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Wild bird feeding: the pros and the cons.

According to the Wild Bird Feed Association, North Americans purchased over 2 billion kilograms of birdseed in 2004. The US Fish and Wildlife Service valued birdseed revenue in 2001 at $2.6 billion and wildlife watching (including birding equipment, feeders, seeds, etc) at $7.35 billion. By comparison, expenditures on veterinary care for dogs, cats, and birds in the same period totaled approximately $19 billion. Although feeding wild birds is obviously a thriving industry, does it really help birds thrive? This round table discussion will look at the impact of wild bird feeding from the disease and conservation perspective. Four participants, all of who are involved in wildlife conservation, will comment. The participants are Patricia Bright, DVM, MS, Dipl ACVPM, The Wildlife Center of Virginia, Waynesboro, VA, USA; Julie Langenberg, DVM, Department of Natural Resources, Madison, WI, USA; James K. Morrisey, DVM, Dipl ABVP (Avian), Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA; and Ian Tizard, DVM, PhD, Schubot Avian Health Center, Department of Veterinary Pathobiology, Texas A&M University, College Station, TX, USA. Although not specifically addressed, the issue of bird feeding and avian influenza is a topic that will need to be addressed in the near future, especially as it may pertain to aquatic birds. As more information on which avian species may act as vectors for the H5N1 avian influenza virus, recommendations about bird feeding may change. At this point, we hope this discussion will stimulate thought about the commonly performed, but not so commonly evaluated, process of wild bird feeding.

Question: Do you currently have, or have you ever had, feeding or watering stations for wild birds? If so, when did you first start feeding wild birds?

Dr Bright:

I started feeding wild birds in my third year of veterinary school after taking an ornithology class. I currently have 4 bird feeders in my yard (2 holding sunflower seeds and 2 for hummingbirds), and I have 2 watering stations. In the past, I also had a thistle feeder in my yard, but I eventually removed it because I was concerned about disease. The thistle seed feeders tend to promote fungal growth. I tried multiple types of feeders and could not find one that kept the seed from getting moldy.

Dr Langenberg:

Yes, I currently have a winter-season bird feeder at home, and I have also, at times, had bird feeders at some work locations. I think I put up a feeder for the first time after having a child and observing how interested young children are in birds at feeders.

Dr Morrisey:

I currently have and have had feeding and watering stations for birds in my yard throughout the year. I have suet, thistle, and oil seed feeders and I have planted a variety of flowers to attract hummingbirds. I have been feeding birds since I was a child, whenever I've lived in a place conducive to feeding them.

Dr Tizard:

Yes. I actively provide feed and water for several different species of songbirds, including hummingbirds. I started feeding the birds when I first arrived in North America 35 years ago.

Question: Did feeding wild birds influence your decision to become an avian/wildlife practitioner/conservationist?

Dr Bright:

Although I went to veterinary school with the intention of becoming an avian veterinarian, I grew up in the city, and before taking an ornithology class I did not appreciate native birds. While I was growing up, my knowledge of native birds was limited to robins, pigeons, and house sparrows. Taking the ornithology class and watching birds (especially dark-eyed juncos and titmice) at my feeder became the catalyst for my seeking out preceptorships in wildlife medicine.

Dr Langenberg:

I don't remember my family having bird feeding stations when I was growing up, but I do remember being very interested in watching bird behavior around feeders at friends' houses. I certainly think that the close observation of common birds that is possible at feeding stations and while bird watching (especially with enthusiastic birders) fueled my fascination with avian species.

Dr Morrisey:

Not particularly. It has influenced my psychoaddictive bird-watching tendencies, though!

Dr Tizard:

Very much so. I lived in Canada for many years, and feeding birds during the winter was a major stress-relieving project. Learning to identify those birds led to a lifetime of birding, which, in turn, led to a late-life career change to avian medicine.

Question: Does feeding wild birds have a positive or negative impact on the wild bird population?

Dr Bright:

From the perspective of threatened and endangered species, I would say negative. However, feeding birds may, indeed, help keep "the common birds common." I remember reading a study several years ago indicating the overwinter survival rate among chickadees was about 30% higher in areas where chickadees had access to feeders. Personally, I think having access to water during the winter may be even more important for survival, so I provide heated watering stations as well.

In the event of a disease outbreak, such as mycoplasma, having bird feeders available may help infected birds survive by providing a much needed food source. One can also argue, however, that feeders contribute to disease spread.

I think wild bird feeding can have an indirect positive impact on avian conservation, as people who feed birds can be a great target audience for educating the public about conservation issues (eg, keeping cats indoors, putting up bluebird boxes). Wild bird feeding may have a direct positive impact on individual birds, but I don't know whether this impact will be translated to bird populations. Certainly, diseases like salmonellosis and mycoplasmosis kill individual birds. House finch populations declined after the mycoplasma outbreak in the mid 1990s. Surveys conducted at Cornell University indicate that there may not be a long-term impact on house finch populations, as populations appear to have rebounded. If feeders are helping sustain nonnative invasive species (eg, starlings), one could argue that feeders could have an indirect negative impact on native populations.

Dr Langenberg:

This is a key question that needs further research, especially because bird feeding as part of bird watching and appreciation continues to grow in North America. I guess my interpretation is that there is no clear positive or negative impact in general to wild bird populations as a whole. The Canadian Cooperative Wildlife Health Center published an excellent review paper in 2003, "A Comprehensive Review of the Ecological and Human Social Effects of Artificial Feeding and Baiting of Wildlife" (available at http://wildlife1.usask.ca/ ccwhc2003/CCWHC_home.php). Although this report emphasizes the effects of hunting practices on large mammalian game species, its summary of the ecological and human social effects of feeding is applicable to and presents examples from bird feeding. The report also has a great annotated bibliography. An example of a potential positive impact of wild bird feeding is that artificial feeding can increase a bird's physical condition and reproductive success; it has been shown to improve nesting success of eagles in Alaska and Sweden. Potential negative impacts include the concern that feeding can increase local bird density and therefore competition and may introduce exotic plant species that degrade local habitat. It is possible that these negative potential impacts are of greater concern in artificial feeding situations other than backyard feeders (eg, large-scale feeding of waterfowl in parks, feeding associated with bird reintroductions).

Dr Morrisey:

I guess it really depends on whom you ask, but I feel there are both positive and negative aspects to feeding birds. Positive aspects for the birds include feeders as a reliable source of food, which is especially important during long, snowy, winter months. The most obvious positive impact of feeders for me is a greater appreciation for the birds and a greater willingness to help in conservation efforts to protect these birds and other wildlife. The biggest negative impacts are potential for disease transmission and greater concentration of birds for predators such as raptors and cats. Of course, concentrating birds in this way could be interpreted as a positive impact for predator species of birds! Another potential negative effect of feeding is window collisions, which account for a large number of bird deaths each year.

Dr Tizard:

Generally, feeding has a very positive impact, because it likely enhances bird survival at a time when food and water are limited. Enhanced survival can, however, be a mixed blessing. The resultant increase in numbers of overwintering Canada geese and the survival of monk parakeets in northern cities is directly attractable to feeding. Such population increases may not necessarily be a good thing, because large increases in bird populations concentrated in a single area may serve as a means of spreading disease. Remember, some feeding may not be intentional. For example, cowbirds may gather in very large flocks at cattle feed troughs.

Question: What diseases should we be concerned about when feeding wild birds, and how can these diseases be prevented?

Dr Bright:

Mycoplasmosis, salmonellosis, and colibacillosis are the most obvious infectious diseases that come to mind. Giardiasis, trichomoniasis, and poxvirus also may be included. West Nile virus must also be considered, as it is possible that concentrating birds around a water source might increase the risk of transmission of this virus during vector season. Aspergillosis from feeding moldy seeds or corn is another concern. Bacterial or fungal infections especially occur in hummingbirds from unsanitary feeders. I clean my seed feeders with bleach at least once or twice a month, though weekly cleaning would probably be better.

Many decorative birdbaths are not easy to clean, and they probably don't get cleaned properly. I place glass pie plates inside my birdbath to make cleaning and disinfecting easier. I change the water daily and change the pie plates every 2-3 days. In the winter, I use a heating element that sits inside the pie plate. Some of the heating elements on the market are coiled and not easy to clean and disinfect. I prefer the flat kind (made for cow troughs) because they are easier to clean. I keep 2 heaters on hand so I can switch them out every 2-3 days and keep them clean.

One issue that I think does not get enough attention is hummingbird feeders. Most stores sell intricate glass feeders that look wonderful but are very difficult to clean and disinfect. The long glass necks on those feeders are great places for fungus to grow. I buy simple disk feeders that are easy to take apart and clean. During the summer, I have multiple hummingbird feeders. I put out a clean feeder with fresh sugar water every 3 days. I also have questions and concerns about the over-the-counter hummingbird nectar. The directions say to add the powdered nectar to tap water and that there is no need to boil the water. I wonder whether this contributes to bacterial growth.

Dr Langenberg:

Perhaps disease risks are the major concern related to bird feeders that we have significant information about. For many bird species, the use of feeders brings them into closer contact both with other members of their species and with members of different species, directly and indirectly through feces and saliva, than they would experience under natural conditions. It is no surprise that transmission of highly infectious diseases like Mycoplasma gallisepticum conjunctivitis and salmonellosis is facilitated at feeders. Fortunately, good feeder hygiene and willingness to discontinue feeding during disease outbreaks are effective at controlling these problems.

Dr Morrisey:

The most common disease that I can think of is mycoplasmosis, which can be transmitted directly between birds as they congregate at feeders or indirectly with the feeder as a fomite. If affected birds stick their faces in small holes to pick out seed, they can rub off mycoplasma organisms that can be picked up by the next bird to stick its face through the same opening. We have preliminary data suggesting that the organisms are shed in feces, as well. Salmonellosis is another disease potentially spread at feeders. The best way to prevent these problems is to regularly clean feeders with soapy water and dilute bleach. Also, cleaning the ground below the feeder is important to prevent accumulation of seeds, which can become a source of exposure to pests and aspergillosis.

Dr Tizard:

The key disease issue in feeding is salmonellosis. Some types of feeders, especially wooden platforms, may permit very large numbers of birds to congregate in a very small area. Fecal contamination of these feeders permits salmonellosis to spread through these bird populations. Prevention of salmonellosis requires, at minimum, proper and regular disinfection of feeders with soap, water, and bleach. It may also be inappropriate to feed birds all year round.

Question: What are the implications of feeding wild birds on conservation?

Dr Bright:

People feeding or watching birds may act as an informal surveillance system by detecting early signs of diseases (as with mycoplasma in the mid 1990s) or population changes. Someone from the Feeder Watch program at the Cornell lab of ornithology might address this best. Without a doubt, bird feeding is a great way to educate and engage people in conservation issues.

Dr Langenberg:

Certainly, artificial feeding has been used to maintain and support some endangered bird species, including trumpeter swans and certain populations of bald eagles. However, there is real concern that feeding can disrupt population processes by altering spatial distribution of birds, perhaps by changing normal daily or seasonal movements, and that, with feeding on large scales, it also may alter carrying capacity of a habitat. Although these may not be real concerns associated with backyard bird feeding, on a different scale it is clear that bird feeders increase a bird's risk for window collisions, cat predation, and exposure to certain diseases. Whether the cumulative increase in risk to bird populations will be significant as people's interest in backyard bird feeding grows is not yet clear.

Dr Morrisey:

Feeding and providing shelter for birds has helped many species, such as the Eastern bluebird, improve diminishing populations. Thus, there are some positive implications. The negative implications, such as disease transmission, increased predation, and window collisions, have already been mentioned.

Dr Tizard:

The implications of wild bird feeding include explosive growth in population of some waterfowl, increased overwintering survival of songbirds, and a tendency for migrating birds to remain longer in northern latitudes. One positive implication of bird feeding is that because feeding birds is the number one hobby in this country, many people have been "turned on" to birds as a result of watching busy feeders.

Question: Many parts of the country have new nonnative avian flocks (eg, monk parakeets, budgerigars, and cherry-headed conures). Should these birds be differentiated from other wild birds, and should feeding these species be encouraged or discouraged?

Dr Bright:

Although I love parrots, and they have a tremendous amount of charisma, I see these birds as nonnative (potentially invasive) species. I would discourage the feeding and propagation of these birds.

Dr Langenberg:

In consideration of the long-term health of our native ecosystems, I think it is best, where possible, to avoid feeding nonnative bird species. We are learning that there can be real problems for our native birds when nonnative species are introduced and supported by people. In Wisconsin, a good example of this occurred when European mute swans were introduced to compete with trumpeter swans for habitat; mute swans have been a significant limiting factor for the reestablishment of trumpeter swans in some areas of the state.

Dr Morrisey:

Once these nonnative flocks have become established feral populations, it is difficult to get rid of them, so this question may be a moot point. Some would argue that we've already lost some of our own native psittacine species, such as the Carolina parakeet, so that the establishment of other psittacine species may not be that important. Certainly, people enjoy watching these nonnative birds, though die-hard birders are against nonnative species. We know nonnative birds can do damage to native populations, as the case of the European starling and house finch have shown us. My feeling, however, is that it's difficult to restrict access to feeding stations for these species, so they should just be considered part of the avifauna in that area. Then the decision can be made whether or not to support all the possible species in that area.

Dr Tizard:

I favor the feeding of nonnative, introduced psittacine species. They are wonderfully attractive birds. They present, as far as we know, no significant threat to our native birds and should be encouraged, within reason. There are concerns, however, that some species, such as monk parakeets, could become agricultural pests.

Laurie Hess, DVM, Dipl ABVP (Avian)

Associate Editor

Robert Groskin, DVM

Conservation Committee, Association of Avian Veterinarians
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Title Annotation:Round Table Discussion
Author:Hess, Laurie; Groskin, Robert
Publication:Journal of Avian Medicine and Surgery
Article Type:Discussion
Geographic Code:1USA
Date:Jun 1, 2006
Words:2788
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