ARE THEY DONE YET? By Mark McKellar Yellow Warbler's nest with egg. photo courtesy of Linda Williams Eggs are fascinating structures and the variety of shapes and colors have intrigued people for years. One of the most commonly asked questions this time of year is “How long does it take for an egg to hatch?” As you can easily guess, the answer is highly variable and depends of many factors including the size and life-style of the bird. One major factor that dictates the length of incubation time is the life-style a bird leads. Ground “living” birds like Northern Bobwhites and Killdeer are known as precocial birds. To survive the many perils that these hatchlings face, they have to be ready to “hit the ground running”, literally. Precocial young hatch fully covered with down feathers, have strong leg muscles, good eyesight and hearing. The price that these birds pay for this advanced development is a longer amount of time in the egg. The 24 days a Bobwhite requires to hatch her young means she has to remain in the vulnerable position of a ground nest longer than her “tree dwelling” cousins. Eastern Kingbird's nest with altricial hatchlings. photo courtesy of Linda Williams Most of our most common birds take a very different approach. Altricial birds incubate their eggs for a relatively short period of time (12 to 14 days is common), but their young are naked, blind and defenseless at hatching. While hatchlings grow quickly, a high degree of parental care is required for their young’s ensured survival. Most of our songbirds adhere to synchronous hatching times. They don’t start incubating eggs until they have all been laid to ensure that they all hatch close together. Purple Martins on the other hand are among those who have asynchronous hatching. Their eggs hatch over a period of several days. While this would seem to give the first young to hatch a huge advantage over the others, this doesn’t always hold true. For birds like martins who’s food source of flying insects can be drastically affected by weather, the first young may not make it if food is scarce. A crucial insect hatch may not occur until the first couple of young have starved. Like so many aspects of a bird’s life, eggs and nesting is a fascinating subject. The ultimate goal is to make sure their genes are passed along. You can bet that the size of the eggs, the number of eggs laid, the number of nests per season and all factors are genetically imprinted in birds to ensure success.

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