“I don’t think there is anyone today who can hold a candle to what these guys could do, both physically and in terms of thinking deeply about what they were seeing,” Patton says. “We’re too attached to our mechanical digital devices to really look at it.”
While Grinnell collected and studied specimens using shotguns and deadly pressure traps, the Pattons set 200 live traps each night, recording their catch for four or five days. They have kept a few specimens for the museum, spending eight weeks each spring and six weeks each fall from 2015 to 2018 in Death Valley.
The results were unexpected, says Beissinger. “We were very surprised to find that what we saw was the resilience of small mammals,” he adds. “When we looked at the proportion of sites a small mammal occupied a century ago, when Grinnell and his colleagues were away [surveying] and the proportion that we have now, it was almost a straight line.
Patton, who has studied small mammals for over 50 years, says they’re buffered by their nocturnal nature, burrows, and ability to meet water needs by metabolizing seeds. Birds, on the other hand, feed in the heat of the day and often need open water sources, such as springs, swimming pools and surface water. “Many birds need exogenous water to survive,” he says. “But most small mammals make their own water [through seeds]. “
Beissinger puts it in simple terms: birds are more exposed to heat and are more sensitive to the effects of climate change.
To understand these differences, they brought Eric Riddell, assistant professor of ecology, evolution and biology of organisms at Iowa State University. Riddell had been a postdoctoral researcher at Berkeley and had built computer models to calculate the cooling needs of 49 desert birds. While Patton and his wife camped in the wilderness, Riddell camped at the museum, spending six months out of two years starting in 2017 taking measurements of bird specimens, determining their approximate dimensions, length and density of their birds. feathers, and even how much sunlight bounces off them or is likely to pass through their plumage to their skin. From models created from these measurements, he was able to estimate the amount of additional water needed for evaporative cooling by each species of bird today compared to 100 years ago. The species that have declined since Grinnell’s time were the ones that had the most difficulty keeping cool, especially the larger birds, especially those like the green-purple swallow and the white-throated swift which shoot the major part of their insect water.
For small mammals, he returned in 2019 to do the same, cataloging body size and fur density for another six months. The models looked at how their bodies absorbed or reflected heat, including direct sunlight, reflected sunlight, and radiant heat from the ground. A fluffy furry rodent can transfer this heat slowly while a short furry rodent, like a ground squirrel, can transfer it quickly.
Its program to simulate the effects of climate change – increasing temperatures and decreasing precipitation – included more than 1,000 lines of code. Riddell used UC Berkeley’s supercomputer: 240 connected computers, running for 18 hours to calculate 1.2 billion hourly simulations. Translated, this means that the model calculated the amount of heat gained or lost by each species of mammal every hour of every day over the past 100 years in the Mojave Desert.
The key to the different outcomes for birds and mammals has been found to be water consumption. Riddell found that the birds took almost three times as much water as small mammals to cool off. “In the desert, water is very limited, and there is not much. And you need this water to cool you down, ”he says. “In the last century, birds have experienced this really massive increase in the amount of water they need to stay cool, just to function, and small mammals haven’t experienced this change.”