small lakes

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LMG_2782 Muskellunge Chicks Hide from Intruders

Linda Grenzer’s striking photo from two weeks ago got me thinking about loon breeding success. The picture is a sight that will please loon fanciers — two big healthy 9-week-olds resting side by side while their parents circle with intruders. (The chicks are holding their legs out of water, as resting loons commonly do.) Since territorial pairs almost never lay more than two eggs or hatch more than two young, the photo depicts a monster year for the breeders on Muskellunge Lake. Despite black flies and raccoons (which threaten nests), eagles, muskies and snapping turtles (which attack chicks), and constant intrusions by competing adults (which seek to drive adult breeders off of their lakes), the male and female on this lake reared two chicks to adulthood. Quite an achievement!

For Muskellunge, 2016 marks the sixth year in a row of chick production. Ten chicks in all have been raised by the pair during this stretch (including one rehabbed chick we added to their singleton brood in 2014). While I am thrilled to see such an abundance of chicks come from a single lake, it is not the norm. As residents on most lakes well know, loon breeding is a dicey proposition.

Consider, for example, South Two Lake, a normally productive breeding lake where the sudden disappearance of two successful breeders after 2015 left the lake wholly without a pair in May and June of this year, until it was finally resettled by a male and female in July — far too late for nesting. Or look at the Boom Lake-Hodag Park territory, where the pair had fledged five chicks across the past four seasons until the male became entangled in fishing line in the spring of 2016 near Panama City, Florida and never reached Wisconsin. Baker Lake was a consistent chick producer until 2013, when a five year-old male settled there with an unmarked female; they have lost nests to predators each year since then. Most spectacularly, the productive pair on Blue Lake-Southeast weathered the storm of parasites, egg robbers and chick predators only to see the male lose territorial ownership to a young usurper, which resulted in the chick’s death. Finally, pity the pair on tiny Liege Lake or Wind Pudding-West where, despite successful territory defense and incubation, the parents were unable to locate enough food to raise a single chick past six weeks of age.

In light of the many hazards facing loon pairs, it seems remarkable that we ever see a photo such as the one above. As one might surmise from the preceding paragraphs, there are several requirements for successful breeding. Abundant food is essential, of course. Each year, many pairs attempt to breed on tiny lakes where food limitation prevents them from rearing even a single chick, let alone two. Nesting habitat is vital; lack of boggy or marshy shoreline or an island prevents many pairs from even attempting to breed. Two less obvious factors can make or break a breeding effort: 1) the ability of both pair members to maintain their breeding positions throughout the season despite an onslaught of young adults looking to evict them, and 2) the male’s familiarity with proven successful nest sites, which dictates whether the nest is positioned in a location likely to survive four weeks of incubation.

Some breeding pairs have everything going for them, so that they surmount all obstacles and raise chicks to fledging year after year. Muskellunge (see photo) is large enough — at 160 acres — that food abounds, and the lake features several shoreline zones that support nesting. The resident female is much larger than average and aggressively repels intruders that challenge her. She is paired with a tough 18 year-old male — a bird experienced enough to know the locations of multiple nest sites on the lake but young enough to be in good physical condition and not vulnerable to eviction. In short, Muskellunge Lake is currently in a “sweet spot” for raising chicks, like Townline, Manson, Little Bearskin, East Horsehead, and Buck Lake. Lakes that get on a roll like these produce a disproportionate number of chicks, which will mature, return, and sustain the population. In time, these productive territories will falter, owing chiefly to the loss of one or both members of the vigorous, experienced breeding pair. For now, though, let’s enjoy the bounty of offspring that these lakes produce and look forward to the emergence of new productive territories that will succeed them.

 

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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.

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It has been awhile since my last post. Sorry about that. With our study animals hunkered down in the Atlantic — mostly off of Florida — there has not been much to write about. But they are molting now, beginning to vocalize, and are readying themselves for a return to Wisconsin. Although the northern weather is not cooperating at the moment, our study animals will soon begin winging their way north.

Even after the summer, though, we accumulate data on our birds. How? By receiving reports of recoveries of our loons during migration and on the wintering grounds. Now, a “recovery” is, in essence, an unpleasant event. The term refers to a report of a bird banded with a U.S Fish & Wildlife Service metal band that has died, been found, and been reported to the Bird Banding Lab in Patuxent, Maryland. I get an e-mail from the BBL each time someone recovers one of the loons we banded. When I see the BBL address pop up on my phone, my pulse races, as I fear that one of our valuable breeding birds may have died. Each time we lose a loon that we have known and studied for 15 years or so, I grieve a bit. This happened two years ago when I learned that the long-time breeding male from Hancock Lake had died. More often than not the news from the BBL is sad but not devastating, as most of the recoveries are of first-year loons — birds we banded as chicks the previous summer that did not survive their first fall migration or winter. We are always sad to lose a bird we banded, but we understand that its first months of life pose a severe test for a loon, as it must complete migration, learn to forage in the ocean, and face a set of dangers to which it is unaccustomed.

Something positive emerges from recoveries. As we accumulate a record of which first-year loons have died and which have survived, we have a chance to confirm a pattern that we detected recently from our summer work. Young hatched on small, acidic lakes return to the breeding grounds at a lower rate than those hatched on large lakes of neutral pH. We do not yet know at what point this difference in mortality occurs. Do juveniles from small, acidic lakes fail to make it off of the breeding grounds? Do they die disproportionately during fall migration? Or do they tend to die in larger numbers after reaching the wintering grounds? Recoveries of these young birds during late summer, fall migration, and winter — as sad as they are — can provide us with the valuable answer.

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It is a struggle for chicks to get enough food to reach adult size. Jack Barr estimated in his 1995 paper that a breeding pair with 2 chicks would remove over 400 kg of food from a nesting lake during a summer. It is difficult to discern how that amount of biomass is related to the productivity of lakes and their ability to support loon breeding efforts, but Barr’s estimate makes the point that families  face challenges in finding enough fish and aquatic invertebrates to sustain their chicks.

The situation is especially dire on small lakes. As I have noted in the past, pairs using small lakes for chick-rearing tend to raise fewer and smaller chicks, which, in addition, are less likely to survive to adulthood. So it stands to reason that such pairs might avail themselves of any opportunity to make use of large lakes near their small breeding lake for foraging. Indeed, one or both pair members often leave their chicks for hours at a time to fly to and forage on larger lakes nearby. This behavior — while it seems like child abandonment! — probably makes sense in that it reduces the amount of food removed from the breeding lake, leaving more for the chicks, which do not have the capacity to fly elsewhere to feed.

If the situation gets very desperate indeed, then shifting of adult foraging to neighboring lakes cannot save the chicks. In such cases, the chicks themselves must be moved. In fact, an uncommon but regular occurrence is for loon pairs to move their chicks from small lakes with vanishing food supplies to adjacent, larger lakes that offer untapped reserves of food. Recently, both the Fox and McGrath pairs have shifted singleton chicks to large neighboring lakes (McNaughton and Little Tomahawk, respectively). The move offers the chicks a far more hopeful future.

But what of the move? Unable to fly, chicks must “skootch” on their bellies to cross land. Chicks on land are easy prey for mammals and eagles that happen upon them during land crossings, as they are weaker and smaller than adults. What is more, land crossings are not silent, stealthy events. Loon parents vocalize loudly when urging their young to make land crossings, which would seem to alert predators and increase the danger. Evidently, only loud, persistent vocalizations by adults are sufficient to coax chicks into venturing onto land, so lake shifts must be accompanied by blaring of bugles! Since adults often accompany chicks during land crossings, they are even more conspicuous to observers than chicks alone would be. The extreme danger confronted by loon families that abandon small nesting lakes emphasizes just how depleted food supplies must be in order to justify the move.

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Life is risky for loon chicks, especially on small lakes. Our work and that of others has shown that chicks on small, acidic lakes grow more slowly and that the beta (smaller) chick is often much smaller than the alpha chick. In such cases, the alpha chick commonly pecks its sibling, which gets less food from the parents, often falls behind the family group and frequently dies. Faced with certain death if they remain near their family, many beta chicks engage in a desperate act — they leave the family, strike out across land, and try to find another lake with a breeding pair that will accept and feed them. This is not entirely foolhardy, as breeding pairs with chicks will often accept additional chicks that join their families.

Most beta chicks that choose to search for another lake are doomed, of course. It is a longshot that a chick will: 1) be able to find a nearby lake and travel to it without meeting a terrestrial predator, 2) happen to find a breeding loon pair there, and 3) gain acceptance from the pair, in the event that they have a chick or chicks of their own. Still, if you face certain death, a “Hail Mary” such as venturing to a nearby lake might make sense.

In any event, beta chicks can sometimes be found along roads or alone  in lakes without other loons, and they frequently perish there. But recently an orphaned beta chick found its way to a roadside and was picked up and carried safely to Wild Instincts where it was nursed back to health. We then estimated the size and age of the chick, matched it with the chick of one of our breeding pairs, and released it with that family. Now, two weeks later, the foster chick seems to have been fully accepted by the family and is being fed by its foster parents and accepted by its step-sib. So this seems a rare story of a desperate beta chick getting a chance with a new family that might help it reach adulthood.