The Birds at my Table

by Darryl Jones

  In Great Britain, concerned and vigilant bird watchers had been reporting incidents of sick or dead birds to the Wildlife Enquires Unit of the Royal Society for the Protection of Birds for years. They were also used to taking dead birds found in their gardens to the Institute of Zoology in London, where the specimens were examined by wildlife disease experts. Around the turn of the century, these specialists were particularly busy. During the period 2000–2004, a total of 750 garden birds were examined, with the majority of deaths in various finches and sparrows being associated with salmonellosis, a common bacterial ailment.19 Although cases of trichomoniasis were detected in a few Woodpigeons and Collared Doves, the disease was not evident in any of the many finch specimens submitted. The appropriate tests had been performed for this pathogen—and many others—but had always been negative. This was no surprise. “Trich” was, after all, a pigeon problem, as everyone knew.

  And then, in April 2005, a routine assessment of just another dead Greenfinch yielded a historic and deeply unsettling finding: unequivocal evidence of trichomoniasis in a finch.20 This was the British equivalent of the discovery of the first House Finch with conjunctivitis in the United States and resulted in a similarly rapid response from a range of authorities. Remarkably, well before there had been any hint of this outbreak, the Universities Federation for Animal Welfare had brought together representatives from BTO and RSPB, various government agencies, uni-versities, and NGOs to form a new alliance, the Garden Bird Health Initiative.21 The goal of the GBHI was to develop guidelines explaining how people should feed birds in their gardens while minimizing the spread of disease and other risks. More specifically, they were able to undertake investigations into “the pathogens responsible for garden bird disease.” They had no way of knowing what was coming their way.

  Although there were a modest number of reports of finch mortality during the summer months (June to August) of 2005, the activity during the summer of the following year was utterly unprecedented. Completely unsolicited, a distraught public began to deluge the fledgling GBHI, along with many other bird and veterinary groups, with e-mails, phone calls, and small plastic bags containing dead birds. Between April and September 2006 over 6300 Greenfinch and Chaffinch “incidents” (either observations of sick birds or actual specimens) were lodged, of which 1054 were confirmed as cases of trichomoniasis.22 What was also alarming was that these reports were coming from almost everywhere in Great Britain (though not Ireland), although the highest rates were, at least initially, from the southwestern regions around Wales and Cornwell. This was clearly a national emergency, one, again, centered squarely on the humble back-yard feeder.

  To this point in the unfolding drama, all of the thousands of reports had been entirely unsolicited, the voluntary responses of distressed private citizens at finding dead and ailing birds in their gardens. Many of these people were also participants in the British Trust for Ornithology’s Garden BirdWatch program (as described in Chapter 4). Like Project FeederWatch in North America, members had been diligently sending in sightings of the birds in their gardens for years; the discovery of dead finches beneath the feeder would almost certainly be something that BTO would be interested in. This network of about 15,000 households located throughout Great Britain provided an ideal workforce capable of undertaking a detailed assessment of the spread and scale of the disease. In addition, information on the disease could be combined with data on the local abundance of key species to assess how populations might be being impacted. This capacity to provide a quantitative assessment of the influence of trichomoniasis on national bird numbers was unique, something the House Finch survey was unable to provide.

  At the end of April 2005, the same month “finch trich” had been confirmed, a random sample of 1614 Garden BirdWatch participants were invited to undertake additional surveillance of their gardens. These sen-tinel observers were carefully selected from throughout the country, providing representative samples from all regions. As well as making routine counts of birds, these people were asked to pay particular attention to three species: Greenfinch, Chaffinch, and Dunnock (the latter acting as a “control,” a common species not expected to be affected by the disease). In addition to making regular searches for obviously sick or dead birds, specified signs of the disease were to be reported. These symptoms were rather generic—“lethargy, fluffed-up plumage and dysphagia (the inability to swallow)”—because trichomoniasis simply did not produce distinctive physical signs of the sort easily confirmed in the House Finches. For this reason, specimens suitable for examination were essential for confirming the cause of death. Just how this was achieved is not entirely clear. The bland, succinct “methods” sections in the scientific papers state only that “fresh carcasses were submitted by post or were hand-delivered.”23 I can’t help but wonder at the reaction of the mail delivers on some occasions.

  The laboratory examinations of the thousands of specimens that arrived showed that 80% of the finches submitted had indeed died of trichomoniasis, with Greenfinch accounting for the clear majority (over 62%), and Chaffinch about a third, with the small remainder made up by Bullfinch, Goldfinch, Brambling, and Siskin. (Surprisingly, salmonella, the primary cause of death so recently, was virtually absent.) This was certainly a finch-centric epidemic, and it was having a catastrophic impact. The BTO data showed that in the most affected regions of England the breeding populations of the Greenfinch declined by 35% and that of the Chaffinch by 20%, within a single year. For the whole of Britain it was estimated that approximately 500,000 Greenfinch alone had died during 2006, most during the colder months when they were more likely to be visiting feeders. This is especially noteworthy because, during the preceding twenty years (1985–2005), the national population size of Greenfinch had grown dramatically and steadily, due largely to the expansion of wild bird feeding and especially the use of nyger seed, a confirmed favorite of this species. The arrival of the trichomoniasis epidemic had, in a single year, effectively returned Greenfinch numbers to 1970s levels.

  The finch trichomoniasis epidemic was unprecedented in its severity, marking the first time that a significant outbreak of the disease had been detected in species other than pigeons. The detailed investigations that followed were also the first to demonstrate that the disease could have a major impact on entire species on a national scale. The estimated mortality of 1.5 million Greenfinches for the period 2006–2009 is the largest ever associated with this disease.24 Alarmingly but hardly surprising, trichomoniasis continues to persist in the UK and has now spread to continental Europe, almost certainly through the movement of infectious birds from Britain. It arrived in Sweden in 2008, Germany in 2009, and France in 2010. The first cases were confirmed in Austria and Slovenia in 2012.25 The pattern of outbreaks coincides with the predicted seasonal migrations of Chaffinch. Recent genetic studies confirm that a single clonal strain of the Trichomonas parasite is responsible for the disease throughout this vast region.26 Adding further complexity to this story, there had also been trichomoniasis outbreaks in North America, among House Finch (surely they have suf-fered enough) in Kentucky in 2002, and in the Canadian Maritime Prov-inces in 2007, involving Purple Finch and American Goldfinch.27 Recall that “trich” was unknown outside pigeons and birds of prey prior to 2005. At present it is not known whether there is any connection between the disease in these two hemispheres (transmission via cage birds, for example), but in every case we are inevitably drawn to the role of the feeder.

  We still do not know how or when the Trichomonas parasite first made its way to the previously unknown infection possibilities of finches, but most thinking has the earliest exchange happening on a typical English feeding platform during the first years of the new century.28 The established reservoirs have always been pigeons, but the two most abundant and likely candidates, feral pigeons and Collared Doves, have been sharing the feeders with other species for decades. BTO data show that rates of visits to British gardens by these two species had been more or less
stable for the preceding 15 years at least.29 In contrast, appearances at garden feeders by the much larger Woodpigeon have increased markedly in recent years, suggesting an enhanced possibility of parasite spillover. Traditionally, the Woodpigeon has been a bird of rural pastures, where it can still be seen foraging on pasture and spilled grain in large flocks. Increasingly, however, the species has been invading towns and even large cities, taking advantage of the abundance of foods available on bird feeders. Previously, finches and Woodpigeons would have been very unlikely to interact; the bird feeder has inadvertently brought them together. The long-term consequences may be serious.

  Growing Your Own Emerging Infectious Diseases

  The stories associated with the detection and surveillance of House Finch disease and finch trichomoniasis are certainly dramatic and fascinating. These examples also highlight what can be achieved by well-coordinated networks of motivated citizens working with common purpose. Such highlights should not blind us to the reality that these terrible diseases are still with us, continuing to blind and starve birds, and are now well established across vast areas. Certainly the mass die-offs are less frequent, and the heat of the big epidemics seems to have cooled. Furthermore, the considerable publicity has alerted many to the importance of feeder hygiene and vigilance. Yet while we now know an awful lot about pathogen-host dynamics, the routes of transmission, and the intricacies of the particular genetic strains that are involved30—all essential for developing strategies for prevention and possible treatment—the really fundamental questions remain largely unanswered. How did the pathogens responsible for these diseases infiltrate their new host species? Can the diseases be treated in wild birds? There are plenty of ideas and hypotheses, but very little is certain. Our understanding of the House Finch disease, for instance, is extraordinarily detailed, yet there is still no sign of a cure. While trichomoniasis has been treated successfully in pigeons, the same approach does not seem to work in finches.

  Meanwhile, the new diseases keep on coming. The latest is avian pox, a virally induced disease that causes circular wart-like growths and lesions to form on face, legs, and feet. The disease has been reported in hundreds of species globally, and it appears to persist at low levels in many locations. Most infected birds that develop mild lesions eventually recover. More severe cases may lead to impaired vision, making feeding difficult, while major lesions can result in secondary infections. Although there have been sporadic reports of avian pox from a wide variety of species throughout Europe, these have all been isolated cases and were not indicative of any sort of outbreak. Notably, although a few tit species were included, none of these were from Britain.

  And then suddenly, in a pattern all too familiar by now, a Great Tit visiting a garden in Sussex, England, was found dead near a feeder in September 2006.31 This specimen, which became the “index case” for Britain, had large, unsightly swellings covering the eyes, as well as numerous growths on its legs. Postmortem examination confirmed the pathogen to be Aviparvirus, the virus responsible for avian pox, and the first from a tit in Britain. This diagnosis was interesting but fairly routine at the time. However, it was soon apparent that yet another major and unexpected outbreak was under way. Again, unsolicited reports of tits with “tumors,” “growths,” “swellings,” and “lumps,” as well as many specimens, were delivered by the public to the various authorities (who had only recently been activated by the finch epidemic). The number of incidents rose rapidly from just two in 2006 to over 100 in 2010, with about 90% being tits.32 Great Tits were by far the most common species reported, with Blue Tits a distant second, while Coal, Marsh, and Willows were all represented at much lower levels, probably in proportion to their general abundance. Of the hundreds of cases eventually reported, virtually all were from gardens with feeders. Particularly worrying was that numerous incidents involved a number of birds together, including (with photographic evidence) one alarming case where a householder had photographed diseased Great Tits and Coal Tits at his feeder, as well as a clearly pox-affected nuthatch, a species never before recorded with the disease. The first detailed assessment of this outbreak found that while the virus strain was identical to the virus that was widespread in Europe, its appearance in Britain—pos- sibly borne by migrating continental Dunnocks, since tits do not move as much—resulted in a severe form of avian pox among Great Tits especially.33 And the source?

  Anthropogenic provisioning of wild birds in gardens is a common pastime that influences contact rates among conspecifics and alters species comple-ments: both factors influence pathogen transmission and exposure rates.34

  It would be all too easy to continue describing the apparently increasing numbers of emerging infectious diseases associated with our feeders. Those mentioned already get special attention because they are new, novel, or unexpected, but there are plenty of other more routine diseases that also could be mentioned. The mainly parrot scourge known as “beak and feather disease,” for example, is an exceptionally infectious viral disease of great concern wherever parrots congregate to feed.35 It occurs naturally in many wild species in Australia and Africa but is strongly suspected of being transmitted at feeders. In Australia, Rainbow Lorikeets are a great favorite at feeders, often coming in large, boisterous flocks. Several severe though localized outbreaks of beak and feather disease have been linked, but not confirmed, with feeding (and have led to strident calls for all bird feeding to be banned outright). Thankfully, these incidents appear to have been short-lived, though the risk remains.36

  Far more common, and therefore potentially more significant, are the bacteria E. coli (or to be technically correct, the strain Escherichia albertii) and salmonella, which causes salmonellosis.37 Both are ubiquitous and probably global in presence but can manifest as serious diseases under certain conditions. Both have been associated with disease in a wide range of seed-eating species and appear to be highly contagious, making feeders effective places for transmission. Unfortunately, the signs of illness caused by both organisms are rather vague and nonspecific: general lethargy, a fluffed-up appearance, and a tendency to mope around feeding stations. The E. coli strain has been responsible for significant mortality in sparrows in Europe, caused at least one localized epidemic among North American Common Redpolls, and frequently hits British Siskins.38 Salmo-nellosis outbreaks are frequent though tend to be restricted in range, affecting Greenfinch and House Sparrows most often but readily transferred to other finch species. The salmonella pathogen is particularly hardy and can persist in the environment for months. Both pathogens, unlike the others mentioned already, also pose a significant risk to humans. This means that considerable care is needed when undertaking regular—and essential—feeder cleaning.

  When the Food Is the Problem

  Of course, providing food for impaired and ill birds can also be extremely beneficial. If sickness has rendered them weak and obstructed their vision, utilizing the reliable provisions found on a familiar food table can boost condition, improve struggling immune defenses, and allow time to recover. These factors were found to have been of great value in the recovery of House Finch populations following the epidemic.39 Without the availability of feeders, many of these birds would not have made it. Provi-sioning quality food on scrupulously clean feeders can be enormously important, providing sustenance while breaking the infection cycle.

  Conversely, providing poor quality, nutrient deficient, or inappropriate food is unlikely to be helpful. Sick or recovering birds are much less likely to respond and could be pushed closer to the edge. In any otherwise healthy animal, a prolonged diet with insufficient energy and protein is known to seriously weaken cell function while nutrient deficiencies (especially zinc, iron, folic acids, and the B vitamins) often lead to inadequate immune defense. In other words, an inadequate diet means animals are less able to combat inevitable infections and are much more likely to succumb to disease and other problems. For example, iguanas subsisting largely on a carbohydrate-dominated diet (mainly br
ead supplied by tourists) had far higher internal parasite loads than those that the dominant individuals kept away.40 In some cases, access to feeding stations actually improves tolerance of infection, allowing heavily infected individuals to survive better while transmitting even more pathogens. Indeed, there is good evidence that many birds that utilize long-term feeding stations substantially reduce their daily movements, spending much more of their time close to the feeder.41 When significant numbers of other birds also do so, this increased density is likely to lead to an accumulation of pathogens in the local area, in turn raising the risk of transmission, even away from the feeder itself.

  Poisonous Peanuts

  The groundnuts universally known as peanuts were among the first “seeds” to be used extensively for the feeding of wild birds. In the pre– birdseed mix days, before the advent of ready-made packages, the easi-est source of seed was the farming industry. With large amounts of corn, wheat, oats, and barley as well as peanuts readily available from produce stores and pet shops, these were convenient places to obtain food that could be put out for wild birds. Peanuts were early, consistent favorites, and remain so today, especially in Britain. These nuts—whole, in pieces, or as “hearts”—are eagerly sought by many species, and lots of people concocted their own peanut and fat balls and spreads, much to the delight of hard-pressed birds during winter. Unfortunately, many of these peanuts sold as bird food were substandard leftovers or suspect product deemed unacceptable for human consumption: the stuff that had been spilled at the warehouse, was discolored, or smelled strange. With the dramatic increase in demand for bird-feeding products in the 1980s, peanuts began to be shipped from a variety of countries around the world: Brazil, China, India, Argentina, and others. As the industry scrambled to provide sufficient supply, concern for the quality of the products was often neglected or ignored. This remains a significant issue today.