It is a little ironic that all nature enthusiasts know that it is "bad" to feed the animals ... they become dependent on the food, and in some cases will become a nuisance or dangerous, prying open cars or breaking into homes to get more food. Then the animal has to be put down or moved to a new habitat. But that sort of bad outcome is more common with, say, bears than it is with, say, chickadees. The irony here is that bird lovers, who are always nature enthusiasts, do not seem to balk at setting up bird feeders. In fact, approximately on half a million metric tons of seed is put out for the birds in the United States and the United Kingdom.
This must have an effect on the birds, for better or worse. Two studies just published by the same research team address this issue.
Few scientific studies have addressed the ecological effects of backyard bird feeders. So Gillian Robb, an ecologist at Queen's University Belfast in the U.K., and her colleagues gathered as much information as they could about supplemental feeding in any context, for species from sparrows to owls.
Robb and her colleagues confirmed this effect with an experiment of their own in Northern Ireland, where they gave peanuts to dozens of blue tits at five woodland sites and let the birds fend for themselves at another five sites. The birds that nibbled peanuts all winter fledged more chicks in the spring, the team reports
when Florida scrub jays ate too much in winter, they laid their eggs so early that the hatchlings' natural food sources weren't available when they needed them...
If a region's year-round residents plump up on extra seed all winter and get a head start on breeding territories and natural food supplies in the spring, they could present stiff competition to migrants returning from tropical wintering grounds.
Paige Warren, an urban ecologist at the University of Massachusetts, Amherst, says that based on the paper, she won't discourage birders who ask her advice on bird feeders. But she brings up another potential downside, the socioeconomic impact: Birdseed is often grown in regions where farmers are treated poorly. And then there are the environmental effects of growing and transporting thousands of tons of birdseed.
The research was published in two journal articles. The first is in Frontiers in Ecology and the Environment. From the abstract:
... While alteration of the natural dynamics of food supply represents a major intervention in avian ecology, we have a remarkably limited understanding of the impacts of this widespread pastime. Here, we examine the many and varied responses of birds to supplementary feeding at backyard feeders - in large-scale management projects and in focused academic studies - and evaluate population responses to the bird-feeding phenomenon. Our review encompasses a wide range of species, from songbirds to raptors, and compares provisioning with a variety of foods, at different times of year and in different locations. We consider positive impacts, such as aiding species conservation programs, and negative ones, such as increased risk of disease transmission. It seems highly likely that natural selection is being artificially perturbed, as feeding influences almost every aspect of bird ecology, including reproduction, behavior, demography, and distribution. As the effects of bird feeding cascade through ecosystems and interact with processes of environmental change, we suggest areas for future research and highlight the need for large-scale experiments, with a particular focus on the backyards of an increasingly urban and generous, but sometimes fickle, human population.
The second study is in Biology Letters. Again, from the abstract:
Supplementary food given to birds can have contemporary effects by reducing the risk of starvation, increasing survival and altering movements and reproductive performance. There is, however, a widely held perception that birds benefit from extra food over winter, but that it is better that they 'look after themselves' during breeding. Here we describe a landscape-scale experiment showing for the first time that the effects of increasing food availability only during the winter can be carried over to the subsequent breeding season. Even though food supplementation stopped six weeks prior to breeding, birds living on sites provisioned over winter had advanced laying dates and increased fledging success compared with birds living on unprovisioned sites. Thus, supplemental feeding of wild birds during winter, in a manner mimicking householders provisioning in gardens and backyards, has the potential to alter bird population dynamics by altering future reproductive performance. With levels of bird feeding by the public continuing to increase, the impacts of this additional food supply on wild bird populations may be considerable.
It is remarkable that the intersection of science and recreational natural history (i.e., bird watching) has not produced extensive studies of this kind already. There is a great deal of folk knowledge about bird feeding .... that birds may get their moist eyes stuck on metal bird feeders in the winter, that if you feed birds in the fall you must make sure you continue to feed them all winter or they will die, and so on. The idea that feeding certain species will result in their out competing other, perhaps at-risk species does not seem to be part of that folk knowedge, but perhaps it should be.
Robb, G.N., McDonald, R.A., Chamberlain, D.E., Bearhop, S. (2007). Food for thought: supplementary feeding as a driver of ecological change in avian populations. Frontiers in Ecology and the Environment, preprint(2008), 1. DOI: 10.1890/060152
Robb, G.N., McDonald, R.A., Chamberlain, D.E., Reynolds, S.J., Harrison, T.J., Bearhop, S. (2008). Winter feeding of birds increases productivity in the subsequent breeding season. Biology Letters, 4(2), 220-223. DOI: 10.1098/rsbl.2007.0622
Yes but when you think about it, any study on this matter should also take into account the effects of pet felines on the bird population. It could well be we give with one hand and take back with the cat....
I too am struck, like you, Greg, that us academic biologists haven't tapped into all the natural history lore built up by non-professionals. So when we do examine some of these issues, the findings are sometimes rather obvious - although careful study does yield some interesting insights into processes underlying the natural history "folk knowledge".
On the other hand, there are other elements of such "folk knowledge" that we absorb and propagate rather uncritically - for instance the purported villainy of cats against birds. Have you seen the other recent paper on cat predation (in Diversity & Distributions) which (in my cursory reading) doesn't quite find the evidence to support substantial negative impacts on birds?
I'm working on a post or two on these papers for later this week, once I get a few other things under control. Thanks for bringing them up here - and for pointing to that Science article which I hadn't seen, and which contains a quote from a good friend and collaborator! Pleasant surprise.
Amusing that even as I was typing up my comment, sailor jumped in with the "folk wisdom" about cats! That's such a powerful meme, though...
We took our bird feeder down the day we saw a rat sitting in the tray and chowing down.
Sharp-shinned hawks love feeders.
Sharp-shinned hawks love feeders.
Hey, Sharp-shinned Hawks have to eat too!
There are actually quite a few papers on the effects of supplemental feeding on bird survival and fledgling production, including this one dealing with bald eagles. There was another in the Wilson Bulletin about 2000 or 2001, dealing with chickadee populations in Maine. Most of these studies, as I recall (and I am away from my library right now) conclude that supplemental feeding has minimal effects on winter survival or nest success. It can have some effects on population dynamics; the expansion of Tufted Titmouses into the Northeastern US may have been accelerated by feeding. But it will be hard to do that experiment with a control...
I think that bird-feeding is a selfish act, designed to bring more birds in view. My mother kept a bird feeder nearby her large picture window, and granted, she would spend time inspecting and identifying birds. It was also nice for her to see them as in the years leading to her death she was too crippled by arthritis to be able to take a walk in the woods.
I am mixed about bird-feeding, but I think that people need not pretend that they are doing nature a favor. Wait, it can also be a way to make up for loss of bird habitat.
Well, I guess I'm guilty (if we've decided it's a sin) of feeding birds in winter -- basically, we support a good population of sparrows, chickadees and cardinals. We stop in spring as soon as the grackles show up, because all they do is chase off the other birds and then shit all over the yard.
In summer we throw peanuts for the bluejays (and the squirrels who steal from them). Between the feeding and the fishponds, we seem to get a lot of local critters in the yard.
Lets assume that feeding birds has a impact that is objectively undesirable for a given species or maybe even for entire communities. A case could easily be made for the value to the environment of enhanced engagement and awareness of those who indulge in the practice, which as reported in the study may be a large percentage of the population. In fact, it could be argued that a participatory role of any kind that engenders an awareness of natural processes - and our relation to them - is a prerequisite for any lasting conservation ethos. Large numbers of individual animals are lost to hunters and anglers every year, yet it is the collective force of these two groups (latter supplemented by birders) that created the conservation movement in the first place.
I guess my point is that even if the practice of bird feeding where shown to alter community dynamics, it would still be better to promote the practice if only to continually refill the ranks of those who are the prime movers in making sure we have any communities at all.
Just my two cents.
Recently, the feeding of birds in my backyard has brought about a collection of specific friends who come 10 times a day for nurishment.
First, Red and his wife Ruby show up peeking at me constantly from the nearest shrub awaiting unsalted peanuts. They feed each other and for the most part come together. If I ignore them throughout the day, they whistle at me! Who knew retirment would bring about this type of dependency.
Later, the other fine-feathered groups pop over: Big Blue the Bluejay, mourning doves, huge crows, woody the red-headed woodpecker and the sweet sparrows.
One of the old bird books said something along the lines of "You realize you've come south into Massachusetts when you see a turkey vulture soaring overhead."
When I saw a turkey vulture soaring overhead in northern Maine, I suspected the roadside feeding stations were having some effect.
I love to feed the Cockatoos and Rainbow Lorikeets. They are so beautiful and smart I cannot resist it. The female Cockatoo tries to communicate in a sweet way. They are guests most welcome and more sociable than my pet birds (lovebirds). I feel blessed.
we should feed the birds.
lets feed the birds its good for them