Finch Mothers Can Subconsciously Control the Gender of Their Little Ones

By Eliza Strickland | March 20, 2009 6:11 pm

Gouldian finchesThe Gouldian finch female has a neat trick for maximizing her offspring’s chance of survival: If she mates with a male who is a poor match for her genetically, she increases the proportion of male chicks in the resulting brood. In a new study, researchers say they’ve found unprecedented evidence that these birds can exert control over the gender of their offspring.

The endangered finch, native to the northern savannahs of Australia, can have either a black or red head, and the two different “morphs” have significant genetic differences, lead researcher Sarah Pryke says. “Gouldian finches wear their genes on their head so it is easy for a female to assess the genetic suitability of the male,” she says [Australian Broadcasting Corporation]. The birds prefer to mate with males that have the same head coloring, as chicks from a mismatched mating – particularly the females – are weaker and more likely to die very early [BBC News].

In the study, published in Science, researchers took 100 red-headed and 100 black-headed female birds and mated them with a male of the same head colour and a male with the different head colour. They found females in mixed pairs produced broods that were 82.1% male, whereas females in matched pairs produced an unbiased sex ratio with 45.9% males [Australian Broadcasting Corporation].

Then the researchers set about testing whether the females in mixed pairs were deliberately producing more sons. They tricked the females by taking red-headed males and dying their heads black. When red females mated with pseudo-black males they produced significantly more sons (72% males) despite in fact being genetically compatible. When black females mated with the pseudo-black impostors they produced similar numbers of males and females (55% males) [Cosmos].

 In birds, the sex of an egg is already determined before it is fertilised by the male…. “It is pretty amazing to think that the female herself has so much control – subconsciously of course – over this basic physiology,” said Dr Pryke [BBC News]. The exact mechanism by which females determine their offspring’s sex “is a big mystery,” she said, but one possibility is that the sight of a mate with a differently coloured head raises female stress levels, producing hormones that interrupt the normal processes of fertilisation [Sydney Morning Herald].

Related Content:
DISCOVER: Sex, Ys, and Platypuses examines how gender is determined in those complicated animals
DISCOVER: A Good Reason for Sex looks at the evolution of gender
DISCOVER: The Biology of Sex Ratios  wonders whether humans can unconsciously influence the sex of their offspring

Image: Sarah Pryke

CATEGORIZED UNDER: Living World
  • Parker

    firs comment. theees is quit intareeesting tooopik, theeenk yous for eet

  • Roger

    How do the finch mothers know what color heads they have?

  • tom

    more proof that darwinism is a sham. Individual birds generate their own adaptations (and prepare their offspring for entrance into the world) RMNS is a fairytale.

  • Jo

    @Roger: a finch mother wouldn’t need to know the colour of their own head. They’re not choosing mates on the basis of similarity to themselves. They’re choosing mates based on a genetically determined preference (black-headed females inherit a preference for black-headed males, as red-headed females do for red-headed males). If you dyed a red-headed female’s head black, it wouldn’t start preferring black-headed males.

  • http://www.kuxas.com Compton

    How do they know it’s ‘subconscious’? Did they get the female birds to fill in a questionnaire?

  • Eric

    There’s no way you just read this. It’s the paragraph that starts with “Then the researchers….”

  • Michael

    Hah, that reminds me of the Bene Gesserit in Dune.

  • http://blogs.discovermagazine.com/80beats/ Eliza Strickland

    Hi, Roger — Jo answered your question well, I thought, but I’d already fired off a question to the researcher, Sarah Pryke, asking her to clarify. Since she was gracious enough to write back, I thought I’d share her response:

    “This is a good question…. How does a grasshopper know it is a grasshopper? Or a cuckoo know it is a cuckoo (even when it is reared by another species)? Basically, females don’t know what colour they are – their preference for males of the same head colour is simply an innate genetically-determined response (i.e. hardwired) where females prefer their own type (as is seen in most species). Although they definitely use head colour to choose among different males, they are not trying to match their own head colour to their mate’s (i.e. changing their colour won’t change their mate choice as it is an inherent response). At the moment we are actually looking at the exact genetic architecture of this mate preference….”

  • SDZ

    @ Michael: I see what you mean there; it’s almost as if they’re trying to create their OWN “Kwisatz Haderach”, or “superbeing”…..ROFLMAO!

  • Bella

    Jo and Eliza were so wrong on this. The study is a perfect sample to REFUTE sarah’s gene-determining theory.

    quote: “When red females mated with pseudo-black males they produced significantly more sons (72% males) despite in fact being genetically compatible. When black females mated with the pseudo-black impostors they produced similar numbers of males and females (55% males).” – if it is “an innate genetically-determined response”, the red females would still have 50-50 chance to have sons with red males even with fake black heads.

    come on, is this a joke?

  • Mick

    @ Bella: Did you actually read the bit you quoted?

    Red female + Red male -> 46% male, 54% female
    Black female + Black male -> 46% male, 54% female

    Black female + pseudo-Black male -> 55% male, 45% female

    Red female + pseudo-Black male -> 72% male, 28% female

    Red female + Black male -> 82% male, 18% female
    Black female + Red male -> 82% male, 18% female

    The afore mentioned innate genetically-determined response is in regard to sexual preference, not genetic compatibility. The behaviour itself is genetically-determined (it has nothing to do with specific gene pairings in the offspring), just like bipedal locomotion, syntax driven language and the invention of deities are genetically-determined behaviours in humans.

    @ Compton: Think about your sexual preferences and how you determine whether you find someone sexy… I’ll put money on it that it’s 100% subconscious, and sometimes you don’t even know why you find some people so attractive. If you can look at someone and know instantly that they’re attractive then it’s obviously not a conscious categorization. It’s assumed that most animals’ sexual selection mechanisms work in a similar fashion.

    Plus, since all the birds in the study behaved in the same way, it’s highly unlikely to be a conscious process. No aspect of the behaviour even seems to be learned, indicating that it’s a genetically-determined subconscious process.

  • Amateur6

    Doesn’t it seem that the main point of this article seems to get lost by the end? Ultimately the females’ behavior is increasing the fitness of “mixed breed” finches. Clever girls.

  • Stephen Wharton

    I came across this “discussion” while I was searching for some content for an e-book I’m planning on writing about keeping Gouldians as a free range aviary bird. Rather than my book focusing on their keeping for the purpose of being a successful large scale breeder like all the other books available on the market, mine will focus on the joy of having a back yard aviary that sustains some Gouldians for the pleasure of “just admiring their beauty”. As someone who has owned a “flock” of Gouldians in a free range aviary since 1981 I’ve heard quite a few theories about head colour and the outcomes of mixed colour breeding.
    Although I’ve had Gouldian’s for a long time I’m not an expert in regards to successful breeding and I have not attempted to enter the unbelievable world of colour breeding that seems to characterise this lovely little bird now; (rather than admiring them in their natural plumage). I’m not saying that I don’t like the incredible colour variety that continues to develop; I’m just saying that I don’t consider myself an aviculturalist; I just happen to own an aviary full of Gouldians who continue to maintain their numbers, which are about 50+ birds. (And up to 100+ in the past). I’ve only ever kept them in an open aviary and let them make their own choices in regards to who they think is the cutest in the selection of their opposite sex partner.
    Only dedicated aviculturalists with an understanding of their colour genetics should dabble in this side of breeding our wonderful little Australian.
    So although I have read every book there is on the Gouldian finch (I think) I do have some differences of opinion with some of the opinions expressed by the expert aviculturalists that wrote them.
    And one is about mating based on head colour. I haven’t heard this (your) particular theory about sub-conscious selection based on head colour or the statistical outcomes in relation to clutch numbers; but I have read that matings between different head colours causes colour purity issues.
    I won’t name the author but in his book about Gouldians one particular writer suggests that mating a black headed with a red headed or yellow headed, (I hate that …. they have orange heads), will cause the female offspring to often have a “dirty” colour appearance due to an infusion of some black feathers amongst the red or yellow in the head area that is supposed to be fully red or fully yellow.
    I won’t go into the genetics of the yellow/orange head and how difficult it is to maintain in a mixed colony, but so far I have had all 3 colours in a mixed aviary; I have actually introduced “dirty headed” females into my aviary; I have left and continue to leave the whole aviary with the freedom to chose their own partners; and at this moment I do not have a single “dirty headed” female in my aviary. (I might add that I am fairly certain my birds do not choose their mate based on head colour; so I am stating that I don’t believe the “dirty head” syndrome has anything to do with head colour mixed matings).
    In regards to your assumption that females prefer their own head colour; I have never seen any evidence of that. Because of my casual approach to keeping Gouldians I have absolutely no evidence that my opinion could be correct except for my casual observations and also in relation to my attempts to maintain all 3 colours in my aviary. If it were correct that the female chooses its own colour in preference to others wouldn’t that mean that the keeping of yellow headed stock of both sexes in a mixed collection should not be so difficult? ……. and in fact would cause / result in yellow heads being more prevalent in wild populations ? (Given the clearly understood and described inheritance mode for this colour). Certainly it is probable that this colour might eventually disappear, even if the “like to like” theory is correct, from a mixed aviary like mine, but I speak from experience when I say that the disappearance of the yellow head variety happens very quickly in a mixed aviary. (In my opinion because inter-colour matings are very common).
    I also disagree with your theory that cross colour breeding produces weaker females. While I do lose more females than males, (sorry …. hens than cocks), the poor little girls do have a much harder life than the males in any situation; whether it be in the wild or in an aviary. The fact that I don’t have to introduce extra females into my flock to maintain numbers indicates that my female population is self sustainable. (I have deliberately not introduced stock for many years for fear that I might introduce some stock that are natural colour throwbacks from colour mutated stock; something I don’t want in my stock. You generally only find colour mutated stock for sale by dealers in recent years). Perhaps you should consider the possibility that generally Gouldians are not good parents and that is more of a reason for high mortality in small clutches. (My observation is that the larger a clutch the better the parents and the more likely they are all reared to independence. I have observed that some parents would rather attempt another breeding and hatching than waste their time on a small clutch, especially the single individual clutch).
    Anyhow, this has extended to a far larger reply than I meant to, so I’ll leave it at that and hope I have given you a little extra information that you can use or ignore as you see fit.

  • Tony

    Yeah Tom, more proof that Darwinism is a sham…
    Because it is much more likely that the earth and planets were created by a terrestrial being sitting in a huge throne and putting the whole universe together in 7 days…700 years ago.
    Dude..get real.

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