The European Starling (Sturnus vulgaris) is a species of bird that is native to Europe and parts of Asia. It was introduced to North America in the late 19th century and has since become one of the most numerous songbirds on the continent. But there has been much debate over whether European Starlings should still be considered an invasive species today.
What makes a species invasive?
A species is generally considered invasive if it is not native to an ecosystem and its introduction causes or is likely to cause economic, environmental, or human harm. Some key characteristics of invasive species are:
- They reproduce and spread aggressively in their new environment.
- They compete with native species for resources like food and nesting sites.
- They prey on native species or change ecosystem processes like nutrient cycling or fire regimes.
- They lack natural population controls like predators in their new environment.
- Their populations grow rapidly and often become ubiquitous.
In the late 19th century, Euopean Starlings were intentionally introduced to North America by people who wanted to bring all the bird species mentioned in Shakespeare’s works to the continent. About 100 birds were released in New York’s Central Park in 1890 and 1891. From that small founder population, European Starlings spread rapidly across North America.
Invasive traits of European Starlings
European Starlings exhibit many traits of successful invasive species:
- They are very aggressive and compete with native cavity nesting birds like woodpeckers and bluebirds for nest sites. They evict and kill competitors to take over nesting cavities.
- They form large flocks of hundreds or thousands of birds that all roost together, allowing them to dominate areas and cover the ground in droppings.
- They eat a wide variety of foods including fruit crops, grains, livestock feed, and invertebrates. This allows them to adapt to many environments.
- They breed multiple times a year, producing many offspring.
- They tolerate human disturbed environments very well.
Within 100 years of their introduction, European Starlings had spread across all of North America, occurring in every state and province from Alaska to Mexico. Current population size is estimated at over 200 million birds, making them one of the most common birds on the continent. Their aggressive habits have had negative economic impacts on agriculture and effects on native cavity nesters. Clearly, European Starlings exhibited highly invasive characteristics after their introduction.
Have European Starlings remained invasive?
While European Starlings initially exhibited extremely invasive traits, there is debate about whether they can still be considered an aggressively expanding invasive species today, over 100 years after their introduction. Several factors suggest their invasiveness may have declined:
- Their range now covers all of North America, so there are few new areas for them to colonize.
- In some regions, their populations appear to be declining, though they remain common.
- As time passes after their initial colonization, they may be becoming integrated into the ecosystem rather than dominating it.
- Other invasive species like House Sparrows now compete with starlings for nest sites.
- Familiarity with starlings may have led to some natural population controls evolving.
However, starlings still cause economic damage by feeding on fruit crops and compete heavily with native birds in many areas. More research is needed on how their populations are changing and their current ecological roles before declaring them non-invasive.
Case study: European Starlings in North America
A detailed look at the history of starlings in North America helps illustrate their rapid population growth and expansion in the early years following introduction:
- 1860s-1890s – Starlings introduced to North America in multiple releases, with main founder population from Central Park releases.
- By 1942 – Spread from New York across entire continental United States and southern Canada.
- By 1952 – Occurred in all lower 48 states and most of Mexico.
- 1957 – First breeding record in Alaska.
- 1976 – Breeding recorded in all lower 48 states and all Canadian provinces.
- Peak population estimated at over 200 million birds.
This demonstrates an extremely rapid irruption and colonization across North America in the early decades after introduction. Their populations grew exponentially and they quickly dominated many regions, exhibiting classic invasive species traits.
Geography of starling range expansion
Here is a timeline showing the expanding range of European Starlings after introduction:
Year | Range in North America |
---|---|
1890 | New York City area |
1900 | Northeastern U.S. from New York to Boston |
1910 | Along Atlantic coast from Florida to Newfoundland |
1920 | Expands west to Great Lakes and Gulf Coast states |
1930 | Covers eastern half of continent, Atlantic to Great Plains states |
1940 | Reaches west coast, covers all lower 48 states |
1950 | Occurs across southern Canada from Newfoundland to British Columbia |
1960s | Range fills in northern Canada and Alaska |
Population growth estimates
European Starling populations grew exponentially after introduction, as shown in this table:
Year | Estimated Population |
---|---|
1891 | 100 birds from foundering population |
1903 | 1,000 birds in New York City region |
1930 | Over 1 million birds |
1947 | Approximately 50 million birds |
1970s | Peak of over 200 million birds |
These figures illustrate the incredibly fast growth from just a few dozen individuals to over 200 million birds occupying North America within less than 100 years. This rapid irruption and exponential growth of population size is a hallmark of highly invasive species.
Starling populations today
While European Starlings remain extremely common birds across North America, there are indications that their populations may now be declining in certain areas, a century after their peak invasion period:
- The North American Breeding Bird Survey detected a survey-wide population decline of 1.6% per year from 1966 to 2015.
- Summer surveys in central California indicated a steady population decline from 1983 to 2005.
- Breeding populations in Ohio declined at a rate of 2.5% annually from 1966 to 2016.
- They appear to be declining in regions like New England and the upper Midwest where they were originally most abundant.
Possible reasons for declining trends in some areas:
- Most of continent has now been colonized so less new areas to expand into.
- Other invasive species now compete with them for nesting sites.
- Familiarity with starlings has led to more active control programs in some regions.
- Some predator or disease controls may be evolving.
- Climate change may be shifting range suitability.
However, starlings remain extremely numerous across most of their range. Declines are not consistent across the entire continent. More research is needed to determine if decreases represent a new population equilibrium or the start of a more substantial decline.
Economic and ecological impacts today
While starling populations may be declining in some areas, they still incur substantial economic costs and ecological impacts including:
- Agricultural damage: Starlings consume cultivated fruits and grains, especially cherries, berries, and feed corn. Damage to agriculture still likely exceeds $100 million yearly.
- Livestock feed loss: Starlings consume costly concentrated feeds for dairy and cattle feedlots, costing the industry millions annually.
- Aircraft hazard: Starlings are a major hazard to aviation strike collisions. From 1990 to 2017, over 1500 starling strikes were reported to the FAA, causing millions in damages.
- Native displacement: Starlings still compete heavily for nesting cavities, reducing reproductive success of native cavity nesting birds.
- Health and infrastructure: Large roosting flocks produce copious droppings that present health hazards and accelerate decay of infrastructure.
In summary, even if starling populations are declining in some areas, their overall numbers are still very high across North America. They continue to incur major economic costs through agriculture and aviation damage. They also displace native cavity nesting birds in many regions.
Management and control programs
Because of their continued impacts, European Starlings remain actively managed in many areas, unlike a non-invasive integrated species. Control measures include:
- Exclusion from roosting sites with netting or spikes.
- Population reduction via toxic perches at roosts or trapping.
- Reducing access to food sources at feedlots or fruit farms.
- Removing starling nests from cavities needed by native birds.
- Using hawks or falcons to haze starlings from sensitive sites.
The USDA Wildlife Services division still dedicates major effort to starling control, unlike a naturalized species. In 2017, the program:
- Killed over 1.6 million starlings in roost control programs.
- Dispersed over 33 million starlings from sensitive sites.
- Killed over 19,000 birds to protect native cavity nesting birds.
- Received over $2 million in funding for starling management.
This level of active human management demonstrates that starlings are still not considered a beneficial naturalized species in many regions.
Conclusion
In conclusion, while European Starlings have likely passed their peak invasion period in North America, they still retain many negative traits of an invasive species and cannot yet be considered fully naturalized. Key points supporting this are:
- They continue to cause major agricultural and infrastructure damage, costing millions annually.
- They aggressively compete with native birds for nesting sites in many areas.
- Large control and harassment programs are still dedicated to reducing starling impacts.
- Their populations remain extremely high across most of the continent.
However, some evidence does suggest starlings may be shifting towards a more stable equilibrium with the ecosystem. Questions requiring further study include:
- Are declining population trends continuing and what are the causes?
- How have their ecological roles shifted over time since introduction?
- Can control programs be adjusted to account for any decreased invasiveness?
So in summary, the evidence suggests European Starlings are still best considered an invasive species across most of North America today, over a century after their introduction. However, data points towards possible decreasing invasiveness in the long term, which warrants continued monitoring and re-evaluation of their ecological status and appropriate management strategies going forward.