Walking on Egg Shells

“A box without hinges, key, or lid,
Yet golden treasure inside is hid.”

- J.R.R. Tolkien, The Hobbit

My first thought was that it was a leaf.  My second, almost immediately, upon seeing that it was three-dimensional, was that someone, for some reason, had put a lime there.  A very fresh, very vibrant green lime, obtained from who knows where, that had somehow wound up in an unlikely crevice in our aviary.  It took me a while to process it further - the texture smooth and shiny, not rough and pitted - before I realized what I was looking at.

An egg.

I feel embarrassed to admit it now, but my world view wasn't broad enough at that young age to entertain the possibility of green eggs.  I mean, Dr. Seuss wrote about them, for Pete's Sake, how real was I supposed to think they were?  There it was, however, very beautiful and very smooth and very green, laid in a shallow burrow behind a fallen log in our South American aviary.  The egg of an elegant-crested tinamou, a chicken-sized bird that boasts of the ostrich as one of its closer relatives.  It wasn't a big egg, but in proportion to its diminutive layer, it was huge.  Over the next few days, there was a clutch of them.

Eggs are one of the most extraordinary parts of working with birds.  One day you have a bird, the next, you have a bird... and an egg.  And then you have to figure out what to do with it.  Where did the bird lay the egg?  Does it look like she's seriously nesting, or was she out for a walk, paused to drop an egg in the middle of nowhere, and then sauntered on, merrily (our ducks do this all the time).  Does it look like there will be more coming?  Is she sitting on it - if so, should I leave it to her (or him, as it happens with some species... tinamou being one of them), or pull it an put it in an incubator?

Is it even fertile?  Female birds lay eggs, regardless of whether they will hatch or not.  Females housed alone or with other females will lay infertile eggs.  Those chicken eggs you buy at the grocery store?  Pop them in the incubator for as long as you like - most of those hens never saw a rooster.

When birds at our zoo lay eggs, my number one choice is to always leave it to the professional... and I don't mean the zookeepers.  Mother birds are much better at controlling the temperature of their eggs than I'll ever be, even with an incubator, so I prefer to leave it to them.  I keep an eye on the nest (if it really is a nest) and see if that egg, or just a fluke.  I make a note of when I first saw the eggs, then look up what the incubation period (how long it takes the egg to hatch) for that species is. 

If the female sits tight and acts like they're going to hatch, I leave her alone as much as I can.  If they're abandoned, I might candle them - taking them into a dark room and using a flashlight to illuminate the inside of the egg to see if any development is occurring.

Sometimes we don't want an egg to hatch - let's say the parents are brother and sister - or we do, but mom doesn't have the best track record of raising her chicks, or it's just too rare of an offspring to risk it.  In those cases, we may remove the egg and give the parents a fake one (a dummy egg) to sit on, just so they can feel like they're still doing something productive. 

If you just remove the eggs flat out, their usual response will be to lay another one.  Maybe even another after that... which can eventually drain the body of the hen of calcium (although this tendency to lay new eggs - double-clutching, in the trade, has been used to help some endangered, slow-reproducing species, such as condors and cranes, to produce more offspring in less time).

Sometimes eggs or chicks are pulled so the offspring can be hand-reared, but usually it's best to let the mother do the job herself.  She's got the evolutionary know-how... and she doesn't have fifteen other exhibits that require her attention.  Even if an egg is pulled for incubation, it can often be given to the mother shortly before hatching so that she'll raise it.  Similarly, you can give an egg to another female, one that doesn't have offspring of her own, to share the load.

However you go about it, there are few things more satisfying than coming in to work one day and finding your egg has been replaced by a baby bird.  Or, more exciting yet, to actually watch the shell pip and the youngster fight its way into the world.

And so, with respect to Tolkien, I think Bilbo was wrong.  The real treasure of an egg isn't the tasty yolk.  It's the promise of a new life - a flamingo, a penguin, an eagle, a parrot - inside, waiting to come out and meet the world.