opposite sex together – until you are sure they have settled down. That is doubly so in the case when a change of breeding partner is involved. If the cock is observed treading the hen – but no eggs appear – the hen must be the suspect member of the partnership. If, on the other hand, eggs are laid but turn out to be infertile, there is a strong possibility that it is the cock that needs to be replaced.
Zebra Finches mating
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
18 BIRD SCENE
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