It is usually no fun to be wrong, but maybe this is an exception. In my blog post yesterday, I surmised that the sudden appearance in flight of the male from Little Bearskin meant that he and his mate had failed in their second nesting attempt. This seemed a safe presumption; I knew from many years of experience that males do not often leave females alone with small chicks. Yet I was mistaken. A lake resident (thanks, Nancy!) corrected me by pointing out that at least one chick had hatched on Little Bearskin this year, and Martha found two chicks on the lake during her early-morning visit today.
As we have explained in an earlier publication, there are three reasons why males tend not to leave their breeding lakes when their chicks are in their first two weeks of life. First, females cannot yodel, and therefore they are unable to discourage intruders from landing in the lake and approaching chicks by means of this aggressive vocal signal. Second, by virtue of their greater size, males are better equipped to intimidate and drive away intruders that do approach chicks. Third, having two parents guarding chicks when they are small permits breeding pairs to cover two bases — they can send one parent out to engage intruders and leave the other to protect the chicks, in case an intruder should come close.
In fact, years ago on Langley Lake we witnessed the danger that parents face if one of them ventures off territory when their chicks are small. In this case, two intruders landed when the male was off the lake, forcing the female to choose between: 1) staying beside its week-old chick, and 2) leaving its chick to interact with the intruders. She chose the latter course, but that strategy backfired when the intruders dove and split up. At this most inopportune moment, the chick happened to give an alarm call that one of the intruders heard. The intruder quickly found the calling chick and, with no parent nearby to intervene, killed the chick in a matter of seconds.
With that horrid incident seared into my brain (and a good deal of quantitative data on chick attendance to back it up), I was fairly confident that the appearance of a breeding male on a lake not his own meant that he had failed in his breeding attempt at home. In fact, I am still scratching my head over the Little Bearskin male’s decision to leave his mate, his two helpless chicks, and his home lake with its abundant food supply, in order to visit a neighboring lake that held nothing but failed and displaced conspecifics. I guess I will have to continue my research for a few more years to make sense of that odd bit of behavior.