Every year a curious thing happens, house finches suddenly seem to follow bluebirds around. In fact, if you’re getting started with bluebirds, you might have started noticing this curious relationship. But year after year, it becomes more famous, and more interesting to watch.
But it might also have you a little worried. With other competitive bird threats like house wrens and house sparrows, it may raise questions in your mind about whether or not house finches are a problem for bluebirds.
House finches are not a direct threat to bluebirds. They are not known for attacking bluebirds or invading nest boxes. However, there might be an indirect risk that house finches pose when it comes to bluebirds, and that involves the transmission of a common bacterium found in house finches.
We did extensive research on this topic to give you the most well-rounded answer on this subject by examining several peer-reviewed articles along with discussing our experience and the experience of other bluebird trail monitors.
The relationship between house finches and bluebirds
In doing a lot of research, it is not clear why house finches seemingly follow bluebirds around. But it is a highly documented observation coming from several trail monitors and bluebird hobbyists.
Each year, especially after the first round of bluebirds fledge and the bluebird family is starting their second nest, it almost seems as if several house finches start coming around the nest boxes or chasing after bluebirds for food.
Despite this activity, they’re not a know threat to bluebirds. It is highly unlikely that they would enter a nest box, and if the did, it would be out of sheer curiosity rather than competition.
What is really happening during this time is that around the same time bluebirds fledge, house finches are also fledging.
Of course, that only really explains why so many are observed near bluebirds. It does not explain why we see this special relationship between bluebirds and house finches, and not so much with other bird species.
In diving into peer-reviewed papers, we didn’t find the answer there either. Instead, we found another big topic surface. And that had to do with the bacterium Mycoplasma gallisepticum.
A possible indirect threat house finches may cause bluebirds and other songbirds
House finches are a known vector or vehicle for spreading a bacterium called Mycoplasma gallisepticum.
Birdwatchers and backyard bird hobbyists will notice this plainly when they discover a house finch with a swollen eye – or something wrong with its eye.
The biggest observed symptom of a Mycoplasma infection in house finches is conjunctivitis. It’s easy to think that since we don’t observe this in other songbirds, they must not get the infection.
But that is not the case. There are several research papers documenting Mycoplasma gallisepticum in other songbirds. However, the bacterium does not localize in the eye like it does with house finches. And this is why conjunctivitis isn’t observed.
Even though we bird watchers and bird conservationists aren’t seeing a visual symptoms, doesn’t mean songbirds aren’t suffering poor health.
This is where that indirect threat comes up when talking about house finches and bluebirds. There are several research papers studying the symptoms of a Mycoplasma infection in bluebirds and how it can even spread to nestlings.
When a bluebird is infected with Mycoplasma, the infection is localized more in the bird’s palate rather than the eye. And other symptoms of infection include low hemoglobin and a loss in body mass – they lose weight.
The more infected a bluebird is, the more weight it loses.
Action We Backyard Birders Must Take
What this all means is that even though the relationship between bluebirds and house finches is amicable, we as backyard birders and conservationists at heart need to be vigilant stewards of our yards.
While we may not observe this infection in a bluebird, if we do see it in a house finch, we need to take immediate important steps:
Steps to take in our yard if we find an infected house finch/ house finch
- Take down all bird feeders. Clean them thoroughly.
- Leave bird feeders down for at least a week to 10 days to get the infection out of the population and prevent it from spreading more.
- Clean bird baths thoroughly.
- Once cavity nesting birds (bluebirds, chickadees, tree swallows, etc.) have fledged a nest box, clean the nest box out using a 10% bleach solution. Be sure to rinse very good and let the boxes dry all the way out.
- Do not attempt to catch and treat an infected house finch yourself. Contact a licensed wild bird rehabber for advice.
Ultimately, watching house finches and bluebirds interact is a lot of fun. You’ll see such incredible differences in their personalities. So the good news is that there is not direct problem between the two species. However, when watching, always pay careful attention to the health and safety of your birds.
References
Amonett, S. D. (2020). Transgenerational Effects Of Mycoplasma Gallisepticum Infection In Eastern Bluebirds (Sialia Sialis) (Doctoral dissertation, The University of Mississippi).
Denton, M. X. (2019). Effects of Vertical Transmission of Maternal Antibodies to Mycoplasma Gallisepticum on Growth and Condition of Eastern Bluebird Nestlings (Sialia Sialis).
Dhondt, A. A., Tessaglia, D. L., & Slothower, R. L. (1998). Epidemic mycoplasmal conjunctivitis in house finches from eastern North America. Journal of Wildlife Diseases, 34(2), 265-280.
Farmer, K. L., Hill, G. E., & Roberts, S. R. (2005). Susceptibility of wild songbirds to the house finch strain of Mycoplasma gallisepticum. Journal of Wildlife Diseases, 41(2), 317-325.
Fry, M. A. (2019). Effects of Mycoplasma gallisepticum on experimentally infected Eastern Bluebirds (Sialia sialis).
Ley, D. H., Berkhoff, J. E., & McLaren, J. M. (1996). Mycoplasma gallisepticum isolated from house finches (Carpodacus mexicanus) with conjunctivitis. Avian diseases, 480-483.
Line, L. (1995, December 12). Epidemic is killing house finches while other songbirds are spared. The New York Times. https://www.nytimes.com/1995/12/12/science/epidemic-is-killing-house-finches-while-other-songbirds-are-spared.html
