Physiological responses of birds to urban hazards
Urban environments are a new kind of ecosystem that present birds with unique challenges and opportunities. Among other things, urban birds are often faced with excessive heat, chemical pollution, and light pollution. In the Abolins laboratory, we study how these factors, and their interactions, affect the health, physiology, and life history of native birds. We focus specifically on American robins, a native songbird that is among the most common, but perhaps among the most vulnerable, urban birds. Our work is funded by the Kentucky Ornithological Society and The Green Heart Louisville Project.
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Birds as sentinels for air pollution exposure

We collaborate with the Christina Lee Brown Envirome Institute and the Green Heart Louisville project to understand to what extent can wild birds serve as sentinels for environmental health in humans. Birds have respiratory systems that are extraordinarily sensitive to pollutants in the air, and they therefore may serve as bioindicators of air pollution exposure in local human populations. The Green Heart Louisville project is a large-scale interventional public health study that studies the effect of increased urban greening on human health. The Green Heart project uses cutting edge techniques in monitoring pollution and measuring urban vegetation. In collaboration with this public health study, we are asking how stress, inflammation, and signs of DNA damage in wild birds predict health outcomes in the local human population. This work is funded by the UofL Center for Integrative Environmental Health Sciences NIEHS pilot grant.
Other projects and past research
Stress response and reproduction

It is common knowledge that stress can suppress reproductive function. To understand WHY this is, however, we need to turn to the life-history theory. This branch of evolutionary biology predicts how much time and energy organisms should invest in one function as opposed to another. Given that organisms cannot do everything at once, they are faced with trade-offs. One of the most important trade-offs in animal life-histories is that between reproduction and survival.
Stress is a physiological response that has evolved to enable organisms to survive in the face of various stressors, so that they can survive to the next breeding opportunity. Stress can therefore be studied in the context of the survival function in life-history trade-offs. Importantly, life-history theory predicts that the effect of stress should differ depending on the costs and benefits of the stress-response and reproduction, which often differ between the environments that the organisms inhabit.
I showed that the suppression of reproduction by acute stress is lessened if animals live in a high-disturbance environment (Abolins-Abols et al. 2018): while stress normally lowers testosterone levels, such effect was absent in birds that had spent weeks in environment with a frequent disturbances. The regulation of testosterone levels in response to stress and disturbance seems to be achieved at the neuronal level.
In addition to studying the effect of reproduction in the lab, I also study stress in wild birds, specifically in the context of urbanization. Opportunities for reproduction and the frequency of stressors differ between urban and rural landscapes. I showed that, compared to rural birds, urban birds are more stress-tolerant and reduced their aggression less in response to stress (Abolins-Abols et al. 2016). This observation is consistent with lower benefit of mounting a stress response, or conversely, with higher cost of a missed reproductive attempt, in urban environments.
Finally, I study how variation in individual condition in the same environment predicts differences in how individuals respond to stress. With the help of brilliant undergraduates, I studied how the risk of predation affects male behavior. I showed that Dark-eyed Junco males in better condition - individuals that have "more" to loose - are more sensitive to stressors than individuals in lower condition (Abolins-Abols and Ketterson 2017).
Stress is a physiological response that has evolved to enable organisms to survive in the face of various stressors, so that they can survive to the next breeding opportunity. Stress can therefore be studied in the context of the survival function in life-history trade-offs. Importantly, life-history theory predicts that the effect of stress should differ depending on the costs and benefits of the stress-response and reproduction, which often differ between the environments that the organisms inhabit.
I showed that the suppression of reproduction by acute stress is lessened if animals live in a high-disturbance environment (Abolins-Abols et al. 2018): while stress normally lowers testosterone levels, such effect was absent in birds that had spent weeks in environment with a frequent disturbances. The regulation of testosterone levels in response to stress and disturbance seems to be achieved at the neuronal level.
In addition to studying the effect of reproduction in the lab, I also study stress in wild birds, specifically in the context of urbanization. Opportunities for reproduction and the frequency of stressors differ between urban and rural landscapes. I showed that, compared to rural birds, urban birds are more stress-tolerant and reduced their aggression less in response to stress (Abolins-Abols et al. 2016). This observation is consistent with lower benefit of mounting a stress response, or conversely, with higher cost of a missed reproductive attempt, in urban environments.
Finally, I study how variation in individual condition in the same environment predicts differences in how individuals respond to stress. With the help of brilliant undergraduates, I studied how the risk of predation affects male behavior. I showed that Dark-eyed Junco males in better condition - individuals that have "more" to loose - are more sensitive to stressors than individuals in lower condition (Abolins-Abols and Ketterson 2017).
Mechanisms of behavioral diversity

Obligate avian brood parasites lay their eggs in host species nests, forcing the foster parents to raise unrelated young. While some host species are forced to do the best of a bad job and take care of the parasitic egg and chick, other host species have evolved an ability to recognize and reject the foreign eggs before they hatch.
Brood parasite and host interactions have fascinated people ever since Aristotle first pondered about the reproductive biology of cuckoos in ancient Greece. It is both an evolutionary riddle as well as a physiological one. Why do many host species fail to recognize and reject parasitic eggs and offspring? Why do host individuals within a species differ in their response to a foreign egg? How is the evolution of egg rejection possible, if maternal care is otherwise so hardwired in the songbird lineage?
Together with an international team of scientists I am working towards unraveling cognitive, hormonal, and neural mechanisms that underlie the recognition of eggs and regulate the decision to reject them. We've shown that the perceptual environment explains variation in the propensity of egg rejection (article in press) and that hosts use specific colors to discriminate against foreign eggs in their nests (Abolins-Abols et al. 2019, Manna et al. 2020).
Brood parasite and host interactions have fascinated people ever since Aristotle first pondered about the reproductive biology of cuckoos in ancient Greece. It is both an evolutionary riddle as well as a physiological one. Why do many host species fail to recognize and reject parasitic eggs and offspring? Why do host individuals within a species differ in their response to a foreign egg? How is the evolution of egg rejection possible, if maternal care is otherwise so hardwired in the songbird lineage?
Together with an international team of scientists I am working towards unraveling cognitive, hormonal, and neural mechanisms that underlie the recognition of eggs and regulate the decision to reject them. We've shown that the perceptual environment explains variation in the propensity of egg rejection (article in press) and that hosts use specific colors to discriminate against foreign eggs in their nests (Abolins-Abols et al. 2019, Manna et al. 2020).

Even when faced with exactly the same perceptual environment, host individuals often differ in their decision to reject or accept the parasitic egg. Our hypothesis is that this inter-individual variation in the likelihood of egg rejection is regulated by hormones (Abolins-Abols and Hauber, 2018). Hormones are intricately involved in the regulation of maternal behavior, aggression, vigilance, and the stress response. Because egg rejection can be viewed as a stress- or vigilance-induced modification of maternal behavior, hormones may therefore regulate the rejection of parasitic eggs by hosts. While the hormonal regulation of behavior is one of the oldest ideas in biology (in 1849 Arnold Berthold showed the testosterone is necessary for rooster aggression), we do not yet understand how and if hormones regulate the fascinating host defenses against brood parasites (or, to that matter, the behavior of brood parasites themselves). The perspective that we need to study hormones to understand host behavior was recognized by the American Ornithological Society's Katma award, an award given to "ideas that could challenge long-held views and change the course of thinking about the biology of birds" (read about it here). To this end, we have so far shown that experimentally suppressing hormones involved in the stress response in free-living birds leads to suppression of egg rejection, indicating that glucocorticoids may regulate this widespread and important host behavior (link to the preprint). We have also shown that the concentration of maternally-deposited hormones in the eggs correlates with individual variation in egg rejection (Hauber et al. 2020).
Mechanisms of color diversity in birds
Feathers represent some of the most spectacular diversity in nature. Scientists across the globe are capitalizing on new sequencing tools to understand the genomic mechanisms that underly this diversity. Furthermore, we can now use tools developed in melanoma research to study how the pigment cells - melanocytes - produce feather color in birds.
I study the color diversity of the Dark-eyed Junco. Juncos are a songbird species with an extraordinary variation in coloration across subspecies that has evolved rapidly since the last ice age. In addition to the between-subspecies diversity, individual juncos from the same population differ in the coloration of feathers used in social signaling. I am interested in what genomic and cellular mechanisms underly both the between- as well as the within-subspecies diversity in feather color. |
Together with Borja Milá and Etienne Kornobis, I showed that the difference in feather coloration across subspecies can be explained by variation in WHERE the pigment is deposited in the growing feather miscrostructures, as well as what pigment-cell related genes these feathers express (Abolins-Abols et al. 2018).

I also study the mechanisms that underly the within-population diversity in feather color. I focus specifically on junco tails: juncos, similarly as many other songbird species, have white pigment-less patches on their tails, and the size of these patches varies across individual birds. Juncos display their tails, and the amount of white coloration, during courtship and aggressive interactions. I study the genomic and hormonal mechanisms that underly the variation in the amount of tail-white in juncos, with the goal to understand what ecological and evolutionary factors drive variation in feather color in general. In collaboration with Dr. Cheng-Ming Chuong at the University of Southern California and Dr. John Foley at Indiana University, I showed that white, developing junco tail feathers contain melanocytes, but these cells do not produce pigment. However, when grown outside of the feather in a cell culture, pigment cells from white junco tail feathers CAN produce pigment. This suggests that there are local inhibitory mechanisms in white feathers that suppress melanocyte development or function.
To understand what inhibits melanocyte function in white feathers, I use transcriptomic studies coupled with pharmacological manipulations to study the effect specific genes and hormones on developing feathers. So far, it seems that somewhat popular assumption that testosterone regulates social ornament size seems not be true in juncos. Currently, I am testing the role of specific target genes in the regulation of feather color development. This work has benefited immensely from undergraduate researchers, specifically Hannah Kassab.