A growing body of research shows that birds and other animals change their behavior in response to humanmade noise, such as the din（喧嚣） of traffic or the hum（嗡嗡声） of machinery. But human clamor doesn't just affect animals. Because many animals also pollinate（授粉） plants or eat or disperse their seeds, human noise can have ripple effects on plants too, finds a new study. In cases where noise has ripple effects on long-lived plants like trees, the consequences could last for decades, even after the source of the noise goes away, says lead author Clinton Francis of the National Evolutionary Synthesis Center in Durham, North Carolina.

The study appears in the March 21 issue of Proceedings of the Royal Society B.

In previous studies, Francis and colleagues found that some animals increase in numbers near noisy sites, while others decline. But could animals' different responses to humanmade noise have indirect effects on plants, too?

Because they can't move, many plants rely on birds and other animals to deliver pollen（花粉） from one flower to the next, or to disperse their seeds.

To find out what animal responses to noise might mean for plants, the researchers conducted a series of experiments from 2007 to 2010 in the Bureau of Land Management's Rattlesnake Canyon Wildlife Area in northwestern New Mexico.

The region is home to thousands of natural gas wells, many of which are coupled with noisy compressors for extracting the gas and transporting it through pipelines. The compressors roar and rumble day and night, every day of the year.

The advantage of working in natural gas sites is they allow scientists to study noise and its effects on wildlife without many of the confounding factors often associated with noisy areas like roadways or cities, such as pollution from artificial light and chemicals or collisions with cars.

To find out what animal responses to humanmade noise might mean for plants, first the researchers did an experiment using patches of artificial plants designed to mimic a common red wildflower in the area called scarlet gilia.

Each patch consisted of five artificial plants with three "flowers" each -- microcentrifuge tubes wrapped in red electrical tape -- which were filled with a fixed amount of sugar water for nectar. To help in estimating pollen transfer within and between the patches, the researchers also dusted the flowers of one plant per patch with artificial pollen, using a different color for each patch.

Din levels at noisy patches were similar to a highway heard from 500 meters away, Francis explained. When the researchers compared the number of pollinator visits at noisy and quiet sites, they found that one bird species in particular -- the black-chinned hummingbird (Archilochus alexandri) -- made five times more visits to noisy sites than quiet ones.

"Black-chinned hummingbirds may prefer noisy sites because another bird species that preys on their nestlings, the western scrub jay, tends to avoid those areas," Francis said.