We recently heard from a customer who was concerned about cowbirds disrupting her nesting birds. So we put together an informative article to help you know what to look for, as well as a few tips on how to deter cowbirds, also known as brood parasites. Since this is a topic we come across once in a blue moon, we’ve compiled some additional reading for you at the bottom of this article, so you can learn more about these interesting species. You may be interested to learn there are three different kinds of cowbirds, including the Brown-headed Cowbird, the Shiny Cowbird and the Bronzed Cowbird. They all appear to have a sleek bodies with dark feathers, yet the Brown-headed appears to be the only one with a brown crown!
When looking for the signs of whether cowbirds exist in your area, you must first ask yourself: Which one of these is not like the others? Cowbirds look different from other birds because they’re larger. In the nest, cowbird eggs are often the large egg with a shell ranging in color from white to grayish-white with brown or gray speckles or streaks. However, cowbird eggs can look similar to other species’ healthy, yet unusual-looking eggs, which can be confusing. Not to worry, there are other factors you can look for! For size reference, cowbirds’ eggs are the same size as the Northern Cardinal’s eggs. As for the nest, instead of making their own, cowbirds quickly lay an egg or two in another bird species’ unattended nest. Female cowbirds can lay an egg in 41 seconds! For reference, female cowbirds are a soft, pale brown or gray color with a slender shape, as you can see in the photo below. Juveniles have similar colors with a lot more speckles or streaks in their feathers.
Here’s another identifying feature you can look for: an egg that “dropped” on the ground below the nest, while the nest is still occupied with other eggs! In this case, it’s likely a female cowbird has evicted one of the host’s eggs in order to make room for the cowbird’s egg. When you see an unusual egg in your native bird’s nest with no egg on the ground, it’s just as likely the female cowbird ate the egg because cowbirds can be ruthless. Or she may have damaged the egg and left it in the nest, alongside her own intrusive and freshly laid egg.
Once the eggs in the nest have hatched into nestlings, you may notice one of the hungry nestlings is larger than the rest of them. Combined with its louder and more insistent call for food, the cowbird nestling is often successful at gaining more of the available food with detriment to the native nestlings. The cowbird nestling also has a bright red “gape,” which refers to “the brightly colored areas in the corners of a nestling’s open mouth.” The red gape is a noticeable feature on cowbirds because most songbird nestlings have a yellow or otherwise pale gape, making it more obvious a cowbird nestling is in your presence! Since cowbirds spend 8 to 13 days developing before they fledge, you may find the rest of the nestlings are still in the nest, not yet ready to fledge. This is another key identifier you have a cowbird in your midst!
The last thing to look for is a rather unusual pairing, where you can see a smaller bird feeding a much larger, unrelated bird. Since cowbirds are raised by a completely different bird species, the juvenile cowbird is often much bigger than their parent, who continues to feed them and nurture their development. When you see this, look for speckled or streaked feathers on the pale brown or gray bird. See it? Then you may have a cowbird in your yard.
Now that you know how to identify cowbirds eggs in a nest, how do you deter these undesirable birds? You can start to discourage them by using feeders made for smaller birds. This includes hanging tube feeders with short perches, smaller ports and without a seed catch tray on the bottom. When choosing a feeder to deter cowbirds, it’s best to avoid platform trays, as well as spilled seed on the ground. This requirement makes our No-Waste seeds without hulls convenient to use in hanging tube feeders.
When choosing which food to use, remember cowbirds prefer to eat cracked corn, millet and sunflower seeds. With this said, it’s a wise choice instead to offer Nyjer seed, nectar, safflower seeds, suet or whole peanuts. By preventing seed from spilling below your bird feeders, you’re creating a bird-friendly environment for smaller songbirds, while discouraging parasitic cowbirds from disturbing your beautiful nesting songbirds.
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SOURCES & INTERESTING READING:
“Bronzed Cowbird.” All About Birds, The Cornell Lab of Ornithology, 2015. Mar. 22, 2016. <https://www.allaboutbirds.org/guide/Bronzed_Cowbird/id>.
“Brown-headed Cowbird.” All About Birds, The Cornell Lab of Ornithology, 2015. Mar. 22, 2016. <https://www.allaboutbirds.org/guide/Brown-headed_Cowbird/id>.
“Focal Species Close-up: Brown-headed Cowbirds.” Celebrate Urban Birds, The Cornell Lab of Ornithology, Jun. 7, 2013. Mar. 22, 2016. <http://blog.celebrateurbanbirds.org>.
“General Bird & Nest Info: Brown-headed Cowbirds.” NestWatch, The Cornell Lab of Ornithology, 2011. Mar. 22, 2016. <http://nestwatch.org>.
“Shiny Cowbird.” All About Birds, The Cornell Lab of Ornithology, 2015. Mar. 22, 2016. <https://www.allaboutbirds.org/guide/Shiny_Cowbird/id>.
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