Tropical songbirds reproduce less during severe droughts

A new study from the University of Montana describes a previously unknown strategy used by tropical songbirds to adjust to the stress of climate change. The researchers have discovered that these birds reduce their reproductive activity during severe droughts, and this actually works to their advantage.

“We were extremely surprised to find that not only did reductions in breeding activity mitigate costs to survival, many long-lived species actually experienced higher survival rates during the drought year than during non-drought years,” said study co-author Thomas Martin. “In contrast, shorter-lived species that kept breeding during droughts faced strong reductions in survival.”

Over the course of his career, Martin has spent months at a time living in remote jungles to study birds. For the current investigation, he observed 38 different tropical bird species in Venezuela and Malaysia over multiple years. At each field site, there was one drought year during the study period.

The scientists modeled future population results for the birds using three different climate change scenarios. They monitored nests of each species to evaluate reproductive activity before and during the droughts. The researchers also marked birds with colored material to estimate survival rates. 

The analysis revealed that drought reduced reproduction by an average of 36 percent in the Malaysian species and by 52 percent in the Venezuelan species.

“The negative impacts of drought on survival are well documented,” said  Martin. “We therefore also expected the droughts to reduce survival, but thought that the reduced breeding activity might limit the decrease in survival.”

He said the population impacts of droughts were largely offset by the reproductive behavioral shifts in longer-lived species, but shorter-lived species did not benefit as much.

“Overall, our results have several major implications,” said Martin. “First, we show that understanding behavioral responses to drought are critical for predicting population responses. Behavioral responses to environmental conditions can help buffer the most sensitive vital rates for a given species and mitigate the overall effect on fitness.”

“Second, our results provide unique support to the idea that reproduction can negatively affect survival. This idea of a ‘cost of reproduction’ is central to life history theory but only rarely documented in wild populations.”

The research suggests that many longer-lived tropical songbirds may actually be more resilient to droughts than previously expected.

“Ultimately, we hope our study can help motivate future studies into behavioral and demographic responses to shifting patterns of rainfall in more species so we can better anticipate the different impacts of climate change among species,” said Martin.

The study is published in the journal Nature Climate Change.

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By Chrissy Sexton, Earth.com Staff Writer