Because of climate change, spring is arriving earlier in many parts of the planet. This shift carries huge repercussions for animals that time their annual reproduction cycles with the environment.
One animal group that may be especially sensitive to shifting seasons is birds, who commonly migrate hundreds or thousands of miles to breed each year. To know when to make this pilgrimage, birds rely on environmental cues and their own biological mechanisms.
Understanding the interplay between these two factors is the focus of a new study led by Adam Fudickar, the Environmental Resilience Institute Migrations Mechanisms Fellow, and Indiana University biology professor Ellen Ketterson, ERI’s founding director and science advisor. The four-year study is being funded through a $1.1 million grant from the National Science Foundation.
“To predict the capacity for bird populations to be resilient against global warming, we have to understand the cues in the environment that they respond to and how they integrate those cues into their physiology,” said Fudickar. “For example, a cardinal who stays in the same place year-round is in a much better position to respond to seasonal shifts than a tropical migrant who can’t rely on local environmental cues to know it’s time to make the trip from South America to the Midwest.”
The study builds on years of research Fudickar and Ketterson have conducted on the dark-eyed junco, a common North American sparrow, and has three primary goals.
The first goal is to understand the genetic mechanisms that underpin reproductive behavior by comparing the DNA of two junco populations who share the same Appalachian environment for part of the year. One population is migratory and breeds later in the year; the other does not migrate and breeds earlier.
“We have the same species, same environment, but different reproductive schedules,” Fudickar said. “They essentially have the same genome, so it allows us to make comparisons between birds transitioning into reproduction mode and birds that aren’t.”
The second focus of the study aims to identify fine-scale reproductive mechanisms by comparing the behavior of individual non-migrants within the same population. Past experiments have revealed that early-breeding juncos and late-breeding juncos respond differently to hormone injections designed to activate reproductive behavior.
“We think this difference may have to do with the number of receptors these populations have for these circulating hormones,” Fudickar said. “By studying within a single population, we hope to see if sensitivity to these hormones is associated with breeding dates.”
The third objective of the study places the relationship between day length and bird reproductive cycles under the microscope. Past studies have shown that seasonal changes in day length are the primary cues that birds use to know when to reproduce.
To test how flexible this mechanism is, Fudickar will capture newborn juncos from the wild and raise them under different daylight schedules to measure the impact on the birds’ reproductive cycles.
“If exposure to light during development is a flexible mechanism, you could shift the reproductive cycle of a population within a generation,” Fudickar said. “If this mechanism works, it could help species expand their ranges because they can adapt to the new environment in a couple generations.”
Though the study uses birds as the model organism, Fudickar said the general principles the team is working to uncover could apply to other wildlife as well.
“The questions are really about reproduction,” Fudickar said. “Animals across the board are faced with the challenge of reproducing at the right time to maintain their numbers.”