In our latest Insight, Micah Scholer, a PhD student in Zoology at the University of British Columbia Biodiversity Research Centre, talks about his new paper, Survival is negatively related to basal metabolic rate in tropical Andean birds and his path into ecology.
What is your paper about?
Over a century ago the observation that the faster a machine runs the quicker it wears out gave rise to the notion that animals may experience a similar phenomenon―live fast, die young. In other words, animals with greater energy expenditure should have reduced survival rates. Indeed, scientist in the late 1800s noted that larger animals outlived small ones, and that larger animals tended to have lower basal metabolic rates (BMR). Yet empirical studies linking BMR to survival rates have been limited, especially in wild vertebrates.
Our paper explores the relationship between BMR and avian survival rates in the Neotropics. Between 2011–2016, we captured over 15,000 birds from more than 400 species in southeastern Peru, tracking their survival and measuring metabolic rates in a subset of these individuals. We hypothesized that species with lower BMR would also have higher apparent survival probability. Ultimately, we were able to test this idea in a diverse group of Passerines (i.e., perching birds) across the tropical Andes Mountains to see if trade-offs between survival and BMR were mediated by elevation (higher elevations are colder so may act to increase BMR) or if factors associated with elevation had a direct effect on survival. Our findings suggest that low BMR is associated with higher survival, regardless of where birds occurred across the elevational gradient.
Obtaining estimates of survival or BMR from free living birds can be difficult, especially in remote regions of the tropics. Obtaining both of these measurements from the same populations of birds, however, is almost unheard of. But that’s exactly what we were able to do, and what makes this dataset so unique. Previous work by members of our author team measured BMR in over 250 species of birds at our study areas (see Londoño et al. 2015 Functional Ecology). The same birds used in the metabolic studies were banded, released, and later used in our mark-recapture study as part of my PhD work. My plan was to use the banding data to estimate apparent survival for as many species as possible and explore what aspects of their natural history best predicted their survival. Using the BMR data became an obvious choice and allowed us to test the long-standing idea that lower metabolic rate is associated with higher survival. The other novel aspect of our study is that we were able to measure survival and BMR in different species that occurred across a nearly 3000 m elevational gradient. This gave us the opportunity to ask whether BMR was mediated by temperature at colder high elevations sites or if survival differed independent of BMR between highland and lowland birds.
Were you surprised by any of your results?
We were a bit surprised to find that high elevation species exhibited lower apparent survival rates than lowland birds. I guess we didn’t really know what to expect here. Previous research from our study areas found that the lowlands have notoriously high rates of nest predation compared to higher elevation sites. Although nest predation isn’t a proxy for adult predation rates, the number of avian predators in general also drops with increasing elevation. We figured that the decline in predators might out weight any negative physiological effects of living at high elevation, such as increased hypoxia and thermoregulatory costs, or potential negative effects of harsher climatic events, such as prolonged storms. An alternative explanation is that survival does not differ across the elevational gradient in Manu, but that high elevation species have lower sight fidelity and are therefore more likely to make larger movements that placed them outside of our sampling areas.
What is the next step in this field going to be?
Since these data are one of the first to show a link between BMR and survival in the same population of birds, we want to replicate the study design in other areas of the tropical Andes. Colombia seems like the next likely target. We are also particularly keen to test whether these same patterns emerge for birds living in temperate regions, where BMR is a more flexible trait and species are thought to have lower survival rates compared with their tropical counterparts.
How did you get involved in ecology?
As an undergraduate, I was fortunate enough to spend a semester abroad in Costa Rica studying tropical ecosystems and this piqued my interest in avian ecology. I began work as an educator for the University of Minnesota Raptor Center soon after graduation, teaching the public about raptor natural history and conservation. I made the jump to field ecologist a few years later when I accepted a position working with the Institute for Bird Populations monitoring Spotted Owls in Washington’s Cascade Range. Much of my initial experiences as an ecologist focused on North American raptors. I now work with a diversity of landbird species with a focus on Neotropical montane birds.
What is the best thing about being an ecologist?
As an ecologist, I get that same sense of discovery and excitement I felt when I was a kid trying to catch frogs along the Mississippi River in central Minnesota. Which one is it? Where did you find it? How many were there? Now I get to ask those same types of questions in a slightly more structured way. Being an ecologist has also taken me around the world and exposed me not only to new ecosystems and species, but to other cultures and different ways of thinking and being. I find that to be a really rewarding part of the job as well.
What are you currently working on?
I am currently examining global patterns in avian survival rates to better understand the extrinsic and intrinsic factors driving their variation. I also am a keener for bird molt and am working to develop sexing and aging criteria for a number of tropical birds from our study area in Peru.