This week Science Sensei reveals the secret life of deadbeat dad juncos, small North American sparrows that are able to alter their level of testosterone...with mixed consequences.
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Testosterone can turn a Mister Mom-type dad into a deadbeat Don Juan. But it's not the actual amount of the male hormone that matters.
Juncos, a kind of sparrow that's common across North America, is probably best known for its tendency to stick it out in snowy climates throughout the winter rather than retreating south. But biologists wanted to reveal some of the mysteries behind its mating and parenting behaviors.
A multi-university team made up of National Science Foundation-funded researchers from Indiana University Bloomington (Ellen Ketterson), University of Virginia (Joel W. McGlothlin) and University of Southern Mississippi (Jodie Jawor), studied dark-eyed juncos in the wild. Throughout the study, the researchers briefly captured the birds and measured their testosterone levels.
Male juncos have been observed to exhibit different mating and parenting behaviors: Some males are very sexually aggressive and won a lot of mates, but seemed uninterested in parenting their young; other males were less sexually aggressive but more attendant fathers.
It was previously assumed that the overall level of testosterone might be the culprit, but in this new study — the first to study the effect of natural changes in testosterone levels in the wild — the researchers found it's not so simple.
It was previously assumed that the overall level of testosterone might be the culprit, but in this new study — the first to study the effect of natural changes in testosterone levels in the wild — the researchers found it's not so simple.
As the researchers will report in the December issue of the journal American Naturalist, testosterone levels in male juncos fluctuate throughout the year. Males with large fluctuations turned out to be the absentee father Don Juans, while male juncos with more stable testosterone levels were the mild-mannered Mr. Moms.
What's interesting about the biological and behavioral differences is that all of them have survived the trials of evolution and genetic competition. The researchers suspect that the Mr. Moms are more successful during years when food is scarce and predators are plenty, and insuring that their chicks survive to maturity is more important. Otherwise, when food is plentiful and predators scarce, a Don Juan can reproduce often without concern about their chicks' survival.
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