Photo: Andreas Geh / Alamy
What does a hot bird in a big city have to do to stay cool? They can’t turn on the air conditioning – but they can take advantage of ours. According to a study published in Biology Letters this week, rosy-faced lovebirds in Phoenix, Arizona, flock to vents in greater numbers as temperatures rise. Birds’ inventive adaptation to extreme Phoenix summers is the latest example of how birds and wildlife are changing their behavior to stay cool in the heat, and will likely become more necessary as climate change makes an already hot region even hotter .
Rosy-faced lovebirds are refugees from the pet trade who are native to southwest Africa and were first documented in Phoenix in the 1980s. They thrived in the city where they nest in cavities in ornamental palms and native cacti, and their population is now estimated at more than 2,000 individuals. But the parrots haven’t ventured far outside the city center, suggesting they are relying on humans to survive in a desert hotter and drier than their home. In their home’s arid forests and scrubland, temperatures rarely exceed 100 degrees Fahrenheit, and the birds can stay cool and hydrated by visiting surface water sources. In the Sonoran Desert of Arizona, on the other hand, temperatures regularly exceed 100 degrees and water sources such as springs or streams are scarce.
Temperatures in Phoenix are even more intense than in the surrounding area thanks to the urban heat island effect, and the city’s climate has changed in the few decades since the arrival of the lovebirds. Phoenix is already the hottest city in North America and also the second warmest city in the country. Compared to 1970, the city is now experiencing an additional 6.2 days above an average of 110 degrees, according to Climate Central. The local wildlife can feel the heat. Rising temperatures and drought have brought down bird communities in the nearby Mojave Desert – a microcosm of major changes in the southwest that affect humans as well. In 2019, Maricopa County, which includes Phoenix and its suburbs, saw triple-digit temperatures for 103 days and 197 people died in the heat. Conditions are likely to get even more extreme in the not too distant future: Scientists predict that Phoenix will have 132 days a year with temperatures above 100 degrees by 2060.
Phoenix ‘lovebirds have found a creative way to defeat the heat of the desert. Since they first arrived in town, the Arizona State University Science Building has been a reliable place to see them. During the summer, the brightly colored birds sit near the building’s vents, apparently taking advantage of the cool air that escapes – but no one had ever officially investigated the behavior.
“Several generations of graduate students of mine have independently commented on the lovebirds,” says Kevin McGraw, who heads a behavioral ecology laboratory at the university. “I said enough is enough.” He decided to officially document the observations in a scientific study.
Photo: Kevin McGraw
McGraw found the perfect student to begin studying at Raegan Mills. “I would say that my love for lovebirds really motivated me to take part in the study,” says Mills. “I was interested in their behavior as a wild population in an urban area.”
To better understand why the lovebirds huddled up against the vents of the campus building, Mills and McGraw approached a handful of students who were unfamiliar with their working hypothesis for help. For one year, from August 2, 2018 to August 2, 2019, students counted the birds each week on a randomly selected morning, afternoon, and evening. They identified various conditions that could affect the birds’ behavior, such as temperature, humidity, cloud cover, and human foot traffic.
One day as temperatures neared 115 degrees Fahrenheit, the students counted 43 lovebirds.
In the end, they made a total of 537 observations. Most of the time they didn’t see lovebirds by the vents, but 9 percent of the time they saw at least one. The lovebirds only appeared when the local temperature exceeded 90 degrees (with the exception of two cases where only a single lovebird was counted). The birds were most numerous on the hottest days, and the number of birds near the openings increased exponentially once the temperature rose above 99 degrees. One day when the temperature was nearing 115 degrees, the students counted 43 lovebirds. When they put the numbers together, Mills and McGraw found that temperature was, in fact, the biggest factor influencing whether the lovebirds showed up, though humidity also played a role.
It makes sense that the birds seek the cooler air out of the vents on particularly hot days when they’re likely to hit the limits of heat tolerance, says Blair Wolf, a researcher at the University of New Mexico who studies the effects of climate change Birds in the southwest. Birds gasp to stay cool – a strategy that uses a lot of energy and a lot of water. Because they are small and so much of their body is in contact with the outside air relative to their overall size, birds become dehydrated quickly. “Birds have to be very attuned to their environment because they have to balance their water and energy budgets every day,” says Wolf.
This means that the energy saved by just a few degrees difference can keep the birds below their maximum thermal limit and bring much-needed relief. This is an example of what scientists refer to as “microsite selection” when animals find a cooler place than the surrounding habitat and crouch when it’s too hot to forage for food and water. Microsites are often found near water and shade plants, but the lovebirds seem to have found an ideal microsite in ASUs Ventilation slots, says Wolf. Since their home habitat never gets as hot and dry as that of Sonora, they are likely to be particularly dependent on human-provided resources to meet their microsites and water needs. You won’t necessarily know how to get water from a saguaro cactus fruit, he says, like a native species might do.
Their dependence on humans is likely to minimize direct competition for resources between the lovebirds and native wildlife, says Simon Kiacz, an avian ecologist who studies parrot populations in Texas. If the lovebirds were able to draw water from a saguaro cactus fruit, they would potentially deprive native wildlife of the resources. “I think native species will have the upper hand over the parrots in most cases,” he says. “There may be some competition for nest boxes, but this is unlikely to be significant as the parrots are restricted to urban areas while the native species are not.”
But the habits of both native and non-native species could change as conditions get more extreme. Drought and high temperatures will put increasing pressure on all wildlife. Hence, it is important to understand how they adapt or fail to adapt to increasingly extreme conditions. The study provides a critical reminder of how species are pushed to adopt new behaviors as humans change the planet.