by Darryl Jones
Stephan Schoech, Reed Bowman, and Jim Seymour are three researchers engaged in long-term studies of Florida Scrub Jays who have taken a particular interest in the influence of food and nutrition in the lives of these birds. In an initial study in the 1990s, Schoech supplied dog food, peanuts, and mealworms (a diet fairly similar to that available to the Scrub Jays in nearby suburban developments in Highlands County) to some groups and not to others, all birds living near the Archbold Biological Station.54 After decades of continuous interaction with researchers, the birds were only too willing to participate in the study. As Schoech explained: “Group members quickly learned where the feeding station was and if they were not already waiting for me, rapidly responded to my whistle.”55 The results were spectacular: breeding was advanced by an average of 16 days. (Recall that we were excited about differences of just a few days in fed tits.) Obviously, the provision of additional foods is of primary importance to decisions of when to start breeding in this species. Interestingly, the study also tested one of the key hypotheses about the causes of cooperative breeding: helpers don’t breed because there is insufficient food. However, although two of the fed female helpers did forsake the life of an au pair, found a partner, and went on to breed themselves, the others (thirteen of fifteen) did not. It would appear that among Scrub Jays, there is more to such a fundamental change in behavior than simply food supply.
These findings have obvious implications for Scrub Jays with access to the well-filled suburban feeders, increasingly available as suburban developments expand in central Florida. Generally, these birds do not live in suburban areas but visit periodically from their territories in the scrublands nearby. This proximity to a year-round supply of foods such as pet food, peanuts, and food waste led to about a third of the diet of breeding female Scrub Jays being provided by people.56 As expected, these birds started to breed earlier compared to their scrubland relatives.57 Presum-ably, this was due to the relative reliability and higher fat content of the human-provided foods, but teasing this apart requires more control over the variable; that is, a proper supplementary feeding experiment.
Jim Reynolds from the University of Birmingham in the UK (whom we met earlier) is a long-term collaborator with extensive experience working with the Scrub Jays. An experiment he conducted with Stephan Schoech and Reed Bowman was designed to assess the influence of different fat and protein levels within the foods provided.58 Of course, these issues had been previously studied by other researchers, using the usual commercial seeds as supplements and assuming standard nutrition content. What Reynolds and his colleagues wanted was far greater control of the actual levels of the fats, proteins, and carbohydrates present in the foods provided. To do so, they had their own made, arranging for a commercial operator to produce vast amounts of little cylindrical pellets to a very specific recipe. These were of two “flavors”: high fat and high protein, or high fat and low protein. Both types had, however, identical energy content. This was supplementary feeding science on a new level altogether.
Clever, yes, but only if the Scrub Jays agreed that the odd-looking, gray-brown pellets appearing in their feeders were edible. After all, they looked nothing like the dog food, peanuts, or mealworms they were used to. This particularly adventurous species had no hesitation, however; they loved the pellets and the experiment was off to a good start.
As usual, Scrub Jay territories were randomly assigned to either high fat, low fat, or no fat (that is, the “control” group, who were offered welcoming but empty feeders). Supplementary feeding started in midwinter and continued until just before the start of laying. In the second year, everything was again randomized and no group received the same diet two years in a row. Again, the results were remarkable and, because of the sophistication of the experimental design, the particular dietary influences could be teased apart. First, as we would now expect, the start of breeding was considerably earlier for fed birds compared to the unfed, although again the extent was extreme: on average almost two weeks earlier. What was unexpected, and to my knowledge has not been shown in any other supplementary feeding study, were similarly strong effects on three other fundamental breeding characteristics: clutch size, egg mass, and egg composition. Unfed Scrub Jays produced an average of 2.8 eggs while those on the low-protein diet laid 3.8 eggs and those on high protein laid 3.5 eggs, although this difference only occurred during the first year. This is especially remarkable given that the normal clutch size for this species is only three.
But simply laying more eggs does not necessarily translate into more chicks: the survival of hatchlings is closely associated with both the size of the egg and the way it is provisioned for subsequent embryo development by the female. In most birds, egg size declines steadily with each additional egg produced, with the last laid being the least likely to survive. While a steady decline in the mass of eggs as each was laid did occur in each of the three dietary treatments, Scrub Jays on the high-protein diet were able to maintain the mass so that the third egg produced was actually much heavier than the equivalent egg laid by each of the unfed females.
Studies such as this Scrub Jay experiment indicate an increasing interest by researchers in some of the finer details of the relationship between food and a wide range of aspects of animals lives. Carefully designed and well-conducted experiments on wild species have been essential to uncovering the links in this complex chain of influence and consequence. Additional food almost always changes something. As we have discovered here, supplementary feeding experiments have also revealed unexpected and unwelcome findings. Some of these results may well alter the way we think about and practice our own wild bird feeding.
Maggie’s Meat
As a final example of the way that our feeding can affect garden birds we return to the unusual scene at a typical feeding station in an Australian back yard. Instead of sunflowers, peanuts, and suet there is often salami, ground beef, and cheese. And that’s because rather than birds like tits, chickadees, or even Florida Scrub Jays, the most likely visitors are all large, assertive, and often—strangely enough—black and white, with a distinct taste for meat (though just about anything vaguely edible will do). These pied picnickers may include (Pied and Gray) Butcherbirds and (Pied) Currawongs, as well as (the non-pied) Laughing Kookaburras. But far more probable are the Australian Magpies introduced at the beginning of the chapter. Not only are these big, bold birds the commonest species at Australia feeders, they are also the most welcome. More people try to attract “Maggies” than any other species: hence all that meat.
As demonstrated by numerous examples described already, researchers are often intrigued, if not concerned, by the physiological impacts of anthropogenic foods on wild birds. Such was the case with the overly meaty diet of Australian Magpies being fed throughout the suburbs of the country. In an important experiment conducted by Go Ishigame and colleagues from the University of Queensland, three types of common foods—minced meat (ground beef), pressed dog food (“dog sausage”), and shredded cheese—were supplied to groups of free-ranging magpies.59 These were typical foods available at feeders used by local magpies. Experimental provisioning occurred over a series of several month-long sessions, during which each group received one food type or none. Rather than the usual breeding parameters we are now familiar with, the focus of this experiment was on blood chemistry. Critics of wild bird feeding have suggested that some of the foods being consumed by urban birds may be harmful to their health. Certainly, the foods offered—and accepted—by magpies could be included in this category. To assess this, at the end of each monthly feeding session, Ishigame and company caught the birds and obtained tiny blood samples, which were tested for several parameters.
Interestingly, both cholesterol and uric acids levels were found to have increased significantly but only for the dog sausage. Both parameters are well known as indicators of negative health conditions. The result is also noteworthy because the birds consumed similar amounts (about 40 grams [1.4 ounces] per day)
of each food type, yet the mince and the cheese had no discernible effect. This finding may be associated with the relative level of commercial processing involved, with both the meat and cheese being considerably simpler foods compared to the dog food. Indeed, the fact that this item is manufactured and marketed as a balanced pet food— albeit obviously for dogs—but produced a marked spike in cholesterol levels in birds may be of some concern. And while plenty of magpies are known to partake of such pet foods—both as supplied by feeders as well as by sneaking bits from pet bowls—there are also vast numbers of birds being provisioned daily with processed meats such as salami, German sausage, and other cholesterol and fat-rich fare. And we already know what happens when these foods are eaten to excess in human diets.
Food for Thought
That’s probably enough examples of supplementary feeding experiments for now. Those featured here are only a fraction of the many such studies that have been published, but they represent a fair selection of those that relate directly to urban birds. As we are obviously interested in understanding the influences of providing additional food to wild garden birds, those dealing with other bird groups or topics associated with conservation and wildlife management were not included here. Furthermore, the studies featured have tended to be those with the more marked results. That is hardly unusual as it’s always easier to write about—and more interesting to read—the research where the findings were spectacular or unexpected. Nonetheless, it is also important to be aware that plenty of well-designed and carefully conducted experiments did not find an effect. I suspect that many such studies simply do not get published, leading to a definite bias toward positive and significant findings in the available literature. Some, however, have made it through the rigors of the peer-review process and these also need to be acknowledged.
Although there are several excellent reviews of supplementary feeding experiments available (see Boutin’s 199060 review for many examples), a particularly readable summary of relevance to this discussion is that of Gillian Robb and colleagues (whose study of winter feeding of tits in Ireland we described earlier).61 In their article, titled “Food for thought,” the authors reviewed as many supplementary feeding studies on birds as they could find and determined whether the addition of food resulted in either a positive or negative or no response on each of seven commonly measured breeding parameters. Although these researchers looked at a number of different bird groups, we will concentrate on their “small passerines” category, as the most representative of the species that come to feeders.
The breeding parameters featured in “Food for thought” were as follows: laying date, clutch size, egg size or quality, incubation time, hatching success, chick growth rate, and fledging success. Considering the direction (positive, negative, or none) of the response of all these features together, two conclusions are immediately clear. First, negative responses to supplementary feeding were very rare; only a single study, reporting a later laying date with feeding, was cited. Second, the most common response, by far, to supplementary feeding among small passerines was none. Only for laying date and fledging success did positive responses outnumber no response. While this was most pronounced for laying date effects, with eighteen out of twenty-eight studies reporting earlier egg production due to feeding, almost a third of studies found no effect. Bear in mind that an advance in the timing of breeding is certainly the most publicized effect associated with the provision of additional food. These studies suggest that this commonly reported outcome is far from ubiquitous. Indeed, when all the bird groups included in the review are considered, thirty-four studies reported earlier breeding while twenty-four—that’s 40%—found no change at all. For the only other breeding parameter where a majority of studies found a positive response—fledging success—the ratio was even closer: ten were positive compared to nine with no response. Food for thought indeed.
Good News and Otherwise
We have traversed a lot of territory in this chapter, providing perhaps too much detail to remember. The main message to be gained from these experiments is that feeding garden birds often really does change things. For example, feeding does assist survival through the winter and especially during periods of prolonged severe conditions and lean years when natural foods may be scarce. Winter feeding also leads to better survival of chicks, due in part to the elevated body condition of the breeding females. Providing additional food may therefore lead to the presence of more birds locally, through the attraction of visitors to an abundant foraging resource as well as through the enhanced breeding of the residents. All of this is surely good news. However, these changes may also include unwelcome outcomes we did not expect.
One of the roles of scientific rigor is to ensure that we see beyond what we hope is happening or what we might logically expect. Certainly, some of the researchers conducting these supplementary feeding studies were surprised—and sometimes alarmed—at their own findings. For example, to discover that a study replicating typical continuous (“year-round”) feeding practices actually led to fewer offspring is of considerable concern. This is because the experimental results appear to mirror what is now widely appreciated more generally: that suburban birds tend to lay fewer eggs and have smaller broods than rural populations of the same species. Feeding is directly implicated. Similarly, studies mimicking the fat-heavy diets of many typical feeders found that this can impair yolk and embryo quality, with real risks to the survival chances of the hatchlings. Again, a worrying result, although this important study may also have come up with a possible solution (the addition of an antioxidant such as vitamin E).
This is a suitably sobering note on which to conclude our discussion of the science of supplementary feeding. As we have seen repeatedly in the examples described here, a proper scientific approach requires a genuine willingness by researchers to be critical, clever, and open-minded. When conducted with appropriate rigor and attention to detail, careful experimentation may be essential for progressing ideas beyond what is possible through observations alone. This is certainly the case for anyone seeking to understand the apparently obvious, actually complex interaction between birds and the foods we provide for them.
So, in conclusion: feeding almost always changes things although sometimes in ways that are different from what we were expecting.
6
TAINTED TABLE?
Can Feeding Make Birds Sick?
I have met plenty of keen bird watchers who also feed, but none come close to Frank Wilston for infectious enthusiasm and scientific dedication. I visited his home in a small town outside Washington, DC, late in spring and was overwhelmed by his hospitality, master naturalist’s knowledge, and wicked sense of humor. Having just celebrated his 85th birth-day (and shared his cake with some excited Tufted Titmice, perched on a steady hand), Frank admits that he doesn’t get out birding in the nearby woods as much as he would like these days. A self-confessed “avid birder” (he says his friends are more likely to say “darned fanatic”) from his earliest days, Frank now channels his considerable energy into ensuring that the birds come to him. This has meant a fundamental redesign of his large yard, with every feature—the position of the garden beds, the selection of each shrub and tree, the numerous “no-mow” sections full of grasses and weeds—strategically positioned with viewing birds in mind. Fundamental to this aim are the feeders. As Frank guides me through his remarkable garden, I try to keep count: there are lots of tube hangers of all sizes, including fine-mesh tubes for the tiny nyger seeds, as well as large-mesh peanut balls. There are also several simple platforms, a large and fancy transparent hopper feeder, several “thistle” socks, and at least a couple of little feeders stuck to the windows. “I think that comes to fifteen feeders, Frank,” I venture. “That means buying an awful lot of seed.” “You missed the two ‘woodpecker feeders’ in those trees yonder,” states Frank matter-of-factly, pointing to a stand of Scots pine. “And yes, that is a bunch of birdseed. It costs me a packet, but I’m happy
to spend my hard-earned money on these delights. Better that than let my lousy relatives get it!”
It’s late afternoon when we settle into a couple of chairs on the high-set veranda overlooking Frank’s marvelous garden, home-brewed beers in hand. As I glance around the yard, the genius of Frank’s attention to the placement of his feeders is obvious: from this single vantage point I can see eight, at different heights and settings, providing a lot of foraging— and viewing—opportunities. As we watch, a small flock of pinkish birds flutters onto a nearby platform, expelling a couple of cardinals and immediately squabbling among themselves over the remaining safflowers. “House Finches,” says Frank quietly, instantly peering through his ever-present binoculars. This is a common and familiar species around here, sometimes disliked because of their rather quarrelsome nature. Nonetheless, Frank is paying close attention, his intense gaze subjecting each individual to unexpected scrutiny. After a few minutes, Frank puts down the binoculars and promptly makes some notes in the battered notebook he takes everywhere. “Just six today, but all clean,” he murmurs as he writes. “No sign of sore eyes for quite a few months now.”
The reason for my visit to Frank here in small-town central Maryland is because of these House Finches, and Frank’s role in the discovery and tracking of what is now one of the most carefully studied examples of a major wildlife disease outbreak anywhere. This very important phenomenon was first noticed right here in January of 1994 by Frank and other attentive bird feeders in the area. But how these “ordinary” folks became such significant players in an extraordinary story of citizens and science begins at least a decade earlier, with the advent of the Cornell Lab of Ornithology’s Project FeederWatch program in the 1980s (as discussed in Chapter 4). This program was ideal for diligent and observant bird watchers like Frank, who had been systematically recording the birds visiting their feeders for years already. Project FeederWatch was a perfect way for such people to contribute their existing skills to a large-scale science project. “I was completely untrained but I did know my birds,” Frank explains. “When I learned that the Cornell people were looking for regular folks to help them learn more about our birds, I got right on board. I’m quite proud to say that I was one of the original FeederWatchers.”1
