Mockingbirds Become More Aggressive After Lead Exposure

Despite Reductions in Use, Lead Pollution Remains a Global Issue

Mockingbirds exposed to lead pollution in urban areas display significantly heightened aggression, according to Morris Animal Foundation-funded researchers at Tulane University.

Findings highlight the possibility that lead exposure may be common among other wildlife living in urban areas and more work is needed to better understand its full effects.

Millions of Animals Exposed to Lead Pollution

“There’s considerable lead contamination in soils around the world, and that means literally billions of animals, both urban wildlife and pets, are likely exposed at sub-lethal levels,” says Dr. Jordan Karubian, Associate Professor at Tulane University’s Department of Ecology and Evolutionary Biology.

Mockingbirds exposed to lead in urban areas display significantly heightened aggression
Mockingbirds exposed to lead in urban areas display significantly heightened aggression

“The levels aren’t killing them, but they may affect their behavior or physiology. Heightened aggression among mockingbirds may just be the tip of the iceberg,” Dr. Karubian adds.

The team used simulated territorial intrusion on dozens of northern mockingbirds in urban New Orleans neighborhoods with either low or high levels of lead in the soil.

Researchers placed a taxidermized mockingbird on a tripod, 25 feet away from nests that pairs of mockingbirds were constructing, a situation in which the birds act most territorial.

They also played recorded songs of singing males to alert the mockingbirds and make the intrusions more realistic.

Lead Exposure Leads to Heightened Aggression

In neighborhoods with low lead levels, the mockingbirds responded to the threat somewhat conservatively, with scolding call vocalizations, raised-wing displays or fly-bys.

In neighborhoods with high lead levels, the mockingbirds responded far more aggressively, attacking the perceived intruder and even ripping out its feathers.

After the Mockingbirds showed sign of aggressiveness, researchers placed the fake bird in a cage to protect it from damage to continue the study.

“This is an issue that definitely deserves more attention as lead is still so commonplace in our environment, despite efforts to remove lead from products such as paint,” says Dr. Kelly Diehl, Morris Animal Foundation Interim Vice President of Scientific Programs.

“Studies like these are important to raise awareness that lead is still a major problem,” Dr. Diehl adds.

Lead enters the ecosystem through removal of paint during renovations. Those particles are ingested by insects and worms and then eaten by birds (Pictured is a juvenile Mockingbird)
Lead enters the ecosystem through removal of paint during renovations. Those particles are ingested by insects and worms and then eaten by birds (Pictured is a juvenile Mockingbird)

Lead Pollution Remains a Global Issue

Lead pollution remains a global issue.

Despite the reduction of lead use, it persists in urban environments from the once-common use of leaded gasoline and lead paint.

Residual dust remains in the soil, and lead continues to enter ecosystems through removal of paint during renovations.

Those particles are ingested by insects and worms, which are then eaten by birds.

Read the study published in Science of the Total Environment.

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