Collaboration: Migratory birds can’t fly far from long-lasting pollutants

It’s a tough life for Neotropical migrant songbirds. With little more than a chirp and flash of feathers, some of these birds can fly as far as 16,000 kilometers.

Alejandra Maldonado and a warbler. Courtesy of Alejandra Maldonado

Their migration takes them from the top of Canada to wintering grounds in Argentina and Chile. But this long journey may be contributing to their dramatic population loss over recent decades. Wildlife ecotoxicologist Alejandra Maldonado is set to find out why some of these birds are facing an 80% decline in numbers. Using the help of experts on ResearchGate, she’s investigating their exposure to slow-degrading toxins during their migratory cycle.

Warblers, flycatchers, hummingbirds, thrushes, swallows – they vary in size and song but are all part of the Neotropical songbird family. They fly from Canada and North America to the tropics for winter, and then back again for the summer months. But somewhere along the way Maldonado thinks these birds may be exposed to harmful contaminants. “Due to their annual movements, migrant birds may be exposed to a wide range of pollutants over large geographic areas,” the PhD student at A&M Texas University (USA) says. But where, when and how is largely unknown.

Maldonado hones in on persistent organic pollutants, or legacy contaminants, for answers. These toxins are released in the environment from pesticides to products, and stay in the air, soil and water for years after use. They are hard to break down and not soluble in water, so residue accumulates in sediments and in animals’ fatty tissues, meaning they can be passed on through the food chain.

Female and Male Common yellowthroats
A female (left) and male common yellothroat. Courtesy of Alejandra Maldonado

The toxins have been linked to various health problems in birds. This includes abnormal behavior, interfering with their reproductive development, and impacting their ability to withstand the physical stresses of migration. To find out, Maldonado has tested various songbird species in Texas, and followed them to their wintering grounds in Mexico and Costa Rica for further analysis. She’s looking for potential differences in contaminant levels during the migratory cycle, as well as genetic damage and effects on their nervous system. Resident, or non-migratory, birds are used as a control: “Migratory songbirds may provide a framework for understanding broad scale scenarios of contaminant accumulation, whereas resident birds can provide information on local background contamination levels.”

Dangerous toxins have proven to wreak damage on birds – especially for aquatic and raptorial species. While songbirds are largely under-researched in comparison, Maldonado was keen to show that a substance ban can have a dramatic effect on their revival. She needed data to prove this so asked peers on ResearchGate for help, using a banned legacy contaminant as an example.  Within days she had her answer: “They helped me find temporal figures demonstrating this decline of contaminants in birds and wildlife.  It shows that while there have been declines, these toxins are persistent. That means they’re still in the environment and can still pose this problem.”

Maldonado is still analyzing her data and hopes to be finished early next year. She can’t reveal much, but says it’s possible the birds may be exposed to more industrial-style contaminants during their time on their breeding grounds. This could refer to increasingly popular pollutants like brominated flame retardants - used to make plastics, textiles and electronics less flammable.

Figuring out which toxins are affecting the songbirds, and where it’s happening, may help protect the species in the years to come. It could also provide a better understanding of pollutants for humans and other organisms. But before any of this is known, Maldonado says, it’s important researchers work together to find the solution: “Birds cross geographic and political boundaries so it’s important to foster collaborative work with other countries – they’re a shared resource and therefore a shared concern.”