Because of warmer winters, Florida scrub-jays are now nesting one week earlier than they did in 1981. But these early birds are not always getting the worm. 

A new analysis of data from a long-term study, published Oct. 24 in Ornithology, finds that warmer winters driven by climate change reduced the number of offspring raised annually by the federally threatened Florida scrub-jay by 25% since 1981.

Warmer temperatures, the scientists hypothesize, make jay nests susceptible to predation by snakes for a longer period of the Florida spring than in the past.

Researchers from Archbold Biological Station and the Cornell Lab of Ornithology examined 37 years of data to assess the impacts of warming on reproductive effort. From 1981 to 2018, the average winter temperature at Archbold Biological Station increased by 2.5 degrees Fahrenheit.

“There is significantly more snake activity in warmer weather,” said Sahas Barve, lead author and director of avian ecology at Archbold, “and snakes are the primary nest predator.”

These losses are compounded by additional stresses. In an effort to produce young each season, Florida scrub-jays will keep building nests and laying more eggs after nests are lost to predators – “until they finally give up,” said John Fitzpatrick, director emeritus of the Cornell Lab of Ornithology.

“Despite increases in the number of nests built and eggs laid over the longer breeding season, Florida scrub-jays are not producing more young,” said Fitzpatrick, co-author of the paper. “In the bird world, there is a well-known trade-off between the number of breeding attempts and longevity. The more breeding effort expended each year, the less likely the bird is to be alive five or 10 years later.”

“The idea that over the long-term jays are experiencing an average reduction in reproductive success along with reduction in longevity is alarming,” Fitzpatrick said. 

The findings suggest that climate change could dampen the success of conservation efforts for this threatened species.

“Even in permanently protected areas like Archbold, jay populations face ever-worsening odds of persistence,” Barve said. “We’ve spent decades managing habitat for the Florida scrub-jay, but there is one thing we can’t control and that is climate. What might be a healthy and stable population of jays now might not be in the next 10 to 20 years despite nothing changing on the ground.”

This study was funded by Archbold Biological Station, the Cornell Lab of Ornithology and the National Science Foundation.

Kathi Borgmann is communications manager for the Cornell Lab of Ornithology.