Posts Tagged ‘ecology’

The other day I was browsing Etsy for garden art, and came across some beautiful whimsical bird feeders, and was about to buy them when I thought, “Wait- should I even be feeding the birds?”

What are scientists saying about bird feeders? It definitely can make a difference in both the survival and behavior of birds, but calling those changes good or bad is tricky.

A few of the effect of feeding birds that researchers have figured out:

  • Feeding birds during the winter and spring can cause birds to lay their eggs earlier, lay larger eggs, or have larger clutches. Both laying earlier and larger eggs tends to increase hatching and survival rates. Like all the other results I’ll mention, some bird species seem more susceptible to these changes than others. The magnitude of these effects also depended on the quality of the food provided to the birds- in a study of Florida Scrub Jays, birds fed high-fat high-protein diets layed first, birds fed high-fat low-protein diets layed next, and the control group that had only food that they foraged layed last. Extra food makes the most difference in tough environments such as cold winters and poor-quality habitat.
  • Adult birds sometimes feed their chicks the human-provided food, or sometimes eat the provided food themselves, which allows them to give more of the food they forage to their chicks. Unsurprisingly, when the chicks themselves receive the human-provided food, high-quality food has a positive effect on the growth of chicks, but low-quality human-provided food can have a negative impact on the growth of chicks. This is one of the clearer lessons in whether feeding birds is a good idea- for those who are tempted to toss bread crumbs or other human food out for the birds without considering whether it is nutritious to birds, consider that you may be doing them more harm than good.
  • Fast growth in chicks is considered good, but once birds are adults, many bird species regulate their weight to balance their perceived risk of starvation with the ability to get away from predators quickly. At first glance it may seem like if feeders aren’t constantly full, we’re messing up the birds’ body-weight calculations, or if they are always full birds might become dependent on them, but we should remember that most birds expect to get food from several different places. Even when easy food is available in a feeder, most birds will also keep track of several other patches of food, expecting some of them to disappear now and then. This lack of dependency was confirmed for black-capped chickadees in a study during a Wisconsin winter, where feeders were suddenly withdrawn, and chickadees that had previously used the feeders did just as well as ones who hadn’t. The authors point out that since the study was done in a rural area, where natural food may be more available than urban areas, the results might not hold true for cities. Since Seattle gets very little snow in the winter, I’m guessing that even the city gardens in my neighborhood have plenty of natural food for little birds like chickadees to get by.
  • Some folks are concerned that bird feeders increase the number of little birds getting eaten by predators. It turns out that how many birds are caught by predators depends on how and where your feeders are set up. Overall, though, researchers actually think that little birds get eaten at feeders less often than they would in the wild. The biggest predators at feeders are hawks and cats, though if you have eagles or snakes in your yard, they might be your biggest suspects. The feeding setups with the highest levels of hawk predation are near deciduous woods, have large feeding areas, year-round feeding, and lots of feeders. Cats got the most birds when bird feed was on the ground. If you want to prevent your cat from eating birds, put a bell on your cat, and keep bird food off the ground. Especially since bird feed on the ground is also rat food.
  • Researchers know that some diseases and harmful microbes spread through feeders, including mycoplasmal conjunctivitis and salmonella. To prevent this, take your feeder down and give it a good washing with hot water and soap, making sure to thoroughly rinse out the soap. For the same reason, wash your hands after handling bird feeders.
  • The ranges of several birds has expanded in the last 50 years, as bird feeding has become more popular, and some bird populations are overwintering in places they used to migrate away from. There are a few things that could explain these behavior changes, but feeding of birds is the most likely cause for many populations. All of the earlier issues I mentioned set off little red flags in my brain, but as someone who’s studied how plants, animals, and diseases spread, changes in range and migration patterns set off big warning bells. Messing with the physical location of species tends to wreak havoc in ecosystems, and though I’m not a bird expert and can barely guess what changes have occurred due to these behavior changes, I’m not excited about contributing to this experiment, even though those feeders were adorable.

While all this research has convinced me not to put a bird feeder in my garden, it leaves out the main reason other people choose to have them- they like to see birds. Just like owning a dog doesn’t make economical or environmental sense, there are other, more social benefits to having animals around to entertain us. My squeamishness about causing ecological change may also be misplaced, since gardening is at its heart, creating my own little ecosystem. I think I’ll take the middle ground this time though- I’ll design the plants in my garden with feeding the birds in mind, with native berries, seeds, and flowers making a strong showing and a clean pool of water in the bird bath year-round. Maybe I’ll even get those little bird feeders, but hang them empty as garden art and let the plants feed the birds.


[1] M.C. Brittingham, S.A. Temple, “Does Winter Bird Feeding Promote Dependency?,” Journal of Field Ornithology, vol. 63, 1992, pp. 190-194.

[2] E.H. Dunn and D.L. Tessaglia, “Predation of Birds at Feeders in Winter,” Journal of Field Ornithology, vol. 65, 1994, pp. 8-16.

[3] G.N. Robb, R.A. McDonald, D.E. Chamberlain, and S. Bearhop, “Food for thought: supplementary feeding as a driver of ecological change in avian populations,” Frontiers in Ecology and the Environment, vol. 6, Nov. 2008, pp. 476-484.


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