July 12 – What A Croc!

Today’s factismal: A female Nile crocodile determines the sex of her children by changing the temperature of the nest; too hot or too cold means more girls!

When Alice went to Wonderland, she recited a poem about Nile crocodiles; the poem praised their “shining scales” and “gently smiling jaws”. But what she should have praised was their ability to determine the gender of their children. As is the case with many other reptiles, the Nile crocodile can change the sex of its children simply by changing the temperature at which the eggs are incubated. If the eggs are kept between 89.1°F and 94.1°F, then the babies that hatch are male. But if the eggs stay too cold or too warm, then the babies that hatch are female.

A baby Nile crocodile hatching (Image courtesy Africa Wild Trails)

A baby Nile crocodile hatching
(Image courtesy Africa Wild Trails)

This would normally just be an interesting and somewhat puzzling phenomenon; biologists could (and have) argue for years over why such a mechanism for determining the sex of the offspring is necessary. But the world is currently undergoing something of a heat wave. The past fifteen years have been stuck on “hot” and the next few decades don’t look much better. And what that means is that the Nile crocodiles will have a harder time keeping their eggs in the temperature range needed for male hatchlings. In effect, the number of male Nile crocodiles will serve as a proxy for the temperature.

And Nile crocodiles are far from being the only critters that will change as the climate does. Trees will sprout further up on mountains, and butterflies will migrate earlier in the year. Flowers will bloom earlier or later. And even fish may change their spawning in response to changes in the climate.

Naturally, phenologists (scientists who study the timing of natural events) would love to record all of these changes. But Nature has the phenologists out-numbered eleventy billion to some. And that’s where you come in. If you would like to spend a little time each week observing the flowers in your backyard or the birds in your neighborhood or any other regular natural event, then the folks at the National Phenology Network would like you to become a Nature Observer! Just mark down your observations and add them to the easy-peasy web form and watch as the phenologists use your data!

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