Great tits can adapt to climate change, but only to a point

Global warming could have dire consequences for species that depend on a stable food supply at specific times of the year. If warming takes place too quickly, these species may not have enough time to adapt. This could be precisely the case for great tits as the larvae they depend on for survival are hatching earlier, according to a new study. 

“If the changes happen too fast, species can become extinct,” said study first author Emily Simmonds, an associate professor in the Department of Biology at Norwegian University of Science and Technology (NTNU).

The researchers investigated how great tits may be affected if the availability of larvae changes in the spring. These birds depend on an abundant supply of larvae to feed their young. If this supply peaks earlier in the spring than usual, there may be a lack of food for the hatchlings.

Spring is arriving earlier and winters are becoming warmer. This causes some trees to sprout their leaves early, which prompts the larvae that feed on the plants to hatch out earlier. “When the climate changes, the interactions between different species changes too,” said Professor Simmonds.

In collaboration with experts at the University of Oxford, the researchers used population models to estimate the consequences of different climate scenarios for great tits. The team wanted to identify the tipping point at which the changes would happen too fast for the great tit to modify its behavior and keep pace with the hatching larvae.

Due to genetics, great tits have varying abilities to adapt to different conditions. For example, an earlier supply of larvae can be advantageous for great tits that hatch their young earlier in the spring. This advantage can be transferred to the next generation of birds and they will hatch their young earlier in the season as well. 

For this strategy to work, however, the great tits have to evolve fast enough and be flexible enough to keep up with the behavior of their prey.

“Given conditions with big greenhouse gas emissions, the great tits won’t always be able to keep up with the changes in the larvae supply,” said Professor Simmonds.

In the worst case scenario, the researchers found that entire populations of great tits will simply disappear by the end of this century because they cannot find enough food for their young.

“This could happen even if the great tits are also modifying their behavior faster in a rapidly changing environment. The larvae might be changing even faster than the great tits,” said Professor Simmonds. 

The tipping point for populations of great tits, or the point at which they will not have a chance of survival, will be reached if larvae begin hatching 24 days earlier compared to when they hatch now. According to the researchers, this threshold even applies to populations that appear to be completely stable today.

“It could be that the apparent stability today is hiding a future collapse,” said Professor Simmonds. “The good news is that the populations will be able to survive scenarios with lower or medium warming trends.”

The study is published in the journal Ecology Letters.

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By Chrissy Sexton, Earth.com Staff Writer