May 28, 2008 -- High-tech satellites combined with low-tech methods on the ground will soon be used to help understand how bees are responding to climate change, and to predict how far aggressive Africanized bees -- sometimes called "killer bees" -- will spread in North America.
The project combines two passions for leader Wayne Esaias of NASA's Goddard Space Flight Center in Greenbelt, Md. Esaias is an oceanographer who specializes in remote sensing via craft such as satellites -- and a master amateur beekeeper.
What triggered Esaias's interest in the new project was data he collected in his backyard. When the flowering plants that bees rely on for food are blooming, beehives pack on up to 25 pounds per day, through reproduction and storing honey. This weight gain is easily detected when hives sit on scales (they are then called scale hives), and provides a precise and reliable way to track the flowering of local plants.
"It only lasts about 4-6 weeks and then it's over," Esaias said.
Esaias recorded hive weights every night for 15 years. One day he decided to plot the numbers. What he saw was the peak hive weight gain -- corresponding to plant flowering -- stepping back more than half a day per year.
Combining his results with historical data he dug up from the area, he found flowering is happening almost a month earlier than in the 1970s.
"It's an astounding advance," Esaias said. "Even though I work at Goddard with remote sensing data, and the ice folks are across the hall, and we're aware of climate change, I was just shocked that it had been taking place in my backyard for the past 20 years ."
"The good news is there's a lot of variability from year to year caused by short-term climate variations like El Nino," he said. "Our bees have co-evolved with this and they're used to it, so they tend to be very resilient. The disturbing thing is that there's an overall trend … That might put them outside the realm of their experience."
Now Esaias wants to use satellite data to get a better handle on changes in the timing of flowering plants and how bees might be affected. Sensors on NASA's EOS satellites collect images of Earth at different wavelengths, allowing them to estimate leaf cover and when different types of vegetation emerge.
That's not the same as plant flowering, but Esaias is hoping to link satellite information about when plants go green to when they flower to get large-scale information about the timing of flowering. "The scale hives form that link," Esaias said.
Esaias presented his plan at a meeting of the American Geophysical Union today.
"One of the questions is how well they'll be able to pick up the flowering events that are important for bees" from the satellite data, said Jon Harrison of Arizona State University in Tempe, who is a part of the project.
Esaias and collaborators also aim to better understand the spread of a nasty invasive species: Africanized honeybees, also known as killer bees. These bees are widespread in the southwest United States and more recently arrived in Florida. Their more aggressive nature means municipalities and beekeepers need to change their practices when Africanized bees arrive.
"There's been a tremendous disparity in predictions for how far north Africanized honeybees are going to go," Harrison said, in part because what limits their expansion is not understood.
As a first step, Esaias's collaborators overlaid satellite climate data with the current Africanized bee range and used a model to predict the future range based on where similar conditions exist.
This shows the bees moving into California's Central Valley and parts of Georgia, but missing most of the eastern United States, which many had predicted would become a core part of the range.
"This is the baseline, but it's startling new information for the beekeeper," Esaias said.
The team hopes to improve these predictions by including EOS's satellite data on vegetation type and greening, coupled with information about what bees forage on and when these plants bloom nationwide.
Esaias aims to refine forage information by developing a national network of hive weight data contributed by volunteer beekeepers.
"It's going to be an issue of how many scale hives we're going to accumulate over time and how may areas we get," Esaias said. "Right now we don't have the volunteers."
Esaias believes that the Africanized bees thrive in places where flowering is triggered by rainfall, rather than the onset of spring, which is why the dryer southwest is a suitable place.
Scale hives could help demonstrate this.
"If we have sufficient scale hive records from Arizona and west Texas, I think they will reveal a startlingly different pattern of nectar flows from the mid Atlantic states that will be due to the type of forage available. And the same for the Midwest… We expect the scale hive data to reveal those patterns in detail."
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