Birds die every day. So do people. Learning why may help scientists understand what can and cannot be controlled about life spans.
That’s why my research group and I have been following a population of marked songbirds known as dark-eyed juncos, or snowbirds, at Mountain Lake Biological Station in Virginia for more than 35 years. We track how many offspring the birds produce and how long they live by marking them with leg bands. We return each year to determine who is still alive and what attributes the survivors have.
Long-term field research can help answer some crucial questions. Males are more likely to be recaptured over time — are they healthier than females or just more sedentary? Is the likelihood of recapture constant over time? Do we see signs of aging – what we call senescence – in older birds? Or are there periods when the odds of surviving and reproducing are independent of age and more attributable to the luck of the draw, being born into good food years or into a glut of predators? Does breeding early or late in response to climate-induced earlier springs alter survival?
2020 is the first year since 1984 that we could not do our annual census. Because of the COVID-19 pandemic, we couldn’t travel and the biology station where we work was closed. We decided the need for caution exceeded the value of what we lost: a continuous record of individual bird lives and a chance to band each year’s offspring to follow in the future. We missed the continuity and the companionship of field research.
We can’t make up the gap, but we will resume in 2021, as long as the COVID-19 situation has improved. Ornithologists are committed to determining why North America has lost 3 billion birds in the past 50 years, and long term, seamless records of individual birds’ lives will help us learn the answer.