Seasonal Update (August 2023)

Misty sunrises tend to be associated with autumn and winter, but if we get cooler spells in summer it can produce some stunning dawns. - Credit: Marc Baldwin

August, the fifth of seven months with 31 days, heralds the end of meteorological summer here in the northern hemisphere and the end of winter in the southern, although summery conditions may continue into September for us, particularly as our climate continues to change. This month, originally called Sextilis as it was the sixth month in the original Roman calendar, was named after Caesar Augustus, the founder of the Roman Empire. History has it that Emperor Augustus chose this month because it matched Caesar's month (July) in length, and many of his major conquests took place around this time of year.

Newly published

A new book charting Arnold Cooke's personal take on amphibian conservation in Britain is due for release later this month. - Credit: Arnold Cooke / Pelagic Publishing

A new occasional feature to this site is books that have recently caught my eye. There are two, in particular, this month. The first is a personal account of amphibian research and conservation in Britain over the past five decades by herpetological pioneer Arnold Cook. The book, called Tadpole Hunter, is produced by Pelagic Publishing and available from 15th August. The second is the revised and updated edition of the Field Guide to British Deer, published by the British Deer Society at the end of last month, which contains some fantastic artwork by the super-talented Katie Hargreaves.

Weather roundup

Despite the presence of a westerly airflow to start July, temperatures remained below average for the first week or so, widely in the mid to high teens Celsius, because the airflow originated from Svalbard. Along with the strong, chilly wind came showers that were, at times, heavy, most places seeing some welcome and significant rainfall. Summer returned briefly at the end of the first week, with temperatures in England widely climbing into the high 20s Celsius (low 80s F), courtesy of a transient Spanish plume, before a cold front pushed in over the weekend, dropping temperatures back around average and sparking thunderstorms.

The second week and mid weekend of last month was a stormy one, with several low pressure systems pushing through and bringing wind and rain more akin to October than July. Indeed, on the third Saturday, much of England and Wales were under a Met Office yellow alert for unseasonably strong winds, with gusts of 50 to 60 mph occurring quite widely. Temperatures stayed on the cool side, peaking in the low 20s Celsius (mid-70s F); conditions continued unsettled through the third and fourth weeks with a keen north-westerly airflow, and gale force winds battered large areas of the south and west on the penultimate weekend. A jet stream that dipped unusually far south for the time of year kept the intense heat in southern Europe and brought the UK its unsettled conditions.

Outside of the UK, July saw abnormally high temperatures in the core of Antarctic winter, above freezing widely across the Peninsula. Vernadsky recorded +8.7C (48F), which easily took the highest temperature record for July. Fierce heat was recorded from North Africa to the Middle East, with stations in Algeria above 49C (120F), and the first 50C (122F) and 45C (113F) on record for July in western Iran and Turkey, respectively. During mid-July, Sanbao in China's arid north-west saw 52.2C (126F), while just over a quarter of a million people were evacuated in the south-east as typhoon Talim made landfall, bringing ferocious winds and torrential rain. South Korea and Vietnam were also badly affected, with several Koreans losing their lives following days of torrential rain and landslides.

The temperature anomaly in Europe during mid-July, showing how Britain was below average while much of Europe were significantly hotter than normal. - Credit: WX Charts

It was also very hot in Spain, Italy, Greece, Croatia and into Russia, with temperatures into the 40s Celsius. A new European record temperature of 46.7C (116F) was set in the Sardinian village of Nuraminis. This intense heat sparked wildfires in many European countries. An unseasonably deep low-pressure system named “Storm Poly” brought rain and gale force winds reaching 90 mph to Germany and The Netherlands during the first week, bringing down trees and powerlines. During the first half of July, parts of the US northeast saw their worst downpours in over a decade, with two months' worth of rain falling in just two days triggering flash floods. New South Wales, by contrast, experienced a cold spell, with some of the lowest winter temperatures for many years recorded last month; Mangrove Mountain fell to -1C (30F).

As mentioned in last month's blog update, June was the hottest since records began in 1874, with temperatures an average of 2.5C (4.5F) above the seasonal average and only about two-thirds of anticipated rainfall, and we saw a number of large-scale fish die-offs as temperatures remained high for much of the month. Warm water holds less oxygen than cool water, which combined with the high levels of sewage discharge we've experienced further depletes oxygen. The Environment Agency sent teams around the country to deploy oxygenation equipment on rivers to help reduce fish deaths after The Angling Trust raised concerns about a spike in die-offs last month.

Website news

After a neglectful month without any updates, the next section of the water deer article is now online, covering the birthing process. I'm delighted that Raymond Chaplin let me use some of his home cinefilm of one of his hand-reared does giving birth to accompany the article, as parturition is rarely observed in water deer.

News and discoveries

Baby talk. Bottlenose dolphins produce a “signature whistle”, which is unique to each individual. Recently, Woods Hole Oceanographic Institution biologists looked at whether these whistles changed when mothers were communicating with their calves. It transpired that mother dolphins spoke with their children using whistles of higher pitch, and a much wider range of frequencies than when whistling at other times. The researchers suggest that these higher pitch whistles mirror the “baby talk” humans use when talking to their babies.

Scalloped hammerhead sharks take deep breaths before diving. - Credit: Kris-Mikael Krister (CC BY 2.0)

Poor pollinators. Western honeybees (Apis mellifera) are native to Eurasia and Africa and were widely imported into the US during the 1800s where they now form large feral populations, accounting for three-quarters of the local honeybee populations in some parts. A new study from the University of California, San Diego suggests, however, that these non-native bees are less efficient at pollinating native plants. Indeed, native plants pollinated by non-native bees produced offspring that were significantly less likely to survive and reproduce than plants pollinated by native pollinators.

Deep breath. It's instinctive for us to hold our breath when diving into water and it seems that it's not only air-breathing animals that do it, or at least something similar. New research in the journal Science reports how scalloped hammerhead sharks (Sphryna lewini) appear to close their gills when making deep dives. Dives can often reach 800 metres (0.5 miles) and take the sharks from surface waters of around 26C (79F) to deep water of maybe 5C (41F) and with their copious blood supply, gills rapidly lose heat to cold surroundings. To reduce this convective heat loss, hammerheads close their gill slits to prevent their body temperature dropping so low that they cannot hunt.

Wall of sound. Many mammal species are reliant on sound to alert them both to dinner and danger, and perhaps none more so than bats. Bats are highly sensitive to sound, employing it with pinpoint accuracy to navigate and hunt prey in darkness, and they unsurprisingly seem highly susceptible to disturbance from humans. A new study from the University of the West of England suggests that music festivals and illegal raves, which are often held in rural open areas with peripheral woodland, are highly disruptive to bats. They found that loud music playback alone reduced the activity of some bat species, even in the absence of other anthropogenic factors commonly associated with music festivals such as lighting and habitat disturbance. Interestingly, while larger bats (i.e., serotines and noctules) were impacted, reducing activity by up to 47% compared with quiet nights, smaller pipistrelles and Myotis bats showed less of a response to the music, possibly because smaller bats echolocate across a wider frequency range and therefore overlap with the music less than the larger species.

Seasonal highlight – the European blackbird (Turdus merula)

Blackbirds are among the most familiar of British birds and even if your garden isn't a wildlife haven, it is still quite likely to be visited by a blackbird. For me, the blackbird's melodic song epitomises the summer, calling forth memories of sitting in the garden late into the evening enjoying the long days. Despite being common visitors to, even residents in, our gardens, many people overlook the fascinating lives of these humble birds, fledglings of which are around this month. An appreciation for blackbirds is all the more important because, having seen numbers fall by over one-third between the 1970s and mid-1990s, the British Trust for Ornithology has raised concerns for the species.

European blackbird (_Turdus merula_) - Credit: Marc Baldwin

Just a black bird?

It is interesting that the small thrush-like bird visiting our gardens should have been dubbed the “blackbird”, when there are many contenders for that title - why not ravens, crows, rooks or jackdaws, which were all familiar to early settlers and naturalists? The reason appears lost in antiquity, but the first use of the name blackbird to describe this species appears to have been in 1486, and the Oxford English Dictionary has references of the use of “blackbird” back to at least 1350. The name was clearly associated by the 18th century, and when Swedish naturalist Carl Linnaeus formally described this bird in 1758, he gave it the scientific binomen Turdus merula, Turdus meaning “thrush” and merula “blackbird”. The scientific name proposed by Linnaeus still stands today.

Blackbirds are members of the order of birds we call Passeriformes, a group containing some 5,000 species which represent about half of all the bird species known to science. Passeriformes are the 'perching birds', so called because of their foot arrangement, which has three toes to the front and one to the rear, allows them to grip branches. Within this order sits the Turidae, which is the thrush family containing about 155 species. Blackbirds are small to medium sized birds: adults grow to about 25 cm (10 in.) long, have a wingspan of around 36 cm (14 in.) and weigh in at between 80 grams and 110 g (3-4 oz.). They're among only a few of our garden birds that show sexual dimorphism (i.e., males and females look different). Adult males are jet black, with a distinct yellow ring around each eye, while females are mottled brown, without the eye rings - both sexes of British blackbird have a bright orange-yellow beak. Juveniles can be more difficult to sex; both sport a mottled brown coat like that of an adult female, although with pale stripes on the back and wings. As males begin their first moult, they turn black from the feet up.

Albinism and leucism is known in blackbirds, although completely albino birds are rare. Full albinism manifests as a total lack of pigment in the skin and feathers, so the bird appears white, with a pale, pink-coloured beak and red eyes. More common are leucistic birds. In most cases, leucism is a phenomenon during which normal pigment production occurs but the pigment cells aren't distributed properly during development. The result is a variable appearance, depending on the degree of leucism: some have a few spots of white on the feathers, others have only a few spots of black, while others are completely white - with leucistic animals, however, the eye and beak colour remain normal. In some cases, leucism may result in reduced melanin production or deposition, causing the animal to have a “washed out” appearance. It is worth pointing out that the commonly referenced “partial albino” syndrome is a misnomer. Pigments in the skin and feathers of birds and mammals are the result of chemicals called melanins, which are created from an amino acid called tyrosine. For this conversion to happen, the body's cells need an enzyme called tyrosinase, and it is this enzyme that is lacking in albinos. An animal either lacks tyrosinase or it has it; it doesn't have tyrosinase in some cells but not others. Consequently, an animal cannot be partially albinic.

Here, there, everywhere

Blackbirds are highly territorial, remaining on the territory year-round if food and shelter allows. - Credit: Marc Baldwin

The blackbird is common throughout Britain. They're found in most habitat types from small city gardens to remote mountain forests and the various parks, woodlands, coastal scrubland, and farmland in between, and are a significant contributor to the spring dawn chorus in urban parks and gardens. Outside of the UK blackbirds are found throughout Europe (including Iceland) down into the Mediterranean to Turkey and east to Iran, along the north African coast of the Mediterranean Sea and on the Canary Islands. Blackbirds are also found in parts of south Asia and India and in south-east Australia and New Zealand, where they were introduced in 1857 and 1862, respectively.

BirdLife International suggest that the global population of blackbirds may be as many as half a billion individuals, with an estimated 80-160 million birds in Europe alone and just over five million breeding pairs in Britain. Most blackbirds in the UK by late spring are residents, although some will migrate south into Europe come winter. Many more birds migrate south from Scandinavia and northern Europe into the UK each winter, swelling our population to 10-15 million. These migrants overwinter in Britain before flying back north as spring approaches, and can typically be distinguished from our native birds by their characteristically duller beaks, which appear brownish yellow.

Blackbirds are highly territorial, a pair remaining in their territory throughout the year if the conditions (i.e., availability of food, temperature, and shelter) permit. Both sexes defend the territory, chasing off interlopers—and even larger thrushes that stray too close—using a “bow and run” threat display: they raise their head and bow, raising the tail, before making a short run at the intruder. (Indeed, bowing is a more general characteristic of blackbirds; their flight is usually a low, quick swoop into cover, but upon touching down they raise their tail, causing them to bow on landing.) Females are most aggressive in spring and, although fights involving females are generally rarer than those involving males, they tend to be more violent.

Invasion of the urban blackbird

Although most of us are now used to seeing blackbirds in our towns and cities, only recently has any detailed study of how city living affects these birds been undertaken, and it's not all good news. The earliest records of blackbirds breeding in urban areas appears to be from Rome in the 1820s, but recent work by researchers in Norway suggests that blackbirds didn't start to colonise British towns and cities until the early 1920s. It seems that partially migratory populations started to over-winter in urban habitats where it was warmer than the surrounding countryside and, over the course of several decades, some hung around to breed in the summer. More interestingly, it seems that it takes a certain type of bird to put up with city life. A study by the late ornithologist Ryszard Graczyk, published in 1974, compared the survival rates of urban and rural blackbirds released in the Polish city of Poznan, where blackbirds were well established, and in Kiev, Ukraine, which didn't have its own urban population of blackbirds. Graczyk found that only the urban birds survived in both locations, suggesting that city birds had some kind of edge over their rural counterparts. Since Graczyk's experiment, several studies have been done looking at the physiology of blackbirds and how city living impacts their blood chemistry.

Urban areas can be good for blackbirds, and the limited data we have suggest city-living birds are better adapted to stress than their rural counterparts. - Credit: Marc Baldwin

In a paper to the Journal of Experimental Biology, University of Antwerp biologist David Constantini and his colleagues assessed how well urban birds dealt with city stress by sampling their blood. The scientists were looking for evidence of oxidative stress in their blackbird subjects, commonly considered a sign of more general stress. The results suggested that urban birds suffered lower oxidative stress than rural birds; in other words, city birds were better able to “detox” from city life than their country kin. Being able to cope with the rigours of living in the city is beneficial to a blackbird because it allows exploitation of the warmth and pretty much year-round food supply that urban areas have to offer. Other studies suggest that blackbirds are also generally less concerned by human activity when building their nests, unlike song thrushes, and this has probably also helped them colonise our parks and gardens.

Life in the city isn't entirely a bowl of cherries, as many of us can testify, and blackbirds face considerable challenges when they share our conurbations. One of the biggest problems for blackbirds, in common with many birds, is the light pollution that has been a growing issue in urban areas since the first commercially produced light bulb illuminated the streets of New York in 1879. Light pollution has long been linked with earlier (pre-dawn) activity in urban birds, which may start singing and foraging for food earlier in the day and continue later into the evening than their rural counterparts.

Female blackbird. - Credit: Marc Baldwin

A recent series of studies by biologists, led by Davide Dominoni at the Max Planck Institute in Germany, have looked at the impact of artificial light on blackbirds in some detail. The researchers kept one group of birds in total darkness at night (the “rural” or “dark night” birds) and exposed another group to light levels of about 0.3 lux, which is common in larger cities at night (the “city” or “light at night” birds). The results showed that city birds had lower levels of the “sleep hormone” melatonin in their blood than the rural birds. (An increase in melatonin as it gets dark causes us to feel tired and sleep, and it has been suggested that our use of tablet devices and computers late into the evening suppresses melatonin production and disrupts our sleep patterns.) This suppression of melatonin “tricks” the birds into thinking that the days are longer than they actually are, causing them to start singing earlier and continue singing later, sometimes even singing through the night.

This reduction in melatonin has other, less immediately obvious consequences too: it triggers the reactivation of the bird's reproductive system much earlier (up to a month earlier) than in rural birds. Worryingly, however, Dominoni and his colleagues also found that young blackbirds exposed to light at night initially developed gonads earlier in the season than birds kept in darkness at night, but in their second year all the “night light” subjects failed to develop reproductively at all, with testosterone remaining at baseline levels throughout the year. This suggests that light pollution may have a serious negative impact on the breeding ability of some blackbird populations. Dominoni and his team also observed that “night light” birds exhibited an irregular (drawn-out) moult, compared with the birds kept in darkness overnight. More work is needed to establish just how representative these findings are, but they certainly suggest that some blackbirds may pay a heavy price for their city lifestyles.

Bringing up baby

The aforementioned notwithstanding, blackbirds typically breed between March and August—with male blackbirds experiencing a peak in testicular activity between April and June—during which time they may produce two to four broods, depending on how favourable the conditions are. In his 1988 book, A Study of Blackbirds, David Snow described the courtship display of these thrushes: it consists of oblique runs by the male combined with head-bowing, an open beak, and a “strangled” low song, after which the female remains motionless until she raises her head and tail to allow the male to mate with her. Blackbirds are generally socially monogamous (i.e., the pair will stay together and defend their territory together throughout their lifetime), but genetic analysis suggests that almost 1 in 5 chicks may be fathered by a male other than the female's territory mate.

Following successful mating, the female will lay between three and five greenish-blue eggs with red-brown speckles in a shallow cup nest made from grass, twigs, and moss (sometimes incorporating mud) and situated in bushes, low in trees/hedges or even at ground level behind cover such as a log pile. Each egg measures about 3x2 cm (1.1x0.9 in.) and weighs about 7 g (0.25 oz.), and the female will incubate them for 12-14 days until the blind and naked chicks emerge. Both parents will provide food for the ever-hungry chicks and remove their faecal sacs until the chicks fledge at about 14 days old (although anywhere from 10-20 days, depending on food supply). David Snow noted that the young are fed by both parents for up to three weeks after leaving the nest, and the fledglings will follow the adults begging for food. In most cases, the newly fledged birds hide in cover on or close to the ground and await their parents' return. If the female starts another brood, the male alone will feed the fledglings. Blackbird chicks are independent by 5-6 weeks old, at which point they may be chased off the territory by the parents.

Male blackbird feeding blackberries to a fledgling. - Credit: Marc Baldwin

Adult blackbirds are primarily invertivorous, taking a broad range of invertebrate prey including worms and a variety of insects and spiders. Blackbirds will feed on berries and other fruit, particularly during the late summer and autumn, and will visit bird tables to take bread, suet pellets and mealworms. More unusually, there are records of blackbirds taking tadpoles, newts, and even small fish. To my mind, there are few things more comical that watching a blackbird noisily explore the leaf litter looking for food, chucking leaves all over the place! Typically, a blackbird will live for about two and a half years in the wild, although ringing studies suggest some regular garden visitors reach five years of age, and the oldest wild-rung bird of which I'm aware lived to be almost 22 years old.

Sing it loud, sing it proud

For many, the song of the blackbird conjures memories of summer, and listening to bird song in general is well-known to boost mood. Indeed, it has long been known that green spaces in cities and contact with nature have considerable health benefits: reducing stress, improving mood, and boosting our immune systems. Recently, we've had an insight into how some of these elements link together to affect our experience. A paper published in the journal Urban Forestry and Urban Greening a few years ago looked at how people's opinion of an urban green space was affected by the inclusion of birds singing. The research found that bird song, and particularly a medley from different species, generally enhanced and improved young people's appreciation of these green spaces.

A male blackbird singing. - Credit: Marc Baldwin

Blackbirds are known for their very melodic warbling song, which often ends on a weak, almost scratchy note. The song has many phases and variations to it and, in his 2009 BirdGuide, Lars Svensson described it as:

“... a clear, loud fluting (almost in the major key) at slow tempo and on a wide, often sliding scale, with a soft twitter appended; verses rather short, repeated at 3-5 sec. intervals.”

Alongside their typical song, blackbirds have a variety of other calls, resulting in quite a diverse vocal repertoire. Two alarm calls are employed. Each has different meaning and serves to tell the other blackbirds from where the danger is coming. A low tuk tuk tuk call is used while dodging about in the undergrowth to draw attention to danger on the ground - e.g., a stoat, cat, fox, etc. By contrast, a loud agitated screeching, often made while the bird is in flight, signifies danger from the air - e.g., an owl, sparrowhawk, etc.

I hope this brief introduction to one of our most familiar garden visitors has given you a new appreciation of the humble blackbird. Urban living can be tough for these guys, and they can use our help whenever we are minded to offer it.

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

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