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Ontogeny Recapitulates Ornithology

Since I got the news that I'm going to be an aunt, I've found myself becoming interested in fetal development. This is not a subject I had previously given much any thought to. As I count down the weeks until I meet my future nephew, I've been keeping track of his size using the customary fruits and vegetables that websites suggest. This is problematic because vegetables are variable in size and also boring. My mind went instead to birds. I started looking up a bird that matched the mass* of the fetus each week, much to the possibly feigned delight of my pregnant sister. I now present a full list for the enjoyment of pregnant folks and the birders who love them.

* Note that most birds are less dense that a fetus, and therefore greater in size at the same mass.

Week: 9
Mass: 2 g
Bird: Bumblebee Hummingbird

Week: 10
Mass: 4 g
Bird: Anna's Hummingbird

Week: 11
Mass: 7 g
Bird: Wilson's Warbler

Week: 12
Mass: 14 g
Bird: Vermillion Flycatcher

Week: 13
Mass: 23 g

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