Many well-meaning households across the UK could be feeding the seeds of change to Britain’s garden birds.

Putting out food for the birds that visit our gardens, be it purpose-bought seeds or leftover scraps, is a popular way of interacting with wildlife for many people across the world. In some areas of the UK it is thought that up to 75% of households partake in what is known as ‘supplementary feeding’. And why shouldn’t they? In an increasingly urbanised world, attracting such charismatic birds as blue tits, goldfinches and robins to a garden can provide a lifeline to the natural world, and a feast for the eyes as they feast on the feeders.

As the breadth and significance of this pastime becomes apparent, so researchers have grown increasingly interested in the potential effects, both positive and negative, on the ecology of these garden guests. (Although technically not guests as they’ve existed long before gardens have!)

Concerns have been raised that feeding garden birds could encourage the spread of avian diseases such as trichomoniasis – after working in a wildlife hospital for the last four summers I know first-hand how easily this disease spreads between individuals and species! Questions as to the quality and suitability of supplementary food compared with natural foods have also been asked, and whether or not wild birds will become dependent on the food provided.

An extreme ecological trap - this robin was tricked into believing his chicks want scones.

It has even been suggested that garden bird feeding could create an ‘ecological trap’ for birds, as the food provided could belie the quality of a habitat. What on the surface may appear a bountiful territory may turn out to be unsuitable for rearing young in terms of food quantity and quality. Like moving to an area with a Waitrose, only to find out it had been taken over by Aldi.

First-world problems aside, researchers at the University of Birmingham found concerning results in their study populations of blue and great tits in a wood in north Worcestershire. It seemed that providing supplementary food reduced the number of eggs laid and the number of offspring that hatched, compared with an area in the same woodland where no supplementary food was provided.

To avoid the risk of over-sensationalising, it must be said that most supplementary feeding studies report either positive findings or no significant effect at all. Impacts include a change in egg quality, clutch size (number of eggs laid), chick survival, and adult overwinter survival. It has also been found that the date on which eggs are laid is often brought forward, which has the potential to desynchronise birds with their food source, contrary to the old idiom, the early bird is too early to catch the worm (or caterpillar in this case). The extent to which these effects are positive or negative depends on the species in question, highlighting the difficulties faced by wildlife organisations and researchers in providing garden bird feeding advice to the public.

A further quandary facing researchers is the uncertainty surrounding the quantity of supplementary food actually being consumed by birds. Short of direct observation which is time-consuming and impractical to implement twenty-four hours a day, there is no simple way of estimating this. New research however, conducted by Gillian Robb and colleagues, has shown that by assessing ratios of stable isotopes in birds’ tissues, it is possible to infer the source from which food has come. Tissues such as claws can be clipped in a relatively uninvasive manner and by looking at from where the constituent nutrients have come, the relative importance of supplementary food to the bird’s diet can be determined.

Research into the affects of supplementary feeding is ongoing and innovations in the field such as this are invaluable additions to the armoury of methods. However the myriad effects of supplementary feeding on different species makes progress extremely difficult. We are still a long way off from finding out the full effects of supplementary feeding on the ecology of garden birds, and whilst we are blissfully ignorant, we might as well sit back, continue providing food, and enjoy the avian attendees to our gardens.

Evidence suggests birds fed in the winter can reap the benefits the following breeding season.

As a brief coda, my final-year undergraduate project at the University of Birmingham aimed to identify key demographic groups to which garden bird feeding advice should be directed and determine the public’s motives for feeding birds. It was based on a questionnaire launched last summer through collaboration between BBC Midlands Today and the University of Birmingham. David Gregory’s (BBC Science Correspondent for the West Midlands) coverage of the results can be found here.

I recently volunteered to help Project Parakeet conduct a roost count at Stanwell Park in Staines. This home-grown Imperial College research group was set up to assess both the economic and ecological impacts of the invasive rose-ringed parakeet on native UK species.

A picture I wish I'd taken. Source: http://pixdaus.com/single.php?id=236948

For those like me, not from an area in which parakeets are common, it comes as a surprise that they have been successfully breeding in the south-east of England since 1971. Natively from Sub-Saharan Africa and Asia, they have managed to firmly establish themselves in and around London over the last forty years. The origin of their introduction is under debate. It is often said that their presence can be attributed to Jimi Hendrix, who apparently released a pair as a symbol of world freedom. Although the perpetuation of this story is probably down to repeated attempts to liven up wildlife articles, programs, and blogs to attract a wider audience. The inclusion of it here is testament to this.

More realistically, parakeets were simply an accidental release from a private collection. Regardless, their presence is contentious and divisive. Some see them as an exotic, exciting addition to the UK’s suite of garden birds, with the power to transform a West London park from Staines into Senegal. Others express valid concerns as to their potential negative impacts on agriculture and native bird species.

It is true that parakeets are a major agricultural pest in their native land and have the potential to seriously damage UK crops, although only minor evidence has been seen of this as of yet. There is also the possibility that parakeets will compete with native species such as the nuthatch, great tit, and blue tit for tree cavity nesting sites. Researchers, including one with the apt name Dave Parrott, are yet to support this with significant evidence. Parakeets do however have the potential to intimidate and negatively impact native species, and if a continued increase in numbers is seen, there is no telling what the future consequences will be.

Which brings us to Staines – more likely to be described as “a wretched hive of scum and villainy” than the location of a stunning wildlife spectacle, yet Staines is the home of a large parakeet roost site. Nearly all the parakeets in a five kilometre radius will flock to the same location night after night to roost in the same set of trees. This provides an excellent opportunity for researchers to count the birds as they descend on their lodgings for the night. If you can estimate numbers at all roost sites, you can estimate the total UK population.

Parakeets roosting in East Ewell. Source: http://www.projectparakeet.co.uk/popdynamics.html

It has been said that war can be characterised by prolonged periods of boredom punctuated with moments of extreme terror. The same can be said of field-work.

I arrived at the roost site around half an hour before nightfall. All seemed quiet and the group of intrepid volunteers gathered round to discuss tactics. It was the calm before the storm, or to use the war analogy, the soldier’s wait for an unknown enemy. And then without warning the first parakeet troops started to flood in across the park in the dusk light. First groups of one and two came, before all hell broke loose and groups of fifty plus parakeets swarmed from all angles swooping as low as five feet from the ground before settling in their chosen tree. The chaos lasted no more than half an hour and we were left to combine our counts from different corners of the park, arriving at a grand total of 6273 parakeets. A seemingly impossible number for the small number of trees they managed to squeeze in to.

This video doesn’t do the maelstrom justice, but it gives an impression:

This new count was a staggering 2000 birds more than the last at this roost, just four months prior. So it would seem that at this site at least, parakeets are increasing in numbers. Bad news for local residents due to the cacophony of squawks emitted from the roost at dawn and dusk, and bad news for nearby Heathrow whose planes are increasingly at risk from squadrons of green spitfires. (Seriously though there is the possibility a flock could hit a plane).

But why are parakeets so successful at invading foreign lands? A plausible explanation is that parakeets are freed from their natural predators and parasites when taken out of their native range, enabling them to flourish. This is known as the ‘enemy-release hypothesis’. It has also been suggested that our climate is matched well to their requirements for survival, allowing them to thrive. But which explanation is correct? Very rarely in biology is an issue simply linear and so it has been found that both factors contribute to their success as an invasive species.   

The question is now raised, should we intervene? Some would argue no, as the likely outcome would be a cull – the possibility of this as a last resort has already been admitted by the RSPB. But at what point are the benefits of having London’s parks and gardens filled with a species described by Sir Attenborough as “glamorous oriental strangers” trumped by the hindrance caused to agriculture and native species?

Answers will not come easily, and even if a cull was decided upon some would argue that parakeets are so proficient as an invasive species, it would be a futile endeavour.

On a positive note, there is always the wishful possibility that the negative impacts of the parakeet will not come to fruition, and a state of equilibrium will be reached with our native ecology. This naturalisation has occurred with both pheasants and muntjac deer, two species that are now very much at home in the UK. Let’s hope the same will happen with the rose-ringed parakeet.