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    • Bird Academy
      Bird Academy
      Bird_Academy
      1. Inbreeding is not common among wild animals.  What threat might the level of inbreeding in American Crows pose to them?
      2. Extra-pair fertilization is relatively common among birds.  Is this surprising to you? Could this be beneficial?
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    • john
      Participant
      Chirps: 2
      john.w.hadley
      The problem of exaggerated recessive negative genes  is always a danger, as with most mammals (I think).  Without diversity in the gene pool, they may all become susceptible to the same pathogen or negative survival behaviour. Extra pair fertilization broadens the gene pool, providing better balance against group susceptibilities.
    • Ellen
      Participant
      Chirps: 9
      ebadelman123
      1. The usual genetic abnormalities and increased risk of illness/death (just as with humans).  2. This wasn't surprising as I had learned that many other bird species have extra-pair fertilization (I believe most of those who pair up for either many breeding cycles or for life, do this), so why not crows as well. I think it would be beneficial in terms of increasing genetic diversity. Not that the crows probably care about genes, per se, but they likely do care about long-term survival, and increased genetic diversity can improve survival.
    • alice
      Participant
      Chirps: 14
      AlasitsAlice
      1.  I’m no biologist - but i have always believed that inbreeding can not only stunt development/evolution of future generations, but perhaps contribute negative issues.  Do crows suffer from this same issues with inbreeding?  I would imagine that inbreeding may cause possibly some areas where birds may not become disease resistant - or not fully able to genetically consider the impact of global warming through out the entire region?  I wonder, as stated, why such birds who travel far distances remain homebodies with regard to mates.  Why aren’t there more sub-sets of crows due to evolutionary changes that may occur in different regions? 2. I suppose the more invested adults may enlarge the family network of crows?
    • Sallie
      Participant
      Chirps: 11
      SallieG
      I was surprised that there was inbreeding among the American Crow population, especially the mother son inbreeding.  The threat to the Crows from the inbreeding could be that there are genetic problems like deformities that could cause early death for some Crows.  I would imagine the "extra-pair" fertilization would be helpful in maintaining the population of Crows, but, again, I have concerns about the above mentioned problems of inbreeding.
    • Wendy
      Participant
      Chirps: 3
      takemetoarizona
      Could it be , that crows aren’t thinking about their genetic makeup at ALL (AND ) that males could , since they are dominant, affect an outcome more so, than the other way around? I also think that maybe, just maybe,  genetic science isn’t ‘all there’ yet as many would like us to believe . Do not get me wrong; I believe that the science as we know it probably is right......but 25, 50 a hundred years from now , something new will ‘pop up ‘ and we’ll have a more concise understanding of the data we may be getting .
    • Elaine
      Participant
      Chirps: 9
      Elaine0421
      1.  I'm not sure about the specifics of the genetics of crows, but perhaps it could cause genetic deformities in future generations, especially with the mother-son inbreeding? 2.  Perhaps it's an instinctive survival behavior that helps to increase the species population where disease and enemies may be a factor?
    • Dennis
      Participant
      Chirps: 20
      JeffersonTW
      Inbreeding can have same result among crows as with humans. Recessive genes can combine to create deformity or genetic weakness among the group. Apparently, inbreeding was not uncommon among early isolated human groups and even humans today isolated by geography, social or religious structure. I don't find any of this surprising.
    • Karrin
      Participant
      Chirps: 47
      klukacs
      If breeding is really all about preserving genes, then I guess inbreeding makes sense. But still, I am disappointed to hear that some crows practice incest.
    • Gigi
      Participant
      Chirps: 1
      gvkguthrie
      Good day, I'm very much enjoying the "Anything but Common: The Hidden Life of the American Crow" course. After watching the "Secret Sex Lives" video, I have a question: What is the evolutionary purpose for the female crow to seek additional breeding opportunities outside of her existing pair bond? Would love any feedback, even if speculation, thank you! Gigi Guthrie
      • Dennis
        Participant
        Chirps: 20
        JeffersonTW
        A related question might be do females seek younger, possibly more virile partners, outside their own pair bond?  If so, this might have advantage toward producing healthy offspring, especially if her mate is older and less virile.
    • Susan
      Participant
      Chirps: 2
      susanr222
      Inbreeding, just as with humans, could increase the likelihood of harmful mutations becoming expressed as disabled offspring or death before reaching breeding age. I didn't know birds paired up so much, so extra-pair fertilization is not so surprising to me. It could be beneficial in widening the gene pool.
    • Paul
      Participant
      Chirps: 5
      FairmontFarm
      There was an interesting paper on inbreeding in black robins showing both positive and negative effects.  I can't remember the citation. The "secret sex life" and small amount of this inbreeding behavior might help maintain crow social bonds in some ways that might offset the deleterious genetic problems that might occur.  While it may seem very strange to humans, it might "work" in some ways for crows and other animals.  Extra-pair fertilization is not at all surprising to me in birds, humans and many other so-called monogamous animals, and could definitely add some "genetic diversity" to these close-knit groups.  A risk-benefit analysis played out over the long evolutionary history of such behaviors . . .
    • Diane
      Participant
      Chirps: 6
      djohnson6141
      1. Inbreeding may cause genetic issues such as weaknesses and shorter life span perhaps. 2. This is not that surprising. It is always nice to think that crows are monogamous but oh well...Yes, I believe it could be beneficial for their genetics especially if the extra male is from a different family.
    • Lynn
      Participant
      Chirps: 8
      Lemmolo
      1. The most obvious problem would be genetics.  As shown in several monarchs, inbreeding has negative hereditary implications. 2.  Not really, it seems like a smart solution to sustaining the species.  
    • Shea
      Participant
      Chirps: 24
      runnerboy13
      2. Yes, I didn't know that crows had such weird sex lives, but then again so do humans. It depends whether it could be beneficial or not, depending on the relationship
      • Karrin
        Participant
        Chirps: 47
        klukacs
        I agree. I wonder if they’re being so much like humans is why crows do it when the majority of other birds do not?
    • Fred
      Participant
      Chirps: 4
      glockf
      1. Genetic damage and body/mind abnormalities are well known among humans that inbreed, so I suspect crows would suffer the same sort of flaws in the offspring. 2. I have learned that genetic diversity is generally good, minimizing inherited flaws; so I expect that extra pair fertilization would be beneficial.
    • Kathy
      Participant
      Chirps: 1
      Katebys
      1. It may make them genetically less hardy and less able to withstand diseases. 2. I was somewhat surprised by this but it may be beneficial for genetic variation in the species.
    • Audrey
      Participant
      Chirps: 5
      AQHall
      Inbreeding is not good; it decreases genetic diversity. ):
    • pat
      Participant
      Chirps: 4
      prestivo1967
      I imagine inbreeding will bring weaknesses into the crow family just as happens with humans.
    • Rebecca
      Participant
      Chirps: 6
      raheagle
      2.  I've read articles about some bird females having a roving eye peeled for males that may have certain breeding assets they find appealing (I think with some chickadees.).  This could be beneficial by enhancing the gene pool.  And for keeping things interesting!
    • Susan
      Participant
      Chirps: 30
      susangreta
      1. Weakness, as Andrea Townsend points out, lower probability of survival for the inbreed young. Also I would think it would add stress on the parent crows having to provide for all the nestlings - hunting & gathering - when some of them are probably not going to survive already due to their genetics. 2. It's not surprising to me... I think that we humans anthropomorphize when we say "monogamy" or "mating for life" in reference to other species. The concept hardly works for humans. I think they maybe have a main partner but the extra pair-bond copulation could be an evolutionary strategy or maybe just working off some hormonal callings (designed to create these extran pair-bond flings?).
    • Angela
      Participant
      Chirps: 7
      Angela.Snow
      I was surprised that this lesson seemed to imply that the extra-pair matings were initiated by the female “fooling around with the neighbors.”  In a previous talk, Dr. McGowan proposed that these extra-pair matings were most likely forced copulation events.  I am wondering if the change was due to new data from Dr. Townsend, or if they were just trying to make the course less disturbing for people (like me) who have a tendency to anthropomorphize crow behavior.
    • Jim
      Participant
      Chirps: 13
      Jim Fuehrmeyer
      The fact that Prof Townsend observed a 25% inbreeding rate is rather troubling.  I suspect that the crow populations observed have a higher instance of disease and other genetic weaknesses as a result. It may leave them more vulnerable to the impact of climate change. On the other hand, if 75% are not related and have a higher survival rate than other species, perhaps the overall survival rate of the population is still greater than one sees in other species that do not have that level of inbreeding. I would be interested in seeing more followup studies on crow populations  which seems possible given the extensive banding that you all have done over the last couple of decades.  
    • Amy
      Participant
      Chirps: 3
      ajojac
      1. Limiting genetic diversity is not a winning long-term strategy. I have no way of judging whether 2% represents a significant limitation of genetic material. As a "generalist" animal, I would expect that the best long term specie survival strategy would lean towards diversifying the genetic pool, not narrowing it. Again, though, it's not like any of these animals are saying to themselves, gee, what's best for the specie? Individual birds will do what they do, and only time and survivability will tell whether the actions of the individual were successful for the group as a whole. 2. No, not surprising. From the viewpoint of a gene, lots of good reasons for extra-pair fertilization. What seems surprising is that 83% of the off-spring were the result of intra-pair fertilization. How is this explained? Is it just proximity and opportunity?
    • Jonquele
      Participant
      Chirps: 7
      jonquele
      1. Inbreeding carries a lot of risks when it occurs regularly across a small gene pool (see purebred dog/cat/horse breeds for current easy examples.) And yet breeders DO deliberately back-breed to reinforce some desirable traits. As long as the total population of crows doesn't fall to the near-endangered level, they probably aren't in too much genetic danger. Does the incest occur in small families trying to maintain a large territory? Or, in the case of the West Nile virus, where the family group dynamics have been disturbed by significant losses? 2. I wasn't surprised. Out-crosses usually keep the gene pool stirred up. Curious as to how related each family is to its neighbors. If you marry the girl next door, your offspring have a foot in both territories. So how far do you have to go to get a true non-related out-cross?
    • Jen
      Participant
      Chirps: 6
      tweettweet
      1. Possible increased risk for genetic mutations. 2. I was not aware of extra pair fertilization but it appears to be beneficial as a method used to ensure continuation of the species.
    • Peggy
      Participant
      Chirps: 10
      MPage815
      1. The threat of inbreeding is usually a reduction in genetic diversity, correct? That means that unfavorable traits might be inherited, such as susceptibility to disease. 2. It isn’t surprising that birds breed outside the pair bond. In fact, it’s surprising that this doesn’t happen more often in crows! It seems beneficial to the female in making sure she passes along the best genes to her offspring. Yes, she chooses a strong, successful mate and breeds with him because of these attractions. But she hedges her bet a bit by breeding with other males - just in case she made the wrong choice for her primary mate!
      • Desiree
        Participant
        Chirps: 16
        Weeziehupy
        And maybe breeding outside the pair bond is another way of making up for any genetic weaknesses that might be caused by inbreeding?
    • Student Birder
      Participant
      Chirps: 7
      elydick
      1.  Inbreeding has been shown to result in reduced viability in wild populations -- our mountain lions in So Cal are showing the results of inbreeding by increased number of abnormalities, liked kinked tails and cleft palates.  I've also heard that decreased immune resistance to disease has occurred in other wild inbred populations (maybe one of the reasons that facial tumors are common in Tasmanian devils). 2.  Yes beneficial because the female is not relying solely on the genetic contribution of one male -- what if there are some abnormalities that show up later in life in their offspring?  Having multiple mates increases her chance of mating with a strong male and producing successful offspring.
    • Sherry
      Participant
      Chirps: 6
      sherrybay
      1. Inbreeding could lead to a higher rate of genetic disease? Less ability to adapt? 2. I guess extra-pair fertilization is not that surprising to me, but I'm wondering about the timing. Would the female crow lay eggs at different times? It could be beneficial in that there would be greater genetic variation in the young.
Viewing 28 reply threads