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A marmoset looks on during the final round of the LPGA Brazil Cup at the Itanhanga Golf Club in Rio de Janeiro, Brazil.
Crows in Japan have the strangest habit. They carry nuts in their beak and drop them on crosswalks. Passing cars run over them, cracking them. It's not just that the crows have outsourced the heavy lifting, they've even come to realize that it's easier to collect their reward on a section of asphalt where traffic consistently stops, and then goes.
Foxes, songbirds — even whales — have something in common with those wily crows from Japan. When they wound up in a man-made city habitat (or a human-impacted area), they've come up with new tricks to survive. What about the animals that can't adapt so well? It's up to humans to adjust their behavior for the sake of the critters, say researchers.
In their new paper in Animal Behavior, Daniel Sol and collaborators at Catalonia's Center for Ecological Research and Forestry Applications survey species who've learned to make the most of their new circumstances when humans started meddling with their natural habitat. It's not uncommon for species to change when their environment shifts, but behavioral changes for urban life tend to be the most spectacular, Sol told NBC News.
Scientists have drummed up a long list of behavioral changes that have allowed small mammals and birds to get comfortable in cities around the globe:
- The black-capped chickadee belts out a shorter, shriller song when it needs to be heard over the sound of moving traffic. When traffic noise subsided, they return to a slower, deeper melody that is more familiar to potential mates. Its flexibility is part of what makes it a successful urban dweller.
- Pigeons have become used to human hands feeding them, so much so they can now recognize their regulars when they show up with birdseed. But not all people are pigeon-friendly, the birds have learned. They also quickly learned to avoid humans who had previously chased them away.
- Similarly, urban mockingbirds in North Carolina learned to recognize people who had threatened their nests fairly quickly.
- Near Bristol in the UK, traveling urban red foxes now tend to cross roads more often at night, when they are less likely to be hit by a car.
- Black tufted marmosets living in a public park in Belo Horizonte, Brazil, avoided noisy sections of it, even if there is plenty of food to be had there, and instead move to quieter locations.
- Coyotes have made themselves at home in cities like Chicago, where they live in public parks, and among apartment complexes and industrial buildings. If you watched "The Lion King," you may have guessed that they usually hunt in packs, but the urban coyote flies solo and prefers to hunt at night. Coyotes even seem to be doing a bit of good, however unknowingly — they control the spread of Canada geese in the city by sneaking up on their nests and stealing their eggs.
And out in the ocean, where there's no sign of city life, man-made sonar tends to challenge the typical behavior of whales. Single male humpback whales sing for hours during the breeding season, in what scientists believe is a mating display. So when sonar interfered with their serenade, their songs got even longer. (Though, data made public later showed that this isn't always the case. When the military tests their sonar equipment, whales stop diving for food and singing.)
Why are some animals better city dwellers? A species might naturally be a curious, bold sort — that would give it an advantage. Another possibility is that cities select for certain genetic traits, so the songbird that survives in city is one that is biologically different from its country cousin. But so far, it looks like it's the most innovative species, like the careful foxes and nut-cracking crows and song-switching birds, that stand the best chance, Sol explains. If they can change their behavior, they're most likely to do well.
Species set in their ways may have a harder time, Sol says, but there are ways we can help. Breaking up the concrete some and building green spaces and parks helps new species find their feet. "If the environment is more similar, [if] they contain gardens, more green space, then birds or other animals can do much better," Sol says.
Of course, neatly trimmed hedges and astroturf aren't a complete replacement of the wooded homes most animals enjoyed. "We need to build cities that have more gardens and parks, but we also need to maintain natural habitats as they are because they are crucial for biodiversity," he says.