The great-tailed grackle is a blackbird found across much of the Americas. Known for its long, keel-shaped tail and iridescent plumage, this opportunistic omnivore has thrived in human-altered environments from farmlands to city parks.
While great-tailed grackles can be seen as pests by some, they have also given rise to an intriguing myth – that they spread disease to humans. This article will examine the origins and veracity of the so-called “great-tailed grackle myth”.
What are great-tailed grackles?
The great-tailed grackle (Quiscalus mexicanus) is a large, lanky blackbird found from western North America down through Central America and into South America.
Some key facts about great-tailed grackles:
- They measure 18-24 cm in length with a wingspan of around 50 cm.
- Males are all black with an iridescent sheen of purple, green and bronze on their feathers. Females are slightly smaller and less glossy.
- Their most distinctive feature is a long, keel-shaped tail that makes up over half their body length.
- They are omnivorous and opportunistic feeders, eating anything from grains, fruits and small animals to garbage and scraps in urban areas.
- They are highly social and travel in noisy flocks.
- Native to Mexico and Central America, great-tailed grackles have expanded northward and can now be found from the southwest U.S. to Canada.
Overall, great-tailed grackles are adaptable, communicative birds that thrive around humans. But it is their close association with people that has led to suspicions they may spread disease.
Where did the grackle disease myth originate?
Like many myths, the idea that great-tailed grackles spread serious illnesses has a grain of truth that has become exaggerated.
Several factors have contributed to this myth:
- Grackles often gather in large flocks around human food sources like farms and landfills. This raises sanitary concerns.
- They are known carriers of several bacterial and parasitic diseases communicable to livestock and poultry such as salmonella and West Nile virus. This has raised fears they may also infect people.
- Their global range expansion over the last century has coincided with outbreaks of diseases like avian flu. This correlation has falsely implied causation in some people’s minds.
- Their dark coloration and noisy, aggressive flocks have long made them unpopular birds associated with negative omens in some cultures.
While grackles do present some health risks, the idea they are major spreaders of serious human illnesses is not supported by evidence. Nonetheless, the myth has persisted over decades.
What evidence is there related to disease risks?
A fair amount of research has examined the actual disease risks posed by great-tailed grackles. The evidence indicates they pose minimal risks to human health.
Bacterial Diseases
Great-tailed grackles can carry bacterial diseases like salmonella. However, their role in transmitting them to humans is minor compared to other species:
- Grackles sampled across the southern U.S. had low rates of salmonella – between 0-3% of birds, compared to up to 70% in some poultry.
- Contact with grackle feces is an extremely rare source of salmonella infection in humans.
- Other animals like house sparrows and European starlings more commonly bring salmonella into feedlots and dairies.
In general, grackles do not seem to be significant carriers of bacterial illnesses that affect people. Their salmonella rates are far below major livestock reservoirs.
Parasitic Infections
Great-tailed grackles can carry certain parasites, but their role in infecting humans is again negligible:
- They can carry parasites like the eye worm Oxyspirura petrowi. However, this species only infects birds and does not cause human illness.
- West Nile virus circulating in grackles poses little direct risk to humans. Mosquitoes are the primary vectors infecting people, not birds.
- Grackles are considered dead-end hosts for most parasitic diseases. The parasites they carry cannot mature enough within grackles to subsequently infect humans.
Researchers conclude grackles are incidental hosts of parasites and play little part in infecting people.
Influenza
The highly adaptable great-tailed grackle has expanded its range alongside human development over the last century. In that same period, major influenza pandemics have emerged like the Spanish flu of 1918. This coincidence has fueled the myth that grackles somehow spread deadly new flu strains.
In reality, there is no evidence implicating grackles in influenza outbreaks:
- Most influenza strains occur in wild waterfowl and shorebirds, not terrestrial birds like grackles.
- Grackles are not natural reservoirs for influenza viruses. At most they are infrequent vectors spreading local outbreaks between poultry flocks.
- Claims that grackles spread major pandemics like Spanish flu are completely unfounded. That outbreak emerged from Europe, outside the grackle’s natural range.
Influenza viruses nearly always originate from wild waterfowl, not land-based species. Grackles’ role in transmission is minimal at most.
Why does this myth persist?
Despite scant evidence that great-tailed grackles spread illnesses, the myth has continued through the decades. Some reasons this misconception has such staying power include:
- Coincidence – Grackles expanded alongside disease outbreaks, but correlation does not mean causation.
- Mistrust – Black birds like grackles are associated with negative omens in some cultures.
- Misinformation – Early studies exaggerated their disease risks and media continues to overstate the threat.
- Visibility – Highly social and vocal grackles around humans stoke fears of disease transmission.
- Data Gaps – More research on grackles’ microbiomes may further limit their role in spreading illnesses.
Even minor risks from grackles like salmonella have been improperly amplified into this myth. Teasing out correlation from causation can be difficult, especially with coinciding events like range expansions and disease outbreaks. And information, whether accurate or not, persists stubbornly once it becomes lodged in public consciousness.
Should great-tailed grackles cause concern?
The bulk of current research indicates great-tailed grackles pose minimal risks to human health. However, reasonable concerns include:
- Poultry farmers should continue biosecurity measures, as grackles can contaminate feed and spread certain illnesses to livestock.
- Public health officials may monitor grackles opportunistically for diseases like West Nile virus circulating in the environment.
- Homeowners may discourage grackles from nesting on properties through humane exclusion or habitat modification.
But grackles should not be vilified or persecuted as major sources of human disease. Their reputation appears far worse than reality. With sustained research, their contributions to disease spread will likely continue shrinking.
Conclusion
The idea that ubiquitous great-tailed grackles spread serious illnesses is largely unfounded. While they can carry certain bacteria and parasites, their low infection levels and dead-end host status means they pose minimal risks to human health.
This myth originated through early exaggerations, persistent misinformation, and simple coincidence in expanding ranges alongside disease outbreaks. But current research makes clear that other species like poultry, mosquitoes and wild waterfowl are far more important disease reservoirs and vectors relevant to human health.
Great-tailed grackles’ adaptability ensures they will continue thriving around people across the Americas. But future research will hopefully dispel myths and reveal their true impacts – both positive and negative – on human health and ecosystems. These intelligent, opportunistic birds are more than the sum of campfire stories and superstitions. Understanding the great-tailed grackle’s role based on facts rather than myths will foster more sustainable relationships between people and nature.
