I had a hint that the territory was in flux on my May 29th visit. Though it was late morning, there was a persistent intruder on Towanda. Intruders sometimes visit in late morning, and do not always depart quickly, but I filed this observation away as a worrisome sign that the Towanda pair might not be fully in control of their territory. I relaxed a bit when, on my June 15th visit, the pair had deposited two eggs at a safe location in the southeastern bay. Whatever had happened early in the year, I thought, the pair seemed to have put it behind them. Pairs do not reproduce in the midst of territorial instability.

Yet the breeding female and two intruding adults were locked into an intense round of circle-dancing and excited diving at the northern end of the lake on June 24th, when I had again drawn Towanda on my circuit list. Oblivious to that unease, the male incubated the eggs quietly at the southern end. Well, I reasoned, the female is in a tussle, but the male is far away and unaware of the action. Once he takes his next turn off the eggs, perhaps he will use his size, aggressiveness, and voice to drive off any residual intruders. On Martha’s visit five days later, calm indeed seemed to have descended on the lake; the male foraged casually while the female sat on the eggs. Likewise Annie reported nothing unusual on July 6th: the male was back on the nest, and the female foraged and swam on the surface nearby. Moreover, these last two visits occurred shortly after dawn, when intrusions peak. The absence of intruders on these two early-morning visits seemed a good indication that the pair was firmly in control.

The last two uneventful visits to Towanda had prepared us poorly for what Allison encountered today. From the look of the nest (see Allison’s photo), all seemed well. Clearly both eggs hatched right on schedule. But no chick was with the loon pair, and the male’s behavior was odd. He seemed exhausted and barely budged when the wind carried Allison’s canoe to within a few meters of his resting spot. As she sensed something amiss and worked hard to nail the male’s bands, she came to an important conclusion: this was not the right male. Somehow the territorial male, banded 12 years before, had been replaced by a new, younger bird just at about the time that new chicks had disappeared.

We can infer what happened on Towanda this past few days, because we have seen it many times before. In the wake of a successful hatch, the long-term male breeder had been evicted by a young whipper-snapper, and the whipper-snapper was this male who seemed determined to rest and recover. The young male had likely killed the chicks, as male lions do when they take over a pride that is raising the offspring of other males, and as we have seen before in loons. His bands revealed that the male was a seven-year-old, hatched and reared on Arrowhead Lake in Woodruff, just a few miles south of Towanda. Allison noticed something else strange; the young male was unwilling or unable to open his right eye. Exhaustion and damage to the head or neck of a loon almost always indicate a prolonged and recent territorial battle. We are left to wonder: if the winner of the contest is in this kind of shape, what does the loser look like?

This contest fits the profile of terminal investment by male loons. That is, the original 17+ year-old male resident might well have poured all of his energy into holding his territory — possibly dying the in the process — especially since he had two chicks to rear that would have contributed greatly to his lifetime reproductive fitness. But the day comes for most breeders — male or female — when a fit, determined youngster intrudes that is able to overwhelm you in a territorial battle. According to our measurements of males a different ages, seven-year-old males have reached peak condition and offer a stiff challenge to older males — even determined ones. At least the old fellow made the youngster work for it!