Aussie Finch Forum

Well we knew about this for gouldians but its true for the BFPF too. Have a read of the ABC article here.

So if you want more females in each nest don't crowd your aviaries!

Also true in a number of other species, including zebra finches, though the skew isn't always in the same direction. It depends on the relative 'costs' of producing a son rather than a daughter.

Thanks again for posting this information Greg.
Much appreciated and always interesting

Thanks Greg

I had a pair of BFPF fledge 5 young and they are all hens not crowded that aviary.And in another aviary 1 pair of BFPF fledged 4 cocks aviary slightly crowded

I thought the article proved a hypothesis about poor nutrition skewing sex ratios not the density in the wild or captivity??? Did I miss sometinig or are we drawing a long bow??? Maybe we should be looking more at our nutritional aspects in captivity to help skew ratio's in species that seem to throw predominately male or females.

I agree with you trilobite,i think there is a lot of work to be done in these areas before anybody can positively come to these conclusions ,garyh

This article mainly discusses nutrition, though it does mention that researchers are beginning to look at the roles that stress hormones play in skewing sex ratios, and the stress caused by crowded aviaries may cause some skew. But yes, you are correct that there isn't anything that proves crowded aviaries per se are causing changes in sex ratio.

Then there is the study which suggested that some hens throw more cocks when paired to brightly coloured cocks, but produce more hens when mated to poorly coloured cocks - the theory being that poorly coloured cocks are less likely to be competitively successful so if you are mated to one then producing more hen offspring gives your offspring a greater chance of breeding success- producing poorly coloured cocks is less likely to result in breeding success.

Mike Fidler had circumstantial evidence of this helping him produce more Peter's Twinspot hens when previously he bred a huge surplus of cocks.

There appear to be many mechanisms at work here...

Certainly the article is about the influence of nutrition on on gender assignment and not directly on the influence of crowding however it's not a "long bow" to consider this since in crowded aviaries there are two possible stresses that affect the birds. Firstly there is strong competition for food which causes nutritional stress in the hatchlings and unfortunately it is the females that succumb more often than not as Sarah found however what she is reporting in the Proceedings of the Royal Society is a prezygotic effect. The nutritional stress didn't just affect the fledgling ratio it affected the sex ratio at hatchling. This is probable cause to believe that it is under hormonal control as suggested by Myzo. In crowded situations too psychological stress elevates stress hormones (corticosteroids) which also would provide a mechanism for influencing the maturation of the cells carrying either a W or Z chromosome. Don't forget that in birds, it is the female that carries the sex determining chromosome which is the opposite of to the situation in mammals. During meiosis the chromosome pairs separate halving the chromosome number in each daughter cell which then divide again mitotically (maintaining the chromosome number) and it is these cells that mature to become the gametes however in males all four become spermatozoa but in females only one matures and the others become the sterile polar bodies. In crowded situations not only is nutritional stress more likely but competition for all resources is greater thus inducing stress. There is selective advantage to a hen that does not increase this stress by adding more females to the population since their compounding offspring will increase the population making the situation worse however more males competing for her favours or those of the few daughters she does produce will select for birds better adapted to to this resource limited and stressful environment. The article speculates that gender selection might be under female control in mammalian species however they won't have as an efficient prezygotic mechanism that birds have since female mammals possess homologous sex chromosomes.

Again another informative study and debate that I for one would not have seen if not for AFF members bring them to our attention.

To the people without an understanding of these previously mentioned studies it would be advantageous to read through and try to apply the information, if applicable, to the needs of you own aviary management strategies.

Unfortunately the terminology contained in peer reviewed journal articles are directed towards academics. The Save the Gouldian Fund press releases found in the Bird Keeper and Just Finches magazines are an excellent examples of dispersal of research based information at a level that most can understand.