Hatching success roosters versus hens

I am curious if anyone has noticed a trend of more males hatching this year. ik have noticed with my chickens that I have had more roosters consistently. Other people I have talked to have made the same comment. As well, I have talked to people with other livestock and they are mentioning a higher proportion of males as well. One person did not have a single ewe in her sheep flock this year. Just curious.

My first hatch was 9 girls to 1 boy. High humidity.

Second hatch 1 girl, 7 boys...4 unknowns. Low humidity

Third hatch. Maybe one girl, 10 boys, 5 unknowns. Low humidity.

Weird. Last year I hatched 90% girls.

A woman I met at the watrous sale got bred Boers, 6 of them.  All but two had twins and of those two, one had a single and the other triplets.  All boys.

My ratio of roosters seemed higher this year as well, however my view is skewed as most of the birds that got killed were hens, so now I just seem to have an overabundance of meat wagons running around, all pretty-like.

I did, however, earlier this year, feel as though I was more 50/50.  Like I said, you start watching the young ones and their stances change and by the time you're sure they're roosters, they fail to grow saddle feathers and so on.

I ALSO figured there's something with humidity. I was leaning more towards temperature because last year I found when I hatched later in the year, I ended up with more hens. BUT, it makes sense it would be more humidity than temperature.

They'll tell you there's no 'evidence' but I'd love to do controlled trial hatches.

All but one of my Shetland sheep had twins and all but one of those were one male one female. That set of twins were both female.

Highland calves were right on 50% male female. Same with piglets I think.

I am hatching very close to even. My first hatch had lots of cockerels but the next few were pullet heavy.

Temperature cannot influence gender ratio of eggs (that's genetic, in birds and mammals), but it is possible that one sex might be more compromised by incubation conditions. In other words, if your gender ratio at hatch is skewed by temperature, it's because you're killing off one sex preferentially.

ipf wrote:Temperature cannot influence gender ratio of eggs (that's genetic, in birds and mammals), but it is possible that one sex might be more compromised by incubation conditions. In other words, if your gender ratio at hatch is skewed by temperature, it's because you're killing off one sex preferentially.

That's what I figured. A couple years ago I had a very high roo to pullet ratio. I've wondered if something about temp or humidity is killing off one gender.

If it helps, I tend to have more females, but I hatch at a lower temperature. 99.3, not 99.5.

I've got double the amount of cockerels running around as pullets from my first few hatches. Regular old rooster fest here. lol I'm happy though, I like lots of selection when choosing male breeders. And my last hatch looks almost all female, although they are still a little young too be sure.

Generally the variation in sex ratios we find in our relatively small hatches is just due to chance. I thought there was one exception though, in a bird that uses rotting vegetation to provide heat for incubation:

". . . there is, so far, no evidence that incubation temperature can affect sex ratios in birds, although this is common in reptiles. Here, we show that incubation temperature does affect sex ratios in megapodes, which are exceptional among birds because they use environmental heat sources for incubation. In the Australian brush-turkey Alectura lathami, a mound-building megapode, more males hatch at low incubation temperatures and more females hatch at high temperatures, whereas the proportion is 1 : 1 at the average temperature found in natural mounds. "

But then I read this:
"Temperature-dependent sex determination (TSD) is a type of environmental sex determination in which the temperatures experienced during embryonic development determine the sex of the offspring. It is . . . absent among birds, including the Australian Brush-turkey, which was formerly thought to exhibit this phenomenon."

Interesting info ipf, I really appreciate all the genetic info you provide for us. I don't understand all of it but always find it interesting to learn.
So..."science" still says no to temp/humidity influencing sex in birds . But we find otherwise?, interesting  
I agree that in small samples the ratio is much more likely to be skewed.

Well, it's impossible to prove that there is absolutely no effect.

That's one of the big confusions of science - it's impossible to prove absolutely that ANYTHING has absolutely no effect. One can only put limits on that effect, say for example, that adding substance z to a chicks diet makes less than a 0.01% difference in weight at age 10 weeks - you can never prove that the effect is 0.

So when scientists say "evidence does not suggest that a causes b" that's exactly what they mean. They are NOT saying conclusively "a does not cause b, ever". it all comes down to statistics and probabilities, which are phenomenally useful - they provide those shades of gray that leave questions open. E.g. if something is demonstrated with p=0.1, that means there's a 10% chance that the effect noted was simply by chance. If p=0.0001, there's only 1/100th of 1 % likelihood that the effect occurred by chance, and it's reasonably to conclude that the effect was real.

It generally comes down to sample size - an effect that looks quite large, for example 4 females in a hatch of 5 chicks, or 80% - will have a high p value, suggesting that it's just chance. However the same sex ratio in a large sample - say 80,000 females out of 100,000 chicks, is likely to have a pretty low p, saying that gender ratio almost certainly differs from 1:1.