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.

 

2016-01-09 20.55.16-2

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.

2016-01-09 20.53.47-2

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.

Screen Shot 2015-08-20 at 1.20.25 PM

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.

IMG_4317

“Wow”, Lainey said, “that band number is right next to the female we caught last night on Sherry”. She was right; the adult male from Skunk, which we had just netted and whose band number I was reading aloud to Lainey for data entry during banding, had a number imprinted on his aluminum USGS band that followed immediately after that of the Sherry female from the previous night. The reason for consecutive bands is that the Sherry female is the mother of the Skunk male and was caught and banded with him a decade ago (less two days) on Sherry Lake. I remember July 31st, 2005 on Sherry vividly, because I was equipped with a video recorder on top of a helmet with which we recorded the capture process for research presentations. But the recapture of mother and son on back to back nights ten years after we had first marked them has also caused me to reflect upon several key features of loon biology that have become familiar to me through my work.

First, loons live a long time. In this twenty-third year of my work, I still encounter birds in the study area that were on territory, as adults, when I first started covering them. Females, in particular, are survivors. While males have rather high mortality –partly owing to their proclivity for battling dangerously — females linger. When their mate dies, females find another; when a female is evicted unceremoniously from her territory, she stoically moves to a new lake nearby and awaits a chance to re-insert herself back into the breeding population. So it goes with the Sherry female whose worn-out band from 2005 is pictured on the bottom in the photo. She was “widowed” suddenly in 2009 (a possible eagle kill) but hung onto her territory and was joined by a new male in short order, who has been her mate since.

Second, young males do not disperse far from their natal lakes to breed. The Skunk male, from whom we removed the top band in the photo last night, moved about 15 miles from his natal haunt, Sherry. That dispersal is, actually, a bit longer than average for males, many of whom settle to breed on a lake adjacent to where they hatched years earlier. Short-distance male dispersal is essential to my work; without it, I would not have a large marked cohort of 2 to 5 year-olds of known age and natal origin in the study area at all times whose territory settlement strategies could be investigated. (At last count, we had seen 295 adult loons in the study area that were marked originally as chicks.)

Third, loons vary tremendously in their behavior towards humans. My assistants and I dread the Sherry female, because she is the most skittish individual we know. She cannot be approached easily within 100 meters on the water; she tremolos (i.e. alarm calls) incessantly when a chick is present and a canoe appears on the water. In fact, my assistants tell me that she begins to tremolo in anticipation of a canoe being placed on the water and that they have begun a strategy of hiding behind bushes and trees along the shoreline in order to make observations of her when she is with the chick. (Fortunately, Sherry Lake is tiny, so this observation strategy is workable.) I joked that we should wear camouflaged clothing when visiting Sherry; my assistants did not find this funny. Oddly, the Sherry female’s mate is among the tamest loons we study and never tremolos at us when we collect data there.

The great variety in loon tameness is a topic of great interest to us, as I have mentioned. It amazes me that an adult such as the Sherry female could react so strongly (and, it would seem, maladaptively) to humans, which she encounters constantly. Doesn’t she waste energy with her fruitless calls? Shouldn’t skittish birds like her leave fewer offspring and live shorter lives than other adults who tolerate humans without constant complaint? If so, she is not a good example of the pattern, as she has behaved this way for the ten years we have known her while cranking out chicks. Indeed, the Sherry female and the Oneida-East male, another vociferous but fecund individual with whom my staff has to cope, make me wonder if I have got it backwards. Maybe loud-mouthed loons warn humans away, lessening the likelihood of injury to themselves and their brood, and are rewarded with high evolutionary fitness.

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!

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.

A lot can happen in a short time, it seems. I have spent only three days in the study area so far, but already we — Joel, Eric Andrews and I, and our incredible citizen scientists Linda Grenzer and Al Schwoegler — have found 8 active nests. Considering the territories we have visited recently and those we have not, I estimate that about 15-20% of all pairs in the study area are already incubating. Clearly the pairs have shortened the window between ice-out and egg-laying in order to compensate for the very late spring this year. I suspect this is possible, in part, because females were able to recoup much of the energy consumed during spring migration by foraging for weeks along rivers in the study area, before their breeding lakes opened up. That is, the extra foraging time near their territorial home apparently compensated for the foraging time that would normally occur on their territory.

Territorial turnovers have been common this spring; many marked pair members from 2013 either failed to return in the spring or did return but were evicted from their territories. The evicted birds include a young “ABJ” (“adult banded as a juvenile”; meaning a loon we banded as a chick) male from Schlect Lake. This ABJ male, hatched on Fox Lake in 2005, produced two chicks, of which one fledged, in 2012. But in early 2013, the Fox ABJ had been replaced by another ABJ male, this one also hatched in 2005, but on McNutt Lake. In late 2013, the Fox ABJ was able to retake his territory (possibly after the McNutt ABJ left it) and lived there the rest of the summer. However, two days ago, Eric and I witnessed a nasty battle between the Fox and McNutt ABJs (now both 9 years old) that culminated in the exhausted and defeated Fox male taking refuge on shore to avoid further attack from the McNutt male. Quite a grim spectacle! It remains to be seen whether the Fox ABJ can recover, drag himself off of this tiny 25-acre lake and get on with his life.

While our problems pale in comparison to the desperate life-and-death struggle that the Fox ABJ is facing, this latest contest is troubling to us as well. You see, we have hypothesized that dangerous contests of this kind likely occur when very old males (with very little reproductive fitness to lose) roll the dice by battling to win a few more years on their territory rather than accepting displacement by a younger, stronger male. (This is termed the “terminal investment hypothesis”.) Naturally, we must use statistical tests on a large body of data before drawing any conclusions. Still, it was unsettling to see a vigorous young male — and one that doubtless would have many potential future years of reproduction ahead of him — suffer a life-threatening encounter that flies in the face of our pet hypothesis.

1991 was the first year that marking of loons occurred in our study area. In that year, Dave Evers and his crew captured and banded seven adult loons, five males and two females. It was not until two years later that I began my behavioral study of the population.

Of those seven marked adults, two survived for at least 15 years, but none had been observed for the past two years. I had given up hope that any of the “Magnificent Seven” was still alive.

All of that changed recently, when Kristin nailed the bands on the male that had been caught on Little Bearskin Lake in 1991, produced 14 fledged chicks between that year and 2005, and was finally evicted by a younger male in 2006. (He tried to breed on Heiress Lake in 2008, but his nest failed.) Last spotted in 2010, this old fellow is at least 26 years old. Here is how we know this: He was first spotted as an adult in 1991, and no adult has ever nested at an age younger than 4 years; so he must have hatched no later than 1987.

So….kudos to Kristin for IDing this old guy and especially to the old guy himself, the only remaining member of the Magnificent Seven.