues into February, becoming increasingly centred around the future nest site. The female will call to the male to encourage him to deliver the meal, after which there is an exchange of what Mikkola described as “disjointed hooting” from the male and a mixture of contact and soft calling by the female. The delivery of food helps reaffirm the pair-bond between the male and female, reassuring the female that her partner is a competent hunter who can provide for her offspring. Mikkola described the courtship as such:

“...the male may indulge in wing-clapping and when pursuing the female will utter screeches, mewings, groans and rattles which have often given rise to tales of ghosts. During courtship the male perches near the female and sways from side to side, then up and down, raising first one wing then the other and finally both together. The male's plumage is puffed out, making the bird almost round, then tightly compressed. Meanwhile he grunts softly, sometimes sidling a foot or so along the branch and back again.”

Urban birds may lay eggs as early as February, owing to the increased food density, while woodland and farmland birds tend to lay from late March onwards. Three or four eggs make up an average clutch, laid at roughly two-day intervals. The eggs are brooded for about four weeks after which time they hatch and the owlets remain in the nest for a further three weeks, fledging to nearby branches at around 25 days old.

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

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