I have often trumpeted the high survival rate and steadfastness of adult females. Female breeders are masters at perceiving when the tide of battle is turning against them, fleeing from their stronger opponents, and living to breed another day on another territory. Females are survivors.

Male loons, it seems, are not so clever. Perhaps because males control nest placement and, therefore, gain critical familiarity with territories that females do not, males value their knowledge and ownership of a territory highly and seem to fight too hard to hold familiar territories. They often lose their lives as a result.

Against this backdrop of pragmatic, long-lived females and reckless, short-lived males, our capture of a certain male a few nights ago was particularly striking. “Silver over White, Blue over Blue-stripe” first settled on clear, 221-acre South Two Lake in 2002 — when my current field interns were infants or toddlers. The next year, however, Silver over White was booted off of South Two. He settled ultimately on the the Lake Tomahawk-Thoroughfare territory. Thus began one of the most productive runs of chick production we have seen in the history of the Loon Project. Silver over White and two different females reared at least 12 chicks over seventeen years. Moreover, we could hardly help loving this affable male, who year after year nested in plain view and within a stone’s throw of the busy channel that connects Lakes Tomahawk and Minocqua. Dodging indifferent motor-boaters, the Tomahawk-Thoroughfare pair each year led their tiny chicks out of this dangerous channel to the relative safety of the big water of northwestern Lake Tomahawk.

This spring, Silver over White’s second mate apparently did not return. Not missing a beat, he paired with the former female breeder on tiny Schlect Lake — whose mate was also missing — and again nested in his favorite spot along the thoroughfare. Fortune did not smile upon the pair this year, and they did not hatch chicks. When it became too late to nest, both Silver over White and his new mate seemed destined to ride out the year loafing and foraging on Lake Tomahawk.

But Silver over White, who at 25 years of age was well past the time in life that most males look to take a territory by force from another male, was not satisfied with that laidback plan. Instead, he returned to South Two Lake — where we had not seen him since 2003 — and apparently evicted its young owner. (We caught Silver over White a few nights ago, as the featured photo shows.) Silver over White’s feat was especially impressive, because his territorial opponent had two three-week-old chicks and no doubt fought viciously to protect his territory and young.

I returned to South Two today, in daylight, to confirm the territorial situation there. (Marge and Gerry Perner were kind enough to take me out in their pontoon boat.) The scene was chaotic: seven loons socialized distractedly, coming together, splitting apart, and converging again. One fact seemed clear though; Silver over White and a new female — a seven-year-old hatched on Silver Lake, near Minocqua — are the new territorial pair. The freshly-evicted male was nowhere to be seen; we hope he is still alive somewhere. The old female, who was rearing two healthy chicks with the evicted male a few days ago, appears also to have lost her breeding position. As she did two years ago, when she settled on South Two after losing her mate on Little Carr Lake, this female will have to bounce back and find a new place to breed.

Silver over White’s remarkable ability to win a battle against another territorial male at 25 raises two exciting questions. First, how can this male defy the odds and make an aggressive, risky play for a new territory, when most males his age are merely hoping to hang onto their territory for another year or two? Second, it is astonishing and unprecedented to have an adult breeder return to a lake that s/he had been away from for more nineteen years. (The longest stretch of time that a loon had been a breeder on a territory and then had returned to it after eviction had previously been six years.) Did Silver over White try to take over South Two because he still remembers safe nesting sites there and thus knows that he can quickly resume a successful breeding career on the lake? If so, his seizing of his old territory suggests that loons have impressive long-term spatial memory.

I wonder why I have been rooting so hard for Silver over White. I suppose it is because — at a time when I have turned rather silver over white myself — I find it quite inspiring to see his dogged determination to be productive despite the passage of years.

I try not to steal a glance through the lab window each time I pass. But I usually fail. You see, Marco Bisoffi, a molecular biologist and colleague of mine at Chapman, has restarted our study of telomeres* in loons as a possible tool to measure age and the effect of stress. Each week Marco churns out telomere measurements on a new set of loons, as he tries to troubleshoot the PCR** procedure. So when I walk by his lab and see him bent over his laptop, I wonder whether his promising early finding that telomeres indicate age in loons has held up.

It has. Now that Marco has run twelve males and ten females of known age, the trend is stronger than before. If you study the plot above, in fact, two patterns are evident. First, old males and females have shorter telomeres than young males and females. Second, males as a group have shorter telomeres than females. (This latter finding repeats what Jeremy Spool had found a few years ago.) There is some scatter in the data, especially among females, but both patterns show high statistical significance. Of course, we will have an even better fix on these patterns when we have run the other 83 DNA samples we have collected from adults of known age.

It is hard to exaggerate the value of these findings for loon biology and our own research in Wisconsin and Minnesota. There are countless benefits to studying loons, but one drawback has always been our inability to “age” individuals effectively. To our enormous frustration, we cannot even distinguish a 5-year-old from a 30-year-old. If this telomere pattern holds up, however, that source of vexation will be considerably diminished. In the future, we will be able to take a DNA sample from an unknown adult, measure its telomeres, and assign it to an age-class. Indeed, if the unknown bird is a male and we record both its yodel and its tendency to yodel at intruders, we shall be able to narrow its estimated age range still further — probably to within a few years.

Why does it matter that we are on the brink of being able to age adult loons accurately? First, age has a strong effect on a great range of behaviors, including aggressiveness, ability to hold a territory — which increases in young loons and then declines later in life — and even willingness to incubate eggs when black flies are abundant. Second, age impacts survival rate, especially in males. So knowing the ages of loons helps us refine our estimates of survival and improves our models of population dynamics.

Speaking of age and decline, the featured photo for this post is Linda’s Grenzer’s pic of “Clune”, the male on her lake. Despite the inevitable shortening of his telomeres, this 23-year-old still looks pretty fit in his winter attire!


*telomeres — protective DNA sequences (“end caps”) on chromosomes that permit DNA to be replicated many times but become shorter with age and stress

**polymerase chain reaction — a common molecular technique that permits efficient study of specific regions of DNA