2016-07-31 01.32.29

Loon capture is a blur. We set out from our house at 8:45 pm, launch our small motorboat on the first lake, wait for nearly complete darkness, and catch any loon chicks and parents that we can net easily. By the time we have repeated the process four more times, we are rubbing our eyes, our weariness justified somehow by the presence of the sun lurking just below the horizon.

As an essentially negative person, what I often recall after a night of capture and banding are the physical demands of the process and my complete exhaustion. But there are dimensions of the work that are exciting and rewarding. Each loon is unique, and one never knows whether an individual will permit itself to be approached closely and netted or will be wary and elude us. So we experience many disappointments, but they are tempered by the occasional thrill of capturing an individual that, at first glance, appeared too skittish to catch.

The fruits of loon capture are obvious. By marking individuals and resighting them year after year, we learn about survival rates of adults and juveniles, territory fidelity, natal dispersal, and habitat preference. We glean a good deal of important information from these data. For example, survival rates of young and adults allow us to learn whether the  local population is increasing, decreasing, or remaining stable. And tracking of young loons from egg to first territory has revealed that loons develop strong preferences for breeding lakes that closely resemble their natal lake. Finally, capture is essential as a means to disentangle loons that have been run afoul of angler’s lines or lures.

This year’s capture exposed another distinctive pattern in loon ecology: the presence of ecological traps. An ecological trap is a breeding habitat that appears at first glance to be a good one but ends up being poor for reproduction. For example, a field might experience a burst of insect activity during early spring, enticing songbirds to settle there for breeding, but a crash in insect levels after eggs hatch might occur that suppresses the number of young birds produced. Two nights ago, we captured two chicks from two different lakes back to back. The first territory was a shallow 11-hectare portion of Wind Pudding Lake (my favorite lake name). The chick captured there was a five-week-old that weighed a scant 0.92 kg — less than half what we would expect from a chick of that age. Our daytime observations show that the chick’s parents are no slouches; they respond to its constant begging by making frequent dives and retrieving what food they can to feed it. Moreover, the chick itself dives often to forage. But this shallow lake, covered almost entirely by lily pads (which impair loon foraging), offers scant sustenance. I am afraid that the emaciated Wind Pudding chick will ultimately starve to death, as did the chick on nearby Liege Lake, another shallow lake choked by vegetation. Loon parents on small, acidic lakes struggle to rear even a single chick, whereas those on large lakes of neutral pH often raise two. This stark contrast was highlighted for us, as the lake we visited following Wind Pudding was 1373-hectare Lake Tomahawk. To be sure, loon parents on Tomahawk must steer their chicks through countless jet skis, water-skiers, anglers, and speed boats at all times of day. But vigilant parents are rewarded with abundant food for themselves and their chicks. The Tomahawk-Sunflower Bay chick held by Mina in the photo weighed 3.02 kg, yet it was only a few days older than the chick on Wind Pudding. Clearly the strapping youngster in the photo is heading for a healthy future and likely fledging.

Why on Earth would loons settle to breed on lakes that often provide too little food for their chicks? The answer might relate to the disconnect between nesting and foraging requirements. Alas, large lakes that contain many fish for loons often lack the islands, emergent marshy bays, and bogs that allow loons to avoid egg predators like raccoons. So loons looking to breed seem to be lured onto small, marshy lakes that yield successful hatches but doom their offspring to starvation.

The goose population has been increasing in northern Wisconsin. Ten years ago, a Canada Goose was an infrequent sight on one of our study lakes. Geese were confined chiefly to a few large lakes and seen overhead only as they migrated northwards. But no more. Now we encounter adult geese and often pairs with goslings on about half of our study lakes.

Apparently the increased availability of waste grain from agriculture, the proliferation of lawns, and increased temperatures have fueled the explosion in goose numbers, which has the potential to impact loon reproductive success. You see, geese and loons both prefer nesting sites safe from mammalian egg predators like raccoons and foxes. Such sites are often on islands and are limited in number. If a small island offers the only available safe nesting on a lake, goose and loon pairs are both likely gravitate to it.

The problem is not merely that loons must now compete with geese for nesting sites; geese actually get “first dibs”. While both loons and geese incubate their clutches for about four weeks, geese initiate their clutches two weeks or so in advance of loons. (The earlier onset of goose nesting is evident right now in our study area, as many goose pairs are rearing their broods of two to six goslings, while the earliest loon nests will not hatch for another week or ten days.) On occasion geese and loons nest within a few meters of each other on islands — as we observed on Oneida Lake a few years ago. Coexistence between the species is possible. But the presence of a sitting goose appears to discourage loons from nesting nearby, which often forces loon pairs to select sub-optimal sites for incubation.

Consider the plight of the Clear Lake loon pair. The safest, most desirable nest location on Clear Lake is a small shrubby island off of the public boat landing. Loons have shown a strong preference to nest on this island during most years. This year, the geese got their first, and the loons had to settle for a new nesting location on a long peninsula about two kilometers south. They may hatch chicks off of this peninsula, but the site is not offshore, like the shrubby island, so it is clearly vulnerable to mammalian egg predators.

I am optimistic that this spunky loon pair will be able to pull off a hatch. As can be seen from our shaky video, the male (on the right in the video) is still working on improving the surrounding nesting area, and the pair has a well-constructed nest with two eggs (visible to the left of the female, after the camera pans left). Still, this well-constructed nest will not protect them from a scavenging raccoon that ambles by.



LMG_5401 Crystal Lake NestOn its face, the photo is comical. A loon sits on its egg on a swim raft, a meter from an American flag. A garish McMansion is visible on the opposite shore. Few photos of the common loon are more at odds with the image of the species as a symbol of the northern wilderness. Yet Linda Grenzer’s photo of the nest on Crystal Lake is a poignant portrait of the situation faced by most territorial pairs in north-central Wisconsin.

Many popular accounts describe common loon populations as holding on for dear life. To be sure, loons are threatened by shoreline development, which reduces nesting habitat. Recreational fishing and boating kills many adults and chicks prematurely each year. And methylmercury in the food chain, swollen by coal-based power production, likely impacts the loon population as well.

Against all odds, however, loons appear to be holding their own in northern Wisconsin. Despite consistent losses caused by collisions with boats and entanglement in fishing lines, populations have bounced back in recent decades. The surprising resilience of loons seems to result from two facts. First, loons prefer to nest on small islands and on boggy and marshy habitats that humans avoid. Thus, loon pairs continue to produce young on lakes that are virtually encircled by human dwellings. Second, as illustrated in the photo, loons tolerate — and rarely even benefit from — human alterations of aquatic habitats.

The pair on Crystal Lake, whose nest is pictured, were in a real bind. Crystal is a very pleasant lake, but it lacks islands — the nesting spots most favored by loons — and also features neither bog nor marsh. Previous nesting attempts by the male (reared on nearby Muskellunge Lake in 2006) and a parade of 3 or more different females since 2011 ended in abject failure, the eggs an annual donation to local raccoons. Although they crawl onto it with great difficulty and complete loss of dignity, the Crystal pair decided a few weeks ago to place their nest on a low-lying swim raft. The raft is high above lake level and not equipped with any sort of ramp to assist small chicks in re-mounting the raft once they have entered the water, so we are concerned that the chicks will not be able to return to the nest (to be kept warm by a parent in the first few days of life) once they have left it. Still, the likelihood of hatch is good, and Linda and her helpers placed nesting material on the raft to keep the eggs from rolling off. We are hopeful that the loons can cope with the problem of nest height just as they do with a host of other anthropogenic obstacles each day in northern Wisconsin.

I shall keep you informed. If the Crystal pair can hatch and rear their chick to adulthood, they will be a vivid example of the capacity of loons to adapt and thrive in an environment thoroughly dominated by another species.

LMG_4295 one day old chick on back

After 2014’s disastrously low chick production owing to black fly infestation, I was anxious that breeding success would rebound in 2015. My concern defied reason. Loons are long-lived, of course, and a few or even several consecutive years of below-average chick production are not enough to have a lasting negative impact on the population. Still, blinded by the irrational human tendency to infer long-term impacts from short-term patterns, I wished to see our loon pairs come back and raise many chicks in 2015, just as Linda Grenzer’s pair has (see photo).

This year is shaping up to be a very good year indeed. As of this date, 31 of the 120 territories we follow (25.8%) have already hatched chicks. In contrast, only 2 breeding pairs (of 112 pairs; 1.8%) had chicks on this date in 2014. That is an unfair comparison, because the black flies devastated early nests in 2014. However, 2013 was a rather good year for chick production, and in 2013 only 20 of 108 pairs we followed (18.5%) had chicks on this date. Although these data are slightly biased because of yearly differences in nesting schedules — that is, 2013 was a slightly later year than this year — 2015 should be an awfully productive breeding season for loons in northern Wisconsin. As a scientist, I am breathing a huge, sheepish sigh of relief!

LMG_3382 JCF Male

We have almost completed the first round of visits to study lakes. Our ever-expanding list of lakes makes this no mean task, as our list has grown from 95 territories in 2008 to 123 this year. Kudos to the field staff of Joel, Eric, Chris, and Linda (whose photo appears above), who have worked hard to visit lakes and ID loons from leg bands — and also Al on West Horsehead and Pat on Silver Lake, who have e-mailed with data from their lakes.

Of 162 banded loons on territories as of late 2014, 141 (or 87%) have reclaimed those territories this spring. Among 21 missing territory holders from 2014, 4 have been resighted in 2015, but were apparently evicted from their territories early this year. Thus, the minimum survival rate from 2014 to 2015 for territory holders is about 90%. This figure agrees closely with survival rates calculated from Wisconsin and elsewhere within the breeding range.

Sky-high return and survival rates for our population highlight a simple pattern in the life history of common loons. In ecological terms, loons are “K-selected”. That is, they are long-lived, take several years to reach sexual maturity, produce few offspring during their lives, and invest heavily in parental care for the few offspring they do produce. Loons are not explosive reproducers that “shot-gun” many offspring out into an uncaring environment in hopes that a few survive. Rather, they work hard to maintain ownership of their breeding territory, eke out one or two chicks a year (in a good year!), and defend their chicks vigorously against all comers!

By any reasonable measure, 2014 has been a dreadful year for loon reproduction. Even if we capture every remaining loon chick that we know of, our total number banded will be almost exactly half of last year’s total. Clearly, the black flies hit the loons’ breeding efforts in the mouth, and they could not recover. Still, it is only one year. As my work has shown me over the past two decades, breeding success is a roller-coaster. In fact, if you combine last year’s bumper crop of chicks with the withered output of this year, the message is that loons are producing enough chicks to sustain the population. So all is not lost.

There have been a few bright spots this year. Though we were alarmed in early June when the Jersey City Flowage male ingested a fishing lure and became hopelessly entangled, the folks at REGI were able to save the bird, he was released near his old territory and recovered — except for possession of his territory! The REGI folks were brought an emaciated chick found by a roadside that they fed back to reasonable health and that we were able to foster successfully to a loon family that has raised it as their own. We recently banded both this fostered chick and its sibling, a true biological chick of the pair. Both chicks have become big healthy, strapping young birds, thanks to their parents’ tireless efforts.

In short, life goes on. I am confident that we will long remember 2014 and not wish to repeat the experience. But perhaps we should best remember 2014 as a year that, while dismal for chick production, was balanced out by strong reproductive years surrounding it and did not pass by without a few cheerful tidings.

black fly impact


Since 2014 marked by far the most intense explosion of black flies in recent memory, I wanted to look at how loons are faring reproductively this year compared to last. It has now been over a month since the peak of “black fly season”, which was miserable for loons but lasted only about a week. Yet the flies were thick enough and their outbreak coincided so closely with the start of incubation for most pairs that about 70% of all loon pairs in our population abandoned their nests.

It seemed certain that the epic abandonment of early nests in 2014 would negatively impact the number of chicks produced by our population. And it has. Based on my analysis of 96 territories covered in 2013 and 2014, I have the following results. Last year, 41 pairs  had hatched chicks by 30 June, while 14 had nests close to hatching, 10 had early nests whose outcome was uncertain, 21 pairs had failed for the year, and 10 pairs had never nested (to our knowledge). In 2014, the numbers were 6 chicks, 30 promising nests, 15 early nests, 21 failed pairs, and 14 pairs without no nest during the season.

The disparity in chicks produced is alarming, of course. This is the most important number. The picture gets a bit rosier when you crunch the numbers and recognize that many pairs currently on nests will eventually hatch chicks. Based on an assumption of 70% hatch rate among pairs in the “likely hatch” group and 40% in the early nest stage — perhaps slightly optimistic — the total estimated chicks produced in 2013 and 2014 are 54.8 and 33.0, respectively. To put it another way, about 57% of all pairs reared chicks in 2013; 34% will in 2014. This is a decline of 40% in the number of territorial pairs producing chicks.

Now, we need to step back here. Loons are long-lived animals, and most pairs that failed to raise chicks, owing in large part to black flies, will try again next year. So, in the big picture, the decrease in rate of chick production is not so awful. In a few more years, we will look back on 2014 as just a worse-than-average year for loon chicks, not a year that threatened to end loon life as we know it. But it is hard to be very upbeat at the moment.

It is still early, but I can already see that 2013 will be a good year for chick production in northern Wisconsin. Thirty-nine of about 120 pairs that we follow have hatched chicks already, and 24 other pairs still have active nests and might produce chicks. Since it is always a dicey proposition to incubate eggs for four weeks without a raccoon eating them or some other calamity befalling them, having almost half of all pairs rear chicks successfully is cause for celebration. We are feeling good about the population.