I was on pins and needles last week when I visited Cunard Lake. Cunard, some may recall, is the 45-acre lake where two strapping six-week-old chicks and their parents fell victim to a devastating series of events in the last few days of July 2018. On July 27th one of the chicks swallowed an angler’s bait and hook, which kept the youngster from feeding itself and led to its death within five days. On July 29th, the Cunard male found himself challenged for territorial ownership, lost the battle, and vacated the lake. In the wake of that eviction, the surviving Cunard chick too vacated the territory and blundered into nearby Hasbrook Lake, where a different pair was rearing two slightly younger chicks. The lone positive that emerged from those events was that the Hasbrook pair let the huge refugee join their family and fed it thereafter as one of their own.
Naturally, I was intensely curious to observe the aftermath of this territorial carnage. Even what little we had seen in the few weeks following the loss of the Cunard family was tantalizing. The lake was left vacant. The evicted male, the male that had evicted him, and the female from the lake all went missing. The lack of loon activity in Cunard was odd, particularly in the case of the victorious male. This male had scouted out Cunard, observed the chicks, challenged the male breeder for this proven territory, and defeated him in battle, only to desert the lake after driving away the former owner and seizing ownership.
My visit to Cunard a week ago was anticlimactic. While I had expected to see the usurping male paired with the original Cunard female — the normal aftermath in cases of eviction — both original residents (a 15 year-old female hatched on nearby Woodcock Lake and a 13 year-old male reared on North Nokomis) were back and acting as if nothing had happened. It was a complete territorial reset. To be sure, there is a slight chance that the usurper had died during migration or over the winter. But it is far more likely, given the 94% annual survival rate of young males in their prime, that he had simply changed his mind about settling on Cunard.
We have seen this behavior before. I had always expected that evicting a territory owner and settling on its territory would occur in one fell swoop, but it is not so. On numerous occasions, nonbreeders (either male or female) have taken the great risk of challenging an owner in battle, defeated the owner, and then not settled on the territory they had invested so heavily to win. Why?
We can only speculate at this point. One peculiar behavioral pattern that might help us understand the failure of usurping loons to settle is natal habitat imprinting. Natal habitat imprinting refers to the strong tendency of loons — both male and female — to choose breeding lakes that closely resemble the lake on which they were reared. There could be a variety of benefits to settling on a lake like the one you were raised on, such as having similar prey to eat, availability of similar nesting areas, or simply being able to use one’s natal lake as a model of what sort of breeding area to look for, which might speed up the territorial search. At this point, let’s take natal imprinting as a given, since we know it occurs strongly in this species, and ask the obvious question: “Why would a loon not decide if a territory was to its liking before engaging in a dangerous battle to win it?”
As is so often the case, I can merely state a plausible hypothesis based on what I have observed of loon behavior. Territory owners, of course, are intolerant of intruders. Thus, while a loon that attempts to evict a resident from its territory is likely to have visited the territory on numerous previous occasions, the strong tendency of the breeding pair to drive out all intruders shortly after they enter prevents non-residents from learning much about the territory. As a result, once it has defeated the resident and taken ownership of its territory, a usurper might find (to it chagrin) that its hard-won territory does not resemble its natal one as closely as it had seemed. This hypothesis will be difficult to test, but not impossible. It predicts that many nonbreeders will battle for and win territories that are similar to its territory in obvious ways (like overall size) but that usurpers that find that their new lake is unlike their natal one in more subtle ways (like available prey species) might not stay.
So, we must keep working. In the meantime, enjoy my photo of a new pair that has settled on Swamp Lake. The female (on the right), evicted from Prairie Lake in 2015, seems gung-ho to settle and breed. Let’s hope the male (left) finds Swamp similar enough to his natal lake, East Horsehead, to stay.