Winter Heart Rate Telemetry in Grand Teton National Park
Following birds on snowshoes can be HARD, particularly after a deep, cold, fluffy, fresh snow or a warm, mushy snow-melting day. But the rewards are immense - at least for a family of field biologists. We spent 6 weeks chasing red crossbills by snowshoe in Grand Teton National Park, based out of the Murie Center of Teton Science Schools. These little finches are fascinating. The last day we tracked in early March was "warm" at 45 degrees F, and we were watching a pair of crossbills feed their three recently fledged young. At the same time the female was busily snapping off little twigs and collecting moss to make a second nest! Crossbills - given their unique bill and high proficiency at extracting tasty conifer seeds from cones - are able to breed in the deep winter in places like Jackson Hole. While my husband and I are making snowshoe tracts to run back and forth in order to keep warm enough, these little rule-breakers are singing, laying eggs and feeding little growing bodies. How do they do it? It's a good question. Days are short in winter, allowing for less foraging time. Temperatures are extreme and storms are frequent. We already know that successful reproduction in these conditions requires the female to sit full-time - excepting bathroom breaks - on the eggs and very young nestlings to keep them from freezing. This in turn requires the male to feed both himself AND the female (and any young babes) entirely. We witnessed the work this requires first hand this winter. For a period of several weeks there wasn't a female crossbill to be seen and the males were little foraging machines... pausing only to take a drink of water or preen a feather now and again. The data are yet to be tabulated, but I suspect that the time spent foraging and heart rate is going to be immensely different for breeders and non-breeders in winter - and maybe even when comparing with breeders in the much warmer summer season.
Pictured right: Two old nestlings are visible in a winter nest. This picture was taken just two days before they fledged (left the nest). Notice the bill is not yet crossed. It takes another month of growing and learning outside of the nest for a crossbill to be an independent forager, and they depend on their parents to get them to that point.
Heart rate is a good estimate of metabolic rate, and here's why: our bodies (and crossbill bodies) use oxygen in order to turn food into energy for cellular processes. As the cells use more oxygen to fuel their processes and do their jobs, the levels of oxygen in the blood start to deplete. Sensors in the body and brain pay close attention to these levels and within seconds the brain has ordered the heart to start pumping blood faster (this is why your heart beats faster and harder when you exercise) and the lungs to start expanding further to draw in more oxygen at a faster rate (this is why you breathe harder when you go up stairs). In wild animals, the relationship between heart rate and oxygen consumption is quite linear. There can be some differences depending on if an animal is walking or running - but all things considered, measuring heart rate is a fantastic method to estimate metabolic cost in an animal that is living it's life in the wild. What's more, you can measure the heart rate in real time and continuously. So if a bird is chased by a predator, or experiences a storm, or hatches young while wearing a heart rate monitor - then we can learn how much energy these things take for a bird to survive and meet those energy challenges. To a biologist this is extremely valuable information - because energy is the currency of life. If you don't meet the energy challenge of reproduction then you don't raise the next generation and populations begin to fail. If you don't meet the energy challenge of migration or an immune challenge or finding food - then you don't live to raise the next generation and populations decline even faster. This value, combined with the fact that tracking birds for several days of their lives gives us FANTASTIC natural history information, makes me really excited to be out there harassing finches. I hope information like this eventually improves the lives of these animals as much as it already improves mine. Living for 6 weeks in a tiny cabin in Grand Teton National Park is an amazing experience - and one that I am so incredibly happy to share with Cash, Huck and Taylor (and some grandmas too... more info on that in a coming-soon post about families and field work).
Pictured below: Cash (2.5 yrs), Huck (9 months), Taylor and myself celebrating the last bird we tracked. It was a beautiful day and one that wrapped up an 8-year ongoing project!
