Pigeons are quite literally neighborhood birds: they tend to spend their whole lives within a radius of just a few city blocks. This means they could serve as sentinels capturing information about toxicants in highly localized areas of a city, researchers are increasingly realizing.

“Pigeons breathe the same air, walk the same sidewalks, and often eat the same food as we do,” says Rebecca Calisi, an environmental health scientist at the University of California, Davis. “What if we could use them to monitor possible dangers to our health in the environment, like lead pollution?”

A few studies in Europe and Asia have used pigeons as bioindicators of heavy metal contamination. Calisi recently led the first such study in the United States, and the first to tie the patterns of blood lead levels in pigeons to those in children.

Calisi, then at Barnard College of Columbia University, worked with Barnard undergraduate Fayme Cai to test the blood of 825 pigeons at the Wild Bird Fund, a wildlife rehabilitation center in New York City. All of the birds were suspected of having lead poisoning, and had been brought to the facility because they were ill or behaving oddly.

The pigeons came from 13 neighborhoods in four of New York City’s five boroughs, with the largest number from Manhattan. They were collected throughout the year from January 2011 to March 2015.

Pigeons’ blood lead levels varied by season and were highest in summer, the researchers reported July 18 in the journal Chemosphere. Similar patterns have previously been identified in children.

For people, sources of lead exposure include paint in old buildings and contaminated dust from soil, roads, and construction sites. Indoor paint probably doesn’t pose much of a risk to pigeons, but the birds may also be exposed to lead from rocks they swallow to help with digestion. For both species, the reason blood lead levels peak in summer is unknown.

Statistically speaking, the researchers couldn’t find a difference between lead levels in pigeons from different neighborhoods. (This makes sense, since all of the pigeons tested were suspected of having lead poisoning. So these birds would all have elevated blood lead levels and may not be representative of the broader pigeon population in each neighborhood.)

However, they found a correlation between pigeons’ blood lead levels and the rates of children with elevated lead in their blood. That is, the neighborhoods where pigeons tended to have the highest levels of lead – Soho, Greenwich Village, Lower Manhattan, the Lower East Side, and the Upper West Side in Manhattan – also had the highest rates of children with elevated lead levels according to city health department data.

The lead levels in sick birds from these high-lead neighborhoods averaged over 20 micrograms per deciliter (mcg/dl). In people, blood lead levels even less than 10 mcg/dl can harm health and neurodevelopment. The U.S. Centers for Disease Control and Prevention has set the threshold for lead exposure in humans at 5 mcg/dl.

Calisi is now looking at other pollutants, including other heavy metals, pesticides, and fire retardants, in pigeons from cities in California. – Sarah DeWeerdt | 26 July 2016

Source: Cai F. and R.M. Calisi. “Seasons and neighborhoods of high lead toxicity in New York City: The feral pigeon as a bioindicator.” Chemosphere DOI: 10.1016/j.chemosphere.2016.07.002

Header image: A pigeon in New York City. Credit: Nick Harris via Flickr.