• For female vampire bats, an equal chance

    From ScienceDaily@1:317/3 to All on Wed Jul 7 21:30:38 2021
    For female vampire bats, an equal chance to rule the roost

    Date:
    July 7, 2021
    Source:
    Ohio State University
    Summary:
    Female vampire bats establish an egalitarian community within a
    roost rather than a society based on a clear hierarchy of dominance
    that is often seen in animal groups, a new study suggests.



    FULL STORY ========================================================================== Female vampire bats establish an egalitarian community within a roost
    rather than a society based on a clear hierarchy of dominance that is
    often seen in animal groups, a new study suggests.


    ========================================================================== Researchers observed more than 1,000 competitions for food among
    a colony of 33 adult female bats and juveniles living in captivity,
    assigning a rank to each bat based on a calculation of wins and losses
    in those contests.

    The team found that, unlike in many mammal societies, the higher-ranking
    animal didn't necessarily win every bout over food, and there was a
    randomness to the ranking order -- no specific quality they measured
    gave a bat a better chance at dominance, so any adult female had an
    equal opportunity to rank very high or very low on a scale of dominance
    in the roost.

    Traditionally, research on group-living animals -- especially primates
    -- in the wild has focused on how a dominance structure factors into
    survival, longevity and healthy offspring, and only later considered
    the importance of friendship in those same communities.

    Senior study author Gerald Carter has worked in reverse order. His
    research on highly social female vampire bats, whose behaviors resemble
    what's been observed in some primate groups, has focused on cooperation, finding that vampire bats make "friends" through a gradual buildup of
    trust and show signs of maintaining those friendships in the wild.

    "We realized we don't know anything about dominance among female vampire
    bats, so this is a first step in the direction of trying to identify
    how similar they are to primates in this way," said Carter, assistant
    professor of evolution, ecology and organismal biology at The Ohio State University. "We can say quite clearly that they're definitely not like
    some of the well-studied primates.

    They don't have a very clear social rank that they're constantly
    enforcing." The study is published today (July 7, 2021) in the journal
    Royal Society Open Science.



    ==========================================================================
    The research team video-recorded 1,023 competitive interactions concerning
    food over three months in a captive colony of common vampire bats at the Smithsonian Tropical Research Institute (STRI) in Panama. The colony
    consisted of 24 adult females captured from two distant sites as well
    as nine young bats -- four males and five females.

    Winners and losers were identified from five types of events at the
    blood-meal feeders: displacement of a feeding bat by an intruding bat with
    or without physical contact; a feeding bat's maintenance of its position following an approach by another bat, with or without contact; and a
    nearby bat waiting to eat until after a feeding bat leaves the feeder.

    Researchers assigned social rank to individual bats based on wins and
    losses and found widespread variability in adult female bat rankings,
    with essentially no predictors for how these community arrangements played
    out. No associations were found between body size, age and reproductive
    status and dominance ranking, and common vampire bat behaviors of grooming
    and sharing food were not associated with social rank. Being related
    to each other had no effect. The only possible predictor detected, when
    male juveniles were excluded, was smaller forearms in the more dominant
    adult females.

    When compared to data that exists on communities of female yellow
    baboons and female long-tailed macaques, the vampire bats were also far
    less likely to show a consistent pattern of wins by the more dominant
    community members.

    "Basically, with these primates, almost 100% of the time the dominant individual wins," Carter said. "With vampire bats, even when you have two individuals that are 10 rankings apart, the more dominant individual is
    not necessarily displacing the other one." The findings suggested that
    young males are subordinate to adult females, and the same is likely to
    be true for adult males because they are smaller than female vampire
    bats. Previous research has shown that male vampire bats do compete
    with each other and fight -- and within a colony, males tend to focus
    on establishing territory rather than carrying on social relationships.



    ==========================================================================
    A comparison of group-level dominance measures between female vampire
    bats and 14 other documented female mammal groups -- including African elephants, bison and numerous primates -- placed the bats as either 12th
    or 15th in the overall dominance ranking, depending on the metric used.

    Though the single study of animals in captivity doesn't provide all
    the answers, the research does suggest vampire bats live in communities
    that are "more fluid and open," Carter said. A fluid and open society is different from, but not necessarily better than, a group characterized
    by dominance and hierarchy, he noted. A clear power structure actually
    helps prevent conflict.

    "In a group of animals that's always together, it's really important to
    work out who's dominant, because when you come across food, you all come
    across that food together," he said.

    "With vampire bats, they have this society inside of a tree, and all of
    the relationships are worked out. But we think vampire bats don't hunt
    as a stable group -- they go out and forage, and come back together. So
    what that means is that they're not always coming across a food resource together and having to decide who's going to get access to it first." ========================================================================== Story Source: Materials provided by Ohio_State_University. Original
    written by Emily Caldwell. Note: Content may be edited for style and
    length.


    ========================================================================== Journal Reference:
    1. Rachel J. Crisp, Lauren J. N. Brent, Gerald G. Carter. Social
    dominance
    and cooperation in female vampire bats. Royal Society Open Science,
    2021; 8 (7): 210266 DOI: 10.1098/rsos.210266 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2021/07/210707112411.htm

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