Aussie Finch Forum

Myzomela wrote: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.

Well it seems we are driving ourselves down the road of less hens being bred in an aviary, overcrowded or not. As I would think most breeders would choose the best coloured of either sex to keep as breeding stock.

My own experience with BFPF breeding over many seasons and with higher protein diet than that described is extra males reared most (but not quite all) seasons. I firmly believe this experience is similar to many (perhaps most) other breeders of BFPF. As with the Gouldian research, we have some interesting observations which pose many questions for further research BUT as all long-term bird breeders know one season's sex ratio of offspring in one collection don't amount to anything near conclusive species-wide fact in the breeding outcomes of that species. This is no less anectdotal than MF's Twinspot observations - very interesting (an probably may eventually turn out to be totally reliable fact with sufficient further research) but at this stage we simply don't know this to be the case at all.
I think it is drawing a long bow to reach the conclusions which have been already drawn at this stage & to take this any further at all is entirely hypothetical.

"one season's sex ratio of offspring in one collection don't amount to anything near conclusive species-wide fact in the breeding outcomes"
I wonder how many of us would take an accountants word that a business was a winner on just 1 years results, and invest our life savings?
LML

GregH wrote: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.

This is true to a certain extent (in some species), where stressed mothers can 'choose' to produce offspring of the dispersing sex, rather than the sex that remains in the natal area.

bluebutterfly213 wrote: Well it seems we are driving ourselves down the road of less hens being bred in an aviary, overcrowded or not. As I would think most breeders would choose the best coloured of either sex to keep as breeding stock.

Not quite. Everything is species-dependent. In some species, males are more 'expensive' to produce (i.e. require more parental resources to produce a good quality son), while in others females are. It is also related to how polygynous a species is (e.g. a good quality male can mate with many females, so a mother in good condition in a stable environment should produce more males, as this increases her own reproductive success. A mother in poor condition should produce more females, which will almost definitely mate, rather than a poor quality male that will be out-competed by other males), genetics, seasonality, laying/hatching order, as well as hormone concentrations (oestrogen, testosterone, and corticosterone- stress hormone- are the top 3 contenders), and a bunch of other things.

Bear in mind that these studies are generally carried out in controlled conditions (i.e. cages in lighting and temperature/humidity controlled rooms) so may not be applicable to outdoor aviary environments which are far more volatile. Should you start frightening your birds when they're laying, in an attempt to change the sex ratio of their offspring? Of course not, but this research does present an intriguing possibility, and shouldn't be dismissed out of hand.

I totally agree that this information is still not definitive, but interesting-yes.

As Tiaris and Niki have pointed out, the real-life experiences of aviculturists may not reflect the same results as a 3 month study in a lab.

An experiment's results are only as good as the experimental design. That is why so many studies are produced that seem to contradict each other.

As a scientist, one of the things you are taught is to critically evaluate the results of a study by assessing the experimental design and techniques used.

In the most prestigious scientific publications, the editors usually do this and so reject many,many papers based on this alone. The less reputable publications are less fastidious and will publish studies which may not be acceptable elsewhere.

Always be critical of information presented, and don't be afraid to question the credibility of this information.

I believe we are fortunate on this forum to not only have a range of scientifically trained people of different backgrounds, but also untrained people with much practical experience, common sense and questioning minds to assess all information presented, and to put forward a variety of opinions.

That is fantastic!

here here, well put Myzo, and never a truer word.

Fascinating stuff.

The limitations of a single study have been well documented above...

I am just delighted that some serious scientific study is being performed on the finches that we keep.

Good work
Brett

It's not so much that this is 'new'; I think it's more that this information is now being made more available (via google scholar, and general media) to the general public. Sex ratio studies on finches and other passerines have been carried out since the 1980s, and studies in chickens and geese were even further back than that (before the 50s, if I remember rightly), thought it's only relatvely recently that primary sex ratio (the sex ratio at fertilisation/laying) has been studied simply because the technology to sex unhatched eggs wasn't available.

Certainly be sceptical but be open to new ideas. Niki_K is right when she says that this type of investigation is hardly new but using finch rather than poultry models is a different approach. Very few of us have collections that would accommodate such an investigation not all of us have the will to keep records for sex ratios at hatching and fledging for 50-200 nests of a single species with age controlled populations or much other immutable controls over our lifetimes as keepers or even in a single season. If it is a criticism that the data was collected over a single season then you may have missed the point of doing a controlled experiment - it's very difficult to guarantee that stresses experienced in one season are the same as the next and in short-lived species like finches a year is a very long time (it has been speculated in the literature birds of varying ages could have different reproductive strategies see review by Sheldon 1998). The problem of sex ratios is enormously complex so breaking down the elements that might affect them and then controlling for them is very important and not to be dismissed. We all bemoan the effect of high summer temperatures on our birds but that too may affect sex ratios at hatching because of selective embryo death as seems to happen in mallee fowl - who's to say it doesn't happen in finches too. There are contradictory "finch studies" like those of Postma et al 2011 who found no evidence of adaptive sex allocation but their model was not an Estrillid but a song sparrow. Dr Pryke's move for Gouldians to Blue Faced Parrotfinches is also like another control since they are genetically so close that it's not surprising she has found similar results to her earlier studies - so these aren't isolated unreplicated results from a single season. I maybe reading to much into her results but I'm excited by their implications and what it means for successful finch management in our aviaries and in the wild.

The answer to sex allocation in birds is not likely to come from a single study but a suite of studies over a long time and as has ben pointed out it the details are likely to be species specific. I'm wondering if there's room for a review article here however I feel it would put half the forum to sleep and still not provide believable evidence for those just know academic investigation is no match for experience.

GregH, I wrote a review piece based on sex allocation in regards to stress/corticosterone last year (so it needs updating now)- you're very welcome to read it if it's of interest to you It's an update from Alonso-Alvarez's 2005 review. I don't believe you're reading too much into Pryke's results; this is an area which is just beginning to take off, and it's very exciting!