Reducing reproduction helps some birds survive drought

In the final year of Thomas Martin’s songbird study in Venezuela, he noticed some birds just weren’t breeding.

In fact, one species — the gray-breasted wood-wren (Henicorhina leucophrys) — went from having 65 active nests to just seven. The reason? Martin thought it was probably a drought that struck during the last year of his study.

“The tropics have always been portrayed as this stable environment, where climate or temperature doesn’t change much of the year,” said Martin, a senior researcher with the U.S. Geological Survey and the University of Montana. “Most people haven’t picked up on the huge variation that occurs in rainfall.”

Martin moved on to study songbirds in Borneo, where he remained for 12 years. He knew a drought should be coming based on the El Niño and La Niña weather patterns. Sure enough, it happened in 2016.

Martin, who co-led a study in Nature Climate Change with TWS member James Mouton, suspected that drought in both study areas would prompt the birds to reduce reproduction and that the birds’ survival would decline as well.

But after reviewing the data from both short-lived and long-lived songbird species in both places, he was shocked. Species with short lifespans saw their survival decline with drought. But for long-lived species,” the surprising finding was that the survival actually went up,” he said.

Reproduction takes a lot of energy and can impact survival. In dry years, Martin’s team found, long-lived species like the eyebrowed jungle flycatcher (Rhinomyias gularis), which can live nine or 10 years, lowered their reproduction, resulting in higher survival. This increased survival allows them to breed later when it’s more profitable. “If they live a long time, they can afford to wait for a better year,” Martin said.

But this may not be all good news for the long-lived species. If there are repeated droughts year after year, longer-lived species may continue to delay reproduction, putting the species at risk. For shorter-lived species, their survival will go down, but they’ll still produce offspring.

Because both long- and short-lived species are impacted by drought, Martin stressed the importance of conservation. “The main thing is maintaining as much habitat as possible,” he said.

Martin’s team found that songbird species occupying creek beds or marshy areas were most impacted by drought. Maintaining strong watersheds that keep wet areas wet during droughts is critical to their survival and reproduction.

This research may not only apply to species in these tropical areas. “People haven’t really thought about the influence of longevity in the north temperate zone,” Martin said. “I think there’s a lot more that can be done in North America with respect to that, targeting species in terms of their sensitivity to climate impacts.”

Header Image: An indigo flycatcher (Eumyias indigo) visits its nest in Malaysia. Credit: Thomas Martin