The saying “success breeds success” was not coined with loons in mind. But we humans know from experience that an initial success can increase the likelihood of a second one. Indeed, I relearn the value of accumulated experience each spring during the period when I train field observers. With no background in the technique, new observers are utterly astounded when we locate the first nest of the year. After five more nest discoveries, though, they begin to develop a “search image” for nests. It is a thrill to see them learn quickly over a period of a few days to the point where they begin to point out loon nests to me!
Loons are not complete strangers to the benefits of learning. Males often place nests in poor locations when they first attempt to nest on new territories. After a bit of blundering about and some poor decisions, males typically find a nesting spot that results in a successful hatch. Afterwards, they reuse that good spot again and again, enjoying much greater success than during their first attempts. Thus, nesting success following an initial period of failure leads to further nesting success.
The impact of a loon pair’s nesting success on territory defense is another matter. The loon territorial system differs in a crucial respect from those described in other species. In many birds, most notably colonial seabirds, young adults prospect for good breeding sites by looking to see where other adults have produced chicks. When these young seabirds settle to breed, their settlement has little or no negative impact on adults already breeding at the huge colony. Not so in loons. Young adult loons prospecting for territories use chicks they spot on a specific territory as a badge indicating quality of that territory alone. Young prospectors must battle the current residents for ownership of such high-quality territories. That is, chicks seen in one year induce prospectors to return the next seeking to evict the owner of their sex and claim the territory for themselves. So adults that produce chicks experience the joy of parenthood…..but have also placed their future territory ownership in jeopardy.
The mixed blessing brought about by successful chick-rearing is nowhere more obvious than on the Pelican Lake-Mousseau Bay territory in the Minnesota Study Area. Online observers watching via the live nest cam were treated to a lengthy battle between two adult loons a few days ago. While the battle was shocking in its brutality, it was not surprising. We have long known that the successful rearing of chicks leads to a surge in interest in the territory and, hence, the likelihood of territory loss by one or both breeders. After raising two strapping chicks last summer, the male and female of Mousseau Bay must have braced themselves for a litany of territorial intruders and challenges. Indeed, the banded 2022 male apparently lost his position this spring; last year’s marked female is now paired with an unmarked male.
And yet there is hope. Yesterday, the old female laid an egg. She and her new mate both seem anxious to sit on it. If they can weather the blitz of black flies currently dogging their incubation efforts, they stand a good chance of repeating last year’s success.