Male Loons Senesce, While Females Do Not – A Rejoinder to My Mother-in-Law

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My mother-in-law came to visit us in California last week. She is an avid follower of my blog (!), so I was excited to learn what she thought of my most recent post. She hated it. That is, she said of my report that loons get old:”I could have told you that!”. Naturally, I was deflated. To think that 23 years in the field had produced a result deemed pedestrian by my mother-in-law!

While one might argue that she is family and should have been blindly supportive of my work, Joanne is right, in a sense. As humans, we are accustomed to old age and deterioration of the elderly. But, as I tried to explain, senescence is not the rule in all animals. Birds are unusual, in fact, as they exhibit relatively late and gradual senescence compared to mammals of similar body size. So the striking and rather sudden senescence that I reported recently is mildly surprising for the taxonomic Class Aves. Still, I think I agree with Joanne that it is not terribly shocking!

But there is more. The blog where I reported senescence in adult loons was based on an analysis that pooled male and female individuals. Since then, I have analyzed the sexes separately. The results are striking. As the figures below show, the senescence that I reported for the species as a whole (measured by decreased survival) is driven purely by males. While males and females that have been on territory from 1 to 14 years survive at a rate of 95% annually, males with 15 or more years on territory only survive at a rate of 58%. (Old females show a very modest decline in survival to about 91%.) Since males and females that settle on territories are almost always 5 years old or older, we can say with confidence that territorial males in their twenties drop like flies; females, in contrast, are survivors.

young males and females do not differ in survival rate

old males die at a much higher rate then females

I don’t know if my mother-in-law will be impressed by these data. For the moment, I must be content in the knowledge that I have found a strong and highly unusual survival pattern. As a behavioral ecologist, this stunning disparity leads to several other questions. Among them are: 1) Do older males exhibit any other evidence of deterioration such as in territory defense, chick production or body condition? and 2) Does the high mortality of older males cause the adult sex ratio to swing towards females such that females are forced to wait years before finding a mate? Rest assured that I am exploring these possibilities with great enthusiasm.

 

Winter for the Loons — and Me!

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I have been back in California for some months now, my research in Wisconsin a distant memory. A stroll to the end of the pier at Newport Beach changed that. Several of my study species — unbanded animals that probably belong to breeding populations from Alaska, British Columbia, or Alberta — were foraging contentedly off the pier’s end, as fishermen cast their lines all about them. The fishermen appeared to avoid casting near loons, so I was not alarmed by what I saw. Loons are usually adept at avoiding fishing lines (though not always). Furthermore, an ecologist would not be surprised to see loons sharing a fishing hole with anglers, since they are competitors for the same small fish — mostly smelt and mackerel.

Common loons were not the only species diving and pursuing small fishes among the sea lions and occasional pod of common dolphins. It was a treat to find this juvenile red-throated loon out in the waves as well.

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Back home in Irvine I am crunching data, as I do habitually in the off-season. I feel some urgency at the moment, as I am about a week away from having to give a talk on my findings at the Winter Animal Behavior Conference in Colorado.  I will be more positive in a week or so, but I have already confirmed senescence in two different respects. First territorial common loons older than 20 abruptly begin to show much higher year-to-year mortality (roughly 20% annual mortality from 20 on; only 6% mortality up to 20 years). Second, territory holders 20 and older also stand a much greater chance of losing their territory through eviction (again a 20% rate of loss) than do those younger than 20 (12% rate of loss). In the coming days I will explore whether the sexes differ in these respects and whether old territory holders make any behavioral adjustments to this apparent decline in health and fighting ability.

Our Article Is “Editor’s Choice”!

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Several months have passed since Gabby Jukkala’s and my article was accepted for publication in the Journal of Avian Biology. We have been anxiously tapping our feet while the wheels turn and our article comes out in the journal. This has just happened. You may now view our article here.  Gabby and I are thrilled that: 1) our article has been selected as “Editor’s Choice” for this issue of the journal, 2) Linda Grenzer’s nice photo of the female on her lake with a chick from 2015 is the cover photo for the issue (and a second is featured in the blog spot), and 3) the journal has included extra information about us and our article on their website here.

I have already described the findings we report in the article, so I will not rehash those here, but do take a look at the article, which the journal is making available free of charge, since it is “Editor’s Choice”. It is a very small honor, in fact. Still, these days I am often on the Newport Pier, as that is a good local birding spot and I must prepare for the Ornithology class I am teaching this fall. Whenever a member of my study species wanders nearby, as it forages for mackerel or smelt, I find myself smiling a bit more strongly than before.

A Tough Science Lesson: The Sudden Disappearance of Breeding Habitat Preference

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LMG_8014 Fall Molting Loon

Some months ago, I reported with excitement that loons that leave their first territory — usually because they are evicted from it by another loon — have a strong tendency to settle on a second territory with similar water clarity to the one they left. It was a striking finding and one that would have added a fascinating story to ecologists’ limited understanding of how animals choose where to settle once they reach adulthood. That pattern, which initially seemed a robust one, has turned out to be trivial.

Let me explain. When loons are forced to shift from one territory to another (or do so voluntarily), they typically settle on a second territory very close to their first one. Often they move to the lake next door or even settle on a different part of the same lake. What we thought we had found was that those “resettlers” carefully choose to settle on second lakes of similar clarity to their first lakes. But such a pattern is tricky to show conclusively. In order to do so, one has to determine how similar 2nd lakes would have been to 1st lakes if loons had settled at random and compare the actual pattern to random settlement.

The problem we ran into was spatial autocorrelation. Spatial autocorrelation simply means that within a large area, two points that are physically close to each other resemble each other more closely than two points that are farther apart. It turns out that lakes of similar clarity tend to be clustered. That is, if one lake is clear, then its neighboring lake is likely to be clear also. The same is true of murky lakes. So while we thought that loons were purposely choosing to settle on second lakes of similar water clarity to their first ones, they were merely settling on lakes near their first one which happened to be similar in clarity to their first because of proximity. In other words, we have no evidence that choice of lakes is non-random.

It took us a long time to discover the error. In fact, Mike Palmer and I had written up this finding and submitted it for publication before we realized — after running a new analysis requested by a reviewer — that spatial autocorrelation was solely responsible for our result.

Naturally, I am feeling a bit like the female on Muskellunge Lake, photographed recently by Linda Grenzer. A month or so ago, this bird and I were on top of the world — she because she and her mate had just fledged two chicks (a bumper crop for loons) and was in her showy black and white formal attire; I because I had an exciting finding that I could not wait to share with colleagues. Now the luster of the recent past is gone. The female’s chicks have dispersed to fend for themselves, she has lost her gaudy summer plumage, and she is about to resume survival mode during migration and winter. I have lost my thrilling discovery and will have to pick myself up, dust myself off, and attack some other scientific question.

Luckily, the Loon Project supplies an endless string of questions. One that tantalizes me at the moment: do chicks that fledge and leave their natal lakes to forage on other lakes nearby favor those that resemble their natal lakes? Such a result, if it occurs, would dovetail nicely with our finding that the first lake a loon ever settles on as an adult (at 4-7 years of age) tends to be strongly natal-like in size and pH. This result (he adds quickly) is not confounded by spatial autocorrelation, because first lakes tend to be far from natal lakes. At any rate, I shall let you know what I find.

A Rough Week for “Fledged” Chicks

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When loon biologists measure reproduction, they often count chicks older than five or six weeks of age as having fledged. This is reasonable. Even though loon chicks remain dependent upon their parents for 11 weeks or more, almost all chick mortality occurs in the first few weeks of life. If a chick makes it to five weeks, it is almost certain to make it to adulthood.

Not so during this past week. As the unpleasant photo by Dan Pagel shows, one of the the Blue-Southeast chicks died quite violently several days ago after a sudden attack by an adult. Based on the photo and the swiftness of the death, we suspect that severe heart or liver damage caused the death. Since Dan was a few hundred meters away when the murdered Blue-SE chick IMG_3960vicious attack occurred, he was unable to identify the perpetrator. Regardless of what loon committed this act, it comes as a shock. The departed chick was over twelve weeks of age, healthy, and off by itself feeding when it fell victim to the brutal assault. Twelve weeks is much older — I believe as much as eight weeks older — than we had ever observed a chick to be killed by a foreign adult. In light of the tempestuous territorial scene at Blue-Southeast recently, it is tempting to view this chick as a casualty of the conflict that caused its father to lose his territory. Certainly, the new, unmarked male that had taken over on Blue-Southeast and had already been observed to peck the chicks in his first weeks of ownership is a suspect. A second possibility is that the chick carelessly strayed into the west territory on Blue Lake and was attacked by a member of the West pair for territorial reasons. But territory defense is scant and subdued at this time of year, so that explanation is problematic.

I was still coming to grips with the events at Blue Lake a few days ago when I received a second piece of news, equally discouraging. One of the chicks at Buck Lake, near Rhinelander, had died. The cause of death in this case is less clear; the chick’s leg became injured a few weeks ago — a lake resident reported that a snapping turtle latched onto it! — and the chick was not able to move about effectively afterwards. Like the Blue chick, the Buck chick was far past fledging age, having reached 11 weeks.

What can we conclude from the co-occurrence of two deaths in very large and healthy chicks? I think these two unfortunate events simply remind us that, while chicks that have reached near-adult size are far more likely than 2-3 week old chicks to survive to adulthood, they are still young animals. As we have reported in a scientific paper, loons suffer a higher rate of mortality during their early years. Adult loons have had years to hone their ability to feed themselves and cope with environmental hazards, including conspecific attacks; youngsters are still getting it down.

From the Ridiculous to the Sublime – The Season at Crystal Lake

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LMG_7851 Walter n Sammy

The season began inauspiciously at Crystal Lake in Lincoln County, which is along the southwestern fringe of our study area. Though it is a pleasant, rather clear lake, Crystal offers no nesting habitat for loons. Loons love most of all to place their nests on islands but also make use of boggy or marshy areas, which seem to provide safe havens from egg predators like raccoons and skunks. Crystal offers none of these options, as its shoreline comprises upland habitat and is thus easy for a hungry mammal to patrol. In fact, Crystal is such an inhospitable place for loons to breed that loon eggs vanish from its shoreline almost as soon as they are laid.

So I had mixed feelings to see a six year-old male hatched on nearby Muskellunge Lake settle to breed on Crystal in 2012. On the one hand, I was pleased that the young bird had found a territory after wandering around the local neighborhood of lakes for the three previous years. On the other hand, a settler on Crystal seemed doomed to reproductive failure. But the male and his parade of mates (three females in five years) persisted in their breeding efforts. As I reported earlier this summer, the male and his new mate in 2015 (she still licking her wounds from a recent eviction from neighboring Deer Lake) took a new approach to nesting in 2015 by choosing to place a nest on a swim raft off of a resident’s dock.

LMG_6672 dad n chick on raft

Once the egg had been protected from rolling off of the raft with a ring of rubber cut from an old tire and some natural nesting vegetation (thanks to quick thinking and skillful craftsmanship from Linda and Kevin Grenzer), things began looking up for the breeding pair. Although it was a bear for the male and female to clamber up onto the swim raft to incubate the egg, the setup seemed little different from the artificial nesting platforms that many lake residents place on the lake each year for their nesting pair to use. Given the virtually impregnable location, the probability of hatching a chick had gone from almost zero to near one.

As expected, the chick hatched successfully, and though it had trouble maneuvering around the rubber-reinforced nest (as Linda’s photo shows, above), it left the nest with its parents within a few days. Only when Linda reported that Crystal was experiencing a burst of territorial intruders — one of whom, by chance, was the mother of the Crystal male and hence the grandmother of the chick — did she and I become panicked. Intruders pose a grave hazard to small chicks. Would the pair that had so miraculously pulled off a hatch turn around and lose the chick to an infanticidal visitor? The threat was not trivial. As Linda’s remarkable and chilling photo shows, the Crystal parents broke a very basic rule of loon parenting: never permit intruders near your chick when it is less than 2 weeks old.

LMG_6709 Two intruders approach parent n chick2

Yet the chick survived this brush with death. Nourished by a healthy supply of fish from the lake, the chick grew so rapidly that we were able to band it at three weeks of age, much younger than is usually possible for loon chicks. It has continued to flourish since capture. Now, at roughly 8 weeks of age, it looks like a 10-week-old, as the opening photo attests.

I have a tendency to dwell on disasters. Confronted with a large set of events — some positive, some negative — the latter seem to stick with me longer, leaving me with a sense that things are not going well at present and might not go well in the future. Yet at the end of a season when many breeding loons flirted with disaster — and one died — the story of the plucky Crystal chick stands as an odd and memorable exception.

Our Thirteen Oldest Loons

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Recently, Eric, a second-year team member who is experienced at reading colored leg bands, ran across our oldest loon. This male, evicted in 2007 from Little Bearskin Lake, has been cooling his heels in Bearskin Lake since his displacement and shows no indication of regaining a territory. “Blue over Silver, Yellow only” produced 14 fledglings during his breeding career, 7 of which also bred in the study area. That level of chick production places him among an elite few in our study population.

Blue over Silver, Yellow only’s age sets him apart from all others. He is at least 28 years old, because he was banded as an adult breeder, which means he was at least 4 in 1991. He may be in his 30s. But a number of other loons that we have marked during the study approach this male in age — and three exceed him in productivity. The female on Upper Kaubashine (“Silver over Yellow, Red over Green”), for example, is 27 years old at a minimum. (Females first breed at no younger than 5 years of age, so her estimated minimum age is one year older than if she were a male.) She can boast having bred with four different partners on four different lakes, spanning two counties. The 25+ year-old Townline male, “Silver over Red, Orange over Green”, is unrivaled in terms of stick-to-itiveness, as he has held the Townline territory since at least 1994 — and still owns it. He has reared 16 chicks to fledging during his tenure, if we throw in the two from this year. Only two loons have raised more young: the current Oneida-West female (19 fledglings and counting on Oneida-East and Oneida-West) and the former Hancock male (17 fledglings from 1993 to 2009).

Although it is fun to gawk at the age and breeding success of certain star individuals, my quick analysis of the study’s oldest loons reinforces another point that I have made before — and one with substantial scientific importance: females are the ones that generally live to a ripe old age in loons. The reason(s) for this gender disparity are becoming clear. Males seem doomed to die young because of their participation in dangerous battles, and perhaps also their unfortunate proclivity for attacking fishing lures and baits. Inspection of the table above certainly makes one wonder whether males should rethink their high-risk approach to both territory acquisition and foraging. Then again, maybe there are compensating benefits that offset the costs.

Blue Recovery

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If you are following the events on Blue-Southeast, you will recall that the male there, who was caring for two large, healthy, 5-week-old chicks, was evicted and seriously injured by an unbanded male, who drove him off and seized territorial control. The new male was an indifferent stepfather, initially pecking at his stepchicks and then simply ignoring them. Meanwhile, the displaced father licked his wounds on the west side of the lake and waited for the situation to improve. Things did get better; after a few weeks of limited interaction with the female, who was preoccupied with rearing her two voracious youngsters, the new male drifted away, permitting the displaced male, who quickly regained his health, to resume parenting and rejoin his mate.

While I am delighted to see the old, evicted male pick himself up, dust himself off, and recover his position, the behavior of the usurping male on Blue-Southeast presents a puzzle. Why would an outside male hurl himself into a violent, dangerous battle, win a new and productive territory, and then relinquish it shortly afterwards without a fight? We do not understand such behavior well. However, it is possible that a young male that is physically superior to a another male with a territory can battle and defeat that male without great danger, settle and live within the territory for a time, and then decide that the breeding space does not suit his needs. I think that the preferences of loons for natal-like lakes and, later, lakes of certain clarity, might hold the key to understanding this curious behavior.

We will keep collecting data in an effort to understand why loons fight fiercely for territories and then sometimes give them back to owners. Meanwhile enjoy this video of the Blue-Southeast female enduring relentless begging by one of her chicks as she forages for it.

Why Fishing Entanglements Might Hurt Loons More than We Think

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Two days ago we learned that the male on Hilts Lake and the female on the East Central territory on Nokomis Lake have become the latest angling casualties in our study area. The Hilts male swallowed a lure or bait and is dragging line from his bill; the Nokomis-East Central female has line wrapped around her left leg, which she now carried behind her. We are dismayed for the two loons involved, of course. The male on Hilts is among our tamest; since 2007, he and his mate have permitted us to approach them closely without alarm so that we can record an hour of their lives every week or so during the breeding season. Each of us looks forward to visits to Hilts because of the relaxed pair we encounter there. The Nokomis-East Central female too permits us to view her and her mate and young from close by. She contrasts markedly with her mate, who forces us to view from a distance of 50 meters or so to avoid getting an earful of alarm calls. When we spy a lone adult and chick from a distance on Nokomis-East Central, we keep fingers crossed that it is the docile, approachable female, not the male, who happens to be guarding and feeding the chick. (Good news: Seth reports that the Nokomis-EC female leg appeared to be dragging no fishing line yesterday, so perhaps she is out of danger.)

The list of loons ensnared in fishing tackle is longer each year. Observations and reports of this kind have become an unrelenting and disheartening drumbeat. In the early 2000s, close encounters between loons and fishing tackle were anomalies that I wondered about almost dispassionately. Each angling casualty brought sadness and frustration, of course, since one becomes attached to the loons. But such events were so uncommon that I shrugged the losses off as the inevitable consequence of habitat overlap between loons and humans. The steady increase in entanglements in recent years has sensitized me. These days I brace myself for the several – perhaps I should change that to “many” – that will occur during the season and wonder how we can assemble a team to rescue victims without compromising the behavioral and ecological goals of the research. In fact, I have begun to prod Project LoonWatch in hopes of encouraging them to put together a loon rescue squad – a group of 3-5 folks that can remain “on-call” during summers to assist birds injured by human activity.

And I have begun to worry about the loon population. Loons are clearly getting caught on fishing lines more often than before. This makes sense, as fishing activity continues to increase in northern Wisconsin. (It might also be the case that the proportion of inexperienced anglers – those likely to lose lures and fishing line in the water and not make efforts to retrieve and discard tackle that they lose – has increased.) Loons did not evolve in an environment with monofilament line, live bait and lures that mimic small aquatic creatures. Hence, they have developed no system for avoiding these hazards. If the number of loons swallowing and blundering into fishing tackle continues to increase, will so many adults die that the population cannot sustain itself?

A quirk of fishing entanglements makes the situation a bit more severe than it might first appear. As the cases of the Hilts male and Nokomis female illustrate, males and female loons are differentially affected by fishing. For reasons that we do not understand, males appear much more likely than females to ingest lures and baits, as the Hilts male did. We do not understand this difference, although one might speculate that males, having larger bodies to sustain, are less picky in chasing and consuming underwater creatures than are females. In any event, both sexes seem to be equally prone to getting monofilament wrapped around their wings or legs, but males are more threatened by lead-based tackle (sinkers and jigs) — which poisons them and kills them quickly – and by hooks that damage their throats and prevent them from opening their bills and feeding themselves. In short, males are more apt than females to fall victim to fishing tackle and in a way that is likely to kill them.

Why should we care if adult male loons are more vulnerable to anglers? Because, weirdly, males choose the nest site where eggs are to be laid and cleverly reuse nestsites where they have hatched eggs successfully in years past. So males are a reservoir of information about how breeding pairs can best use the nesting habitat within their territories to produce young. When an established, experienced male from a productive territory is replaced by new male (because of death or eviction), the new male does not know where to place the nest and must learn by trial and error. In constrast, when a female is replaced, efficient reproduction can continue uninterrupted, because the identity of the female has no impact on nest placement.

Thus, I grieve for the Hilts male not only because he is a sweet bird who permits us to watch him without complaint but because his demise will cause a new, ignorant male to settle, who must blunder from one failed nestsite to another before he discovers a good one that he will use year after year. And his years of inept breeding will subtract many offspring from the population.

Not Out of the Woods, but…..

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image1Chris checked in on the Flannery-Velvet chick today. The chick, whom lake residents call “Houdini” because of his ability to escape certain death, continues to inhabit this odd world where it is necessary to hide under piers and avoid adults — rather than fraternize with two parents who feed him to satiation. When his mom is not bonding with a new male up on Flannery so that she can prepare herself for future breeding attempts, she spends time with him down on Velvet. Today Houdini begged from his mom repeatedly, but he also foraged for himself during a considerable period.

The photo above, generously supplied by Hugh Jones who lives on Velvet, is notable for two features. First, it shows a chick that is in full adult-like feather. That is, it has outgrown its chicklike, downy plumage and assumed adult attire. This fact, of course, is comforting, as it shows that the chick is getting the nutrients it requires to mature and prep itself for independence and migration to the wintering ground. Second, however, the chick continues its retiring ways. It has learned to avoid adults, because of the occasional beatings it had received from its stepdad. So it seeks protection, using whatever piers and pontoon boats will give it cover.

We have never witnessed a situation like this one. In all other cases, chicks that lost their fathers were either: 1) several weeks old and recipients of abundant feedings from their mothers, or 2) summarily ignored by their stepfathers and permitted to grow and mature without interference. Since we are in uncharted waters, we can only be cautiously optimistic. All we can say is that Houdini — whom LP personnel know attactionately as “white over white, pink over silver”, from his leg bands — continues to pass developmental milestones despite daunting obstacles.

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