Many birds are dutifully sitting on a nest right now keeping eggs warm. Eggs come in all shapes, sizes and even the contents inside vary.
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| An egg shell has thousands of pores to allow for air exchange but they are small enough to prevent bacteria from entering |
Both the shape and size of the egg are determined by the internal structure of the female. Large birds lay large eggs and tiny birds lay tiny eggs. But when the size of the egg is compared to the size of the adult bird, small birds lay proportionally larger eggs.
For example, it would take 60 ostrich eggs to equal the weight of one ostrich but it would only take nine hummingbird eggs to equal the weight of one calliope hummingbird. Looking at percentages, an ostrich egg weighs 1.8 percent of the adult’s body weight, a robin egg eight percent and a wren egg 14 percent.

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