Research Findings in Breeding Canaries (Courtesy Wout van Gils)
The hen imparts increasing amounts of testosterone to her eggs in the order they are laid. This occurs whether or not she has been paired. The testosterone is present in the yolk of the egg and is independent of the male.It has been found that with many birds the eggs laid do not all hatch at the same time and that the young that are later hatched have higher amounts of testosterone in their system. The canary hen is no exception to this and it appears that the hen allows for the fact that not all of her eggs are hatched at the same time and initiates the best strategy for the survival of her young.
The fact that a hen starts breeding before all eggs are laid is not a sign of degeneration but in nature the rule rather than the exception. Where I have removed the eggs to ensure even hatching I have noticed, when banding, that there are significant differences in size amongst the young in a full nest of 4-5 young. I regarded this as an early opportunity for selection and rung the birds in order of size with the lowest numbers going to the “preferred” larger birds and the highest ring number to the eventual laggard presumably born from the last laid egg, the so-called “Schlussei”. The dissimilar sizes of young that are hatched at the same time were found to be determined by the order in which the eggs are laid and inherently by the increasing dosage of testosterone within each subsequent egg laid.The role of testosterone cannot be merely dismissed, because it leads to
- More persistent “begging” behaviour
- Higher growth rates
- Increased aggressiveness
The ranking within a group is positively influenced by the amount of testosterone within the eggs. The hens can introduce something to the eggs (testosterone) that alters the behaviour of their young. These young are higher in the pecking order and more dominant.
These discoveries clearly indicate that dominance increases with each subsequent egg laid so that the last hatched bird would be the “preferred” bird of choice.Researchers from Rockefeller University have performed experiments on the Belgian Waterslager and these have shown that the level of testosterone the hen imparts depends on
- Testosterone levels within the hen
- Environmental factors
- Order in which eggs are laid
Further research showed that the effects of injecting testosterone into eggs with a very fine needle. The tests were based on very large population sizes and also included eggs injected with a placido. The results proved that the young born from eggs injected with testosterone acquired definite advantages over their siblings.It is therefore worthwhile to pay more attention to those eggs that are hatched last since these contain something which is lacking to a lesser or greater degree in the first laid eggs. How this can best be exploited can perhaps best be explained in another article. There are many other factors, for instance, why does a hen leave the nest prematurely before any of the eggs have hatched. I find that about 50% of the hens are already sitting after the first or second egg has been laid. This means that where the eggs are picked and the hen ends up laying six eggs she ends up sitting 4-5 days later than she normally would. So after 10 days she “feels” as if she has already been on the eggs for14.Environmental factors affecting testosterone levels also include breeding arrangements, eg.,
- Breeding one male to 3 or 4 hens in a flight
- Pairing one male with one hen
- Switching one male between two hens
Another experiment showed that when lighting was abruptly changed from 8 hrs light -16 hrs dark to 14 hrs light – 10 hrs dark, i.e., without a gradual phasing in, the first eggs were laid after 14 days.
Our research is ongoing.