by Darryl Jones
So, what is the evidence to support these straightforward claims? Eval-uation of the evidence should be done in the dispassionate manner of the apparently objective scientific method, although that is all well and good in theory. For many people, including myself, being passionate about bird feeding is why we are engaged in the activity, why we are feeders in the first place as well as in the long run. But for me, this also means that we need to ask serious questions and assess the best available evidence. It does not mean searching high and low for data that support our position or refute opposing views. It does mean, however, a willingness to be open-minded. With this in mind, we say with certainty that the main apparent benefits of winter feeding are short-term welfare and longer-term survival. But does winter feeding achieve what is claimed?
As will already be familiar, the amount of reliable information available is quite small. There are some quite obvious reasons for this dearth of relevant information: it is very difficult to obtain. Being able to assess whether having access to feeders assists welfare or enhances survival requires detailed information on a large sample of individual birds, which enables any of the possible changes to be monitored. Two key features that might be examined are changes in body weight and the probability of surviving over a certain period of time. Obtaining these sort of data requires, at least, catching—without harm—lots of birds and taking extremely accurate weight measurements. This is hard enough, but when it involves mist-netting tiny birds such as chickadees and tits that weigh only about 12 grams (half an ounce) in the depths of winter, the challenges are formidable.
Thankfully, some such information is available. Working at the northern limit of the tiny but hardy Black-capped Chickadees in the cold winters of Wisconsin, Margaret Brittingham and Stanley Temple captured and color-banded (ringed) over 500 birds and followed their fortunes over three tough years.25 These birds were not, however, suburban chickadees visiting who-knows-how-many garden feeders. To be certain of the effects of specific amounts of seed, these researchers moved out of town into woodland study sites where they could control the supply of food—at least the amount provided by humans—available to the birds. They had to assume that the amount of natural food was the same in the various sites they worked in. To really understand the influence of the provisions, they had to be able to compare chickadees with access to feeders with those missing out. In other words, Brittingham and Temple did not just observe what was happening, they manipulated the key feature by setting up an experiment, providing food (in this case, sunflower seeds) in one place and not in another. The importance of such “supplementary feeding experiments” in enabling us to assess the effects of bird feeding cannot be overstated; the entire next chapter is devoted to reviewing this type of research. Here, however, we are focused on specific questions raised about winter feeding.
So what difference did feeders make to these chickadees in winter? The careful weights recorded showed that, on average, the fed birds were significantly heavier than the unfed birds. Although this difference was only 0.13 grams (0.004 ounces), or just 1% of adult body weight, it represented about two hours’ worth of foraging time during the coldest periods. Simi-lar results have also been obtained for various species of tits in Europe:26 the additional food made a major difference when the conditions were really cold. At other times or in places where the winters are relatively mild, the birds were less likely to feed so regularly at feeders, finding most of their dietary needs in the wild as natural food. During extreme conditions, however, the seemingly modest differences in weight translated directly into the ability to survive: birds using feeders were much more likely to stay alive into the following month compared to unfed birds. Most clearly, the Wisconsin chickadees with access to feeders were—on average—twice as likely to make it to the next winter, a major benefit for a bird that lives only for a few years.
Okay, these are important findings and certainly provide good evidence in support of the main claims for winter feeding. Nonetheless, we need to be clear about what they do and do not say. First, while these studies are sound and reliable, they are limited to several closely related species (tits and chickadees belong to the same family), and while these are among the most abundant feeder birds in the Northern Hemisphere, we cannot simply assume that the effects will be similar for other species. There are numerous survival studies on a range of birds but, remarkably, none on the garden birds that use feeders. Even more important, the very conditions of these carefully conducted studies—strict control of the amount, type, and timing of the food, ensuring that the subjects don’t have access to other feeders, for example—essential for scientific rigor, mean that these experiments may bear little resemblance to the actual world of a bunch of birds in a suburban backyard. A typical garden-variety chickadee or tit may be able to visit several feeders, as well as nearby parkland, woods, or school yards. They may be at risk from cars and cats rather than hawks or owls, and may have been raised in an environment full of people and their edible refuse. Most wild bird feeding occurs in anthropogenic landscapes— towns and cities—and we need to bear this in mind.
Should We Be Feeding All Year Round?
There is, therefore, at least some support for the idea that feeding birds in winter assists their survival. While the evidence is limited to a few species, this effect does seem fairly logical and sensible (we will deal with these issues in more detail in the next chapter). But what about the equally intu-itive reasons given for why feeding should be limited to winter? This issue was covered quite extensively in Chapter 3, but we are revisiting some of the fundamental claims and may need to be reminded that bird feeding was fairly strictly winter-only in most places until quite recently.
Perhaps the best place to start this part of the discussion is back in the countries where the norm for feeding is still unequivocally restricted to winter. Whether through informal cultural lore or advice from reputable organizations, most people feeding birds in these countries seem to be well aware of why feeding birds should be limited to the cold weather. The Estonian Ornithological Society (to pick a less familiar example), for instance, advises that (my translation): “Birds do not need extra food from people” except during the prolonged cold of winter. Then, however “it is a big help for those species that have decided to stay,” but “bird feeding must be completed no later than April.”27
Two of the most commonly promoted concerns are, first, the possibility that the birds may become dependent on human-provided foods; and second, the risk that breeding birds may bring inappropriate feeder foods to their nestlings. The official guidelines from countries the world over are (or were) full of pleas for feeders to ensure that birds be left to “look after themselves” when not threatened by severe weather, as well as disturbing stories of chicks choking on a peanut.28 In the 1980s, for instance, the Royal Society for the Protection of Birds in the UK stated that birds “should not be allowed to become dependent on the provider” and “that nestlings may be killed when fed with indigestible foodstuffs.”29 There are also emerging concerns about the nutritional influences of typical high-fat winter foods, but these are more recent issues (and are considered in some detail in the next chapter). For the moment, let’s briefly look at what is known about dependency and chicks being fed the wrong foods.
Do Birds Rely on Our Food?
The possibility that the birds we feed may become dependent on the food we provide has been shown to be a central concern to feeders everywhere. It is also among the first issues raised by both opponents and proponents of feeding as reported in a wide range of surveys from throughout the world.30 Obviously, as a passionate bird-watcher and feeder, I need to be comfortable that my pastime is not causing harm, but also that is not changing the natural balance too much. If I was to learn that “my birds” relied entirely on my remembering to fill the feeder, I would be quite concerned. Even more graphically, many of the guidelines on bird feeding strongly intimate that birds could become so used to finding their food at
the feeder that they could “forget” how to forage naturally.31 This would result in (cutting straight to the worst-case scenario) starvation. Hence, the oft-cited “golden rule”: once you start, don’t stop!32 Indeed, this may be among the most widespread and widely accepted of all tips on feeding. And it is worth stating things as starkly as this because I am very much aware that this is indeed the situation many individuals now find themselves in. There really are large numbers of people who feel they cannot stop feeding—ever—because of the potential catastrophe that would surely result. This is the very reason given for having a strict limit to how long feeding should last. In other words (it is argued), we should feed to assist the birds during the really cold periods but stop as soon as possible in order to limit this possibility of dependency.
This issue was of such importance to my own studies of bird feeding that for many years I have attempted to gather all the relevant studies and to speak to as many people as possible from around the world who have thought about this seriously. Surely something so salient to the practice of bird feeding must have been subjected to critical scientific attention. The reality is, again, that there has been extremely limited research on this issue. But, to be honest, this is difficult research to do, especially the kind of experiments that would be necessary to actually test whether birds really were dependent on feeder food. Theoretically, that would require making the tough call of providing food to birds, then stopping the feeding entirely and observing carefully what happened next. Could anyone actually do such a thing?
Well, yes. In a simple but game-changing study, Margaret Brittingham and Stanley Temple again show why they have been among the most important pioneers in the scientific study of bird feeding.33 Focusing directly on the core issue of dependency, these researchers decided to see what might happen if birds—chickadees—were deprived of their feeder food (sunflowers) over a whole winter. What makes this work so compelling is that the site where the feeding was stopped had been providing the local birds with supplementary food for 25 consecutive winters! If any birds were going to be relying heavily on feeders, this was them. To be certain of the outcome, Brittingham and Temple set up a separate though identical site where the chickadees had never been fed. Both sites were surveyed weekly over three winters to check on the presence and behavior of individuals. This point—that the researchers were able to track the fortunes of specific birds—is the main difference from the earlier study by these researchers mentioned previously (which assessed general survival risk at the population level). This new study was focused on individual chickadees, including observing their foraging activities, especially during the third winter, during which no feeding occurred.
The result was spectacularly dull: there was no significant difference in monthly survival rate of individual chickadees at the two sites. Most significantly, the lack of supplementary food made no apparent difference to birds who had previously had access to unlimited seed. How on earth could they have survived? Although they do not say as much, it is clear from the way their paper is written that Brittingham and Temple were not at all surprised by the results. Their intimate knowledge of these otherwise delicate and vulnerable birds indicated that, even in the depth of a snowy winter, the birds were able to find most of their food from natural sources. The researchers observed their birds feeding on a wide range of items including mites, insect eggs, and larvae, as well as grain gleaned from horse dung. The sunflower seeds available at the experimental feeders were just one source of food among many. Indeed, even during the first two years of the experiment, when the feeders were still being stocked, almost 80% of the birds’ diet remained natural. Addressing directly one of the major concerns associated with the issue of dependency, the researchers state: “It is not surprising [after 25 years of feeding] that these chickadees had not lost their ability to utilize natural food efficiently.”34 Even these hard-pressed Wisconsin birds treated the food supplied by people as, well, supplementary.
This is crucial work, but even so, the researchers also caution against applying their findings too broadly. Theirs was, after all, a carefully controlled experiment in a natural woodland; the conditions in a typical suburban garden may be vastly different, especially in relation to the availability of natural foods. The caveat is especially critical in the case of places were the foods provided at feeders may actually represent most or all of the foraging resource present, as is likely the situation where once migratory species now overwinter apparently because of reliable feeders or when climate conditions are pronounced or prolonged. These are obviously situations where continuing to feed in winter is vital. But these are also perhaps best appreciated as appropriate responses to local conditions. The middle of winter is one thing; at other times, provisioning may not be so significant in the lives of the birds. (Note that I did not suggest it was not significant in the lives of the people doing the feeding.) What the Brittingham and Temple study more than hints at is that for most birds, most of the time, our feeders probably provide only a portion of their overall diet.
A couple of more recent experiments are also worth mentioning here: the first looked at what happens in relation to a whole community of birds denied access to their feeders, while the second “withdrawal of feeders” study was actually conducted in the suburbs. Travis Wilcoxen and a large group of colleagues undertook a particularly important feeding experiment in woodland sites in Illinois where they compared a lot of health features of many species with and without feeders.35 Some of these results will be described later, but here we can mention what happened when the feeders were removed after two years. Although some of the positive features associated with having a regular feeding source—higher fat levels, increased antioxidants (see below)—disappeared when the feeders did, for other characteristics there were no differences with feeder-less birds. Significantly, these researchers concluded that the feeders were indeed “supplementary” to the birds’ diet.
As part of her pioneering work undertaken in Auckland, New Zealand, Josie Galbraith asked lots of people to let her set up her purpose-built feeders in their gardens so that she could record the activities of the birds.36 Then she had to convince about half of the willing participants to stop feeding, 18 months after they had started! Yet apparently they did so, because the huge increase in the abundance of the common species that occurred while the feeders were available simply dissipated when the food stopped coming. The concentration of birds at the feeders went back to typical prefeeding numbers, with the birds apparently adjusting to the change in resources. Again, this seems to suggest that birds are more than capable of altering their foraging behavior to differing conditions, even in the apparently “artificial” suburban environment.
This was an issue that I was forced to take very seriously during my own research into the foraging of Australian Magpies living in the suburbs of Brisbane, Australia.37 Aspects of my work are described elsewhere in this book, but the key point was that although we made detailed observations of the natural foods eaten by the birds while they were in view, we really don’t know what they were getting up to when they were out of sight. The same is true for anyone wanting to understand the actual diet of birds in human-dominated landscapes: we have little idea of what they eat and where they go when they leave the place where we were watching them. In the early days of our magpie studies we first became aware that feeding stations for these birds were everywhere! Indeed, they were so common, offering a smorgasbord of meats and cheese, we wondered whether they presented an opportunity for magpies to abandon natural foraging altogether. With so much high-quality protein, so easy to find, why should the birds bother digging up worms at all? Furthermore, we reasoned, this would be even more likely when the adults had a nest full of large, hungry nestlings. If any birds were set up to become reliant on a source of supplementary foods, it was surely breeding magpies.
With this logic in mind, Rebecca O’Leary and I set out to compare the source of the foods parent magpies were feeding to t
heir chicks in territories containing feeding stations and those without.38 Actually finding places where people did not feed magpies proved remarkably difficult. Because suburban magpies have quite compact territories, however, we eventually found similar numbers of magpie pairs that were fed and not fed for comparison. We (well, mainly Rebecca) then got out the telescope and began to carefully document what the parents were bringing to the nestlings.
To our great surprise, almost all the baby food was entirely natural— worms and beetle larvae—for both the fed and unfed pairs. The really notable thing was that the parent magpies were mostly ignoring the readily available meat-laden feeding stations located all around as they searched for good places to probe for grubs in the ground. We concluded that these parent magpies seemed to have a “no junk food” policy when it came to providing for their nestlings.
This was also a conclusion reached (but not known to us at the time) by Richard Cowie and Shelley Hinsley in the early 1980s.39 These pioneering bird-feeding researchers compared the diets of tits in rural and suburban sites around Cardiff, Wales, and learned that despite the abundance of feeders in the suburbs, both groups of chicks were fed high proportions—over 85%—of insects, although some seed was also used regularly. I have discussed this finding with colleagues from around the world, and it turns out to be a familiar story: parent birds of many well-studied species typically bypass all those feeders as they seek out the insect food they seem to “know” their chicks need. This was another reassuring finding and unexpectedly addresses the two concerns we have been discussing: Does feeding lead to either dependency or inappropriate provisioning of nestlings? In the few cases available, the answer appears to be “no” in both cases. Provisionally, then, we feeders can relax a little; the birds seem to know what they are doing. Thankfully.
