by Darryl Jones
Tracking a Disease
One of the most significant contributions of Project FeederWatch to understanding major ecological and conservation phenomena involves the now famous case of tracking a serious eye disease that affected House Finches. Indeed, this example of large-scale monitoring combined with detailed scientific analyses is probably the most important example of well-organized citizen science in action.10 The details of this extraordinary collaboration of feeders and disease scientists over several decades will be covered in Chapter 6. For the moment, however, this phenomenon provides a valuable opportunity for assessing the possible influence of feeders on a species at a large geographic scale.
Formerly common in the drier areas of the western United States, the House Finch now found throughout the east apparently originated from birds released in New York in the 1940s. Starting in the 1960s, the species began to spread steadily westward with the eastern-introduced birds eventually overlapping with the original population on the western plains in the 1990s. This rapidly expanding range was recorded with remarkable precision as diligent Project FeederWatch observers noted the arrival of what was a new species. The birds would have been hard to miss: they are highly social, foraging in big flocks and often dominating the traffic at feeders.
Then in the winter of 1994, people began to notice House Finches with swollen, encrusted eyes. With remarkable foresight and resolve, the Cornell Lab of Ornithology launched the House Finch Disease Survey almost immediately, utilizing the vast capacity of the Project FeederWatch membership.11 As a result, the progress of the disease through the eastern population was mapped with unique precision and detail. It soon became evident that the rapid response was justified: this bacterial infection was highly contagious and lethal. The number of House Finches in the worst affected areas declined massively during the late 1990s. Reports of diseased birds began to level out by the turn of the century. Recovery, however, has been decidedly patchy throughout the eastern states, with the abundances of House Finches in some places now back to pre-outbreak levels, while in others the species remains rare.
The role of feeders in this catastrophe and the aftermath has long been debated.12 House Finches’ tendency to feed in flocks and aggregate in high densities at feeders obviously increases the likelihood of infected birds spreading the bacterium to others. On the other hand, because the disease impairs the bird’s eyesight, the predictable location of a feeder and the reliability of finding food there compared to foraging in natural areas could potentially allow populations to recover quickly.13 Given the rapid impact of the disease and the dynamic nature of the subsequent response over a large area, understanding the long-term relationship between feeders and abundance of House Finches would be extremely valuable. To achieve such a level of knowledge would require data on both feeder density and House Finch numbers from a huge geographical area as well as over a time span covering the outbreak.
Just such information is available, if you know where to look and are able to execute the appropriate analyses. Jason Fischer and James Miller realized that a measure of the density of people feeding birds was available from the numerous National Surveys of Fishing, Hunting and Wildlife Recreation undertaken by the US Census Bureau (discussed in Chapter 2).14 For the abundance of House Finches they used data from the annual Christmas Bird Count,15 a collection of counts of birds in a 24-kilometer radius during one full day in winter. Many thousands of people from everywhere in the United States participate, providing a high-quality snapshot of the presence of birds in winter for the whole country. Using the four national surveys that covered the period of the outbreak—1991, 1996, 2001, and 2006—the researchers were able to explore several key questions. Before the disease, did the density of feeders predict the number of House Finches? After the disease struck, did the habit of feeding in flocks—the likely cause of the increase in infections—result in lower numbers (as has often been claimed)? Or did the species recover more quickly in places where feeder numbers were higher?
Using data from twenty-two contiguous states of the eastern United States, Fischer and Miller obtained some of the strongest results yet of the feeder effect. Prior to the disease, the density of feeders was strongly related to the abundance of House Finches, suggesting that this species was clearly benefiting from the provision of all that seed. Perhaps House Finch numbers over large areas were linked to the number of feeders, more than they were for other seed-eating species. Interestingly, even after the disease hit and numbers declined significantly, the relationship of more feeders, more finches persisted. In other words, there was no clear evidence that the disease was more prevalent and had resulted in greater impact where there were higher densities of feeders. Furthermore, the growth of the finches’ population following the fading of the disease and the restored relationship between feeder density and bird numbers seemed to demonstrate that feeders were providing a positive influence.
Although this study is limited to a single species in a rather atypical situation, it is important in providing clear support for the proposition that feeding is capable of leading to changes at large-scale population levels. While such a conclusion will be either welcome news for some, and possibly regarded as self-evident by others, Fischer and Miller have chosen to highlight some of the more sobering consequences of their findings.16 Noting that the ramifications of these results were “profound,” the researchers point out that while the House Finch appears to be recovering, the species is known to be capable of infecting other feeder species such as Purple Finches, House Sparrows, and American Goldfinches. This is a thoughtful corrective to our tendency to concentrate primarily on what we want to see. As someone mentioned to me while I was in Ithaca, “The Lab is famous for mapping the finch disease as it spread from feeder to feeder. But would it have spread at all if there were no feeders in the first place?” It’s a moot point; feeders are here to stay. Perhaps a better question might be: “What can we learn from all those people watching their feeders?”
British Blackcaps
There is only one other program of a similar scale and significance to the North American Project FeederWatch and that is the British Trust for Ornithology’s Garden BirdWatch.17 While many other similar citizen-based garden bird surveys have been developed around the world, these two are the clear leaders. And as both are focused firmly on gardens, have huge numbers of participants (who each pay for the privilege) regularly submit-ting vast amounts of reliable data, and cover countries of particular interest to the feeding story, they are programs of central importance to the objectives of this book.
When I meet with Kate Risely, the coordinator of Garden BirdWatch, and Kate Plummer, a researcher delving into the riches of the monumental dataset at the BTO headquarters in Norfolk (described in Chapter 3), I asked (among many other things) the same naive question I had posed to David Bonter and Emma Greig in Ithaca: “Is it possible to show whether feeding is influencing birds?” The response was largely as I had come to expect: “Well, to some extent, yes,” said Kate Risely. “But while there is a lot of detailed information on bird numbers, movements, and timing, it is still very difficult to separate out the influences of climate change, habitat loss, farming practices, and lots of other potential factors.” It was a familiar story, and one that usually led into a discussion about the importance of carefully controlled feeding experiments.
But then there was a pause in the conversation as Kate Risely and Kate Plummer exchanged a possibly conspiratorial glance. “Although. . . . ,” Kate Risely hesitantly began, “Kate has just come up with some very new results that you might find fairly interesting,” she said. “Do you know the Blackcap story?”
The Blackcap is a much celebrated little bird, an otherwise typical warbler but with an unusually complicated pattern of migratory movements. During the breeding season, pairs of this neat, proper-looking warbler (the sexes conveniently differentiated by the smart, tight-fitting black skull-cap in males, orangey-red in females) are found throughout t
he shrubby woodlands and riverine habitats of central Europe and the lowlands of the British Isles. As the weather cools, the birds that have bred in the UK and Ireland head south, to overwinter in the milder climes of Spain, Portugal, and northern Africa. While most undertake this fairly typical migration, it has been known for some time (as far back as the 1800s) that some Blackcaps could still be found in the British countryside, despite the wintry conditions. These birds wintering in Britain survived mainly on natural foods—berries and fruits—but gravitated to gardens to access feeders as the cold weather advanced. This late-winter move into gardens allowed keen feeder watchers—especially Garden BirdWatch participants—to record these visits over extended periods of time. Everyone assumed, prag-matically, that these Blackcaps were birds who had somehow “missed the boat” to the south and were therefore stranded for the winter. It was hard to escape the conclusion that they were somewhat lower-quality representatives of the species.
When the number of these overwintering birds recorded in Britain began to increase steadily, from just a few in the 1960s to becoming a regular garden visitor in the decades that followed, other explanations for this phenomenon began to be sought. The German migration authority Professor Peter Berthold (more latterly of all-year feeding fame, as discussed previously) took a particular interest and began ringing Blackcaps at his study site near Lake Konstanz in the late 1980s. The first astonishing discovery was that, rather than these wintering Blackcaps being stranded individuals somehow left behind, the majority were actually birds who had flown northwest from their breeding areas in central Europe.18 This was a dramatically different direction from that taken by other European Blackcaps, which was solidly and sensibly southwest toward the far warmer Iberian Peninsula. Why would some individuals of the same species be heading in such different directions? Traditionally, in this region moving sideways in winter rather than toward the warmth would be disastrous; they would be prolonging their exposure to cold and reducing the chances of survival. Nonetheless, the records from England showed numbers to be increasing, especially since the 1990s. Something rather strange was clearly going on.
With increasing numbers of ringed birds returning to their normal breeding grounds in southern Germany, Peter Berthold was able to study their reproductive activities in detail. He soon found that the Blackcaps that had overwintered in Britain—ostensibly the individuals taking the “wrong route”—were arriving back well ahead of the birds coming from the traditional south, often a full two weeks earlier. This was a huge advantage to these individuals, allowing them to find a mate, breed earlier, lay larger clutches, and produce significantly more offspring that those migrating along the traditional route.19 Recent genetic studies have confirmed that the overall European Blackcap population is progressively separating into two groups: those wintering in the UK and those heading south, with males and females from either group preferring to mate with partners with the same migratory inclinations.20 This is a dynamic picture of evolution occurring in real time before our eyes.
Fascinating though this unfolding story is, a fundamental question remains: Why were the overwintering Blackcaps traveling north in winter doing so well? “Now that is just the sort of question we can answer using the Garden BirdWatch data!” exclaims Kate Plummer. The first task was to verify the apparent increase in the numbers of overwintering Blackcaps. Kate extracted the Blackcap data from twelve consecutive winters (1998/99 to 2010/11) from almost 4000 separate locations, amounting to a total of over 800,000 weekly records. While bird-watchers have been talking about the increasing numbers for some time, Kate’s careful analyses show that the increase has been particularly pronounced since the early 1980s, with numbers peaking each year in late January and February.21 Currently, about a third of all gardens in the program have Blackcaps. But why?
Well, because of food availability obviously, but as there does not seem to have been a major change in natural food supply, feeders clearly come into the picture. But what do Blackcaps like in the way of feeder fare? As it seemed likely that the answer to this question was fueling—literally—the Blackcap boom, Kate Plummer decided to dig deeper. Garden BirdWatch participants who observed winter Blackcaps regularly were invited to report on which types of feeder foods the birds were using. With over 500 people sending in data from all over the country, this was a decent sample of the diversity of feeder supplies. The results showed clearly that Blackcaps preferred fat and sunflower hearts above all else, and that the presence of the birds in gardens was strongly associated with the availability of these foods.22 “This move into gardens seems to be becoming stronger over time,” Kate explains. “It seems to suggest that Blackcaps are progressively adapting to obtaining their food from feeders.” This idea appears to be supported by recent studies indicating that the overwintering Blackcaps have developed a narrower and stronger bill than their traditional cousins, possibly indicative of a more generalist diet.23 Interestingly, many people also noted that this otherwise modest little bird is highly aggressive at feeders, vigorously chasing away other species attempting to use “their” feeder.
Kate Plummer’s well-reasoned conclusion is that the general availability of these foods at feeders over broad areas has provided the foundation for the growth in the overwintering Blackcap population in Britain. The period during which numbers of the species has steadily increased—starting around the 1960s—coincides closely with the growth in popularity of bird feeding and the proliferation of commercial bird foods, including all manner of fatty products. Although it will be difficult to prove conclusively, the advent of the Blackcap as a common winter visitor to British gardens may be one of the clearest examples of the direct influence of feeders on the abundance and distribution of a species.
But wait, surely this period also coincides with the general warming of the climate, a well-documented global phenomenon with a wide range of ecological influences. This would have taken some of the edge off the late winter bite for the birds arriving from Europe and marginally improved their chances of surviving.24 The critical element to this situation is, of course, the availability of suitable foods. Blackcaps are known to depend largely on the fruit and berries found in woods in winter, moving into gardens when these supplies are exhausted. The somewhat milder conditions associated with climate change probably enhance survival rates, but only if appropriate foods are available. Warmer but still hungry just won’t work.
The “Blackcaps in winter” story is compelling but it is also exasperating. It is probably one of the clearest examples of the effect that feeders may be having on a species. But these insights are only possible because we just happened to know a lot about this particular species, and that is because scientists were already focused on other aspects of Blackcap biology—their migration patterns, reproduction, and evolution—and because bird-watchers were gathering data at their feeders in sufficient detail that critical questions could be asked. It is exasperating because despite the staggering amounts of excellent data being garnered by programs such as Garden BirdWatch and Project FeederWatch, there are so few clear examples of the feeder effect.
My time spent discussing the magnitude and limitations of the grand feeder-focused programs with people from the Cornell Lab of Ornithology and the British Trust for Ornithology was also characterized by the possibility of extraordinary opportunities. Both organizations emphasized that while they themselves were frustrated in having too little time to engage in interrogating the information they were so successful in attracting, this data was available to anyone with legitimate interests in collaboration. “It’s a gold mine for the right kind of curiosity,” reiterated David Bonter, as I was leaving. “There are answers here for questions we haven’t even thought of yet!”
This particular excursion has been an attempt to see if it was possible to discern specific ways in which providing food for wild birds in our gardens was actually influencing them in some way. We tend to assume that our private feeding activities are either neutral or p
ositive, if we think about the consequences at all. By now, however, we should be aware that the scale of our collective efforts in supplying vast amounts of bird food over large areas is potentially of enormous impact. Certainly, there are some very strong suggestions—hummingbirds in wintry Ontario and Seattle, the recovery of House Finches, Blackcaps wintering in Britain then breeding early in Germany—but establishing a direct and definite link between bird feeding and such changes is always going to be difficult.
Seeking to understand the possible relationship between the practice of feeding and the outcomes for the birds themselves is perhaps the central objective of this entire journey. The partial glimpses of possible explanations—at best—described above have led me to reconsider some of the more fundamental aspects associated with why we feed birds in the first place. It may seem trivial and even redundant, but I think it is worth asking some of the basic questions again and seeing how much we really know. Bear with me.
Why Do We Feed in Winter?
Well, that is about as fundamental as it gets, but let’s make sure we are clear about why birds are fed in winter in the first place. Although aspects of this question will be dealt with in some detail in later discussions of the motivations for feeding (Chapter 7), the key points need to be considered here.
First and most obviously, winter feeding seems to be about assisting the vulnerable, a humane act to help creatures in need. Although there is certainly an element of birds representing “life in the depth of the apparently life-less winter” (as one correspondent described seeing hummingbirds at a snow-covered feeder), “helping the helpless” seems hardly contestable as a primary motivation. This assistance can have two main forms: providing much-needed sustenance for apparently desperate birds due to current severe conditions; and second, providing additional food that improves their chances of surviving through to the next season. If you like, there is the immediate relief of hardship—an act of welfare—and the longer-term goal of preservation, by prolonging life. For most people, I suspect that these components are not really considered separate: we are simply providing care, now, and hoping that this makes some sort of difference in the longer term. This is pretty straightforward: the primary goal of feeding wild birds in winter is actually about life and death.