Shifting between Lakes by Breeding Pairs with Chicks

It is a struggle for chicks to get enough food to reach adult size. Jack Barr estimated in his 1995 paper that a breeding pair with 2 chicks would remove over 400 kg of food from a nesting lake during a summer. It is difficult to discern how that amount of biomass is related to the productivity of lakes and their ability to support loon breeding efforts, but Barr’s estimate makes the point that families  face challenges in finding enough fish and aquatic invertebrates to sustain their chicks.

The situation is especially dire on small lakes. As I have noted in the past, pairs using small lakes for chick-rearing tend to raise fewer and smaller chicks, which, in addition, are less likely to survive to adulthood. So it stands to reason that such pairs might avail themselves of any opportunity to make use of large lakes near their small breeding lake for foraging. Indeed, one or both pair members often leave their chicks for hours at a time to fly to and forage on larger lakes nearby. This behavior — while it seems like child abandonment! — probably makes sense in that it reduces the amount of food removed from the breeding lake, leaving more for the chicks, which do not have the capacity to fly elsewhere to feed.

If the situation gets very desperate indeed, then shifting of adult foraging to neighboring lakes cannot save the chicks. In such cases, the chicks themselves must be moved. In fact, an uncommon but regular occurrence is for loon pairs to move their chicks from small lakes with vanishing food supplies to adjacent, larger lakes that offer untapped reserves of food. Recently, both the Fox and McGrath pairs have shifted singleton chicks to large neighboring lakes (McNaughton and Little Tomahawk, respectively). The move offers the chicks a far more hopeful future.

But what of the move? Unable to fly, chicks must “skootch” on their bellies to cross land. Chicks on land are easy prey for mammals and eagles that happen upon them during land crossings, as they are weaker and smaller than adults. What is more, land crossings are not silent, stealthy events. Loon parents vocalize loudly when urging their young to make land crossings, which would seem to alert predators and increase the danger. Evidently, only loud, persistent vocalizations by adults are sufficient to coax chicks into venturing onto land, so lake shifts must be accompanied by blaring of bugles! Since adults often accompany chicks during land crossings, they are even more conspicuous to observers than chicks alone would be. The extreme danger confronted by loon families that abandon small nesting lakes emphasizes just how depleted food supplies must be in order to justify the move.