What we can learn from sparrows

To some people the house sparrow is a cute little bird. To others it is an invasive species that competes with native birds, like Eastern bluebirds, for nesting sites. To me, they are an invaluable resource that allows me to improve our understanding of the impact of stress on animals and humans.

I am a post-doctoral associate at Yale University. The focus of my research is to understand how different neurotransmitters and hormones help animals successfully choose mates, raise young, escape from predators, and survive harsh winters and other challenging conditions. The hormone and neurotransmitter pathways I study are very similar in all vertebrate animals, from fish to birds to mammals, so sparrow research can help us understand how these systems work in humans and other animals. One of the major areas of my research is the stress response. While stress helps animals and humans survive and cope with challenges, too much stress is bad and causes health problems. Yet we still don’t have a clear understanding of how and why stress switches from being helpful to harmful, or why some individuals, or some species, are relatively resilient to the negative effects of stress while others are more vulnerable.

Understanding stress in wild animal populations is important because stressors like habitat destruction, climate change, and species invasions now affect most, if not all, animal species. Knowing more about how these different kinds of stressors affect animals may allow us to save some species that might otherwise go extinct. Stress is also a major risk factor for depression, heart disease, drug abuse, and suicide in humans. ~8% of Americans will experience post-traumatic stress disorder at some point in their lives. Understanding more about the physiology of stress could help lead to the development of new medicines and procedures to reduce stress in humans and animals.

Why study house sparrows in particular? First of all, because house sparrows have been so successful at invading new habitats (they are now spreading across Africa), we know that natural selection has favored stress resilience in this species. There is a long history of research on house sparrows, so there is a solid foundation of scientific knowledge we can build upon. Also, we can’t completely understand stress by only studying animals that were born in a cage. Captive-born animals don’t have the same range of physiological and behavioral responses to stress that wildlife and humans show. 

My research has already led to some important discoveries. For example, I became concerned about how oil might affect the stress response in wildlife after the Deepwater Horizon oil spill. To study this, I mixed very small amounts of oil (equal to 1% of food weight) into sparrows’ food. Doing this research in a lab environment allowed me to control a lot of things that might vary in the wild and make it hard to draw clear conclusions about cause and effect. While there were no obvious outward signs this had any effect, and many potential biomarkers of oil exposure in the blood were also normal, blood sampling revealed that birds were not able to secrete normal concentrations of stress hormones after exposure to a standardized stressor (a brief period of restraint in a clean, breathable cloth bag) and an injection of adrenocorticotropic hormone. In my publications on this research, I suggested that stress hormone concentrations could be used as a biological indicator of oil exposure in wildlife. This research is being used by other scientists as evidence that some health problems and deaths they saw in wild dolphins and sea turtles after Deepwater Horizon were due to oil exposure. 

In another study, I investigated the role of stress hormones in wound healing. Wild birds commonly receive small wounds from insect bites, predators, and rival birds, but we know little about how stress hormone receptors in the skin change during the healing process. To examine this question, we used a 4 mm biopsy punch to make a small incision in the skin of sparrows' legs. Birds were anesthetized during this procedure, which is frequently done to human beings. From this study, we learned that birds with a small wound had decreased numbers of one type of stress hormone receptor in the wounded skin, suggesting that reducing the amount of receptors in the skin is necessary for successful healing. 

Wild animals experience stress in many situations, including escaping from predators, fighting rival birds for territories and mates, and surviving severe storms. My current research focuses on one type of stressor that has direct implications for the conservation of endangered and threatened species - bringing birds into captivity. The transition from the wild to captivity is a strong psychological stressor, even if birds have unlimited food and water and large clean cages. To measure the animals’ responses, we take blood samples to measure hormones, keep track of the birds' weight, and observe their behavior. To study receptors in the brain and body, we have to euthanize animals, which is done under anesthesia.

Most of my current research is focused on developing medical imaging techniques (PET and CT scans), which allow me to study receptors in living sparrows. These technologies are used commonly in humans, but rarely in wild animals. I recently worked with an engineering student to design a 3D printed plastic bird holder to safely position anesthetized birds in the scanner. Scans last 30-60 minutes, and sparrows wake up afterwards and are hopping around their cages within minutes. PET-CT imaging allows me to use fewer animals in my research, and to see how levels of a particular receptor, for example, can predict stress resilience in the lab. These technologies will also make it possible for me to image animals, release them back into the wild, and then follow them over time, which is my ultimate goal.

Every study I do must first be approved by a university Institutional Animal Care and Use Committee (or, IACUC). My work complies with all existing laws and regulations and the Ornithological Council's Guidelines for the Use of Wild Birds in Research. The labs, imaging facilities, and animal rooms where sparrows are housed are regularly inspected, and sparrows are monitored by researchers and vets to make sure they stay in good health and don’t lose too much weight in captivity.

I care deeply about openness and transparency in scientific research, which is why all of my publications are freely available here on my website. I also maintain a public Twitter account where I frequently post about my work.

Click here to watch a brief AudioSlides presentation highlighting results from one of my most recent publications, Experimentally reducing corticosterone mitigates rapid captivity effects on behavior, but not body composition, in a wild bird in Hormones and Behavior.