We measure the spatial memory of chickadees using a classic associative learning task but in a very atypical location. To do this, we hang a circular array of eight feeders equipped with radio-frequency identification and filled with seed in several locations across our field site. Birds are tagged with “keys” – transponder tags in leg bands that contain individual identification numbers and allow them to open the doors of their assigned feeders to get a food reward.

The setup allows us to measure the spatial memory performance of individual chickadees, because they have to remember which feeder their key enables them to open. Over eight years, our findings demonstrate that chickadees with better spatial memory ability are more likely to survive in the high mountains than those with worse memories.

However, chickadees may be facing increasing challenges that will shape their future in the high mountains. In 2017, a year with record-breaking snow levels, adult chickadees showed the lowest probability of survival ever measured at our site. This exceptionally extreme winter came with recurrent storms containing cold weather and high winds, making it difficult for even the memory savvy chickadees to forage and survive.

Nevertheless, triumphant populations have persisted in high-elevation mountain environments, but their future is becoming uncertain.

“It’s weather whiplash,” says Adrian Harpold, a mountain ecohydrologist. Harpold works to understand variations in climate patterns within forest environments, and one of his field sites lies alongside our chickadee research site.

The Sierra Nevada and other mountain ranges in western North America have been experiencing more extreme snow years and drought years, amplified by climate change. Extreme snow linked to global warming might seem counterintuitive, but it’s basic physics. Warmer air can hold more moisture – about 7% more for every degree Celsius (every 1.8 degrees Fahrenheit) that temperatures rise. This can result in heavier snowfall when storms strike.

In 2023’s record winter, over 17 feet (5 meters) of snow covered the landscape that our chickadees were using every day. In fact, these intense storms and cold temperatures not only made it difficult for birds to survive the winter but made it almost impossible for them to breed the next summer: 46% of chickadee nests at our higher elevation site failed to produce any offspring. This was likely due to the deep snow that prevented them from finding emerging insects to feed nestlings or even reaching nesting sites at all until July.

Even in years of tremendous snowfall, chickadees can still use their finely honed spatial memories to recover food. However, severe storms can shorten their survival odds. And if they do survive the winter, their nesting sites – tree cavities – may be buried under feet of snow in the spring.

It doesn’t matter how smart you are if you can’t reach your nest.

Extreme snow oscillations also affect insects that are critical for feeding chickadee chicks. Limited resources lead to smaller chickadee offspring that are less likely to survive high in the mountains.

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