Why are urban Peregrines on the rise?
A new study is investigating the impact of city life on Peregrine Falcons. But why is the world's fastest predator turning to an urban lifestyle?
Perched on a towering vantage point – perhaps a cathedral, skyscraper or once-grand derelict building – the world's fastest animal surveys the teeming metropolis below.
The city is this sleek predator's new kingdom, and more and more of its kind are being seen here.
It is the peregrine falcon (Falco peregrinus) – the ultimate aerial predator. This powerful, agile bird reaches speeds of up to 200mph (322kmph) when it dive-bombs its prey mid-air.
To me, they represent true wilderness, yet we are now lucky enough to see them on our doorstep. After locating a victim with keen eyesight and dropping like a bullet in a move known as a "stoop", it delivers a fatal blow with its razor talons, breaking its target's neck.
The birds have even been recorded killing buzzards at a site in Exeter to defend their territory.
About 1,500 breeding pairs currently live in the UK. Peregrines are recognisable by their mask-like facial markings, finely spotted breast and short tails.
Before the 1980s there are a handful of records of peregrines nesting on man-made structures.
Their population has much increased since the 1960s when they were decimated due to indirect poisoning from the since-banned pesticide DDT (dichlorodiphenyltrichloroethane). Ingesting the chemical caused increased adult mortality and eggshell thinning, meaning eggs often broke.
In recent decades the status of the UK's peregrines has, broadly speaking, been stable or increasing, according to the BTO (British Trust for Ornithology).
But their utilisation of our cities is relatively new.
A BTO survey in 2002 showed peregrines lived at 62 man-made structures including those in urban areas. This was an increase of 48 peregrine territories on human sites since a census in 1991. Results are not yet out for the latest survey undertaken in 2014, however, there are increasing anecdotal reports of urban peregrines, with the birds now found in most of the UK's cities.
"Before the 1980s there are a handful of records of peregrines nesting on man-made structures," says Dr Mark Wilson, research ecologist at BTO Scotland.
Experts know of just one urban nesting site recorded as far back as the mid-19th Century: Salisbury Cathedral.
Now a new study by researchers at Nottingham Trent University, UK will be the first to directly compare urban and rural peregrines using remote cameras at nests, to discover what effect urbanisation is having on peregrines.
Researchers hope to shed light on differing behaviour, such as what urban and rural peregrine falcons are eating, the number of offspring and the time of year chicks are hatching.
But what is attracting peregrines to the city in the first place? One draw is the wealth of prime peregrine real estate.
Tall buildings mimic cliff faces, providing urban-nesting peregrines with a good vantage point and a flat ledge to nest on cathedrals are a favourite home for these high-flying city slickers. So too are power stations, tall university buildings and phone masts (much to the annoyance of certain mobile phone customers whose phone service could not be fixed because of nesting peregrines in Southampton).
Tower blocks and skyscrapers provide urban living spaces too, although sadly one young peregrine on a Manchester skyscraper reportedly died after taking its first flight and possibly crashing into a window.
"There is a wide choice of suitable nest and roost sites for [peregrines falcons] in cities," says Esther Kettel, a researcher at Nottingham Trent University who is leading the new study.
"Conventionally, peregrines nest high on crag, cliff and quarry faces, giving them a clear view of potential prey and keeping their young safe from predators. Tall buildings mimic cliff faces, providing urban-nesting peregrines with a good vantage point and a flat ledge to nest on.
"Increasingly, people are installing nest boxes and trays to buildings, encouraging them to nest."
It's the huge abundance of prey on offer however – especially pigeons – that's thought to be the main reason for an increase in peregrines in the city.
Feral pigeons make up a large part of the urban birds' diets.
But city peregrines have been recorded making a meal of a surprisingly diverse range of animals.
Raptor biologist Nick Dixon has been studying peregrine falcons living at the top of St Michaels & All Angels Church in Exeter for 18 years.
To record their diet, he collects daily bags of prey remains – bones, feathers, legs and beaks – from animals the birds have devoured and discarded.
There is the opportunity for peregrines to hunt and catch prey at night by that sort of light pollution – that orange glow that covers every city. An amazing array of over 100 species of birds have been picked up – from wood pigeons, gulls, owls and small ducks to swallows, kingfishers and quails.
Some prey are seen locally, while others are snatched while migrating above the city.
But one prey item has been a particular surprise.
An animal body part collected very recently looked like a "weedy black wader leg" with "seaweed stuck to it", says Mr Dixon. On inspection it turned out to be a bat wing.
Chewed up bat, along with other prey found that is active at night, provides evidence that the birds are hunting nocturnally.
"That would lead us to believe that there is the opportunity for peregrines to hunt and catch prey at night by that sort of light pollution – that orange glow that covers every city," says Mr Dixon.
He says his personal theory for the increase in urban peregrines is that the birds are "imprinted on a man-made environment," explaining that if a young bird fledged from a nest in Exeter, it might look to establish territory in a similar environment in a nearby town or city.
Urban birds do not have the wide, open spaces available to rural birds, thus it is also possible that they use different flying techniques in order to catch their prey.
Nottingham Trent University team speculate their new study might reveal Peregrine Falcons are among the species adapting well to urban life.
"Species seem to fall into three different categories": the 'urban avoiders' where urbanisation is a big problem; the 'neutral ones' and 'the urban adapters', explains team member Dr Louise Gentle, a senior lecturer at the University.
The researchers will take advantage of webcams that have been set up at nesting sites in Nottingham, Sheffield, Derby, Brighton, Exeter, Chichester, Aylesbury and London, among others, which are providing unprecedented insights into the species.
"There are now many cameras on urban nests which are streamed online and are accessible to the public, yet there appears to be little research using this technology," says Ms Kettel.
Webcam footage of behaviour and prey brought to the nest will be compared with footage of rural nesting birds, monitored using CCTV cameras powered by leisure batteries.
I can't, off the top of my head, recall anyone I have discussed peregrines with reacting with anything but enthusiasm and excitement to the idea of peregrines living in towns and cities. As well as differences in diet and night-time hunting behaviour, Ms Kettel suggests the study might find the speedy birds' flying technique differs in the city: "Urban birds do not have the wide, open spaces available to rural birds, thus it is also possible that they use different flying techniques in order to catch their prey," she explained.
"Secondly, due to the year-round abundance of food and a greater protection from the elements, predators and persecution, urban birds are likely to breed earlier on in the year and produce more young than their rural counterparts."
Are urban Peregrines better off than their country cousins? For some experts, it is too early to tell.
Dr Gentle says the Nottingham Trent University team "might not necessarily be able to say the urban ones are doing better," following the study.
"I imagine it will just be that they're doing differently."
Mr Dixon says: "I personally wouldn't want to make a definitive comment.
"However, what I am aware is that you do get quite high breeding success from urban birds both breeding in city centres – their productivity is quite high."
One benefit, he suggests, is that when over-eager fledglings plummet to the ground, often they are returned to their nest by people monitoring the sites, thus improving survival rates.
Dr Wilson however, says in "many situations" urban Peregrines faring better "seems to be the case": "Certainly, if we go by regional population trends, occupancy of known sites has decreased in many rural upland areas relative to that of lowland, including urban, sites."
The increase of peregrines in cities may be bad news for Pigeons. But they have been accepted enthusiastically by many people, a relief for a species that continues to be persecuted in some areas.
"I can't, off the top of my head, recall anyone I have discussed peregrines with reacting with anything but enthusiasm and excitement to the idea of Peregrines living in towns and cities," says Dr Wilson.
They are fast, powerful predators, yet graceful and enigmatic. Dr Wilson has some advice for spotting them.
"Keep an eye out near tall buildings – particularly those where peregrines have been known to breed, or those where people find bits of dismembered bird regularly on the ground below.
"The other [advice] would be to pay especial attention when a wave of agitation passes through birds over a wide area… Reactions of prey species are often the first indication that we get of a nearby predator," he says.
"To me, they represent true wilderness, yet we are now lucky enough to see them on our doorstep, allowing us to explore their lives."
Why are urban Peregrines on the rise?
- Category: School of Animal, Rural and Environmental Sciences