well-known individuals

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In a sense, our ability to identify loons as individuals hangs by a thread. As most of you know, we rely upon a unique combination of three colored leg bands — together with the mandatory numbered USGS metal band — to ID our study animals. The Upper Kaubashine female, for example, is “silver over yellow on right leg, red over green on left leg”, while the Lee Lake male is “blue with white stripe over taupe with white stripe on right, red with white stripe over silver on left”. (He is nicknamed “Stripe Hell” by my staff.)

The system seems simple enough on its face. Together with the DNR, however, we have banded over four thousand adults and chicks in northern Wisconsin since 1991. Thus, we have used a lot of color combinations over that span. Inevitably, certain individuals differ only slightly from other individuals in their band combination. While we make every effort to use contrasting band combos on mated pairs, loons move around between lakes because of natal dispersal (movement from natal lake to breeding lake) and eviction. Sometimes birds with similar band combos end up close together. For instance, the male on the southeastern end of Squash Lake, which we caught last night, is “yellow over taupe stripe, green over silver”, while the female at the northwest end of the same lake is “red over taupe stripe, green over silver”. A single band is crucial to distinguishing one bird from the other on Squash.

I describe our identification system as fragile, because the loss of only one of its four bands by a loon can throw its identity into question. In several cases, a loon with one or more missing bands could only be ID’d when it was captured and we read the number on its USGS metal band. In most years, there is at least one such “mystery loon” in our study area.

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Our mystery loon of late has been the female on Bear Lake (pictured above in Linda’s photo). She has lost one band and is now “orange over mint burgundy, silver only”. A check of our banding records finds four birds that could match that combo, if they lost a single band. All are “ABJs”: adults banded as juveniles. In other words, all were marked as chicks: one in 2004, one in 2005, and two in 2007. I was excited to see that Bear Lake had a chick this year, because this gave us a reasonable chance of being able to capture Mystery Female and learning her age and natal origin from her metal band. But she is a skittish bird, and we failed to catch her.

So we left it to Linda. Linda is a great photographer and a very patient naturalist. Many times she has taken photos so crisp that one can read the numbers stamped into the metal band on birds legs. Below is an example of a photo by Linda in which one can make out several numbers on the metal band on the right leg, above the “auric with red stripe” band. I thought that Linda might pull off the same magic with

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the Mystery Female, which would permit us to discover her age and natal lake. Thus far, she has been able to make out three separate digits on the bird’s metal band. That information has allowed us to eliminate two of four possibilities; we now know that the Mystery Female was hatched on either North Nokomis Lake in 2005 or on Buck Lake in the same year. The tendency of young adults to settle on breeding lakes similar in size to their natal lakes makes us favor North Nokomis as the more likely natal lake. If we are lucky, Linda might get a chance to nail the numbers well enough for a certain ID.

Now you might wonder why we are so obsessed with the identity of a single loon. After all, we have identified scores of other lake settlers who held onto all four of their bands. We have come to feel that each data point is precious, because each one allows us to refine our population models and survival estimates. Females are particularly valuable to us, because most of them disperse so far from their natal lake that we cannot relocate them as breeders. (Males, in contrast, often settle within a few kilometers of their natal lake, so we have far more data on male settlement.) So please send positive vibes Linda’s way, as she hunts the skittish Mystery Female of Bear Lake.

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In many recent posts, I have emphasized a certain theme: male loons begin to die off at a rapid rate after age twenty, while females linger on. Part of the reason for this contrast is the nature of territorial contests in each sex. Territorial males fight hard in attempting to hold their breeding position on a lake and commonly die in territorial battles. With rare exceptions, territorial females survive eviction from a territory, move to an unoccupied lake nearby, and resettle on a new territory when opportunity permits.

While the escalation of male territorial battles is interesting in itself, it also impacts the composition of the breeding population. Specifically, adult male loons’ propensity to die frequently in battle skews the sex ratio towards females in the breeding population.

These excess females are “floaters” — adults capable of breeding but prevented from so doing by the lack of a mate and/or a territory. Floaters are the loons that one sees living alone on small lakes, drifting about aimlessly on large lakes, and intruding into territories from time to time to confront breeders. A large proportion of the loons that gather in flotillas of five adults or more during July and August are floaters. Floaters can be thought of as “hopeful breeders”; that is, they are always ready to settle and breed with a mate and territory, if they can find one. The excess of female floaters means that there are always far more of them looking to settle and breed than there are male floaters able to pair with them. In effect, males are snapped up by females as soon as they become available for breeding.

In May of this year, we re-encountered one of our veteran breeders, “Silver over Blue, Green over Orange” (or “S/B,G/O”), whose breeding history illustrates the striking contrast between males and females brought about by male-biased mortality. S/B,G/O was first captured and marked as an adult in 1997 on Dorothy Lake, where she raised two chicks with her mate. Her mate was evicted in 2001 and died either during eviction or shortly afterwards. But she lingered on. When an opening became available in 2002, she settled and nested with a different male on Hasbrook Lake, just a few miles to the northwest. Having failed to raise chicks on Hasbrook, S/B,G/O (now at least 14 years old) evicted the female breeder on Hodstradt in 2004, paired with a third male, a six year-old, and reared four chicks there during the next three years. She followed this young male to Horsehead Lake in 2008, when he was driven off of Hodstradt, and the pair fledged 3 more chicks over the next four years on their new lake. When the male was evicted yet again in 2013, S/B,G/O traded experience for youth and found a new six year-old male as a breeding partner. We breathed a sigh of relief when she broke up with this youngster after a year together, as he was unfortunately her son from Hodstradt! Then 23+ years old, S/B,G/O again became a floater, forced to return to the breeding grounds in 2014 and 2015 with no clear prospects for breeding.

I have become attached to the birds in the study area, so I was delighted to find S/B,G/O back at Hodstradt in May of this year with her fifth recorded mate. At 26+ years of age, she is perhaps fortunate to be paired again. Her mate this time: a four year-old hatched on Clear Lake. We observed no breeding attempt by this new pair – only a small percentage of four- year-old males that settle on territories actually nest – but it is likely they will nest in 2017.

As a human, I like to think of S/B,G/O’s life as a lesson in resilience – the dogged refusal of an animal to forsake breeding despite repeated setbacks and advancing age. But, as a behavioral ecologist, I think of this female more as a striking example of how animals adapt to maximize their breeding capacity regardless of the breeding environment they face. By the way, S/B,G/O is not the only female in our study area who has continued to breed despite frequent changes of partner. S/R,O/O, another 26+ year-old from Swamp Lake that we recaptured a few nights ago (see photo with Eric), has gone through at least 5 younger mates during her 20 years of breeding there. Clearly the pairing of tough, old females with much younger males is – as my daughter says – a thing.

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He doesn’t look it, but this male from Townline Lake, just outside of Rhinelander, is at least twenty-seven years old. He is among a dwindling few males from among those we banded in the mid 90s. This bird was banded in 1994, at which point he was certainly at least five years old, which means that he was hatched in 1989 or before. Thus, twenty-seven is a minimum estimate for his age.

The age of “Silver over Red, Orange over Green” (as I call him affectionately) is not his only remarkable attribute. What sets this individual apart from most others is his ability to hold onto his territory year after year while fledging healthy chicks. (Below, he relaxes near his mate and two strapping chicks from 2016.) A successful common loon is not only good at locating safe nest sites and defending and feeding young. A breeder that wishes to

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reproduce successfully must confront intruders that land in the territory without warning throughout the breeding period.

Intrusions are especially frequent during the chick-rearing period. A common scenario plays out as follows. Early in the morning, a male is diving for food, while his two chicks track his progress from the surface. Each time he surfaces, the chicks rush over to him, snatch food from his grasp, and nibble relentlessly at his bill, neck and chest, signaling their unquenchable appetites. On one occasion, he surfaces holding a small yellow perch, only to find five adult loons in flight above his lake. He drops the fish, gives a short barking call, and the chicks dive and head to the nearest shore. The male too dives but surfaces near the middle of the lake, drawing the now-descending intruders to himself. Three quarters of an hour later he has driven off the intruders, thanks in part to a lunge and point yodel that caused his five visitors to scatter and tremolo. Shortly afterwards his mate returns, and both parents forage for the chicks. The family suffers no further disruptions until the evening, when another group of three nonbreeders circle and land, causing yet another brief skirmish.

Considering that a large pool of territorial intruders are constantly sizing up the resident male or female of any successful territory for an eviction attempt, it seems remarkable that residents are able to hold on to their territories for even a single year. Yet Silver over Red, Orange over Green has put together a string of 23 years of straight ownership, the only blemishes a half-year in 1996 and another in 2003, when he was briefly deposed. He has fledged 20 chicks during his breeding career with four different mates. This male is not the only resident with an impressive resume. A female on nearby Langley has fledged 17 chicks on that territory since 1995, while the O’Day female has been on territory since at least 1997 and has produced at least 16 full-grown chicks during her breeding career.

But female loons are survivors. Females enjoy a high rate of survival and no detectable senescence well into their twenties. Males, on the other hand, hit the wall abruptly at age 20; almost half of all territorial males of age 20 will perish before the subsequent year. So when we see a male who defies the odds, like this one, it is worth looking closely to see if he possesses an attribute that sets him apart. As a scientist, I am loathe to draw conclusions based on a sample of one. Colleagues in my field would dismiss any such conclusions out of hand. But today Nelson, one of my Chapman research students this year, reported that Silver over Red, Orange over Green is the tamest bird we have ever measured in the study area. So let me invite ridicule by advancing a very preliminary hypothesis. Perhaps the key to lifetime productivity in a habitat rife with human recreation is picking one’s battles carefully. Maybe by ignoring the inquisitive, well-meaning primates in their watercraft, this male has been able to conserve his metabolic resources for provisioning young and driving off pesky intruders.

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Sleet greeted me as I landed yesterday at Rhinelander Airport. Since I had come from 75 degree southern California, it took me a few moments to adjust. I hurriedly dug through my clothing and threw on four more layers of clothing, gloves and a woolen cap. Our research vehicle, a 2007 Toyota Corolla, was as reluctant as I was to face the elements. The car sputtered to life, and I drove from the storage box to our research cottage on Currie Lake. A panicked search at the cottage produced most of the items I would need for a day of field observations: binocs, data sheets, life preserver, paddle, GPS.

Meanwhile, Royce, my first field assistant of the year, had arrived. After equipping him for a day in the field, and a grabbing three hours of fitful sleep, we were ready to hit the lakes this morning.

On the first day out, novelty and adrenaline keep one going. Royce and I raced from lake to lake, doing “quick-hitters” to locate pairs. In other words, we wrote down any leg bands the loons would show us readily, mapped any nests we found, and threw the canoe back on top of the car to go to the next lake. (Truth be told, we took a quick break at Dunkin Donuts for two vanilla-frosted and a chocolate creme to bolster our flagging spirits at one point.) All told we hit Soo, Flannery, Julia, Buck, Hilts, Hildebrand, Townline, Langley (the 28+ year-old female there is pictured in the photo), Squaw and Gross. Four of these pairs had nests and two others were clearly making plans. Based on this small sample, almost half of our pairs are now nesting. Considering that we have about 110 more lakes to cover, we no doubt have 50 or so nests to find in the next few weeks. Sadly many of these nests will fail quickly — before we can visit the lake — so we will never record them. In order to limit that tragic loss of data, we will continue quick-hitters until we exhaust our lake list.

This is a stressful way to start the research year, but it is also traditional. Some years, in fact, are worse, as I am unable to enlist others’ help to make a first sweep through the study area. Kristin and Linda’s first round of visits in April to locate returning and newly settled breeders spared us the trauma of having to nail everyone’s identity AND find nests. So we will endure, cheered on from time to time by a selfie — and a very occasional stop at D&D.

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The first round of censuses in the study area each year is always bittersweet. On the one hand, it is exciting to see the crop of new young adults that have settled and to wonder how well they will defend their new territories. On the other hand, some old familiar loons are missing. This year is typical in that the disappeared veterans are mostly males. Three of 12 males of 20+ years have failed to reclaim their 2015 territory; only 1 of 12 20+ females have not resettled on their territory from the year before. Thus, male senescence lives!

Among the 2016 no-shows are the Jersey City Flowage male, who bounced back from a nasty fishing entanglement in 2014, regained his territory in 2015 and hatched a chick there. Another loss is the Soo Lake male, who was among the most aggressive in our study area. I still tremble when I recall his response when we played a few loon calls in his direction in 2000. He approached my canoe to within 2 feet, sat right next to me in the stern and glowered for the better part of two minutes. A spine-tingling experience for sure!

Yet the news is not all bad. Six young ABJs (“adults banded as juveniles”) have settled in the study area, providing us with valuable data on loons whose age is known precisely. New settlers include two females hatched in Vilas County — a 9 year-old that settled on Manson and a 6 year-old now paired with the male on Harrison Flowage. New male faces belong to an 8 year-old that took over Brandy Lake (near Woodruff) and a 7 year-old that battled and evicted the 22 year-old male from Oscar Jenny. (Thanks to Jeremy, who observed this eviction in progress.)

Perhaps the most intriguing findings from the first round of lake visits by Kristin and Linda are the serendipitous ones. Kristin relocated one of our oldest males — a bird known to be 27 years of age or older. Evicted two years ago from Muskellunge Lake, this loon licked his wounds and got himself back in the game by settling on nearby Swanson Lake, which had fallen into disuse in 2015. We had not seen this bird in two years and were almost ready to give up on him. Linda found a female with even greater resiliency. This old loon produced a dozen chicks over the years as the breeder on Buck Lake from 1998 to 2009. After her eviction from Buck in 2010, she floated, found a breeding position on Hildebrand in 2012 and produced a chick there in 2013. But she was driven off of Hildebrand last year. Her response to this second setback was typical of female loons — she bided her time and claimed that territory again when the opportunity presented itself. As I confront another season of hauling canoes from lake to lake, my back begins to ache in anticipation. I hope the examples of these two dogged old codgers gives me the strength to persevere!

 

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LMG_9628 Manson Lake Male Yodeling

Loons do not settle on territories as we think they should. Traditional models in long-lived animals maintain that hopeful young individuals should be systematic in settling on territories. By current theory, a young loon should explore a certain region within proper habitat, find several territories that might be suitable for breeding, and then routinely monitor those potential breeding spots, waiting for a vacancy to occur. During this exploratory period, it is thought, the young loon gains familiarity with this small cohort of territories that will lead to a competitive advantage in territorial battles with other would-be settlers once a territorial slot opens up. The “foothold hypothesis”, as I call this model, is quite pleasing and logical. What’s more, there is evidence that many territorial animals gain territories in this manner. Loons do not.

We got another reminder of the quirky territorial settlement pattern of loons this past week, when Linda and Kristin scoured the study area and ID’d the pairs that had taken possession of the lakes we monitor. Among these settlers were many familiar faces — including a male on Townline Lake that has been in possession of the territory since 1994 and a female on West Horsehead who has bred there with a series of different males since 1995. One of the surprises was a 9 year-old female hatched on Rock Lake in Vilas County who settled on Manson, replacing a female that had bred on Manson for a dozen years. Owing to Linda’s careful observations, we know this Rock Lake female as a frequent intruder during 2014 and 2015. But she did not intrude into Manson Lake, where she eventually settled; instead she intruded repeated onto nearby Muskellunge Lake! Thus, our expectation that the Rock female was laying the groundwork for settlement on Muskellunge was not fulfilled.

There are several possible reasons why loons often do not settle on lakes that they seem to prefer. One of the most obvious is that settlement is not merely a matter of finding a desirable territory.  A loon bent on settling must also contend with the current resident on a territory where it hopes to settle. So a young nonbreeder that visits Territories A, B, and C might prefer Territory A but be prevented from settling there by a healthy and aggressive territorial resident of the same sex. In that case, the nonbreeder might end up settling on Territory B or Territory C. The Rock female is fortunate; Manson Lake, where she has settled, is one of the most productive territories in the study area. So even if she could not take possession of the territory she seemed to prefer, her future breeding prospects are bright.

You can read more about our testing of the “foothold model” for territory settlement in this blog post, which is based on a paper published in Animal Behavior. E-mail me if you would like a pdf of the paper.

The crisp photo above is by Linda Grenzer. It shows the Rock female performing a wing flap on Manson, her new breeding lake, while her mate, an 18 year-old male, yodels in the foreground.

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This past winter was a mild and relatively short one in the upper Midwest. The ice never became as thick as in most years. So the warming temperatures during the past few weeks succeeded in melting that thin blanket of ice covering our study lakes. I have gotten reports in the past few days that many of our study lakes now are mostly or completely free of ice. And the avian summer residents of those lakes are beginning to return.

LMG_8789 Clune on Territory

The first male reported back was “Clune”, seen here in Linda Grenzer’s photo from Wednesday. Playfully named by Linda after the voice-to-text feature on my iPhone butchered the word “loon” during one of our exchanges, Clune is well known to us. We first observed him as a chick on Manson Lake in 1998, found him when he settled as an adult on Deer Lake in 2003, and tracked him when he shifted to his present territory on Muskellunge Lake five years later. He and his mate have produced a whopping seven chicks since 2011 on Muskellunge — eight if you include the rehabbed chick that we released on the lake in 2014 and that Clune and Honey readily accepted and reared as their own. (Yes…Linda has named the female too!)

I am a scientist. I try to stick to the data and not be influenced by emotions and superstition and unsubstantiated inklings. Nonetheless it cheered me when Linda reported that Clune had returned very early this year and already yodeled to defend his territory from a skittish intruder who dared to enter it. Despite my better judgment, I cannot help but think that this will be a productive year for loons in northern Wisconsin.

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LMG_3139 Clune n Honey Return

 

As this beautiful photo by Linda Grenzer makes clear, time is passing. Chicks have matured and left their natal lakes, territorial pairs have scattered. Juveniles and adults alike are preparing to head south. Most obvious to loon watchers, adults have shed their striking breeding plumage and donned dowdy winter garb.

Although we might mourn the significant loss of beauty that occurs among loons in the fall, molting is a pragmatic biological pattern. Feathers wear out with time and use, requiring replacement, so seasonal molting of some kind is essential to survival. But why do loons lose the white wing spots, the necklace and chinstrap, and the elegant black head? As usual, the answer is that we cannot be certain without experimental investigation. However, these prominent features of the plumage signal readiness to defend a territory and to breed. Hence, they are inappropriate and possibly costly signals to send during the autumn. An adult that maintained breeding plumage during the fall might attract the attention of others and trigger territorial interactions at a time when it should be feeding vigorously in preparation for migration. Moreover, the contrasting breeding plumage would probably make a loon more conspicuous to predators such as sharks, which could be costly during a long winter on the ocean.

The two loons in Linda’s photo are her breeding male and female — and two of our best-known individuals. They appear often in her photos, such as when 5 intruders came to call and when they refused to abandon their nest, despite merciless black flies. After all they had been through this year, it was a surprise to see the male (Linda calls him “Clune”) and the female (“Honey”) spend a short time together on the brink of fall migration, long after most pairs had dispersed. I find this photo poignant somehow. I suppose it symbolizes to me this pair’s unwavering unified front in the face of all challenges and changes that confront them.

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Sorry for the posts on back to back days, but I wanted to report on the status of the Jersey City Flowage male, released four days ago. He is looking healthy and diving normally, it seems, as this photo by Linda Grenzer suggests. Thanks, Linda, for tracking him down!LMG_0964

He has moved about a mile in the large lake where he was released, and has skirted the territory of a pair that nests in the lake. So, while it is far too early to pronounce him out of the woods, things are looking promising. It is remarkable to observe the severe injuries from which loons can recover. Let us hope that this bird — who has both the brightest bands in the study area and the calmest disposition — can add to the short list of loons that have flirted with death following fishing entanglement, been captured and disentangled, and recovered to become territory owners again.