Blundering Males and Black Flies

By now, readers of the blog are aware that 2020 has been a devastating year for black flies in northern Wisconsin. The data are not all in yet, but a rough comparison between 2014, the worst black fly year on record, and this year shows that only five breeding pairs had hatched chicks in by 27 June 2014 — the same number of pairs that have hatched chicks so far this year. So this crude comparison suggests that 2020 is about on par with our worst year ever in terms of breeding activity being hindered and delayed by Simulium annulus.

Of course, 2020 is far from over. Most pairs, having failed once from black fly-related abandonment, have renested or may yet do so. But now I need to refer back to an earlier post, where I pointed out the record-setting rate of territorial turnovers this season. If many birds are newcomers to their territory, it makes sense that they are not fully familiar with the territory and how best to use it for breeding. In fact, since males choose the nest location, the responsibility for picking a raccoon-proof nesting spot — the major challenge that a nesting loon pair faces — falls to the male on each territory. The fact that 23 of 98 marked males in the study area are nesting for the first time on a new territory (twice the normal rate of turnover) means that — from a population perspective — we should expect a higher rate of predation in 2020 than in years past and fewer chicks.

Crunching the numbers again (crudely) in an attempt to predict chick production, we had 54 pairs incubating eggs as of 27 June 2014, compared to 49 pairs still incubating as of today. Although many 2020 nests are looking good because they have been underway for at least two weeks and/or are in proven successful locations, others are new and at untested nest sites selected by inexperienced males. So we should expect a poorer rate of hatch this year, overall, than the 76% rate that occurred among active nests on this date in 2014. If the hatch rate is 65% in 2020, then we will end up with 37 hatched broods, and an estimated 35 fledglings. In short, it is still looking like a weak year for chick production, but not quite the worst year ever. Times are such that we must take solace in that fact!

The good news is that loons learn. Few will ever be as savvy as Linda’s breeding pair, which kept incubating through the black fly period and already has three-week-old chicks (see Linda’s photo). But if return rates come back to normal after a crazy 2020, few territories in 2021 will be occupied by newcomers. Having lost a nest or two or three to raccoons in 2020, when they were learning their way around the territory, the greenhorn males of 2020 will improve their nesting decisions next year and hatch more chicks. So, as snake-bit as I am feeling owing to the double whammy of oppressive black flies and a bunch of new males blundering about in search of nest sites, I look forward to a better 2021.