Rebekah Eliason for redOrbit.com — Your Universe Online
Bumblebees like to make their nests in holes insulated with plant materials. Freshly built bird nests can provide the perfect homes for bees, and they frequently invade newly made bird nests and take them over as their own. But how does a tiny bumblebee scare away a bird many times its size, and how does it choose which nest to invade? Piotr Jablonski and his colleagues from the Laboratory of Behavioral Ecology and Evolution at Seoul National University in South Korea published a study in Behavioral Ecology & Sociobiology researching these questions.
Bumblebees are prey for many types of birds. Yet some prey send signals to potential predators to warn them of the presence of their defenses using bright colors or noises. These signs warn predators to keep their distance or else suffer from poisonous stings or other unpleasant defenses.
Jablonski´s team was interested to find out if the buzzing sound that bees make was enough to scare birds away from their nests. They also wondered if bees preferred freshly built nests over other suitable nesting places.
Jablonski´s team focused on the interactions between bumblebees and two different bird species known as Oriental and Varied tits. Outside of Seoul National University Campus in the slopes surrounding Gwanak Mountain, bumblebees occupied 21 percent of freshly built tit nests in nesting boxes. Interestingly, empty nest boxes attracted no bumblebees, providing evidence that they prefer to invade freshly built nests.
To determine if the bumblebee´s buzzing sound is what scares away the birds, Jablonski´s team glued a dead bumblebee to a toothpick that was attached to a miniature speaker. They then placed the bumblebee buzzing device in a nest while the bird was away. When the bird returned they played a recorded buzzing sound through the speaker, and the bird´s response was observed by a tiny camera. As a control, the researchers also placed a second device into nests that played common bird calls.
When the buzzing sound was played through the miniature speaker, the research team observed that the birds became noticeably distressed and often flew away from their nest. The bird calls, however, did not produce the same distressed response as the buzzing noise.
“The bumblebees’ buzz appears to help them oust birds from their freshly built nests. We have provided evidence that a warning signal, known to help deter predatory attacks on a potentially harmful prey, may also help the prey to win ecological competition with its predator,” concluded the authors.
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