ZooNooz Article - september 2004

Don’t count your chickens

Making the transition from first 'pip' to final 'pop' can be fraught with danger for a brand-new chick, explains TRENA CARNEY.

Photographs Cathy Alexander and Trena Carney

Making an entry into the world is a very dangerous and difficult period in the life of any young chick and there are many things that can go wrong. Luckily for some birds in captivity, help is at hand.

The hatching process

Glossy Black Cockatoo - the membranes are moist and there are no blood vessels present.

This begins several days before the chick leaves the egg. The first step is for the chick to move inside the egg so that its head is at the blunt end, tucked under its right wing with its beak resting against the air cell membrane. The chick takes its first breath at 'internal pip' - the moment when it pushes its bill through the shell membrane into the air cell.

The next step is 'external pip' where the chick uses its egg tooth to crack the eggshell. At this stage the chick is also withdrawing blood from the veins in the membrane that surrounds it and starting to absorb the remaining yolk. The chick then turns inside the egg and continues chipping away at the shell until it uncaps the egg and is free. It usually takes about two days from the time the chick pips internally to when it finally hatches.

The moment of hatching. The chick is left to pull itself from the remaining eggshell.

Cockatoo complications

The main reason we sometimes have to help a chick from its egg is because it is in the wrong position as it starts to hatch. This means that it can't reach the air cell or isn't able to move its head properly to crack through the shell.

One bird at Taronga that found itself in this situation was a Glossy Black Cockatoo chick. The parent birds had a history of breaking their eggs, so this egg was taken from them for artificial incubation. The chick started to hatch in the normal way with external pip happening about a day after internal pip. We expected to see a healthy chick a day later, but the pip site increased only slightly in size and the chick looked stuck. We could tell it was still strong and healthy as it was calling loudly and was active when we 'candled' the egg. (Shining a bright light into the egg during candling lets us see if the veins surrounding the chick have been withdrawn.)

The head is not tucked under the right wing so the beak cannot push against the shell.

When hatching was a day overdue and we could see that all the veins had been withdrawn, we opened the eggshell very carefully to see what was happening. Instead of having the head tucked under its right wing, it was beside the wing and across the chest which meant that the beak was at the wrong angle and the chick couldn't hit the shell properly with its egg tooth.

We were able to help the chick by carefully removing enough of the shell so that it could hatch. Only a day after this very difficult procedure, the little cockatoo was placed back in the nest with its mother. The female started to care for her baby very soon after introduction and the chick immediately started to thrive.

Dotterel dilemma

Chick

Chicks can also have trouble hatching if the egg loses too much weight during incubation. Most eggs lose about 15 percent of their original weight by the time the chick has internally pipped.

One Inland Dotterel egg that was incubated at Taronga had lost about 18 percent of its weight when the chick internally pipped. After weighing the egg every day we knew that too much water had evaporated through the eggshell and we were expecting this little chick to have trouble hatching.

The trouble didn't start until after the chick had externally pipped and then couldn't progress any further. The loss of too much water had caused the membranes inside the egg to dry out and trap the chick so that it couldn't turn inside the egg. This dry membrane also stopped the chick from withdrawing the veins that line the membrane.

To help things along, we dropped tiny amounts of warm saline solution into the egg every one to two hours. This moistened the membrane and helped the chick to move and to start withdrawing veins. We had to wait until this had begun before tiny pieces of shell could be removed with tweezers to free the chick from the egg. If we removed the shell too fast it could result in the veins bleeding, leading to infection or the chick bleeding to death.

It was a very slow process that took all night and most of the next day - everyone, including the chick, was very tired! However, it did eventually free itself from the last of the shell, becoming only the third Inland Dotterel chick to be hatched at Taronga in 10 years. It is now a very healthy young bird that will hopefully start breeding in the next year or so.

Perhaps we shouldn't count our chickens before they hatch, but by assisting some chicks with their struggle to enter the world, we can be at least a little more confident.

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