As a means of learning about territorial behavior and also monitoring the stability of the loon population in northern Wisconsin, we observe and record nesting attempts by our study animals. We now have more than 20 years’ worth of data on reproductive success, which we have provided in an Excel file with legend here.
Although these data have been painstakingly collected by dozens of researchers over two decades and should be quite accurate, we welcome corrections, if you live on or have visited any of the lakes we list in our records and can straighten us out!
Some interesting patterns are evident in these data. Notice that some lakes produce chicks year after year, which suggests that these are simply lakes that offer good nesting habitat and abundant food for chicks. Other lakes seem to produce a chick or chicks every 5 to 8 years. What is not immediately apparent from the breeding data alone is that reproductive success is also dependent upon the birds doing the breeding! In most cases, “runs” of success occur from the nesting efforts of the same two individuals across years and nesting “droughts” occur because one or both pair members have died, leaving the territory vacant or in the hands of a new, inexperienced pair. So it seems that both the territory itself and the birds using it dictate how many chicks it produces.