The extraordinary, far from ordinary, junco
A month back, the Harris Center screened the video “Ordinary Extraordinary Junco” that features one of the most common, widespread birds across the continent: the dark-eyed junco.
Turns out this somewhat nondescript commoner is a “rock star” in the world of evolutionary biology — as in how species are formed, why, and — in the junco’s case — how quickly.
The video can be watched online, at no charge, and I hope you will. Juncos have been researched a lot, and the video delivers information gleaned in a very lively, user-friendly form.
One early junco study, by William Rowan at the University of Alberta in the 1920s, had to do with the effect of changing day length on bird migration.
Back then, temperature and barometric pressure were thought to trigger migration. Also back then, birds weren’t considered worthy subjects of research. Fish and amphibians and invertebrates, yes; birds, no.
In the depths of a Canadian winter, Rowan manipulated light levels for juncos he trapped and placed in an outdoor aviary. He chose juncos because there’s lots of them and they’re easy to trap.
Each day he increased daylight by five minutes as though winter was turning to spring. By December the test juncos were experiencing manipulated light levels equal to late spring. The males started singing for territory and courtship, and measurements clearly showed gonadal development preliminary to the breeding season. Six months ahead of time.
The juncos flew the coop, but as small, nondescript birds, their travels were hard to track.
Rowan’s next “guinea pigs” were crows, easy to see after their tail feathers were painted yellow. In response to photoperiod manipulated to resemble fall, Rowan’s crows migrated north, not south.
In response to spring light levels, the yellow-tailed crows migrated south. Wrong direction both times.
Although people have been manipulating light levels for eons to trick chickens into laying eggs in winter, Rowan is credited with the “discovery” of photoperiodism in animals through his research with the very common junco.
My first bird guide, the 1966 Golden guide ($3.95), shows five distinct junco species including the most widespread one, the slate-colored junco. That’s the familiar junco, slate-gray above and whitish below, that visits local birdfeeders most winters.
Other 1966 species have very different looks and much more limited ranges than “our” slate-colored.
Juncos have tricked the species classifiers for a long time. Back when physical looks determined classification, there were as many as six named species. They’ve been lumped into two, then back to five.
When it was confirmed the groups could interbreed, they were lumped into one, today’s dark-eyed junco, named for one common physical trait: dark eyes.
The different looks and behaviors of the five or six distinct junco population groups have attracted a lot of attention and research.
A central question in evolutionary biology is how species are formed, and genetic analysis of the junco groups is providing information that helps map and time that process.
The “Ordinary Extraordinary Junco” video presents DNA sequencing in ways that are easy to understand. It’s a term I’ve heard a lot, but have been clueless understanding.
The video shows a sequence for each group, each laid out on a horizontal line. They all start out AJPD, let’s say, and then along comes a different sequence for one, and then others at different places along a group’s line or sequence.
That shared AJPD indicates a shared ancestor, and the subsequent changes indicate gene mutations over time. Given enough gene mutations, a new species forms, one that does not breed with any other.
That’s the biological definition of species: able to breed within your species only.
The shared sequencing indicates that the junco groups share a common ancestor, a junco from south of the Mexican border and south of the most recent glacier.
When that glacier melted and retreated northward some 12,000 years ago, the Mexican junco followed, radiating out to different regions. Adaptation to those different regions led to changes in size, bill shape, plumage, song type — and genetic mutations as they bred within their isolated junco group.
The bird that has challenged species classifiers likely will continue to do so. Given enough time and separation, the dark-eyed junco will be split into more than one species.
A process of gene mutation and speciation thought to take millions of years has taken just thousands of years for the junco. The rock star junco.
The video takes you along on lots of journeys to the home ranges of junco groups, well south of the border included, as researchers continue to work on the species puzzle.
The video is arranged in chapters, none too long and none too short. Study guides are available for school groups. I hope a lot of teachers will take advantage of a very compelling learning tool.
Watch the video and then check out the study guide, questions included — with answers.
The video is a good teacher. You’ll do well on the test.
Backyard Birder by Francie Von Mertens appears every other week in the Monadnock Ledger-Transcript.