Nests of loosely arranged sticks, rocks, or dirt are cooler in temperature at the bottom where the egg contacts the nesting material.

用细棍、石子或泥土松散地搭建的巢穴在筑巢材料与鸟蛋接触的巢底温度是比较低的。

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And because they're optimized for swimming rather than walking, it's difficult for penguins to gather a lot of soft nesting material.

企鹅比较难收集到一些软的筑巢材料，因为它们游泳远比走路擅长。

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It was a great opportunity to capture artistic images with high-key sky backgrounds as I did in this photo of a male passing nesting material to his mate.

这是一个能捕捉到艺术图像与高色调背景的绝佳机会，我拍的这张照片上，公鹅正将筑巢材料递给它的另一半。

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So far, though, no one has a clear idea of how much nesting material is needed to keep mice happy.

ECONOMIST: ��and they may return the favour

In general, though, with little nesting material around, the animals laboriously carried strands of paper over to the warmer spot, one or two at a time.

ECONOMIST: ��and they may return the favour

The idea was to check whether the animals would rather build a nest in the cooler cage or move to the warmer one, possibly tugging nesting material along with them strand by strand.

ECONOMIST: ��and they may return the favour