As the Nest Turns: Racy Research on Birds

There have only been three ornithologists in the history of Bowdoin College and Biology Professor Nathaniel Wheelwright happily counts himself among them.

Nat WheelwrightFormer director of the Bowdoin Scientific Station on Kent Island and longtime researcher of its birds, plants and insects, Wheelwright inherited a well-established island field-research station from his Bowdoin predecessor, Chuck Huntington, whose long-term study of Leach’s storm-petrels revealed them to be among the longest-lived birds known (some have been recorded to be 37 years old).

Since beginning his own research on the island in 1987, Wheelwright has made a name for himself for evolutionary and behavioral research on the tiny Savannah sparrow, another of the island’s bird species. It all began when a group of fledgling sparrows Wheelwright had banded during his first summer there actually returned to the island to nest the following year.

“We can see things happening with their mates that the fathers don’t know … We see infidelity all the time.”

“That’s highly unusual,” notes Wheelwright. “Normally, you’d expect to see young birds disperse and end up in Bangor or Albany or someplace. The fact that these birds returned made me realize you could ask a whole set of questions that biologists can’t normally ask of wild animals. What traits or characteristics do birds inherit from their parents? What is their longevity? How does the population change from year to year? What factors affect their ability to attract mates? Can you predict what offspring will look like?”

That triggered his transformation into a self-proclaimed “stalker.” Wheelwright has worked with a revolving bank of student researchers on Kent Island to pursue the mysteries of the Savannah sparrow for going on 20 years.

bandbird.jpgWheelwright and his research partners – some of them Bowdoin students – have banded roughly 6,600 sparrows on Kent Island.

It’s an investigation that has deepened in recent years through genetic analysis: Wheelwright teamed up with Bowdoin alumnus Corey Freeman-Gallant ’91, biology chair at Skidmore College, for a major research grant from the National Science Foundation. Together, they have banded more than 6,600 Savannah sparrows, taken blood samples for DNA analysis, located and marked all of their cryptic nests among the island’s grasses, followed their mating, feeding, and child-rearing activities daily – and entered the above information into a giant database.

“We’re sort of like the IRS here,” smiles Wheelwright, pulling up a sparrow’s data record on his computer. “Each bird has an individual data profile, which lists biological parents, history of nest sites, offspring. We can trace their lineage by individual bird up to as many as nine generations. I don’t have a bunch of birds here, I have a bunch of relatives.”

What he and Freeman-Gallant are finding is giving evolutionary ecologists insights – and hope – as to what the natural world and its denizens may look like as human encroachments into wilderness begin to fragment the landscape into more contained, island-like habitats.

On a purely behavioral level, however, some of his findings are downright salacious.

On the matter of mating, for instance, one might assume the breeding possibilities on a small island populated with aunts, uncles, mothers, fathers, siblings and even grandparents, would be – shall we say – cozy?

In a nine-year study published in 1998 in the journal Ecology, however, Wheelwright and Kenyon College professor Bob Mauck (current director of the Bowdoin Scientific Station) showed that social pairings – as opposed to actual mating – with relatives among the sparrows were so infrequent as to be downright suspicious. Of 550 pairs studied over a nine-year period, only one paired with a relative – far fewer than even a random, computer-based analysis had predicted.

“It indicated they were doing something to avoid mating with relatives,” Wheelwright says (more on that dicey subject anon). Among the strategies Wheelwright believes the birds use is song – each bird possesses a distinctive song that might allow blood relatives to recognize each other and thus avoid inbreeding, which would reduce their evolutionary fitness.

nestlingIn 2003, Wheelwright, Freeman-Gallant and Bowdoin student Kim Tice ’00 published research in the journal Animal Behaviour that showed fathers were just as involved in caring for fledglings as were mothers – even though the paternity of the babies they were caring for was uncertain. Deadbeat dads risked getting the boot from mom, depending on how they nurtured the first batch of offspring.

“We can see things happening with their mates that the fathers don’t know,” quips Wheelwright, who spends most summers with his eyes glued to binoculars. “Fifty percent of all offspring are sired by someone other than the territorial male who feeds them. We see infidelity all the time.”

One might think such sparrow promiscuity would suggest worse things: aforementioned inbreeding, for instance. Wheelwright’s most recent research, which includes actual DNA paternity evidence, blows this theory out of the water as well.

Student in the fog
Every summer, student researchers help Wheelwright gather data on Kent Island. “They’re out there at 6 a.m. and have to find a nest before they’re allowed to have breakfast,” he jokes. Here, Iris Levin ’05, searches for nests.

In an article published in the March 2006 Animal Behaviour, Wheelwright, Freeman-Gallant and Mauck show the vast majority of sparrows not only avoided social pairing with relatives, they also avoided actual inbreeding – only nine cases of social inbreeding and three cases of genetic inbreeding among those 1,110 pairs.

Most surprising of all: None of the cases of social or genetic inbreeding involved a father-daughter combination, and all but two involved a mother-son combination.

“It really is Oedipus,” says Wheelwright. “And like Oedipus, it’s probably a matter of lack of information. Virtually all of those males were one-year-olds, inexperienced, arriving back late to the island when experienced males were already there. I think they were a little clueless.”

Wheelwright is hardly censorious about his findings. In fact, he seems buoyed by the possibilities they suggest.

“The important thing to keep in mind is that inbreeding in natural populations may be rarer than you would expect by chance. Some people have argued that birds aren’t that bright and only avoid inbreeding because it is uncommon to find themselves nesting next to a relative.

“Our study of the Savannah sparrow shows fairly clearly that something else is going on. Females are able to make choices about whom they mate with and the risks of inbreeding may not be as great as we thought.”

The care and discovery of Kent Island has passed through several generations. Here, Wheelwright, compares notes with Bowdoin Professor Emeritus Chuck Huntington and meterologist Bob Cunningham, l. to r.

So, why the fuss over the breeding activities of a tiny sparrow? Wheelwright asserts that the study of the sparrow is a general model of what one may be able to expect in other animals — and even plants — as pressures on habitats break up ecosystems.

“Our study suggests that mate choice is not random and that could bode well for the future,” says Wheelwright. “We don’t know if other animals behave this way, but at the very least, it tells us that we may not be losing genetic diversity as quickly as we had thought in fragmented populations.”