Lead ammunition may be undermining wild animal health

A guest blog by Zeka Kuspa

Last year, a public health emergency regarding lead-contaminated drinking water in Flint, MI reminded Americans of the dangers of lead exposure to children’s developing brains. Some of us may remember that lead was once omnipresent in everyday life, found in products like house paint, gasoline, and residential water pipes. Only decades ago, exposure to lead was responsible for an epidemic of permanent neurological impairment in American children as well as organ failure in occupationally exposed adults. Though exposure rates have declined as the element has been phased out of most household items, lead is still the go-to ingredient for some many types of ammunition. Not surprisingly, lead ammunition use has some serious downstream effects, including lead poisoning in wild species like the California condor.

Author at her urate sampling station. The two kennels contain condors in the stress study.

Author at her urate sampling station. The two kennels contain condors in the stress study.

The California condor has become the poster child for the ecological impacts of lead ammunition use over the past few decades. Lead poisoning was first discovered in the California condor in 1980’s, when one of the last members of a dwindling wild flock was found to have died of lead toxicosis, a painful condition defined by lethargy and paralysis. But where was the lead coming from? A member of the vulture family, condors only eat dead animals. Some of the carcasses they consume have died of natural causes (e.g. a diseased deer or a beached whale), but some have been shot and killed with lead ammunition. For many years, ammunition was the suspected cause of poisoning in the California condor, but it wasn’t until 2006 that research completed at UC Santa Cruz conclusively linked lead ammunition to lead in the bodies of poisoned condors. Since then, many case studies have found recognizable pieces of lead ammunition in the guts of California condors. Today, at least 70% of wild condors in California are exposed to lead annually. Though some of these poisoning events result in death, in many cases the birds survive. What effects are these repeated lead exposures having on the surviving wild condors?

Stress hormone excretion profile over time for condor 488. Arrows indicate baseline (green) and peak (red) hormone concentrations, as well as duration (purple) and magnitude (orange) of the hormonal response to a handling stressor. All of these measurements will be used to assess whether lead exposure alters stress hormone release in condors.

This was the question that inspired my return to graduate school. Specifically, I am investigating how lead exposure might alter the way a California condor responds to stress. The release of stress hormones is what helps a wild animal survive and recover from the many stressful situations they encounter in nature, such as bad weather, food shortages, or predators. These hormones act by efficiently investing an organism’s energy resources, and holding onto energy reserves for later use. Stress hormones also stimulate behaviors (compulsive eating, hunkering down, etc.) that help an individual survive and recover after stressful situations. If this hormonal response is either under- or over-reacting to a stressful event, the animal’s ability to respond to future events can be compromised, potentially impacting their ability to successfully raise a chick or survive through the year. Lead is known to impair the stress hormone response in mammals, but lead’s effect on this system in birds is unknown.

Adult condor is released from kennel after sampling is completed. 

Adult condor is released from kennel after sampling is completed. 

To measure the stress responses in California condors, I collect samples of their blood, urates (analogous to urine in mammals), and feathers during the bi-annual handling events that were established to monitor lead exposures in the wild flock. While a gigantic bird is in hand, we collect blood and a section of the longest flight feathers on the wings, called primary feathers. Stress hormones are among the chemicals in the blood that are incorporated into feathers as they grow, creating a record of the bird’s past. By measuring stress hormones in feathers, I can harvest data on stress covering the previous three months of feather growth. To monitor the hormonal response to this specific stressful event (handling), I collect serial urate samples for up to 6 hours after the handling is over by placing birds in a special sampling kennel (see photo of me above), similar to one you might use to transport a German Shepard. The difference is that I’ve added a raised mesh floor to the kennel, and a tray underneath that I can access without disturbing the condor inside. Each sample represents what was in the blood before it was metabolized and excreted in the urate. This time lag allows me to measure stress hormone levels before and after the handling event (see second photo). By collecting a variety of biological samples, I can measure stress at multiple time scales (from minutes to months!) during a single condor handling event. Condors are closely monitored due to their endangered status, so I have a unique ability to connect the dots between lead exposures, stress response, and survival outcomes. Based on what we know about lead exposure in humans and mammals, I expect that condors with a history of frequent and severe lead poisoning will have elevated and prolonged responses to the stress of being handled compared to condors with a history of lower lead exposure. Heavily lead-exposed birds may also show a chronic elevation of stress hormone concentrations in their feathers. Either of these results would suggest that lead exposure might render birds less able to mount the proper stress hormone response to survive future challenges, such as disease or complications from lead poisoning. I am eager to see what the data will show.

Recent legislation in California has mandated a state-wide ban on lead ammunition for most recreational shooting activities starting in 2019. It will require gun-owners to use less toxic projectiles such as copper-based ammunition, which bodes well for wild scavengers in our state like the California condor and eagles. My work will help determine whether the effects of chronic lead poisoning will continue on in condors even after the ban is in place. Perhaps a greater awareness of the potential silent damage caused by lead ammunition in the condor’s habitat will also influence decisions on ammunition use outside of California, where other scavengers will continue to have access to lead-contaminated carcasses.

Zeka Kuspa is a Ph.D. Candidate in Microbiology and Environmental Toxicology at UC Santa Cruz