Birds wait to reproduce in harsh environmental conditions

When food is scarce, the search for reproductive opportunities becomes too risky. So when these situations arise, some birds choose not reproduce, and instead focus their efforts on surviving.

Animals are constantly looking for two things: food and the opportunity to reproduce – and you could say the same about humans. We’re all just looking to survive and pass on our own genetic material to our offspring. But oftentimes when food is scarce, the search for reproductive opportunities becomes too risky. And when resources are limited and difficult to find, any reproductive efforts may be fruitless anyway. So when these situations arise, it’s usually in an animal’s best interests to not defend their territory or breed, and instead focus their efforts on surviving to the next breeding season. Biologists refer to individuals without a territory during breeding season as “floaters.”

Researchers from Northern Arizona University monitored a population of Willow Flycatchers for a five-year period. They marked each individual in the population with a uniquely colored leg band, and recorded their behavior during the breeding season. Some birds defended territories that contained their nests, while other birds – the “floaters” – moved around the population without protecting their territory or a nest.

During this study – published in The Auk: Ornithological Advances – a severe drought occurred, which allowed the researchers to examine how the birds responded to changes in their environment. Their observations determined that there were one and a half times more floaters during the drought than during a year with average rainfall. Even more interesting, they found that the floaters were more likely to survive than individuals who attempted to nest.

When researchers compared how many chicks a bird had with their floater status the previous year, they found that territorial birds had more chicks than the floaters, but there was one exception. During the year immediately following the drought, former floaters produced more chicks. However, one thing to note is that the researchers did not check the DNA of the chicks during the study, and birds are known to breed with multiple individuals that are not their mate. It’s likely that floaters engaged in this behavior regularly, through which they have the benefit of passing on their genes without the cost of raising another chick.

“In normal years all birds try to breed, and those that don’t breed lose out in long-term reproductive success, but in extreme drought years, not breeding is actually the better strategy,” explains Tad Theimer, lead author of the paper. “But this strategy of patience assumes that next year will be better than this year. As climate change increases the frequency of these extreme environmental conditions, this assumption becomes less certain.”

This means that the birds’ response to changes in environmental conditions may ultimately be their downfall, were the climate to become less predictable as climate change marches on. It’s important for researchers to continue monitoring these animals’ behavior as their environment changes along with the climate.

By Connor Ertz, Earth.com Staff Writer

Image Credit: Tad Theimer