Home & Garden Columns

Wild Neighbors: Junco Testosterone and Water Snake Bites

By Joe Eaton
Tuesday December 04, 2007

A couple of odds and ends: Robert Sapolsky, the Stanford neurobiologist, published a collection of his provocative essays a few years back as The Trouble with Testosterone. Where do you begin? Sapolsky was mostly interested in the hormone’s effect on the behavior of East African savannah baboons (see his A Primate’s Memoirs for tales of fieldwork) and on humans. But it’s not just a primate thing, or even a mammalian one. Birds have testosterone too, as do reptiles, amphibians, even fish: a common vertebrate heritage. 

A recent study by Joel McGlothin at the University of Virginia and Ellen Ketterson at Indiana University Bloomington examined the relationship between testosterone levels and parental investment in male dark-eyed juncos. These are the birds my folks used to call “snowbirds,” because of the timing of their arrival in central Arkansas. There’s an old Appalachian, I guess, fiddle tune with the cryptic title “Snowbird in the Ash Heap.”  

Our local variety, with dark gray heads and reddish backs, used to be considered a distinct species, the Oregon junco. But it, along with the eastern slate-colored junco, the white-winged junco of the Black Hills, and the pink-sided junco of the Rockies, have all been lumped together as dark-eyed. I wouldn’t count on that lasting, though, the way things go in bird taxonomy. Juncos are common Berkeley yard and UC campus birds, and year-round residents. 

McGlothin and Ketterson studied an eastern subspecies. Their working hypothesis was that a male’s total testosterone level would influence both his aggressive tendencies and his monogamous behavior, or lack thereof. The expectation was that high-testosterone males would be more likely to abandon their families and move on to new partners rather than sticking around to tend the nestlings. 

It didn’t quite work out that way. What they found was that all males were willing to help with childcare, to a degree. “If they have higher testosterone they help less,” says Ketterson. “If they have lower testosterone they help more.” But the best predictor of a male’s involvement with the kids was the stability of his testosterone level. Males whose levels rose and fell quickly investing less time in parenting. 

So who is the more fit parent, in evolutionary terms? Do the juncos with less stable testosterone, who are also more aggressive, sire as many successful offspring through extra-pair liaisons as the monogamous fathers do? That’s apparently where the research will go next. 

From birds to snakes: I recently wrote about the rise and fall of the diamondback water snake colony at Lafayette Reservoir (and managed to omit the horror story of the brown tree snake, a New Guinea native that hitchhiked to Guam and ate its way through the island’s bird population, wiping out several endemic species), mentioning how irascible and prone to bite these critters are. This drew a snake-handling anecdote from reader Richard Hodges: 


Back in 1970, I was on faculty at UT Austin. Besides being a computer scientist, I was an inveterate explorer of nature, and part-time snake fancier. One day, walking along Shoal Creek I spotted a water snake. Though I had never seen one before, I had read about it and was familiar enough with the poisonous snakes to be certain it was not a water moccasin. I approached it very cautiously and managed to “collect” it, without stimulating its defensive reactions. I installed it in a cage in my office on campus and over a period of weeks, by sensitive handling I induced it to a state of toleration approaching tameness. 

One day a top researcher in my field, Artificial Intelligence, was visiting the department. I think she was interviewing for a position. I attended the interesting lecture she gave. She was a fairly young and attractive brunette. Hearing about my snake, she approached me and asked to see it. I gladly showed it to her. She asked if she could handle it, saying she was a snake fancier also. I said that while it was tame to my touch, the species was known to be aggressive. She acknowledged the warning. 

Imagine my shock when at her apparently careful approach, the snake struck with a quickness I had never seen in it and bit her viciously. Water snakes have long teeth, useful for capturing slippery frogs, and blood was streaming from her hand! I was quite concerned, not for her health since such wounds usually heal quickly, but for my reputation, perhaps my career. But she just smiled and said “Don't worry, this often happens to me.” She wrapped her hand in a towel somebody found. We talked about it later over a beer and it developed that she was one of those people whom snakes often bite. I was the opposite—I often had handled otherwise aggressive snakes without problems. 


Joe Eaton’s “Wild Neighbors” column appears every other Tuesday in the Berkeley Daily Planet, alternating with Ron Sullivan’s “Green Neighbors” column on East Bay trees. 


Photograph by Joe Eaton. 

The bird formerly known as Oregon junco, in Tilden Regional Park.