by Darryl Jones
The link between reproductive success and the availability of insect foods is very well known and has been studied in a large number of bird species.63 This has led to growing concerns over the possible effects of chemical pollution (including emissions from vehicles) and pesticide use in agriculture on insect populations in general, factors that have been implicated in the dramatic decline in many birds, especially in rural areas.64 Whether supplementary feeding could play a part in this story has, however, not been investigated to any great extent. Almost all such experiments have involved providing various seeds and nuts and almost always avoiding the nestling period. There remains a strong (if probably mis-placed) concern about nestlings being fed something—and possibly choking on—that is sensibly regarded as unsuitable food for nestlings. The obvious solution would appear to be providing insect foods instead, but this has been tried only a few times. One rare example of the use of insect food as a nestling period supplement is also important to our present exploration of the use of feeding for conservation. But this does not take us to some tropical island in search of an exotic species, but to a very different setting indeed.
Saving Sparrows
I am walking briskly through the wintry streets of East Dulwich, just south of the River Thames in inner suburban London. The sky is low and leaden and it is damp and chilly—about what you might expect for early winter in England—but the weather has not dampened the enthusiasm of my friend and guide, Dave Clark. For Dave, a visitor on a week-end is all the excuse he needs to scour his local patch for winter stragglers, birds that are late in leaving or those on their way south from Scotland or northern Europe. As we pass through numerous neatly maintained parks, unkempt vacant woodlands, communal garden plots (allotments), and large recreation reserves, I am amazed at just how much green space— and hence bird habitat—actually exists in one of the most densely urbanized, people-packed parts of the planet. “A lot of it is not that pretty, but the birds don’t seem to mind,” explains Dave as we stride through yet another park. “If you take the time and know where to look, it’s amazing what you can find.” As if to prove his point, a wild, wind-tossed group of Redwings rises from the lawns where they have been foraging on fallen berries. On a dull day like this I had not expected that we would see much but, for me, the sight of these gorgeous thrushes—along with (among others) a Goldcrest, Mistle Thrush, four species of tit, and even a kestrel sheltering in the crumbling steeple of a neglected church—has quickly dis-pelled my notion of a big city being largely devoid of birdlife.
Later that afternoon as we reviewed the day’s wanderings over a welcome pint in a local pub, Dave posed an arresting challenge. “No doubt, you will have noticed what we didn’t see today.” When I failed to respond (I had considered saying, “The sun!”), his answer was provocative and even a little alarming: “House Sparrows!” We had spent a good few hours wandering the streets, parks, and back lanes of London yet had not detected a single “Spadger” (or Spuggie, Spurdie, Spurgie, Sproug, Speug, Lum Lintie, Craff, Cuddyrowdow, Thack, or Thatch, as this once ubiquitous urban denizen has been variously known).65 Once I had considered it for a moment, the significance of this observation slowly grew. There may be no greater example of a bird being synonymous with a city anywhere than sparrows and London.66 The English capital was a key source of enormous numbers of sparrows exported throughout the world at the height of the British Empire’s global expansion. Homesick Englishmen arranged for thousands of the hitherto disparaged little birds to be shipped out to the farthest reaches of the empire as an attempt to install a modest reminder of home. It was an enterprise extraordinarily successful: within a remarkably brief time (mainly the first half of the nineteenth century), the heart-warming chirping of London spadgers was heard from New York to Buenos Aires, from Harare and Cape Town to Adelaide and Dune-din.67 (And even the remoter towns of Australia. Having been liberated at various places starting in the 1860s, House Sparrows—birds typical of the damp English landscape—were the most abundant species I counted during the 1980s in both the hot, dry inland town of Wagga Wagga as well as the tropical streets of Townsville in northern Queensland.)68
My, how times have changed for the sparrow! Once among the most abundant bird species on the planet with one of the greatest global distributions, House Sparrow populations are now in precipitous decline throughout its range.69 While there are few places where the birds have disappeared entirely, their numbers are falling almost everywhere. In many of these places, this is of rather little concern as sparrows are often regarded as invasive intruders, frequently accused of stealing grain intended for farm animals or people, damaging crops, and building unsightly, fire-prone nests in buildings.70 No, in places where they were introduced, their apparent demise has largely been welcomed, if it has been noticed at all.
But the story has an entirely different complexion in the House Sparrow’s natural distribution. Throughout much of continental Europe and the British Isles, the species appears to be disappearing rapidly, although the pattern is extremely uneven.71 For example, European House Sparrow numbers have declined markedly in Ghent and Hamburg but much less so in Berlin and Paris.72 Similarly, in the UK, where the most detailed analyses have been undertaken, the abundance varies enormously across the landscape, and although the number of sparrows associated with farms has declined considerably, these sites continue to support the highest densities.73
The most alarming declines, however, are very clearly associated with suburban landscapes that, in the UK, represent among the most extensive and important habitats for a wide variety of birds. Within Britain’s towns and cities, sparrow abundance is typically highest in private gardens and allotments; not unexpectedly, therefore, the most dramatic losses in sparrows have been in areas where these habitats have been lost to, typically, housing and parking lots.74 This is especially serious because these places are increasingly targeted for “urban infilling” as more people are being crammed into whatever “vacant” space remains.75 But this generalized loss of space and habitat is definitely only part of the sad sparrow story. House Sparrows, like many Londoners, seem to be able to cope more or less happily with high-density living. While their abundance in an area may have been drastically reduced, groups of these birds can hold on in even tiny patches provided a few basics are available: a nice dry niche under the awnings for nesting, some dense bushes for shelter, and perhaps access to a chicken shed, stable, or even a bird table for some seed. Across the landscape, there are thousands of such refuges. The problem is that even these resources are becoming harder to find. Farmyards and back gardens are becoming increasingly tidier, with less uncut grass (reducing the supply of seeds) and more secure holdings for farm animals, while newer house designs are reducing the traditional nesting places such as the open-ings under eaves and roof tiles.76 The widespread practice of replacing old wooden soffit boards with much more tightly fitting plastic versions, for instance, is quickly reducing the availability of an important traditional nesting place. But even where all these factors are present, many populations in urban areas in the UK continue to decline. Overall, the British population of House Sparrows is estimated to have crashed by almost 70% over only a 26-year period (1977–2003), a terrifyingly rapid fall.77 Once the quintessential English bird, common everywhere, the species finds itself listed on the Red List of Threatened Species.
This is a concern that Will Peach of the Royal Society for the Protection of Birds (RSPB) has taken to heart. I met with Will at the RSPB headquarters north of London (described in Chapter 3), and while we discussed a lot of topics, our main focus was on Will’s extensive sparrow work. As Will acknowledged, “[Sparrows] have dominated my life for more time than I would like to say.” One of the first studies was an attempt to understand the condition of the sparrow population in Leicester, a large industrial city in central England.78 This very detailed work, undertaken mainly by Kate Vincent, made two important discoveries: an unexpectedly large proportion of sparrow hatchlings di
ed during their first week of life, and the weight of chicks was much lower than it should have been just prior to fledging. Together, these key parameters seem to have led to a level of reproduction simply too low to maintain the population. Although various factors may have been implicated in this outcome, analyses pointed most clearly to an insufficient supply of insects in the diet, particularly in the first few days after hatching. This was evident in both the inadequate levels of invertebrates (especially aphids) and atypically high levels of vegetable material (as found in the droppings of nestlings). Baby sparrows were being fed too much plant stuff (mainly bread, peanuts, and seeds, almost certainly coming from feeders) and not enough good insect protein, presumably because the latter was simply hard to find. We can be sure that the parent birds know what is needed; it’s just that these were circumstances of desperation.
An obvious scientific approach would be to see what might happen if insect food was provided, particularly during the critical period when the newly hatched chicks are growing rapidly. Collecting the naturally occurring insects most commonly used by sparrows, however, would be just a little too challenging. (Just how many aphids would be needed each day?) Thankfully, an insect food is available commercially: mealworms, which are actually the larvae of a beetle, Tenebrio molitar. These hardy and increasingly utilized additions to feeder offerings were the clear option for an important supplementary feeding experiment. And the spectacular loss of sparrows from the suburbs of London (a drop of 85% from Kensington Gardens between 1925 and 1995, for example) made the capital an obvious place to undertake such a project.
The study that was carried out remains one of very few supplementary feeding experiments conducted in an urban environment.79 Because it was important to see what happens in the typical places where sparrows live, Will and his colleagues recruited suburban Londoners with private gardens already supporting sparrows, who were willing to participate in what was quite a lengthy project (lasting for 4 summers). Specifically, the goal of the study was to determine whether providing insect food would alter reproductive success and, ultimately, the number of adult sparrows. To address these aims, suitable sites (private homes with gardens) were divided into two groups: those where the sparrows were fed mealworms and those where the local sparrows got nothing beyond existing feeders. For the “feeding” sites, volunteers were supplied with sufficient supplies of mealworms to allow both morning and afternoon offerings throughout a 16-week period over the summer. About 100 g (3.5 ounces) of mealworms were provided daily, amounting to 11.5 kilograms (25 pounds) of live grubs for the entire season (about 100,800 individual mealworms). While the residents were topping up their feeders, Will and his sharp-eyed assistants made careful, unobtrusive (not everyone was likely to believe the explanation that they were peering intently into private gardens to look for sparrows) observations of “chirping” male sparrows producing their familiar territorial call, females, and especially the telltale fluffy fledglings. In these authentic conditions, as opposed to the usual experimental studies using easily accessed nest boxes, finding and examining sparrow nests was virtually impossible; old-fashioned observations would have to do.
By the end of this project over a ton of mealworms had been supplied— and eaten quickly—by the presumably grateful sparrows of London. So what effect did this vast amount of additional animal protein have on these populations? Thankfully, there was an important result, at least in terms of the numbers of fledglings being produced. Specifically, all those mealworms meant that a higher proportion of eggs hatched successfully and led to 62% more fledglings compared to the unfortunate sparrow colonies that missed out on the food.80
At the halfway point in the experiment, 2 years in, a review of progress confirmed that the addition of the mealworms was definitely having the hoped-for influence on the first aim—enhancing the breeding success of the sparrows—but strangely this was not translating to larger colony size. The birds were raising more chicks but not adding more adults to the population. The second and crucial aim of increasing overall sparrow numbers was not going according to plan. Will and his team decided, therefore, to turn their attention to providing a supplementary food that should benefit the adults too: rich, high-energy sunflower hearts. So, in addition to the summer mealworms, for the second 2 years of the study the researchers provided enough bags of sunflower hearts to the willing London residents so that the provisioning could be continuous: energy-rich food, on tap, every day, for 2 whole years.81 A metric tonne (over 2204 pounds) of mealworms and 7.5 tonnes (165,000 pounds) of sunflowers over the full 4 years were supplied: now that is what you can call a serious supplementary feeding experiment.
This major study is particularly important because it closely resembles what is happening in the typical suburban environment in which a large proportion of wild bird feeding occurs. Because of its scale, all our private feeding can be regarded as a truly gigantic feeding experiment. And because of its clever design and duration, Will Peach’s London experiment may be about as close as we can get to discovering what might actually be happening in the suburban wilderness. I was, therefore, more than a little keen to hear the outcome. Did the provisioning save the sparrows?
“We must have finished the London field work over 5 years ago, I think,” recalled Will, the substantial effort involved clearly an uneasy memory. “All those containers of hand-delivered mealworms! All those bags of sunflowers! The logistics, the travel, the time, the people; it was a big exercise, you know.” He pauses to sip on his now definitely cold coffee. “When we finally cranked the data—and that was a challenge itself, trying to account for so many variables—we had two clear findings. First, the mealworms definitely had had a large and positive impact on the reproduction of the sparrows being fed. There were certainly more eggs hatching and chicks fledging. And so, when we added continuous supplies of high-quality seed, did the abundances go up? Were we actually producing more adult sparrows? Was that huge effort worthwhile? Well, shockingly, no. Not really. Overall, our 4 years of feeding increased the abundance of territorial male sparrows by a bit—about 8%—and the effect of feeding was only statistically significant in the small colonies.” I, too, was astonished. There was obviously more to the decline of the sparrow than simply food supply, though the clear impact of providing plenty of insect food was a very important insight. “And it was not just a London issue either,” Will continued. “We repeated much the same experiment back in Leicester,82 where we knew the situation pretty well, and got almost identical outcomes: healthy chicks and an increase in breeding success but that’s about all.”
Why?
Will’s hard-won conclusions: the supply of insect food is indeed critical but it does not drive the population; the availability of feeder foods is only part of the picture, at least with House Sparrows and probably other smaller suburban species that make use of our feeders.
“The Most Fantastic Bird Table in the World”
While London sparrows have plenty of challenges, one thing they have not had to worry about (OK, it’s the people who are doing the worrying) for a very long time was being eaten by a bird of prey. For centuries, large raptors were abundant and conspicuous throughout the city; Shakespeare even described London as “the city of kites and crows.”83 One species in particular, the Red Kite, was very well known, thriving on the easy meals provided by the haphazard disposal of organic waste by Londoners. (Numerous travelers long ago had noted that one always knew when they were approaching London by the increasing stench.)84 Despite the public service Red Kites carried out, of reducing the amount of rubbish rotting in the streets, even this well-adapted urban bird of prey suf-fered from the widespread antipathy toward predators generally. From royal decree to gamekeeper’s disdain, British birds of prey of all species— as elsewhere around the world—were subject to unrelenting persecution wherever they occurred. By the 1870s the Red Kite, though formerly a familiar sight, was extinct in England.85 At the start of the twentieth century, the entire Brit
ish Red Kite population had been reduced to a handful of birds that had somehow withstood the shooting, poisoning, and nest destruction, hidden away in the remote hills of mid-Wales. Perversely, this very rarity posed new threats as egg collectors sought what had become a highly prized item. The future of the Red Kite in Britain appeared extremely bleak indeed.
The fortunes of the British Red Kite began to change at least marginally with the formation of the first Kite Committee in 1903, a group of dedicated amateur naturalists deeply concerned about the plight of the species.86 Their first actions aimed to protect the nests from egg collectors, who were destroying about a quarter of all clutches at the time. Their efforts were quickly acknowledged by the recently formed Royal Society for the Protection of Birds, which, in 1905, became involved in what eventually became a flagship campaign for the society. The extraordinary resolve of the RSPB and its various partners has led to the longest continuous conservation project in the world. Today, we can also add that, as well as longevity, the Red Kite campaign has also been one of the most successful—though this was not evident until relatively recently. For much of the early 1900s, progress was slow and the persecution relentless. By the 1970s, however, the egg collecting fad had largely petered out and the indiscriminate shooting of any bird of prey was far less common. Nonetheless, the miniscule size of the remnant kite population meant that natural growth and dispersal were virtually nonexistent. Without radical intervention, local extinction remained a distinct possibility.
The turning point came in 1989 when RSPB and the English Nature Conservancy Council (now Natural England), following the strict guidelines of the International Union for the Conservation of Nature, released the first Red Kites seen in England for over a century.87 (A similar exercise was also undertaken in Scotland at about the same time.) The site selected after painstaking research was a reserve classed as an “Area of Outstand-ing Natural Beauty” in the Chiltern Hills about 35 kilometers from central London and 20 kilometers north of Reading. The aesthetic appeal of the chalk escarpment of this area was about to be significantly enhanced. Because the Welsh population of kites was far too small and vulnerable to provide a source of new birds, the dramatic decision was made to import kites from the healthy stocks of Spain. Over a period of 5 years, ninety Spanish Red Kites were brought to the reserve and, after a prolonged period of settling in on-site aviaries, they were progressively released into the rolling terrain. Only 3 years later, in 1992, the first successful breeding was detected and, from that moment, the birds have literally taken off. Today—only a few decades later—the local population is estimated at well above 500 and more than 1000 pairs throughout southern England.88 In February 2006, for the first time in 150 years, Red Kites were again spotted in London—Hackney to be precise—with considerable excitement (though probably less positively among the local birds).89