Cock Hen Ratio: Breeding, Diet, Lighting, Selection: Tips From The Best of
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I once read something about the quality of foodstuffs and the bird’s ability to
survey the situation and produce chicks based on quality and availability of
foodstuffs. My own personal research has shown me that the “richer” the
nutrition, the higher the number of hens. In my situation, “rich” means protein. As
it stands, I get a consistent 5:1, hens to cocks from every pair here. I prepare a
dry “protein mix” that is about 54% protein (averaged from the items I mix
together), then add about 1 1/2-2 cups of that protein mix to about 10-15lbs of my
breeding seed mix (difficult to give exact amounts because I eyeball it for color
and consistency when mixing).
Over the course of many years and breeding seasons (10+ years), I have
adjusted this amount to see what happens. The years I use no additional protein,
I get cocks 5:1, added protein but less than my current amount, I get closer to a
50/50 split, and the years I use my specific mix, hens 5:1.


Primary and secondary sex ratio manipulation by zebra finches
REBECCA KILNER, Department of Zoology, Cambridge University
Abstract: Wild zebra finches, Taeniopygia guttata, breed opportunistically when
there is sufficient food available, often rapidly mobilizing their reproductive
systems in response to an ephemeral boom in grass seed production. For
females in captivity, fecundity, attractiveness to mates and survival to
reproduction are all correlated with their fledging weight. By contrast, for males,
only attractiveness is related to fledging weight; the relationship between fledging
weight and male mortality is much weaker and that for male fecundity is
unknown. Previous work thus suggests that how much food nestlings receive will
have a profound impact on their reproductive success, and that this effect may
be more marked for females than for males. I manipulated the food available to
domesticated breeding zebra finches to test Trivers & Willard’s (1973, Science,
179,90-92) hypothesis of adaptive sexual investment. When food availability was
restricted, clutch sex ratios were significantly more male biased than when food
was available in excess. Within clutches, daughters hatched sooner than sons
and first-hatched chicks fledged at higher weights than those that hatched last.
Chick mortality was female biased when food availability was low but male
biased when food availability was unrestricted. I compared the song output of
brothers of differing weight at independence, but found no significant difference
between them. These data suggest that zebra finches manipulate both their primary
and secondary sex ratios in relation to food availability to invest
adaptively in sons and daughters, and support Trivers & Willard’s hypothesis.
Copyright 1998,
The Association for the Study of Animal Behavior.
I get more males when the weather conditions are good and I get more hens
when things are colder or wetter. I read somewhere that in the wild the
male/female ratio is based on how harsh the conditions are. If times are bad,
more hens are born to create more babies.
Andy, are your results across the board, regardless of hen? It seems to me that
everyone else is reporting the opposite results – more males in colder/harsher
season, more hens in spring/summer.
There is also an on-going line of thinking and study into the ability of the parents
to manipulate the sexes based on a number of things, including the
attractiveness of either of the parents, numbers in the flock, etc. Whether this is
done prior to the egg being laid or after the chick is in development (and possibly
hatched) is also part of on going studies.
Temperature shouldn’t have much to do with it — it is usually resource availability
(or lack thereof) that is the definition of a harsh environment. When times are
bad, males are often more likely to be reproductively successful, because they
can increase their reproductive output by mating with many females. Females
can mate with all the males they want, but their output is limited to their own
ability to bear/rear eggs/young. So the theory goes that harsh times should favor
males and good times favor females (or at least be more even). Usually
good/bad means the amount of food available (the parents have to have some
environmental trigger that starts this process in motion). Lots of work is being
done to show these processes occurring in mammals and birds, but the evidence
is still fairly sparse as far as I know. And there are all kinds of species-specific
things that could interfere with this simple prediction. For example, if female
offspring stick around and help with the rearing of the next brood, then harsh
times should favor females in that species. This certainly could apply to many of
our finches. In some species, males disperse more widely after weaning, so you
would want more males during harsh times because they don’t compete with you
for food and you can use that food to rear more offspring. So you really have to
know a lot about the species’ natural history and mating system just to make
reasonable guesses about what should happen. Then you have to suppose that
there is some biological mechanism in place for this to actually occur. I all seems
a little iffy to me when it comes to passerine birds, but it definitely occurs in
nature and could happen.
I use to get more female goulds, and red head parrot finches during the winter
months, and more males in spring. Some times 3-1. Since I moved, it has been
about even.
I guess I’m assuming that (1) the birds’ biology hasn’t changed overnight just
because they’re in a cage and (2) what people feed their birds actually isn’t the
same all year long. E.g., what if you don’t feed much egg/live food (or the birds
don’t eat it) in the month prior to breeding? Maybe the amt of animal protein (like
some specific amino acid) is the biological trigger that tells the birds this is “good
times” or bad. Mostly seed diet might indicate bad times and lead to a
preponderance of males.
I’ve heard various theories about sex ratios, from UV light exposure to genetic
predisposition of the parents. I wish I knew was it is, because I get twice as many
girls as boys…which makes selling pairs a problem. If there is a temperature
factor, it’s not the same mechanism that the reptiles employ. They use something
called temperature sex determination.. Those animals don’t have sex
chromosomes. Heat and humidity determine which sex organs develop in the
embryos. Birds have sex chromosomes (that’s why we can DNA sex them, and
can’t do that with most turtles/tortoises and some lizards), and their sex depends
on what chromosomes they inherit from their parents. In my case, I’m inclined to
believe the UV light theory, since my birds get lots of unfiltered sunshine in the
warmer months, and are supplemented with full spectrum plus UV lighting year
long. Of course, if it’s genetic, then I’ve selected for female heavy producers over
the years. Either way, I’d like to get some more males, and I don’t think that’s
going to happen any time soon!


I have been breeding inside my garage for the last 5 months, and I am now
getting almost that same ratio of males to females. No UV light.
I’ve heard of the UV light being the influence, but according to what I was told
and have read, if the birds are breeding in outdoor, UV light from sunshine, the
sex ratio should be equal. When bred indoors, you will get more males. Since
your situation is different, the theory you mention about genetic predisposition of
the parents is one that I have heard from several canary breeders. They feel that
it is the hen that is the culprit in producing more hens. Since male canaries that
will sing is what they are wanting to produce more of, they don’t want to breed
with hens that are heavy producers of females because they swear that all the
hens from those pairings will also be heavy producers of females.
When my birds were housed outdoors, I always got more hens from the pairs
breeding while the weather was warm to hot in the late summer. As the breeding
season went into the fall and winter, the sex ratio reversed to many more males. I
too believe that this is a throwback to the reptiles from which birds supposedly
descended. I was told that the eggs in turtle nests are more male hatches lower
in the nest, therefore cooler, and more female hatches in the upper nest,
therefore the hotter area. Don’t know if that is true or not, but it did agree with my
bird ratios.
Regarding gender of chicks produced: I suspect that over time we get 50% of
each. Some years are heavy in one direction, others in another.
I’ve observed sex ratio variation with many different species of finch, hookbill and
softbill. Based on my observations in hookbills, this phenomena seems more
distinct in “less evolved” species of parrots. I’ve also noted this with Hornbills,
which are a truly ancient speciesMy summer/winter sex ratios with Gouldians (especially) always seemed to
swing heavily male to female and back.
Some interesting new research on maternal hormones and offspring sex ratio in
birds (coturnix quail): If you want more females, add some stress!
Pike, T. W., & Petrie, M. (2006). Experimental evidence that corticosterone
affects offspring sex ratios in quail. Proceedings the Royal Society, Series
B: Biological Sciences, 273, 1093-1098.
Recent studies have shown that some species of birds have a remarkable
degree of control over the sex ratio of offspring they produce. However, the
mechanism by which they achieve this feat is unknown. Hormones circulating in
the breeding female are particularly sensitive to environmental perturbations, and
so could provide a mechanism for her to bias the sex ratio of her offspring in
favor of the sex that would derive greatest benefit from the prevailing
environmental conditions. Here, we present details of an experiment in which we
manipulated levels of testosterone, 17?-oestradiol and corticosterone in breeding
female Japanese quail (Coturnix coturnix japonica) using Silastic implants and
looked for effects on the sex ratio of offspring produced. Offspring sex ratio in this
species was significantly correlated with faecal concentrations of the principal
avian stress hormone, corticosterone, and artificially elevated levels of
corticosterone resulted in significantly female-biased sex ratios at laying. Varying
testosterone and 17?-oestradiol had no effect on sex ratio alone, and faecal
levels of these hormones did not vary in response to corticosterone. Our results
suggest that corticosterone may be part of the sex-biasing process in birds.
I’ve used black lights off and on for the past 4 years; two 18″ lights in the bird
room. The first year, I had at least twice as many hens as cocks hatched out
(gouldians). So much so that I shut off the black lighting for six months. Started it
up again but have not noticed these same results. However, I have changed my
birdroom around. I still only have 2 black lights set up.
I have a friend who has six 18″ black lights set up on the tops of his cages. These
are within six inches of his nest baskets and are on 24/7. He too has gouldians.
His ratio of hens to cocks is VERY high; in fact, it is rare for him to get a cock. His
belief is that this works but only with a number of black lights that are positioned
close to the birds/nest boxes.
Adding black lights (2) in the bird room worked for me, at least with gouldians.
Went from a 2 to 1 ratio of cocks to hens to the opposite after hanging these.
Shut them off, went back to the original ratio. They are back on and so far, the
juveniles that are coloring out are evenly matched in cocks to hens.
Coincidence? Maybe. Black lights are cheap to purchase.
You can read about that work of Robert Black’s in his article posted on
http://www.ladygouldianfinch.com/features_lighting.mgi He found that ultraviolet
light affected male/female ratios by installing a black light in his bird room.
That convinced him of the need for full spectrum light. I, myself, have not
experimented with it. It would be interesting to hear from those who might have.
It may have to do with the time of year they are bred in. More males in spring to
summer, more females in fall – winter. Possibly cocks earlier rounds, hens later
rounds. I cannot say as such with great force because of my limited experience,
but the “cocks earlier, hens later” sex ratio findings were said as such by Jim W
of England (a very respected lonchura breeder).
Before my cages were lighted above, there was only incandescent light in the
birdroom. At the time I only had 2 pr. societies and 1 pr. zebras. The ratio of
cocks to hens was about 3:1 over about 10 clutches, all told.
I mean to say that if the sex ratios are determined based on season, and the
season depends on lighting, then yes, lighting relates to sex ratios. But as far as
determining whether it was a different type of light (i.e. blacklight) there was no
discussion on that as a determining factor. I have my journals records on
breeding my gouldians back to 1971. Unfortunately, one thing I didn’t record was
what the sex produced was for different times of the year. I only did a year-end
total. As for lighting affecting the sex ratio, I have had my goulds in sunny
porches then in basements with just incandescent lighting and now in 3 bird
rooms (out buildings) with regular florescent lightning. no black lights or broad
spectrum lights. The ratio of males to females is almost a perfect 50/50 over the
last 32 years. (This is from a low of the 3 pairs I started with to the 38 pairs I use
now with various numbers in between). I also have records in 10-year groups.
Although there are swings in the ratios, each 10 year period seemed to average
out at almost 50/50 with males usually having a 1-3 point advantage. (My biggest
ratio swing was 80% females to 20% males. this was a year where I replaced a
lot of pairs with first time pairs) my birds have one season here. The temp is the
same (except on really hot days when I cant get the temp below 85-88) and the
lightning is a constant 16 hours, except for the odd times when I have to reset the
light timers due to power outages. As for blacklights, i can’t comment on whether
or not they actually change the sex ratio or if it’s a random thing…can only
comment on my 50/50 ratio.
So the belief was more females are produced as the days shorten, more males
as the day lengthens.
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