Researchers discover bluebirds philandering in Bighorns
Date posted: August 5, 2014
Big Horn — Sex. Deception. Infidelities. Fathers raising youngsters that they think are their own, but actually are the offspring of another.
While this might sound like the typical plot of almost any soap opera, it is actually a glimpse of the findings that bird biologists Scott and Bonnie Johnson have discovered in their years of research in the Bighorn Mountains.
Scott Johnson, a biology professor at Towson University in Baltimore, Maryland, has been coming to the Big Horn area for bird research since 1985.
“I had just finished my master’s degree and came to Wyoming for romantic reasons,” Johnson said. “That didn’t work out but I started doing research on my own. I taught at Holy Name School and I had a very understanding head nun who let me have my first period to use as my planning period. I used it to do the morning bird research. I would come in and teach in my rubber boots and jeans and change clothes between second and third period. It usually took me until lunch to get fully dressed.”
Johnson was joined a few years ago by his wife, Bonnie, and together, based at the Gallatin Ranch, they have studied the biology and behavior of house wrens and bluebirds.
During their years in the area, the pair has conducted research in the Big Horn and Burgess Junction areas. Initial research projects focused on house wrens and more specifically, what the role is of the male bird’s song.
“A couple things we discovered is they use song to attract mates to their territories,” Scott Johnson said. “We did an experiment where we had a speaker playing a recording of a male song next to a nest box where there were no males. Females came and started building a nest even though they couldn’t see a male. Of course we had control boxes where there was no song and no females came.”
“I think some of the more interesting stuff we discovered was extramarital mating behavior or affairs of the avian kind in the house wrens,” he continued.
Early on, the pair noticed that males would sneak into the territories of their neighbors. They primarily did so when the females on those territories were fertile and laying eggs. Most of the time, the intruding males were chased out by the resident male, but if not, they were seen performing their mating display.
“So it suggested these males were making territorial intrusions to try and increase their mating success and spread their genes,” Johnson said.
Later in the 1990s, the Johnsons said the development of genetic testing techniques allowed them to verify what they were seeing in the field.
“We were able to use genetic analyses to confirm that some of the young were fathered by males not on the territory,” Johnson said. “In fact, about 40 percent of the nests had at least one offspring not fathered by the resident male. Some had no offspring of their own in the nest.”
Johnson added that when they began to study mountain bluebirds, they discovered they were even more philandering than wrens and genetic testing revealed that two-thirds of chicks in nests were not the offspring of the male associated with the nest.
One example of the deception that male house wrens can practice is their tendency to attempt having a clutch of chicks with more than one female. During their observations, the Johnsons noticed that once their first female mate was on the nest and incubating eggs, some male wrens would go to a high perch and sing a song signaling to other females that they were unattached and in search of a mate. The Johnsons found that depending on the season, anywhere from 20 to 40 percent of males would have two female mates at a time.
“Not unlike another species we know,” Bonnie Johnson said.
However, the Johnsons still are unsure why this behavior is a benefit to the birds, as once the first nest’s eggs hatch, the male abandons the second female. They do not help raise the second feathered family and consequently, the chicks have low survival rates.
“It is a very bad deal for these mistresses,” Scott Johnson said. “They (chicks) do very poorly. The second female has to do it all on their own.”
The Johnsons’ findings have been published in more than 50 scientific papers and added significantly to scientific knowledge about birds and bird behavior.
“They are relatively easy to study,” Scott Johnson said about why they have chosen house wrens and bluebirds to study, out of the dozens of species that inhabit our area. “The house wrens are fun because they are constantly busy. I admire them because they don’t waste any time. You rarely see them sitting and doing nothing. And the bluebirds are just stunning to look at. I never get tired of watching them. The other thing that is intriguing about them is how they manage to nest in a challenging environment, that high altitude. Up at Burgess Junction they are nesting at about 8,300 feet.”
“They face all kinds of conditions within a breeding season,” Bonnie Johnson added.
In addition to a healthy habitat and an abundance of bird life to study, the Johnson’s said the Sheridan area has been an ideal place to conduct research due to the support they have received from individuals and groups. They said the Gallatin and Garber ranches, as well as staff and management of The Brinton Museum and Bear Lodge have allowed them to have great success in their work.
However, even under the great research conditions offered in our area, unexpected and unwelcome things can happen.
“A disheartening surprise this year was an as yet unidentified disease affecting bluebird chicks on the mountain,” Johnson said.
He noted that they are discovering nests with approximately half the chicks dying or missing (when a chick dies, the female bluebird will push the body out of the nest where it is usually quickly taken by a predator).
Despite otherwise good conditions this year for raising chicks, the chicks are succumbing to a disease that causes black, dead tissue around their mouths, misshapen beaks and emaciation. Photos and samples have been sent to two wildlife veterinary research centers in search of an answer.
“We may end up studying the effects of that disease next year because this is really rare,” Johnson said. “We just don’t see wide spread disease in songbird populations. It is sort of a very recent discovery and we’ll keep working on it.”