Could the mystery of the vanishing sparrow be explained by the gardener's war on bugs?

A A A

The mysterious disappearance of the house sparrow from our towns and cities may all be down to greenfly - or a lack of them. The decline may well be due to a failure of the insect food supply for the young sparrow chicks, research by German scientists suggests.

The mysterious disappearance of the house sparrow from our towns and cities may all be down to greenfly - or a lack of them. The decline may well be due to a failure of the insect food supply for the young sparrow chicks, research by German scientists suggests.

Their conclusion comes in the first detailed study of the bird's decline in a major city - Hamburg, where the sparrow population is thought to have halved in the past 30 years.

The German report comes four months after The Independent launched its Save the Sparrow campaign, which aims to find the prime causes leading to the decline of the sparrow. Dozens of theories have been put forward by experts and readers, but the German study is the first conclusive evidence that a lack of food for chicks is a primary factor in the decline in urban areas.

The report shows that sparrows in the city centre are heavily dependent on one particular type of insect - aphids, the greenfly hated by gardeners - for feeding their young.

Nestlings that do not get enough aphids simply starve, and this may be happening regularly with the first of the three annual broods sparrows need to produce to maintain population levels.

In more than 300 letters to The Independent, readers have given possible theories, the most popular being the predation by magpies and sparrowhawks, formerly rural birds that have moved into urban areas, while other explanations proffered have included cats, grey squirrels, climate change, lack of nesting places and even disease caught from peanuts.

However, some readers with a knowledge of sparrow biology have suggested as the cause a failure of the food supply to the chicks. Although sparrows are seed-eating birds, for the first few days of their lives, perhaps the most vulnerable moment in their life cycle, the nestlings eat only insects.

The value of the German study is that it shows just how crucial the dependency is, and, secondly, the narrowness of the range of insects available to the birds, in Hamburg at least. Breeding can fail if the supply of one species falters.

The report, "House sparrows in Hamburg: population, habitat choice and threats", by Alexander Mitschke, Hilmar Rathjen and Sven Baumung, was produced last November for the Hamburg State Ornithological Protection Station.

It has been drawn to The Independent's attention by the marketing arm of Schwegler, a German manufacturer of nest boxes and other nature conservation products.

The study - prompted by the numbers of the German city house sparrow dropping steeply while other common birds such as blackbirds and blue tits remained constant - looked at sparrows in various control plots across the state of Hamburg and in particular in the Grossneumarkt area of the old city. Its conclusion is that the main population-limiting factor is the ability of the parent birds to find enough insects to feed their young, and that this often does not happen with the first brood in April.

For this brood, the parent birds are almost entirely dependent on aphids, which inhabit the lime and maple trees, and to a lesser extent the plane trees, in Hamburg's streets. For the second brood, the birds use ants, which feed on secretions the aphids produce, and so are also dependent on them. For the third brood, at the end of the summer, the sparrows are able to use flies.

About 40 per cent of Hamburg's sparrow population dies each year, the study found, so it is possible that first brood failure is the reason for the steady decline in numbers. The researchers do not know why the aphid population sometimes fails for the first brood, and they recommend more work should be done to find out, but they feel sure it is a major factor in the decline.

"The important thing is that they have problems in finding enough food to raise their young," Alexander Mitschke said. "They're very dependent on aphids. They need a lot of them because they're very small and they need them near the nest. House sparrows don't move long distances, most of the time searching for insects 50m from the nesting place.

"We don't know if the supply of aphids has halved in 30 years - we think there were probably more sorts of insects available then, but the greenery in which insects live has been greatly reduced as Hamburg has been built up."

The German study raises questions about the severe decline of the sparrow in Britain, in large urban areas estimated at more than 90 per cent.

First, although it is known that all young sparrow chicks are dependent on insect food, no recent detailed work has been done on exactly which insects the birds depend on in British cities - and whether the range is broad, or, as in Hamburg, now very narrow. In the past, sparrows have been known to take a wide range of insects, ranging from weevils to caterpillars.

Second, no work has been done on whether the insect population in British cities might have suffered a sudden and catastrophic crash, which would account for the sparrow's very sharp decline in British urban areas in the 1990s. And thirdly, no work has been done on what might have caused such an insect catastrophe, although pollution would be a major suspect.

There is no doubt, though, that researchers will soon start to look at these topics, and perhaps find a warning for ourselves that may be contained in the mysterious disappearance of our most common bird. Watch this space.

PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
iJobs Job Widget
iJobs General

Ashdown Group: Application Support Analyst- (Customer Support) - £29,000

£29000 per annum: Ashdown Group: Application Support Analyst- (Customer Suppor...

Recruitment Genius: Laser Games Supervisor

£14500 - £15000 per annum: Recruitment Genius: This is an exciting opportunity...

Recruitment Genius: PPC Executive / Manager

£22000 - £28000 per annum: Recruitment Genius: A PPC Executive/Manager is requ...

Ashdown Group: Service Delivery Manager - Retail / FMCG / WMS Operations

£55000 per annum: Ashdown Group: Service Delivery Manager - Retail / FMCG / WM...

Day In a Page

Isis hostage crisis: Militant group stands strong as its numerous enemies fail to find a common plan to defeat it

Isis stands strong as its numerous enemies fail to find a common plan to defeat it

The jihadis are being squeezed militarily and economically, but there is no sign of an implosion, says Patrick Cockburn
Virtual reality thrusts viewers into the frontline of global events - and puts film-goers at the heart of the action

Virtual reality: Seeing is believing

Virtual reality thrusts viewers into the frontline of global events - and puts film-goers at the heart of the action
Homeless Veterans appeal: MP says Coalition ‘not doing enough’

Homeless Veterans appeal

MP says Coalition ‘not doing enough’ to help
Larry David, Steve Coogan and other comedians share stories of depression in new documentary

Comedians share stories of depression

The director of the new documentary, Kevin Pollak, tells Jessica Barrett how he got them to talk
Has The Archers lost the plot with it's spicy storylines?

Has The Archers lost the plot?

A growing number of listeners are voicing their discontent over the rural soap's spicy storylines; so loudly that even the BBC's director-general seems worried, says Simon Kelner
English Heritage adds 14 post-war office buildings to its protected lists

14 office buildings added to protected lists

Christopher Beanland explores the underrated appeal of these palaces of pen-pushing
Human skull discovery in Israel proves humans lived side-by-side with Neanderthals

Human skull discovery in Israel proves humans lived side-by-side with Neanderthals

Scientists unearthed the cranial fragments from Manot Cave in West Galilee
World War Z author Max Brooks honours WW1's Harlem Hellfighters in new graphic novel

Max Brooks honours Harlem Hellfighters

The author talks about race, legacy and his Will Smith film option to Tim Walker
Why the league system no longer measures up

League system no longer measures up

Jon Coles, former head of standards at the Department of Education, used to be in charge of school performance rankings. He explains how he would reform the system
Valentine's Day cards: 5 best online card shops

Don't leave it to the petrol station: The best online card shops for Valentine's Day

Can't find a card you like on the high street? Try one of these sites for individual, personalised options, whatever your taste
Diego Costa: Devil in blue who upsets defences is a reminder of what Liverpool have lost

Devil in blue Costa is a reminder of what Liverpool have lost

The Reds are desperately missing Luis Suarez, says Ian Herbert
Ashley Giles: 'I'll watch England – but not as a fan'

Ashley Giles: 'I'll watch England – but not as a fan'

Former one-day coach says he will ‘observe’ their World Cup games – but ‘won’t be jumping up and down’
Greece elections: In times like these, the EU has far more dangerous adversaries than Syriza

Greece elections

In times like these, the EU has far more dangerous adversaries than Syriza, says Patrick Cockburn
Holocaust Memorial Day: Nazi victims remembered as spectre of prejudice reappears

Holocaust Memorial Day

Nazi victims remembered as spectre of prejudice reappears over Europe
Fortitude and the Arctic attraction: Our fascination with the last great wilderness

Magnetic north

The Arctic has always exerted a pull, from Greek myth to new thriller Fortitude. Gerard Gilbert considers what's behind our fascination with the last great wilderness