With February comes the return of the Great Backyard Bird Count, a weekend-long, worldwide, bird counting event that Sierra and I have enjoyed participating in for the past few years. While you can choose to count birds anywhere birds are found, part of the appeal of the event is that it can be done from the comfort of one’s own home simply by watching for birds to appear right outside the window. If there are bird feeders in your yard, your chances of seeing birds are obviously improved. Watch for at least fifteen minutes, record the number and species of birds you see, then report your sightings online. It’s for science!
Feeding and watching birds are popular activities. In the United States alone, as many as 57 million households put out food for birds, spending more than $4 billion annually to do so. While there are a variety of things one can purchase to feed birds – suet, berries, mealworms, etc. – the bulk of that money is likely spent on bags of bird seed (also referred to as bird feed). Bird seed is a relatively cheap and easy way to feed a wide variety of birds. Unfortunately, it’s also a great way to introduce new weeds to your yard.
Bird seed contaminated with noxious weed seeds is not a new problem. It has been a concern for decades, and some countries have taken regulatory steps to address the issue. In the United States, however, there are no governmental regulations that address weed seed contamination in bird seed. With this thought in mind, researchers at the University of Missouri screened a large sampling of bird seed mixes to determine the number and species of weed seeds they harbored, as well as their viability and herbicide resistance. Their results were published last year in Invasive Plant Science and Management.
The researchers examined 98 different bird seed mixes purchased from retail locations in states across the eastern half of the U.S. The seeds of 29 weed species were recovered from the bags, including at least eight species of grasses and several annual and perennial broadleaf weeds. 96% of the mixes contained one or more species of Amaranthus, including Palmer’s amaranth (Amaranthus palmeri), which was found in 27 mixes and which the researchers refer to as “the most troublesome weed species in agroecosystems today.” About 19% of amaranth seeds recovered germinated readily, and five of the seed mixes contained A. tuberculatus and A. palmeri seeds that, once grown out, were found to be resistant to glyphosate, the active ingredient in a commonly used herbicide.
The seeds of grass weeds were found in 76% of the bird seed mixes and included three species of foxtail (Setaria spp.), as well as other common grasses like large crabgrass (Digitaria sanguinalis) and barnyardgrass (Echinochloa crus-galli). Bird seed ingredients that seemed to favor grass seed contamination included wheat, grain sorghum, and proso millet, three crops that are also in the grass family. No surprise, as grass weeds are difficult to control in crop fields when the crop being grown is also a grass.
After amaranths and grasses, ragweed (Ambrosia artemisiifolia) was the third most common weed found in the mixes. This was a troubling discovery since populations of this species have shown resistance to a number of different herbicides. Moving ragweed to new locations via bird seed could mean that the genes that give ragweed its herbicide resistance can also be moved to new locations. Kochia (Bassia scoparia), another weed on the Weed Science Society of America’s list of top ten most troublesome weeds, was also found in certain bird seed mixes, particularly when safflower was an ingredient in the feed.
A similar study carried out several years earlier at Oregon State University found the seeds of more than fifty different weed species in ten brands of bird feed commonly sold at retail stores. Ten of the weeds recovered from the mixes are on Oregon’s noxious weed list. Both studies demonstrate how bird seed can be a vector for spreading weed seeds – and even new weed species and herbicide-resistant genes – to new locations. Weeds found sprouting below bird feeders can then potentially be moved beyond the feeders by wind and other dispersal agents. Weed seeds might also be moved to new locations inside the stomachs of birds.
Addressing this issue can be tackled from several different angles. Growers and processors can improve their management of weed species in the fields where bird seed is grown and do a better job at removing weed seeds from the mixes after they are harvested. Government regulations can be put in place that restrict the type and quantity of weed seeds allowed in bird feed. Further processing of ingredients such as chopping or shelling seeds or baking seed mixes can help reduce the presence and viability of weed seeds.
Consumers can help by choosing bird feed that is processed or seedless like sunflower hearts, dried fruit, peanuts, suet cakes, and mealworms, and can avoid seed mixes with a large percentage of filler ingredients like milo, red millet, and flax. Attaching trays below feeders can help collect fallen seeds before they reach the ground. Bird seed can also be avoided all together, and feeding birds can instead be done by intentionally growing plants in your yard that produce food for birds. By including bird-friendly plants in your yard, you will also have a better chance of seeing a wide variety of birds during the Great Backyard Bird Count.
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