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History is afoot on Muskellunge Lake. A two-year-old male is making a play for a high-quality territory….which is pretty shocking. 

Let me put this into perspective. Only about a quarter of all two-year-old loons even bother to return to the nesting grounds. The vast majority of all loons of this young age from eastern and midwestern breeding populations are cooling their heels in the Atlantic right now. Some are off of the Carolinas; some New Brunswick. The bulk of all two-year-olds play the long game: they retain the drab grey-brown winter plumage throughout their first two years, stay healthy on a saltwater diet, and postpone any thought of breeding until they acquire sufficient body mass to compete for a territory in their fourth or fifth year.

We have never observed a two-year-old adult male or female settle on a territory. Indeed, we have only once observed a loon as young as three claim a territory — and that was very late in the season and in a vacant space without competitors. (His mate, sad to say, was his mother.)

As territorial intruders, two- and three-year-old adults are nervous Nellies. They sit low in the water while circling with territorial pairs and are deathly afraid of underwater attack. They peer (look under water) and panic dive obsessively. When anxiety overwhelms them, they freak out and flee across the water tremoloing. In short, two- and three-year-olds do not appear emotionally equipped for territory ownership.

But “Junior”– as Linda calls the two-year-old that has settled on Muskellunge — threw out the book on reproductive maturation. When the 12-year-old male that took over on Muskellunge this year became injured in early June after a failed nesting attempt, Junior took possession of the lake and began defending it vociferously with territorial yodels (as you can see in Linda’s photo, above).

For a time, it seemed that Junior would ease into lake ownership without a battle. Yet news that Muskellunge Lake was up for grabs spread fast in the neighborhood, and the last two weeks have seen multiple local males vie for control. One of these males, from nearby Deer Lake, has tried to claim Muskellunge before and is renewing his bid. A second male, this a ten-year-old reared on neighboring Clear Lake, seemed settled on Harrison Flowage last year but is apparently looking to upgrade. 

Junior’s age is not all that makes his story unusual. He is also the only young adult (out of 211 observed so far) that we have ever observed to compete for ownership of his own natal territory. In this he is fortunate; the current breeding female on the lake, who will probably pair with the victorious male, is not Junior’s mother, but instead a female that took possession of Muskellunge last year.

According to Linda’s reports, Muskellunge remains in an uproar. One day Junior is in control and paired with the resident female (or the Bridge Lake female, whose mate did not return this spring). The next day the Deer male has taken ownership and patrols the lake, searching for Junior, who evades him. 

Linda and I are trying to celebrate the oddity of a two-year-old territory owner and not overthink it. But it is difficult to sit back and pretend to be neutral. After all, Junior got his name because he is the son of Clune, the beloved male who settled on Muskellunge in 2009, cranked out 14 chicks during 14 years of territory ownership, and never uttered a discouraging word for canoe nor kayak.

And it is hard not to wonder how a loon as young as Junior even got a shot at such a good territory. Is his territorial gambit an anomaly — a one-time peculiarity that you are bound to observe once if you study a loon population for 31 years? Or must we interpret his premature, longshot bid for territory ownership as yet another indication of the depleted ranks of young nonterritorial loons that epitomize population decline in the region?

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A week or so ago I gave a talk to the Northeast Loon Study Working Group. Inauspiciously-named and -initialled, NELSWG comprises loon conservationists from New England, the Upper Midwest, and a smattering of other regions within the loon’s breeding range. At present, NELSWG is the only group that attempts to pull together data on loon populations and brainstorm strategies for protecting the species. During my talk I shared our data showing that masses of adult loons and chicks decline as water clarity declines. I then updated the group on my analysis of male and female traits that lead to breeding success of pairs.

Impact of male (blue) or female (red) pair member on a pair’s hatching success. Both males and females are a drag on hatching success in their initial year on a territory. Females have a slight positive impact thereafter. Male experience on a territory continues to improve hatching success even after 10 years.

To remind you, a male’s knowledge of the territory makes a huge impact on the breeding success of a pair. Since males choose the nest location, males are a drag on nesting success in their first few years on a territory because they place the nest in lots of dangerous places. (Note the low blue bars for years 0 to 3 above.) On the other hand, males that have been on a territory for seven or more years are a boon to pair nesting success, because they have learned the safest spots to place nests. (Note the blue bars from 8 to 20 years on territory.) Females have an impact too. In their first year on a territory, females cause low hatching success for their pair. In later years, female territory experience boosts hatching success slightly.

It is almost more interesting to see the factors that do not affect breeding success. A male’s age does not affect his pair’s ability to fledge chicks at all. At first glance, this seems confusing. How can the male’s age have no positive impact on breeding success of a pair, when a male’s breeding experience on a territory is hugely important? The answer relates to cause. It is true that old males tend to have very high breeding success, but this is not because of their age but because, in most cases, they have been on a territory for many years. We know that age itself is not causing high breeding success because old males that nest on new territories have no greater breeding success than young males on new territories. It is familiarity with the territory and not age that is the salient factor.

Female age has only a weak negative impact on breeding success. In other words, older females lose chicks at a slightly higher rate than young females. This pattern is a bit difficult to make sense of, because the effect is so steady and gradual. Why would a 15-year-old female lose chicks at a higher rate than a 10-year-old female parent? Both females are in the prime of life, in the loon sense.

Effect of female age on a pair’s fledging success. Females cause a gradual decline in fledging success as they grow older.

To the listeners at NELSWG, though, the pattern that was most remarkable was the lack of a strong effect of mate familiarity. While pairs that know each other nest a few days earlier than pairs that are in their first year together, the pattern is weak (see below). Furthermore, the slightly earlier hatch date among pairs that know each other does not translate into a detectable advantage in overall breeding success. In short, pairs benefit only slightly from knowing their mate well.

Effect of pair-bond duration on hatching date. Pairs in their first year together nest later, on average, than pairs that have been together for at least one year.

How can this be? How can a male and female remain together year after year, raise young cooperatively — and still not benefit from this lengthy association? That was the question asked by Lee Attix at the NELSWG meeting. I don’t have a good answer for Lee. As a male in a 38-year relationship who has raised young cooperatively, I am well aware of the benefits that a long-term partnership can bring in the human species. But loons are different.

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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.

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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!

FOOTNOTES

*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