Our normal system of nest-box inspecting is to check the boxes every other day until the first egg is due to hatch and from that date – whether an egg has hatched or not – inspections are made every day. Once an egg is seen in a nest-box the bird room calendar is marked with the cage number, at 14 days later. This is by no means an exact measure, as, although the standard incubation period for a zebra finch egg is accepted as being 14 days, we have known some to hatch at 13 days. It is also true that not all hens start incubating until more than one egg has been laid. Then, the apparent incubation period of the first egg is longer than 14 days. If the hen lays just one egg and others do not appear at the expected times, the egg is removed after two or three days so that the hen can get on with laying, hopefully, a full clutch. Eggs are examined to check if they are fertile six days before they are due to hatch. Once incubation is well under way, the experienced eye can see whether an egg is clear without the need to handle it. The less experienced may need to hold the egg up to the light. If the


egg appears to be solid, almost pebble like, it is fertile. If a fertile egg has been incubated for at least four days you will see signs of the developing chick. The blood circulation system is particularly obvious in the form of red veins. If light passes through an incubated egg so that only the yellow yolk can be seen, there is every chance that it is infertile – though remember, some hens do not begin incubating until they have laid two or three eggs. If in doubt, leave making any decision about apparently clear eggs for another couple of days and check again. To some extent, the action taken when a clutch of eggs is found to be infertile is influenced by the state of affairs in other parts of the bird room. If, for instance, a very good pair has ten eggs then half of these will be placed under the hen that has laid the clear round. If there is no immediate need for fostering, the clear eggs can be removed to encourage the hen to lay again. Fourteen days after the first egg was laid, we feed soft food to the pair concerned, even if an egg has not hatched. From that point, soft food is offered once a day. We feed it fairly dry,


Occasionally, a chick starts to chip its way out of the shell but then ceases to make progress. In such instances, we keep a close eye on the situation and if we believe there is a risk that the chick will die unless given some assistance, we chip the shell very gently until the crack is just more than half way round…


22 BIRD SCENE


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